1 i SINGLE PULL MACGREGOR TYPE HATCH COVER A PROJECT REPORT Submitted by MANU SHARMA MUHAMMED ASIM M T NASIR ALI NIRAJ KUMAR NITHIN GOPAL NITHIN XAVIER In partial fulfilment for the award of the degree of BACHELOR OF TECHNOLOGY IN MARINE ENGINEERING K M SCHOOL OF MARINE ENGINEERING COCHIN UNIVERSITY OF SCIENCE AND TECHNOLOGY COCHIN JULY 2011
2 ii CERTIFICATE This is to certify that the seminar project entitled SINGLE PULL MACGREGOR TYPE HATCH COVER submitted by MANU SHARMA, NASIR ALI, MUHAMMED ASIM M T, NIRAJ KUMAR, NITHIN GOPAL S A, NITHIN XAVIER to the department of Kunjali Marakkar School of Marine Engineering towards the partial fulfilment of the requirements for the VIII semester of the B.Tech Degree course in Marine Engineering of Cochin University of Science and Technology, is a bonafide record of work carried out by him. Head of the Department K M School of Marine Engineering Cochin University of Science and Technology Project guide Prof. Dr. Sasikumar P.V.
3 iii ACKNOWLEDGEMENT First of all we helmed in all humbleness and gracefulness to acknowledge our depth regards to all who helped team to put this topic, well above the level of simplicity and into something concrete. We express our deep sense of gratitude to Director Prof K.A Simon for providing necessary facilities. We are very thankful to our project guide Prof. Dr.Sasikumar P.V who was always there to show us the right track when team needed the help and guided us in different matters regarding to project. He gave us moral support and guide in different matters regarding to project report and presentation and is very kind and patient while suggesting us the outline and structure of project report.. We are equally thankful to our project coordinator Prof. N.G. Nair for his valuable help. We record our sincere thanks to course coordinator Prof. Roy.V.Paul for his valuable suggestion Last but not least, we would like to thank our parents and friends and all others who helped us a lot in gathering different information, collecting data and guided us from time to time in making the project despite of their busy schedule.
4 iv ABSTRACT Hatch covers are used to cover and protect the cargo in the cargo spaces. Hatch covers close off the hatch opening and makes it water tight. In the days of wooden ships, the hatch covers were made of wooden planks, beams and boards and were covered with tarpaulins. Wooden hatch covers had many drawbacks. Mainly, they used to get spoilt due to continuous exposure to the moisture laden sea winds. Rain and sea water also used to produce detrimental effects on the wooden hatch covers. But with the advent of steel, the wooden hatch covers started disappearing. Nowadays, mostly steel hatch covers are used. The most common type of hatch cover used today consists of a number of steel covers linked together. The design of a hatch cover changes according to the size and design of the ship, but most of the designs are made to make the opening and closing of the covers as quick as possible in order to facilitate faster cargo handling process. One such type of hatch cover is a MacGregor, single pull hatch cover. In this type, the hatch cover moves on rollers attached to tracks fixed on the hatch coaming. The hatch cover is not one steel structure but a series of steel covers linked together by chains. When the cover is opened, the individual steel covers ride up and tip onto a stowage tank at the hatch end. Most of the hatch covers found on board ships are controlled hydraulically by a hydraulic power unit operated from a control box fixed near the hatch cover..
5 v TABLE OF CONTENTS Page no. CERTIFICATE ii ACKNOWLEDGEMENT iii ABSTRACT iv TABLE OF CONTENTS v LIST OF FIGURES ix LIST OF TABLES xii CHAPTER 1 - INTRODUCTION Hatch Cover and Their Function Early Hatch Cover Failing of Wooden Hatches Safety and Security Maintenance Cargo Working Steel Hatches After CHAPTER 2 - TYPES OF STEEL HATCH COVERS Single Pull Side Rolling Folding and Multi Type Lift Away Piggy Back Stacking Covers Reefers Hatch Covers Spring Loaded Covers. 18 CHAPTER 3 - GENERAL REQUIREMENT Regulatory Requirements Rule Governing Access Equipment International Load Line Convention, Freeboard Freeboard Deck Weather-Tightness and Water-Tightness. 22
6 vi Statutory Regulations General Considerations for Access Equipment Coaming Height Cover Stowage Deck Opening Drainage Specific Design Requirements for Hatch Covers Hatch Covers Structural Regulations Cleats Loads Scantling Deformation Seals Gaskets Material Compression Bar Construction Materials Higher Tensile Steel (HTS) Aluminium Glass Reinforced Plastic (GRP) Wood 37 CHAPTER 4 - OPERATIONAL AND SAFETY ASPECTS Basic Advice Monitoring and Inspection Heavy Weather Precaution Safety when Working with Hatch Covers Procedure to Open and Close Hatch Covers Maintenance and Repair 50 CHAPTER 5 - SINGLE PULL MACGREGOR TYPE HATCH COVER DESIGN Parts Design Hold Design Hatch Opening Dimensions Hatch Coaming Design. 57
7 vii Hatch Covers Design Track 1 Design Rising Track Design (Track 2) Jack Design Crane Space Design Motor Casing Motor Specifications Pulley Design Rope Reduction Gear Design Ladder Design Bulwark Design Material Selection 65 CHAPTER 6 - FABRICATION Fabrication of Cargo Hold Fabrication of Hatch Way Hatch Coaming Fabrication Hatch Stay Fabrication Fabrication of Side & End Dog Fabrication of Hatch Cover Sliding Track Fabrication Fabrication of Rising Track Fabrication of Crane Space Motor Reduction Gear Pulley Fabrication Fabrication of Bulwark Fabrication of Ladder 78 CHAPTER 7 - ASSEMBLY OF FABRICATED PARTS Assembly Between Cargo Hold and Hatch Coaming Assembly of Hatch Stay on Coaming Assembly of Side Dogs and End Dogs on Coaming Assembly of Sliding Tracks Assembly of Rising Track Assembly of Hatch Cover Assembly of Crane Space into Cargo Hold. 84
8 viii 7.8 Assembly of Motor Pulley Gear Arrangement into Cargo Hold Assembly of Bulwark Assembly of Ladder Assembly of Locking Arrangement Assembly of Wire Rope 86 CHAPTER 8 - TESTS AND TRIALS Water Hose Leak Detection Test Ultrasonic Leak Detection Test Putty or Moulding Clay Test Chalk Test Tolerance Test for Hatch Covers Results 90 CHAPTER 9 - CONCLUSION 91 REFERENCES 92
9 ix LIST OF FIGURES Figure no: Title Page no: Figure 1.1 Simplified arrangement of a traditional hatch 4 Figure 1.2 Arrangement of an early Mege folding steel hatch cover 8 Figure 2.1 Single Pull Hatch Cover 11 Figure 2.2 Side Rolling 12 Figure 2.3 Folding and Multi type 13 Figure 2.4 Lift Away 14 Figure 2.5 Piggy Back 15 Figure 2.6 Stacking Covers 16 Figure 2.7 Reefers Hatch Cover 17 Figure 2.8 Spring Loaded Cover 18 Figure 3.1 Deck Opening with Coaming 26 Figure 3.2 Beam is treated as a Uniformly Loaded simply Supported Structure 27 Figure 3.3 Detailed Analysis of the Structure of a 20,000 tdw bulk carrier 32 Figure 3.4 Hydrostatic Pressure 33 Figure 3.5 Torsional Distortion of Hatch Ways 34 Figure 4.1 Hatch Panel 40 Figure 4.2 Vessels in Rough Weather 43 Figure 4.3 Check the Lock-Back Mechanism 44 Figure 4.4 Do Not Use Damaged or Unsecured ladders 44 Figure 4.5 Never Smoke in a Hold 45 Figure 4.6 Never Climbs On Top Of Bulk Cargo Without A Lifeline. 45 Figure 4.7 Never Carry Tools or Equipments While Descending or 46 Ascending a Ladder Figure 4.8 Never stand on the coaming top when the hatch covers are open 46 Figure 4.9 Always wear protective headgear when working. 47 Figure 4.10 Inspect wire 47 Figure 4.11 Always takes precautions when fumigating. 48
10 x Figure 5.1 Single Pull MacGregor Type Hatch Cover 54 Figure 5.2 Hold Design 56 Figure 5.3 Hatch Opening Dimensions 57 Figure 5.4 Hatch Coaming Design 57 Figure 5.5 Hatch Cover Design 58 Figure 5.6 Track Design 59 Figure 5.7 Rising Track Design 60 Figure 5.8 Jack Design 60 Figure 5.9 Crane Space Design 61 Figure 5.10 Ladder Design 64 Figure 5.11 Bulwark Design 64 Figure 6.1 Cargo hold 67 Figure 6.2 Hatch way 68 Figure 6.3 Hatch Coaming 69 Figure 6.4 Hatch Stay 70 Figure 6.5 Side and End Dog 71 Figure 6.6 Pantoons 72 Figure 6.7 Pantoons and wheels 73 Figure 6.8 Metallic Wheels on A Pantoon 73 Figure 6.9 Sliding Track 74 Figure 6.10 Hydraulic Jack and Sliding Track 74 Figure 6.11 Rising Track 75 Figure 6.12 Crane Space 77 Figure 6.13 Bulwark 78 Figure 6.14 Ladder 78 Figure7.1 Assembly of fabricated parts 79 Figure7.2 Cargo hold and Hatch coaming 80 Figure7.3 Hatch stay on coaming 81 Figure7.4 Side dogs and end dogs on coaming 81 Figure7.5 Sliding track 82 Figure7.6 Rising track 82 Figure 7.7 Hatch covers 83 Figure7.8 Hatch covers 83 Figure7.9 Cargo spaces into cargo hold 84
12 xii LIST OF TABLES Table no: Title Page no: Table 2.1 Operating mode of hatch cover types 9 Table 2.2 summarizes the most important characteristics of 10 each major type Table 3.1 Freeboard for different ships length 20 Table 3.2 Increase in freeboard 21 Table 3.3 Summary of 1966 Load Line Convention hatch 28 Cover regulation Table 3.4 Access equipment strength calculations 31
13 1 CHAPTER 1 - INTRODUCTION The classic modern hatch cover is the single pull which remains the most common of the all the various forms now in service and may rightly be described as the natural successor to traditional beams and boards. This cover derives its name from its immediate predecessor, the multi-pull cover, which consisted of a series of individual panels similar to those of the single pull, but unconnected. Each panel had to be rigged before being pulled one at a time into stowage. The complete cover consists of a number of narrow panels which span the hatchway and are linked together by chains. In the closed position, the panel sides sit firmly which takes the weight of the cover. Rubber gasket was attached to the side and end dogs over which weight of panel comes forming a watertight seal. Extending from the side coamings at the end of the hatchway where the covers are stowed are steel rails which the individual hatch panels to be transferred to their stowage location when the hatch is opened. To open a hatch hold cover, the securing cleats are first freed and each panel is raised onto its wheel by portable jacks. Entire cover is free to move in a fore and aft direction with its wheel rolling between guides on the top of the coaming. It is set in motion by means of a wire (sometimes called a bull wire) led from a motor wheel and attached to the centre of the furthest edge of the leading panel i.e. the panel which goes into stowage first and comes out of stowage last. As the wire is tightened, the panels are each pushed beyond the end coaming. On reaching the end of the hatchway; the weight of each panel is transferred from its wheels to balancing rollers situated near its mid length which engage with the rail extensions of the side coaming. The centre of gravity of each panel is slightly towards the stowage end of the panel from the rollers so that once the panel is supported from them, it tips into vertical position. It is then pushed further towards the end of the stowage space by the next panel to arrive at the hatchway end. When the hatch is completely open, each panel stands vertically in the stowage space, and all are kept in place with retaining chains. To close a single pull cover, the direction of rotation of motor is reversed. This cause the first panel to leaves its stowage position, its tip through 90 degree
14 2 about its roller to land horizontally with its wheels resting on the coaming. It is then pulled further over the hatchway and the chain linking it to the next panel becomes taut with the result it too is set in motion. On reaching the end of the stowage space, the second panel tips lie horizontally on the coaming behind the first and together they pull across the hatchway. The process is repeated with the third and fourth panels, ending only when all are lying flat on the coamings and the hatch is completely covered. 1.1 HATCH COVERS AND THEIR FUNCTION The purpose and function of a hatch cover and its coamings is to prevent ingress of water into a cargo hold after a large opening has been cut in the deck for cargo access. Hatch covers are a moveable structure designed to a weather tight standard Hatch Cover Construction Typically hatch covers are lightweight steel grillages. Modern design methods using finite element technology enable more efficient material distribution which results in lighter (thinner) structures. Construction from high tensile steel results in even thinner plate being used. For this reason these lightweight structures must be handled with care. Prevention of corrosion is essential safety margins are finite Hatch Cover Function Hatch covers provide a primary structural and weather tight barrier to prevent water ingress into cargo holds. Rigorous inspection, regular maintenance and prompt repair of damaged covers, securing s and supports are essential to maintain fitness for purpose and, in particular:- To maintain sufficient strength to resist green seas landing on hatches in extreme weather; To maintain a barrier against ingress of water during normal seagoing weather conditions. Failure to maintain hatch covers correctly can lead to physical loss of a cover in extreme weather and hold flooding and possible foundering. Minor
15 3 leakage can cause cargo damage and, if over a prolonged period, damage to the ship s internal structure. Long-term structural decline can lead to structural collapse and total loss. 1.2 EARLY HATCH COVERS The upper deck hatches of early steamships, in common with those of sailing ships, were small by present standards: four meters by two would not have been untypical hatchway dimensions, even for ocean going vessels in the mid-19 th century. Deck openings were bounded by vertical coamings and spanned by wooden boards usually laid athwart ships: water tightness was maintained by tarpaulins spread over the boards and secured by wedges and cleats at the coamings, an arrangement which had then been in use for centuries. Web beams were sometimes placed across the largest hatchways but it was not until 1879 that their use became mandatory for all vessels classed with Lloyd s Register of Shipping having hatchways more than 12 feet long. Coamings were required to be of iron constructions. No minimum height was specified and it was not until forty years later that they appeared in Lloyd s Rules. Hatch boards were made of solid woods 63 mm thick and of such an overall size that they could be handled manually. Since they were laid transversely across the hatchway it was necessary to use fore and afters to reduce their unsupported span. These were the heavy baulks of timber placed longitudinally across the hatchway, on the top of the transverse iron beams and supported at each end by brackets attached to the coamings. The hatch boards, in turn, were placed across the fore and after which were so spaced that the unsupported span of the boards did not exceed the maximum allowed. After the turn of the 20 th century, the practice of arranging hatch boards longitudinally began to be adopted. There were sound reasons for this change. A typical cargo ship hatch,7.5m(25 ft) long and 5 m(16 ft) wide, with athwart ship hatch boards, would have been fitted with two transverse web beams and three fore afters which, because of their overall length would each have been made up in three pieces, one for every beam space as shown in figure 1.1. With longitudinal hatch boards the same hatch would have required no more than four transverse beams space 1.5 m apart each of lighter construction than the two webs
16 4 in previous arrangement. Thus the number of heavy components to be lifted every time the hatch was opened and closed would have been reduced from eleven to four. Figure 1.1 Simplified arrangement of a traditional hatch Source: Cargo Access Equipment for Merchant Ships. This arrangement also had the advantage of being safer than the earlier one. As hatches became longer it becomes increasingly necessary to fit force and afters in several actions. These were more difficult to ship when battening down that those modes in one piece, since at least one end of each section had to be positioned on a seat attached to a traverse web before the hatch board could be put on. This meant that the man had to sit astride the web, over the open hold, to guide into place a very dangerous practice. Atharwdship hatch boards and fore and afters continued to be used well into 20 th century although the longitudinal arrangement gradually replaced them. After the implantation of the 1930 international load line conventions fore and after were only found in ships with very small hatches.
17 5 All types of wooden hatch were made watertight by means of tarpaulins and this method is still employed in those ships with traditional hatches that remain in service. The use of wooden hatch cover has declined throughout much of this century to the extent that it is now almost unthinkable that they should be fitted in modern vessel of any size. It is interesting therefore, to consider the reason for their demise. These fall into three broad categories, namely safety and security, cargo working and maintenance. 1.3 FAILINGS OF WOODEN HATCHES Safety and Security It is impossible to exaggerate the importance and secure hatch covers; there can be no question that a ship s survival may depend upon having them. But how efficient are wooden hatch covers? Tarpaulins are the most vulnerable component of traditional hatch covers. There are several common reasons for tarpaulin failure. Slackening of wedges is one of the most important factor. Chaffing is another serious source of weakness, especially at the coamings. Tarpaulins are also liable to suffer damage every time that they are removed for working cargo. Security of the wooden hatches also arose as a result of the comparatively large size of the hatchways of many of the ships, especially colliers, then entering service. Not only were the hatchways longer and wider than had been the customs up to that time, but the ratio of hatch width to overall beam was often greater too. This was particularly apparent in ships employed in the carriage of bulk cargoes and some of the most extreme examples were to be amongst self-trimming colliers where hatch width/ship beam ratios often exceed 0.6. Individual hatch boards were laid loosely on top of the beams in a normal hatchway and they could easily be shipped accidently. In order to prevent this, interlocking boards were developed. These could be handled manually in the usual manner but once landed on the beams; they were retained in place by a simple locking device which was claimed by its manufacturer to enhance the safety of a ship, should it lose its tarpaulins, by preventing the boards from being washed away by the sea.
18 Maintenance The maintenance of the wooden hatches is expensive in both labour and materials. Although individual components were simple and inexpensive, there were so many of them in a typical hatch and they were so easily damaged through continued hard use that the total cost of replacement so often substantial. Wedges which are vital to the security of the hatches were individually very cheap but they were frequently lost or misused. Hatch boards too had to be replaced frequently. Tarpaulins used for traditional hatches were easily chafed and in some ships one man could well have been employed continuously for their repair Cargo Working Time spent in port affects the overall economics of operating ships. Attention was given for higher cargo handling rates and faster turnaround times, and time spent for opening and closing hatches. This become increasingly apparent as hatchways became larger. Every hatch component had to be handled separately; tarpaulins had to be folded back, each hatch board had to be removed manually, each beam had to be lifted from its seat by derrick and winch or shore crane, and the larger the hatchway, the more items there were to be handled. 1.4 STEEL HATCHES AFTER 1927 The earliest satisfactory hatch cover produced by the brothers Joseph and Robert MacGregor, two naval architects from Tyneside, was of the hinged type. It consists to two large steel slabs, each spanning half the hatchway and hinged at the side coamings. When opened by winch and derrick, the slabs rotated through 180 degree so that they rested on the bulwarks to form a convenient platform for working cargo (although obstructing the gangway along the deck). Like other slab hatches they were kept secure and watertight in the conventional manner and their hinges were cunningly built into the coamings so as not to impair the effectiveness of their tarpaulins. However, it was the announcement in 1928 of a horizontal rolling cover which did not require tarpaulins that marked the real beginning of the long association of the Macgregor name with steel hatch covers, which continues to this day.
19 7 The first horizontal rolling built to the design patented by MacGregor & king Ltd. Was installed over the aftermost hatchway of the 9000tdw motor ship sheaf holme which left the Sunderland yard of her builder, Wm. Pickersgill, in August1929 amid rather more publicity than she would otherwise have merited. The event was important because it was not the first time that a hatch cover had been put into service that was easily operated manually, yet depended on tarpaulins for water tightness nor did it forgo any of the strength with which previous steel covers had been endowed. The earliest horizontal rolling covers produced by Macgregor and king (subsequently known as Macanking) came in two forms, although both were basically similar. The first was fitted in fairly small hatchways and consists of two moveable sections fabricated out of steel plate stiffened by channels bars or bulbs angles, with a skirt around their perimeters which rested on the coaming when the cover was closed. They revolved about eccentric bushes which could be rotated so that the clear height of the lower edge of the cover above the coaming could be varied. In the closed position, with the hatch secured for sea, the bushes were aligned so that the perimeter of the cover rested on the coaming throughout its entire length. To open the hatch, the bushes were rotated through half a turn with a marlin spike, thus raising the cover so that it could be easily pulled along on its wheels. This arrangement has become a feature of many MacGregor hatches since. In France in 1934, Captain Mege, of Louis Dreyfus Cie, patented folding steel hatch covers which were first fitted in the cargo ship Louis L.D. two years later. They considered of double panels hinged together and to the end coamings, but, unlike the von Tell covers, they were opened by lifting the panel nearer the coaming hinge. As it was raised, the second panel was pulled towards the end of the hatchway, supported on two trailing wheels which ran along the coaming, until both panels were stowed together vertically. In this way a folding hatch cover could be opened in one operation instead of two. Fig 1.2 shows an early Mege folding steel hatch cover. Closing was carried out by simply allowing the fold hinge to open under the combined weight of the two panels until both were in position resting flat on coaming to which they were secured by bolts. In long
20 8 hatchways, Mege covers were fitted to both end coamings. The folding principle that was incorporated into their design has become widely adopted, for both wire operated and hydraulically operated folding covers. More than thirty ships were fitted with Mege covers before MacGregor & Co. Became the sole licensee for their construction in Figure 1.2 Arrangement of an early Mege folding steel hatch cover Source: Cargo Access Equipment for Merchant Ships.
21 9 CHAPTER 2 - TYPES OF HATCH COVERS Many types of hatch cover are now available and the principal ones are listed in the below table where they grouped according to their mode of operation. Table 2.2 shows the most important characteristics of each major types. Table 2.1 Operating mode of hatch cover types Rollin and tripping Lifting Rolling Roll stowing Folding Sliding/nesting Single pull Pontoon End rolling Side rolling Lift and roll(piggy-back) Telescopic Roll stowing(rolltite) Flexible rolling Hydraulic folding Wire operated folding Direct pull Tween-deck sliding Source: Cargo Access Equipment for Merchant Ships.
22 10 Table 2.2 Summarizes the most important characteristics of each major type NNo Cover type Usual ship types Decks applicable Approxima te %of covers fitted to recent new ships Guide to minimum coaming height 1 Single pull (D) Weather 41 Depends on section lengths but more than(a) 2 Hydraulic (D) Weather/Tween 25 (A),(B) folding 3 Wireoperated folding 4 Direct pull All ships with cargo gear 5 Roll stowing 6 Side and end rolling or(c) (D) Weather/Tween 10 (A),(B) or(c) Drive system Electric, hydraulic or ship s cargo gear Hydraulic Winch Weather 3 (A) Or(B) Ship crane or derrick (D) Weather 2 Depends on drum diameter but usually more than (A) or(b) All, but mainly large bulkers and OBOs 7 Lift and roll All, but mainly bunkers 8 Tweendeck sliding 9 Pontoon (F) Multideck cargo ships Containe r ships, Multideck cargo ships Electric or hydraulic Weather 4 (A) or (B) Electric or hydraulic Weather 2 (A) or (B) Electric or hydraulic Tween and Car decks Cleating system (E) (E) Screw or quickacting Automatic (E) (E) (E) 2 (C ) Electric Token Weather/Tween 11 (A), (B) or (C) Source: Cargo Access Equipment for Merchant Ships. Ship or shore crane (E)
23 SINGLE PULL Figure 2.1 single pull hatch cover Source: - Walter Vervloesem IMCS Description The classic modern hatch cover is the single pull which remains the most common of the all the various forms now in service and may rightly be described as the natural successor to traditional beams and boards. This cover derives its name from its immediate predecessor, the multi-pull cover, which consisted of a series of individual panels similar to those of the single pull, but unconnected. Each panel had to be rigged before being pulled one at a time into stowage. The complete cover consists of a number of narrow panels which span the hatchway and are linked together by chains. In the closed position, the panel sides sit firmly which takes the weight of the cover. Just inside the side plate is a rubber gasket attached to the cover, which rest on a steel compression bar forming a watertight seal. Extending from the side coamings at the end of the hatchway where the covers are stowed are steel rails which the individual hatch panels to be transferred to their stowage location when the hatch is opened. Although single pull covers rarely exceed 16 m in width, larger sizes can be manufactured.
24 SIDE ROLLING Figure 2.2 side rolling hatch cover Source: - Walter Vervloesem - IMCS Description Rolling covers usually consist of two large panels at each hatchway. They are fitted with wheels which roll along a track at both sides of the coaming top. Stowage rails, which may be portable, extend this track via pillars welded to the deck. In some installation, the wheels are not attached to the hatch cover but to the coaming and to fixed pillars on the deck, and the cover rolls across them. Apart from stowage location, the principal difference between side end rolling covers is that the joint in between side rolling panels is longitudinally and between end rolling panels is athwatships. These covers are usually fitted to large ships. They are often extremely heavy owing to their large dimensions and require hydraulic pot lifts (rams) to raise them into the rolling position. These hydraulic lifts are fitted to the coaming below the wheels (in their closed position) and are illustrated in fig. There is no limit to the size of the covers, and panels 20 metres square (20 m*20 m) have been installed in ships.
25 FOLDING & MULTI-TYPE Figure 2.3 folding type hatch cover Source: - Walter Vervloesem - IMCS Description Folding covers may be fitted at both weather deck and tween deck hatchways. In its simplest form, this type of hatch cover consists of two flat topped panels, similar in basic construction to those of the single pull system. Complex configuration may have three or more panels at each end of the hatchway, although installations with an uneven number of panels are rare. Wire-operated covers having more than two panels require special rigging and their operation is therefore slow. A typical hydraulic operated cover is shown below. Adjacent panels are hinged together so that they can fold as shown. The panel at the stowage end is hinged to a plinth welded to the deck and hydraulic rams are usually arranged as illustrated. The ram rod is withdrawn into the cylinder to prevent corrosion when the hatch is closed at sea. Covers up to 26 m wide have been installed in ships.
26 LIFT AWAY Figure 2.4 Lift away type covers Source: - Walter Vervloesem - IMCS Description Lift-away hatch covers for use on the weather deck are divided into two categories as follows:. SINGLE-PANEL COVERS: MULTI-PANEL COVERS: single-opening abreast with longitudinal joints. multi-opening abreast with transverse joints. Single-Panel types comprise one cover for each opening i.e. there are no joints. They are normally specified for bulk carriers in the case of single opening abreast, and for cellular containerships in the case of multi-opening abreast configurations. Multi-Panel covers comprise several separate panels for each hatch opening. They are used for cellular containerships in the case of longitudinal joints, and for multipurpose cargo ships and heavy cargo tonnage in the case of transversal joints
27 PIGGY BACK Figure 2.5 Piggy type Source: - Walter Vervloesem - IMCS Description Lift and roll covers are a development of rolling covers and example is illustrated in fig. Each covers consists of two panels, one of which has powered wheels. In the way of the dumb panel, four hydraulic rams which act vertically upwards are fitted with the coaming. These engage in lugs on the side of the panel to lift it high enough above the coaming for the motorized panel to roll underneath. The dumb panel is then lowered onto the motorized panel so that both can be moved together. The side coaming can be extended so that the two panels can be stowed beyond the hatch end. Alternatively these covers can be side rolling, stowing abreast the hatchway. There is in the theory no limit to the size of these covers composed of two 100-tonne panels for 26m by 23m hatch ways have been supplied for forest product carriers.
28 STACKING COVERS Figure 2.6 Stacking type covers Source: - Walter Vervloesem - IMCS
30 SPRING LOADED COVERS Figure 2.8 Spring loaded covers Source: - Walter Vervloesem - IMCS
31 19 CHAPTER 3 - GENERAL REQUIREMENTS 3.1 REGULATORY REQUIREMENTS Rules Governing Cargo Access Equipment Cargo ships exist to transport goods from one port to another to accomplish this; they must have some means of getting cargo into and out of their holds. Thus ships must have opening either in the weather deck, as in vertically loading vessels, or in the bow, stern or side, as in horizontally loading vessels. These areas are all vulnerable to damage at sea. Thus cargo access equipment must provide access in port while keeping water out, during voyage. One of its prime functions is to ensure the safety of ship, personnel and cargo. In order to maintain acceptable standards of safety at sea, rules and regulations have been introduced over the years, many of which directly concern access equipment International Load Line Convention, 1966 Probably the most important regulations that affect access equipment are those arising from the 1966 load line convention which replaces the first international load line convention in 1930 for determining the freeboard. It provides for two categories. It provides for two categories of ship for freeboard purpose-type. A ships which are those designed to carry liquid cargoes in bulk and whose tanks have small access openings and Type B which includes all other ships. Among Type B ships are certain bulk carriers and ore carriers which are further sub-divided as follows: (a) Ships of over 100 m length having steel hatch cover on all exposed hatchways and which can remain afloat in satisfactory equilibrium with any one compartment flooded. When the length exceeds 225 m, the machinery space is also treated as a floodable compartment. These ships can have table B freeboards given in table B and A summarized in table; such freeboard is referred to as B-60.Tables A and B referred to the minimum freeboard laid down by the Convention for type A and Type b ships. (b) Ships which can withstand flooding of two adjacent compartments may be assigned B-100 freeboard, virtually equal to type A ships.
32 20 Type B ships which are fitted with portable covers, e.g. beams and boards in position 1 hatchways are required to have their freeboard increased above those given in table B Freeboard Table 3.1 shows freeboard from the full tables and compares freeboard for different ships length as required by Load Line Conventions of 1930 and 1966.Corrections are made to cater for non-standard length depth ratios, block coefficient, extent of superstructure etc. The standard ratios block coefficient, extent of superstructure etc. The standards freeboard applies in salt water. Ship length, metres Table 3.1 Freeboard for different ships length Tanker Freeboards 1930, mm Table A Freeboards 1966, mm Steamer Freeboards 1966 mm (3080) (3370) 2946 (4310) (3830) 3262 (4755) 4630 Table B Freeboards 1966, mm Source: Cargo Access Equipment for Merchant Ships. In designated summer zones throughout the world; slightly different values in winter or tropical zones in fresh water, or when timber deck cargoes are carried, as laid down and in the corresponding national legislation, in the United Kingdom. The merchant shipping (Load line) Rules, It can be seen that increasing maximum draft and therefore cargo deadweight. Table 3.2 is derived from the full tables and shows the increase in freeboard required for Type B ships having portable covers
33 21 secured by tarpaulins and battening devices, e.g. beams and boards.position 1 hatch board are defined as those on exposed freeboard decks, raised quarter decks, and exposed superstructure decks within the forward quarter length of ship, while position 2 hatchways are those on exposed superstructures deck is regarded as the deck immediately above the freeboard deck. Table 3.2 Increase in freeboard Length, metres Freeboard Increase, mm Resultant Freeboard, mm Source: Cargo Access Equipment for Merchant Ships Freeboard Deck Regulation 3, paragraph 9 of 1966 LLC defines the freeboard deck and is quoted here in full as it has an important bearing on all aspects of equipment used for closing cargo openings. The freeboard deck is normally the uppermost complete deck exposed to weather and sea, which has permanent means of closing cargo openings in the side of the ship are fitted with permanent means of watertight closing. In a ship having a discontinuous freeboard deck, The lowest line of exposed deck and the continuation of that line parallel to the upper part of deck is taken as freeboard deck. At the option of the owner and subject to the approval of the Administration,a lower deck may be designated as the freeboard deck provided as it is complete and permanent deck continuous in a fore and aft direction at least between the machinery space and peak bulkheads and continuous athwart ships. When this lower deck is stepped the lowest line of the deck and the continuation of that line parallel to upper part of the deck and is taken as the
34 22 freeboard deck. When a lower deck is designated the freeboard deck, the part of hull which extend above the freeboard deck is treated as superstructure so far as concerns the application of the conditions of the assignment and the calculation of freeboard. It is from this deck that the freeboard is calculated. It should be noted that the requirement for a lower deck to complete and permanent in order to be designated the freeboard deck, does not mean that any openings need to be weather tight, only that the structure of a deck is present. Tweendeck hatches may be of steel or wood, but are only required to be watertight if fitted to deep tanks or compartments containing water ballast. The Administrations referred to include the Department of Trade in the United Kingdom, the us coast guard in the united states and equivalent in other countries Weather-Tightness and Water-Tightness Regulation of the 1966 LLC which covers the mean for securing weather-tightness of steel weather-tight covers states that The means for securing and maintaining weather-tightness shall be to the satisfaction of the Administration. The arrangement shall ensure that the tightness can be maintained ain any sea conditions, and for this purpose test for tightness shall be required at initial survey,and may be required at periodical survey and at annual inspections or at more frequent intervals. Regulation defines weather-tight as meaning that water will not penetrate into the ship in any conditions. Weather-tight is not defined into 1996 LLC but is generally regarded as higher standard than weather-tight.it is usually taken to require the closure to be capable of preventing the passage of water through the structure in any direction, under the head of ships margin line, which is line drawn at least 76 mm in below the upper surface of bulkhead deck at the side of ship. In practice the hatch covers of B-60 and B-100 ships must be of steel and made weather-tight by means of special gasket devices. Less commonly, hatch may be made weather-tight by means of tarpaulins and battening devices over wooden or portable steel pontoon covers Statutory Regulations The 1966 load line convention came into force in 1968 after it had been ratified by required number of maritime nations. In UK the convention was brought into the
35 23 force by the 1967 Merchant shipping Act from which the merchant shipping (load line) rules 1968 were made the rules for the constructions of ship laid down by Lloyds register of shipping are consistent with the convention, as are those of other C classification societies. 3.2 GENERAL CONSIDERATIONS FOR ACCESS EQUIPMENT Coaming height Minimum coaming height, derived from the 1966 LLC, is laid down by Classification Societies. Height are measured above the upper surface of the deck, and any sheathing that may be fitted, and for hatchway closed by portable covers secured water tight by tarpaulins and battening devices, they must not be less than: 600 mm (23.5 in) for Position 1; 450 mm (17.5 in) for Position 2, Coaming of hatchways closed by steel covers fitted with direct securing arrangements are usually as indicated above, taking into account any sheer or camber when assessing minimum height. They may, however, be lower, or even omitted entirely, if the safety of the ship is not impaired by doing so, provided the Administration of the country concerned consents. The scantling and securing arrangements of flush hatch covers or those having less than standard height coamings are treated as special cases. Such arrangements have been approved in the past. Dock safety regulations generally require a minimum coaming height of about 760 mm (2 ft 6 in), otherwise additional fencing must be fitted to prevent personnel falling through the hatchway. It is rare for ship to have coamings of lower height than those stipulated, unless they are completely flush. Flush weather decks are required in a variety of circumstances. For instance, vehicles, wheeled cargo, or containers must sometime be stowed over the full deck area including the hatch covers, and clear decks for recreation are desirable in passenger ships. Satisfying the flood ability requirement for B-100 and B-60 ships may result in coaming being increased in height on such ships to meet loadline and subdivision regulation.
36 24 In practice one of the principal determinants of coaming height is the operation of the hatch cover. Other types that are affected in this way are rolling stowing covers where the drum height must be sufficient to allow the stow covers to fit between the drum axis and the deck and single pull covers whose panels stow in an upright position standing clear of the deck. The coaming may also be increased in height to obtain additional cargo capacity. As a result of these considerations, the majority of the ships have in the range m. It is useful if crew and stevedores can see readily into the holds during port operations. Thus if the coaming is higher than about 1.4 m, a step or a narrow platform should be fitted at the suitable height. While the top of the coaming is nearly always at the same level on all its sides, it need not be parallel with the deck. Neither is it essential that the coaming plates be vertical, if by sloping them inwards, a larger opening at deck level can be obtained. Another factor influencing coaming height is the nature of particular deck cargoes. Packaged lumber, for example, is usually stowed abreast hatchways until it reaches the height of the hatch cover top, when it is distributed over its whole width of the ship. Lumber is usually banded into packages, each 660 mm high, which are stowed with a 25 mm batten between them. Coamings should therefore be designed with a height from deck to hatch cover top which is a multiple of 685 mm (27 in). In heavy lift cargo liners, the coaming height and bulwark height are often the same so that awkward loads like barges may be easily supported across the entire ship. In some ship the internal volume bounded by the coamings needs to be a greater proportion of the total hold volume than the minimum 600 mm coaming height allows. In the past certain ships engaged in the grain trade were required to have coamings enclosing 4 percent of the total hold volume to allow for settling, but this requirement have now been suppressed by the provisions of the Safety of Life at Sea Conventions 1974(SOLAS 74). These new provisions do not stipulate a minimum or maximum coaming volume, although it may be necessary to arrange a coaming height in excess of 600 mm in a particular ship so as to meet the stability requirements for the carriage or grain. These assume that the cargo ships in to void spaces below side decks, so producing a heeling moment which depends on the resulting free surface of the grain.
37 Cover Stowage Where a designer is attempting to obtain the largest possible hatchway openings, the question of the hatch cover stowage is especially important. The width of the stowage space is fixed by the hatchway width if the covers are stowed at the end of the hatchway, but the height and length of the space can be varied. If the hatchways are to be the longest possible in a given deck length, the length of the stowage space must be kept to a minimum; this can be accomplished in a various ways depending on the type of hatch cover employed. No special stowage space is required for simple pontoon covers since these are usually stowed on adjacent hatch covers or on the quayside when the hatch is open. Alternatively side rolling covers may be used if the hatchway is not too wide in relation to the ships breadth Deck Openings As deck opening becomes larger, the problem of ensuring adequate hull strength becomes more complex. The necessary longitudinal strength of the hull girder can be readily achieved, even for ships with hatch widths 80 percent of the breadth of the ship, by the use of high tensile steels. But the provision of the adequate torsion strength may require very detailed design and stress analysis, since the torsional deflection of a ship with large hatchways give rise to high stress concentration at the corners of the openings and to deformation of the hatchway.
38 26 Figure 3.1 (a) Rounded deck opening with coaming (b) Coaming plate following deck opening Source: Cargo Access Equipment for Merchant Ships. To avoid high stress concentration in deck plating, the corners of deck openings should be elliptical or parabolic. As the corners of the hatch covers are usually rectangular, provision has to be made to accommodate the hatch coaming. This can be done in two ways: either a square coaming can be built with the rounded deck plating protruding into the coaming space shown in fig3.1 (a) and (b) or the coaming can follow the shape of the deck opening with a filling-in plate welded to its top. In both cases the clear opening for rectangular cargoes like containers will be appreciably smaller than the maximum dimensions to the inside of the coamings Drainage As mentioned earlier, an important function of access equipment is to prevent water entering the ship through the openings in its hull. If the hull is flexing in heavy weather, it is almost inevitable that some water will penetrate the seals of closing devices, especially if they are worn. Thus there must be a second line of defence, such as drains, for removing any water before it can damage the cargo. Drainage facilities must be built into all terms access equipment. Here water which seeps past the peripheral seal of a hatch cover runs along a channel and is discharged onto the weather deck through a hole in the coaming. Where the drain is below the freeboard deck, as in flush weather deck covers, it must be connected to the bilge, or overboard via a scupper and non return valve.
39 27 It is also necessary to provide drainage for the vehicle deck in Ro-Ro vessels. Any scupper which drains a space within an intact superstructure on the free board deck (usually the main vehicle deck) is led overboard through a pipe fitted with a screw-down non return valve having open/shut indicators and capable of being operated from accessible positions above the freeboard deck. Alternatively the scupper may be led down to the bilges or to a drain tank. In an enclosed tween deck space with a continues centre-line casing, additional scuppers must be installed adjacent to the casing on the main vehicle deck. Where the inboard end of a deck scupper would be below the load waterline at an angle of heel less than 15 degree, it should be led to a separate drain tank, which may be pumped overboard. 3.3 SPECIFIC DESIGN REQUIREMENTS FOR HATCH COVERS Hatch Covers The hatch cover structure consists in essence of steel beams or grinders spanning the shorter hatchway dimension, plated over on top completed by steel side and end plates. The top plate provides the top flange of the beams and grinders. For the simpler types of hatch cover panel, e.g. pontoon or single pull, the design and analysis assume a uniformly loaded simply supported beam as shown in the fig 3.2. Figure 3.2 Beam is treated as a uniformly loaded simply supported structure Source: Cargo Access Equipment for Merchant Ships Structural regulations The construction of exposed hatch covers is governed by regulations 14 to 16 of the 1966 Load line convention (1966 LLC). Regulation stipulates that exposed coamings and hatchway covers above the superstructure deck shall comply with the requirements of the appropriate national administration, which means in effect, that
40 28 such equipments must be design in accordance with the current practice of the administration. Table 3.3 below summarizes the other requirements of these regulations for beam and board portable covers, and steel pontoon covers secured by tarpaulins and battening devices, and steel covers fitted with direct securing arrangements. In this context steel pontoons are plated, covered having interior webs and stiffeners, extending the full width of the securing arrangements. Classification society rules embrace these regulations but are more detailed and include non statutory non exposed cargo covers; they vary slightly between societies. Some important aspects of hatch cover design are not the concern of the 1966 LLC, such as increase scantling for special cargo loads. Table 3.3 Summary of 1966 Load Line Convention hatch cover regulation Hatch cover types Materials requirements Portable covers secured watertight By tarpaulins and battering devices Wood board and mild steel beams Minimum thickness of wooden boards assumed load ship length under 24m ship length over 100m ship length 24m- 100m load factor maximum deflection Steel pontoons Assumed load
41 29 load factor maximum deflection minimum platethickness Other steel hatch cover secured weather tight with gaskets and clamping devices mild steel assumed load load factor maximum deflection minimum plate thickness 1) With maximum span of 1.5m. thickness increased proportionately for large spans. 2)Maximum stress to be less than (minimum ultimate strength of steel)/(load factor) 3)The strength and stiffness of covers made of materials other than mild steel must be equivalent to those of mild steel to the satisfaction of administration Source: Cargo Access Equipment for Merchant Ships Cleats The 1966 LLC requires that satisfactory means for securing weather tightness be provided, and gives requirements for covers secured by tarpaulins and battens. For gasket covers, details are usually agreed between the hatch cover designer and classification society.
42 30 An important aspect of the gasket type securing arrangement, whatever its form is that the pressure between the sealing gaskets and compression bars is correctly maintained. Manual cleats are often over tightened despite the steel to steel contact of the cover skirt plates on the coaming bar, with the result that gasket. Life is severely shortened. This problem is overcome by the introduction of resilient and quick acting cleats which means that the correct sealing pressure is consistently and uniformly applied. Cleats on steel covers are generally spaced about m apart, closer adjacent to the corners, and no more than 0.6 m apart for wooden covers. With the advent of larger and heavier hatch covers, the classification societies have, in some cases, approved covers with greater than usual cleat spacing Loads The hatch loading laid down by the 1966 LLC and summarized in table shown take account of the forces exerted on exposed covers by heavy seas breaking over the deck. Once again however, these are mandatory minimum values and the classification societies may require that they are increased in certain cases. Thus for hatch covers on which deck cargoes are rarely if ever carried, the loading laid down are adequate, typically 1.75 tonnes/. This is equivalent to the cargo stowed 2.45 m high at 1.39 /tonnes. Loading for the covers in the foremost quarter of the ship s length may be increased to counter the severe sea water forces likely to be experienced in this region Scantling Minimum scantling (thickness and dimensions of steel plating and stiffeners) and load factors for steel covers respecified in the 1966 LLC, so that the load factor multiplied by the maximum stress in the covers is less than or equal to the minimum ultimate strength of the steel. Corresponding minimum scantling depending on loading are given in classification society rules, alternatively direct calculations of required structural strength may be made using maximum design stress levels. Table 3.4 below shows the requirements of Lloyd s Register with respect to steel hatch covers or other access equipments constructed of grade A mild steel having a minimum ultimate tensile strength of 4100Kgf cm square.
43 31 Table 3.4 Access equipment strength calculations Factor Weather deck Tween-deck Maximum bending stress, kgf/cm square Maximum shear stress, kgf/cm square Maximum deflection * span *span Source: Cargo Access Equipment for Merchant Ships. The top plate of a typical hatch cover panel may be from 6-13 mm thick depending on the spacing of the beams (generally, thickness=spacing/100). This plate is stiffened by beams spanning the hatch cover, usually fabricated tee beams having a depth of about 4 percentage of the span and spaced mm apart. The panel is completely by side and end plates which may be from 8.20 mm thick Deformation As the ship become larger and hatchways take up a greater percentage of the deck area, so the question of hatchway deformation becomes more important. Traditionally ships have fairly small hatchways and so have derived a considerable amount of their strength from their decks. As hatchways have increased in width, so the deck contribution to the longitudinal and the torsional strength of the hull girder has declined, being limited to the strips of deck outboard of the coaming and between the hatches. A ship with hatchways more than 70 percentage of the beam in width has approximately half the torsional rigidity of a similar ship with hatchways which are only 40 percentage of the ship s beam. Compensation in the form of thickened plating and/or box girders may be required. Fig 3.3 indicates the extent of hatchway deformation that may be encountered in a large bulk carrier loaded in alternate holds. Although the deformation is not excessively large and is not permanent, they can be sufficient to allow sea water to enter and parts of the hatch cover to fracture.
44 32 Figure 3.3 Detailed analysis of the structure of a 120,000 tdw bulk carrier Source: Cargo Access Equipment for Merchant Ships. It has been suggested that, since hatchways are always closed by hatch covers, the latter ought to be designed to contribute to the strength of the hull girder. This is however not practical as the devices securing the cover to the coamings would have to be excessively robust, and any deformation due to the loading of the vessel in port could lead to the covers becoming jammed and thus impossible to open. Moreover, to make a significant contribution to vessel s strength, the covers would have to be considerably stronger and heavier than at present, and this could introduce operational difficulties. Hatch coamings can be designed to contribute to the longitudinal strength of the ship but there can be problems associated with this. If it is decided to use the coaming in this way, they must be continuous over the midship portion of the ship and properly tapered at the forward and after into account in calculating the midship section modulus, according to classification society requirements.
45 33 Longitudinal deformation of the top of the coaming is due to the hogging or sagging of the vessel. It depends on hatchway length and may be as much as 7-8 mm at each end. Longitudinal deformation is compensated for by fitting at the ends of the hatch cover with wide gaskets whose rubber absorbs the relative movement of the compression bars as the sip works. Hatch end cleats must allow such movements, which would otherwise be taken up at the cross joint with attendant risk of leakage. Steel to steel contact is must. The purpose of this is to prevent the over compression of the gaskets. However, it gives rise to a frictional force whose magnitude depends on the pressure of the cover on the coaming bar and their relative movement. Transverse deformation is caused mainly due to the vessel s changes in draft as cargo is worked, but also by hogging and sagging. Deformation of as much as mm over the width of long hatchways is possible. Relative movement between the cover and the coaming is allowed for in a similar way to longitudinal deformation, by providing the cover with wide gaskets, and by ensuring that the wheels on one side of the hatch cover panels are free to move laterally as shown in fig 3.4 Figure 3.4 Hydrostatic pressure Source: Cargo Access Equipment for Merchant Ships. Torsional deformation is caused by the combination of non symmetrical loading of the vessel and hydrodynamic forces when the ship heads diagonally into waves. It can rack the midships hatchway diagonal of a large container ship by as
46 34 much as 30 mm. Fig 3.5 shows the torsional distortion and the resultant movement between the hatch cover and coaming. By fitting resilient cleats at the ends of the hatch covers, some movement between cover and coaming takes place, thus reducing the relative movement between panels. Figure 3.5 Torsional distortion of hatch ways Source: Cargo Access Equipment for Merchant Ships Seals The 1966 LLC requires cargo access openings to be weather tight which is generally achieved by an arrangement of sealing gaskets and drainage channels. The main requirements of sealing system are as follows: (i) (ii) (iii) (iv) (v) (vi) It must prevent any transfer of water from outside the ship to the cargo space, On combination carriers, it must be oil tight to prevent any transfer of liquid from the inside of a cargo space to the outside, when subjected to the pressures. It must be able to maintain the weather tight integrity of the cargo space in all sea states and thus, it must be able to accommodate the deformation discussed earlier. It should be resilient and able to accommodate normal irregularities in the mating surfaces, The gasket should be abrasion resistant as it may rub against the mating surface. It must also be resistant to cargo contact, It should be easy to maintain,
47 35 (vii) It should retain all the above properties throughout a long service life, exposed to climate extremes Gaskets material Gaskets material must be of a suitable quality; it should not harden excessively when subjected to neither sub-zero temperature nor soften in tropical conditions. Particularly important in this respect are gaskets fitted to refrigerated vessels. Most gaskets used for seals on dry cargo ships are of natural, synthetic or neoprene rubber, while combination carriers requires a nitrile composition, resistant to chemical attack by oil. In general neoprene synthetics have good heat, ageing, weather and flame resistance, but only moderate oil and chemical resistance but worse cold temperature properties. General construction of seal steel work, welding and painting needs careful attention Compression bars The usual arrangement of compression bars is shown. It is of rectangular section mild steel welded to the coaming bar. After several years of service, these bars can become badly corroded and require replacing. Moreover, they may then have sharp corners which press into the gaskets so that the rubber takes on a permanent set earlier in its life than would be the case for a sealing arrangement employing either a round compression bar, as shown or rectangular one with rounded corners. The latter produces an element of knife edge loading which gives the good seal with the rubber. When such compression bars are fitted, they are often of stainless steel, which, although initially expensive, often worthwhile as it is not usually necessary to replace the bar during the life of the corners 3.4 CONSTRUCTION MATERIALS In general, Grade A mild steel is used for the construction of all cargo access equipment. Grade A is the ordinary mild steel used for most ship building purposes. Certain application requires Grades D and E steel. Grade D is notch-tough steel with a chemical composition largely chosen by the steel producer provided that it retains good weldability. Grade E steel is the highest grade and is also notch-tough but its manufacture and composition are strictly controlled. Grades D and E steel are specified for coaming bars on refrigerated ships where low temperature brittle fracture
48 36 must be guarded against. As these steels have low corrosion resistances, special coating, e.g. epoxies, are often used on the underside of hatch covers where sweating can cause accelerated corrosion. Other materials such as higher tensile steel and aluminium are acceptable to the Classification Societies Higher Tensile Steel (HTS) If the stress level within a structure were the only factor governing its scantlings, the use of higher tensile steel instead of mild steel would result in weight savings of up to 15 percent. However stress is not the only governing factor. Deflection, minimum thickness, ease of construction, initial and maintenance costs must all be taken into account. Higher tensile steel (HTS) can sometimes be used for the beams of hatch covers, with their top plates made from mild steel. This reduces the weight of the covers, without incurring the extra cost of using all HTS construction. Thus, HTS is sometimes used on hatch covers where, by reducing the cover weight slightly, it may be possible to install less powerful operating mechanism. Construction entirely in HTS is sometimes used in pontoon covers for container ships, to keep their weight below the maximum lifting capacity of container cranes Aluminium Aluminium structures can be percent lighter than equivalent mild steel structures. Most of the problems associated with higher tensile steel are not present with aluminium. Since it is not as strong as steel, thickness have to be increased, thereby alleviating problems associated with minimum regulatory deflection, buckling etc., unless the design is such that deflection is significant. Welding aluminium does however require special skills and equipment. Corrosion is less of a problem if the correct grade of material is used and if precaution are taken where steel and aluminium meet, e.g. at coamings. The spacing of stiffeners can be increased in an aluminium structures this has the added advantage that the number of stiffeners and hence the weight and cost of the structure can be further reduced. The major disadvantage of aluminium is that a suitable grade of material for access equipment costs approximately eight times as much per tonne as mild steel, with the overall effect of increasing the cost of the cover by upto three times. Aluminium covers have been fitted to deep tanks because they are so much lighter. Since deep tank covers are often made in one piece, aluminium covers are
49 37 easier to handle without power assistance. Aluminium single pull weather deck covers have occasionally been fitted in the past, sometimes experimentally. Aluminium can be used for Ro-Ro vessel access equipment but it is usually limited to small ramps and car decks. It is less resistant to fire damage than steel Glass Reinforced Plastic (GRP) GRP structures are light but the modulus of elasticity of GRP is only 7 percentages of that of mid steel and excessive deflection is a problem which invariably accompanies its use. Additional stiffening is thus necessary, making the structure heavier and more expensive to manufacturer. For this reason GRP has not as yet found wide application in the construction of cargo access equipment, although development work is in progress. GRP in sandwich construction could be particularly suitable for covers in refrigerated ships because insulation can be built into them during the manufacturing process at very little extra cost, whereas the present system of insulating steel covers is expensive and time consuming Wood Wooden covers no longer supplied to weather decks of new cargo ships, although on rare occasions, they are fitted in tween decks. Classification society rules lay down scantling for beam and boards covers because of LLC requirements; in practice they care now mainly for the benefit of repair to older ships.
50 38 CHAPTER 4 - OPERATIONAL AND SAFETY ASPECTS 4.1 BASIC ADVICE There are procedures which will help to keep ship s hatch covers in good condition. The following advice can be considered best practice Always Carry out regular examination of the hatch covers, hatch beams and coamings to identify: o General levels of corrosion (check with your classification society for corrosion allowances); o localised corrosion at welded connections (grooving); o Cracks in joints and weld metal; o Permanent distortion of plating and stiffeners; Call a Class Surveyor and carry out repairs as soon as possible when there are: o Indications of excessive corrosion e.g. holes or local buckling of the top plate; o Cracks in main structural joints; o Areas of significant indentation, other than localised mechanical damage; Be particularly vigilant after heavy weather; Rectify any steel-to-steel fault before renewal of rubber packing. Renewal will not be effective if steel-to-steel contact points are defective, and expensive rubber packing will be ruined after only a few months of use; Replace missing or damaged hatch gaskets (rubber packing) immediately. The minimum length of replaced gasket should be one metre; Keep hatch coaming tops clean and the double drainage channels free of obstructions. (Open hatch covers to clean coaming tops and the double drainage channels after loading bulk cargo through grain or cement ports); Keep cleats and wedges in serviceable condition and correctly adjusted; Keep hauling wires and chains adjusted correctly; Attach locking pins and chains to open doors and hatches;
51 39 Keep wheels, cleats, hinge pins, haul wires, and chain tension equipment wellgreased; Test hydraulic oil regularly for contamination and deterioration; Keep hydraulic systems oil tight; Ensure the oil tank of the hydraulic system is kept filled to the operating level and with the correct oil; Clean up oil spills. If the leak cannot be stopped immediately, construct a save-all to contain the oil and empty it regularly; Engage tween deck hatch cover cleats when the panels are closed; Give notice that maintenance is being performed so that no one tries to open/close the hatch; Remember that continuing and regular maintenance of hatches is more effective and less expensive than sporadic inspection and major repair Never Treat temporary repairs as if these were permanent. The strength of the cover and ultimately the ship will depend on the quality of repairs carried out; Ignore serious corrosion, cracking or distortion in the covers and supports. These are signs of weakness and are potentially hazardous; Allow grooves to form in the coaming top, especially where the hatch side or end panel rests when the hatch is closed; Apply petroleum-based grease or paint to rubber packing; Remove the rubber ball from a non-return drain valve; Use anything other than the recommended hydraulic oil; Leave cleats unfastened when proceeding to sea; Attempt to open or close any hatch that has a load or cargo on it; Open hatch covers at sea unless absolutely essential; Leave open covers unattended when at sea; Tighten down the cleats so that the hatch cover is unable to move on the coaming top.
52 MONITORING AND INSPECTION Hatch covers and their fittings should be inspected at the end of every cargo voyage and all findings recorded. Inspections should be planned and held in time for repairs to be completed before the next cargo voyage. Empty cargo spaces of all cargo and combustible material if welding torches are used Inspect and Check: Condition, Covers and coamings should be well painted and free from significant corrosion, cracks and distortion. During an inspection look for: o Holes and permanent distortion in the plating o Distortion of beams and/or stiffeners on the underside of the top plate o Corrosion around welded connections of beams or stiffeners o cracking of connecting joints and welds Hatch movement. This should be smooth. If violent movement is observed, investigate and remove the cause. Towing and backhaul wires. These should be free of kinks or broken strands. Repair or replace damaged or worn wires. Use extreme care when handling wires to avoid injury. Hydraulic system for leakage. Hinge pins. Look for wear, particularly at cross-joints and hydraulic cylinders. Worn hinge pins can cause hatches to slew and misalign at the cross-joint(s). Misaligned hatch panels will leak. Drive chain tensioners. Check their condition and adjustment. Cleats and wedges. Check for physical damage, corrosion and tension when locked. Figure 4.1 panel should be in line with next panel Source: Lloyd s Register- A Master s Guide to Hatch Cover Maintenance
53 Drive Chains; Check their Length Drive chains and associated equipment are fitted in pairs, opposite one another. The side towing chains, sprockets and hydraulic cylinders on opposite sides should match. Adjust the tension of chains between panels so that the chains on both sides are exactly the same length. Do this by removing or adding chain links. If the entire length of chain needs to be replaced, then replace the chains on both sides at the same time. Always consult the hatch cover manufacturer for details of chain length. As a rule, chain sag, measured from the assumed horizontal at mid-point along the chain, should be a fist wide Steel Landing Pads; Check for Wear Worn landing pads will damage hatch gaskets and cause hatch leakage. When newly fitted and closed in the sea position, the top plates of adjacent hatch panels should be level. Any deviation from level is an indication of landing pad wear or permanent distortion. If noted, investigate fully and repair immediately End Stop Pads; Check for Damage End stop pads prevent hatch panels from overrunning when hatches are fully open. Look for physical damage Hatch Wheels; Check for Alignment Hatch wheels should align squarely with the hatch track way. If the wheel axle is worn the wheel will loll. If it does, repair immediately Rubber Seals; Check for Elasticity, Mechanical Damage and Permanent Deformation When hatches are opened, rubber seals should regain their original shape. If they do not, check for ageing. Permanent deformation should not exceed 75 percent of the design compression Locking Devices and Hydraulic Cut-Outs; Check that they Operate Locking devices are often pins or hooks, these should engage when the hatch is open. Look for physical damage, rusting and seizure. Hydraulic cut-outs should move freely.
54 Spares Rubber packing and adhesive has a limited shelf life, so check the date stamp and discard if beyond the use-by date. There should be sufficient spare parts (cleats, wedges and gaskets) to complete planned routine maintenance. Always use manufacturers approved spare parts. 4.3 HEAVY WEATHER PRECAUTIONS The following precautions should be taken if rough or heavy weather or when high swells are expected or when it is likely that water will be shipped on deck Prior To Rough Weather: Check that hatch cleats are properly secured and adjusted. In rough weather, hulls are subjected to high racking forces, so it is essential that hatch covers are held in place but allowed to flex. Check that all drain valves are operating correctly and that they are open. Drain valves are the last defence against water entering the cargo space. The drainage system will be needed during heavy weather, so it must be fully operational. As a precaution, briefly pressurise the hydraulic system to ensure that it is fully charged and that the piping is filled with oil. This has two benefits, first, it prevents the possibility of seawater entering loose couplings or seals, and secondly, it eliminates any creep which may have occurred After Rough Weather: Inspect all cleats, drain valves, guides and hydraulic components for damage. If hydraulic components have been damaged, do not attempt to open the covers. The emergency opening procedure should be followed until the hydraulic components have been checked and tested. Check hatch covers for buckling or distortion. When opening the hatch covers check for uneven movement and any unusual noises that may indicate damage. Check all grease points and re-grease.
55 43 Figure 4.2 Vessel in rough weather Source: Lloyd s Register- A Master s Guide to Hatch Cover Maintenance 4.4 SAFETY WHEN WORKING WITH HATCH COVERS The avoidance and prevention of injuries is of paramount importance. Before working on a hatch, a risk assessment should be completed to identify all hazards. Control and safety procedures should be examined and modified so that hazards are reduced to minimal levels. The following points should be borne in mind: If entering the hold alone, always ensure someone else knows you are there and leave a prominent notice at the hold entrance. Check the lock-back mechanism on the hold access door or manhole is operational figure 4.3.
56 44 Figure 4.3 Check the lock-back mechanism Source: A.Bilbrough & Co. Ltd., Holds and Hatch Covers Do not use damaged or unsecured ladders, accept in emergencies and then only with a secured safety harness (figure 4.4). Check lighting is adequate particularly at the bottom of the ladder. If the hold is unlit, use a powerful torch attached to a sling or strap across the shoulder. Figure 4.4 Do not use damaged or unsecured ladders Source: A.Bilbrough & Co. Ltd., Holds and Hatch Covers
57 45 Figure 4.5 Never smoke in a hold. Source: A.Bilbrough & Co. Ltd., Holds and Hatch Covers Figure 4.6 Never climbs on top of bulk cargo without a lifeline Source: A.Bilbrough & Co. Ltd., Holds and Hatch Covers Always have both hands free for climbing up or down ladders; lower or haul tools and equipment by rope.
58 46 Figure 4.7 Never carry tools or equipments while descending or ascending a ladder. Source: A.Bilbrough & Co. Ltd., Holds and Hatch Covers Figure 4.8 Never stand on the coaming top when the hatch covers are open. Source: A.Bilbrough & Co. Ltd., Holds and Hatch Covers Always wear protective boots or shoes for working on deck. Do not stand under openings.
59 47 Figure 4.9 Always wear protective headgear when working. Source: A.Bilbrough & Co. Ltd., Holds and Hatch Covers Always clean up oil spills. If the leak cannot be immediately stopped, build a save-all around and regularly empty it. Exercise extreme care when handling wires. Figure 4.10 inspect wire for wear, kinking or broken strands at regular intervals. Source: A.Bilbrough & Co. Ltd., Holds and Hatch Covers
60 48 Figure 4.11 Always takes precautions when fumigating. Source: A.Bilbrough & Co. Ltd., Holds and Hatch Covers 4.5 Procedures to Open and Close Hatch Covers Prior to opening or closing a hatch, the watch officer should be informed and the condition of the hauling wires or chains checked; the hydraulic system should be topped up. Never open or close more than one set of hatch covers at a time Opening Procedures Check that the hatch cover panel stowage area is clear of people, equipment and dunnage; Disengage all cleats; Attach towing or hauling wires; switch the power on and ensure the controls are in neutral; Ensure that all personnel are clear of the hatch and its tracking. Position crewmembers to observe both sides of the hatch; Raise hatch covers to the roll position by jacks or by raising the lifting system. (The panels need to clear the hatch guides); Check that towing chains are free and do not foul tracks or the coaming top; Start to open the hatch, slowly at first, then at normal operating speed until the hatch is almost open and then reduce to slow speed until fully open. Care must
61 49 be taken when opening hatch covers especially when the speed of opening can be only partially controlled; When fully open, secure the hatch with the safety hook or pin before the power is switched off. If applicable, remove the towing and hauling wires; Install portable safety rails, if supplied Closing Procedures Check that the coaming top is clear of cargo or debris; Check and clear drain channels and entrances to the drain valves; Check that any damaged wheel tracks, compression bars and landing pads have been repaired; Ensure that the hold is clear of people and that access hatches or entrance doors are open. Check towing chains are free; Attach towing or hauling wires, switch the power on and ensure the controls are in neutral; Remove portable handrails; Release hatch locking pins or hooks; Avoid injuries by ensuring that all personnel are clear of the hatch. Position crewmembers to observe both sides of the hatch; Check that towing chains are free and do not foul tracks or the coaming top; Start to close the hatches slowly at first with the speed of closure being gradually increased to the normal operating speed. As the hatch reaches the closed position the speed should be gradually reduced. Great care must be taken when closing hatch covers; Lower hatch covers into guide pockets using jacks or lifting cylinders. Some hatches are lowered automatically; Attach cleats before removing the towing wire or switching power off; Finally, check no one is in the hold before closing hold access hatches or other hold entry points.
62 Maintenance and Repair Poor maintenance of hatch covers causes leakage leading to cargo damage and represents a hazard to the ship and its crew. Although hatch covers are simple and durable, their sealing gaskets are easily damaged. The quality of sealing is affected by lack of alignment and poor gasket compression. When hatch covers are opened at the end of an ocean voyage, look for signs of leakage such as rust staining or drip marks. Regular adjustment and repair, by ship s staff, will reduce the overall cost of maintenance. Painting double drainage channels will help to prevent corrosion. Always keep a detailed record of maintenance. Take care during extensive hatch cover repair to avoid cover distortion Rubber Gaskets Keep clean and free from paint. If physically damaged, permanently set-in or aged, replace with minimum 1 metre lengths. Always follow the manufacturer s instructions when renewing gaskets Gasket Channels If gasket channels are badly corroded, causing the hatch packing to hang loose, the packing should be removed and the channel repaired by welding new metal strips which should be painted before fitting new rubber. Always follow proper fire prevention safety procedures. Make sure that cargo spaces are free of cargo and combustible material. When conducting extensive structural repairs, remove the hatch covers to shore Hatch Cover Structure Repair or replace any damaged, worn or defective hatch covers or coamings. Consult with the ship s classification society before commencing repair. Paint new structure immediately Compression Bars Effective sealing is only possible with a straight, undamaged and non-corroded compression bar. Compression bars which are not in this condition should be repaired or replaced, taking care to align the bars properly.
63 51 Remember to carry out a chalk test to check alignment, both during and after repair Landing Pads Hatch sealing is arranged by design to give the correct compression of the gasket when there is metal-to-metal contact on the hatch landing pad, side plate, or interpanel block. If landing pads are reduced in height (check with manufacturers drawings) because of wear, repair is essential Hatch Wheel Track Ways Track ways can corrode. They are weakened by abrasive wear and tear. When weakened, track ways can distort and break, affecting hatch movement and alignment. Deterioration is visible to the naked eye. Repair by replacing the worn or damaged material with sufficient new material to restore strength. Always keep hatch wheel track ways clean and painted Hatch Coamings Look for cracks at coaming corners. If any are found, consult the ship s classification society before commencing repairs in case the coaming needs to be reinforced. Examine coaming support brackets for corrosion where they connect with the ship s deck. Make sure coamings and their support brackets are painted. Coamings can be damaged by cargo equipment during loading or discharge. Look out for damage and repair if found Hatch Cleats and Wedges It is important for compression washers to be adjusted correctly. A locking nut for adjusting compression is situated at the base of the cleat. The procedure to alter compression (see illustrations) is as follows: Close hatch and secure for sea; Place the cam of the cleat in the hatch socket as if to lock it, but leave it unlocked (the cam should move freely and fit snugly in its housing); Adjust the locking nut until the compression washer touches the underside of the hatch coaming or its steel washer; Turn the locking nut one full turn to achieve the desired tension;
64 52 Do not over-tighten; Protect the thread on completion. When closing and securing a hatch for sea passage, check the tension in side cleats. Cleats should never be adjusted in isolation, adjust all cleats along the hatch skirt at the same time Hatch Cross-Joints It is essential for the cross-joint to be in good condition and properly aligned. Maintenance and repair should focus on: Examination of the cross-joint structure for corrosion. Examination of joint hinges for pin wear, blade cracking or weld failure. (Re-grease the hinge pin bushes making sure grease reaches the hinge pins). Examination of the steel-to-steel inter-panel blocks and locators for wear. (Check the top plate of hatch panels, they should be level when closed). Checking the gap between panels when they are closed. Misalignment could be caused by an incorrectly adjusted cylinder or the wheel tracks could be worn Hatch Wheels Hatch wheel spindles and bearings (where fitted) need to be greased regularly. Check the wheel spindle for wear and the wheel housing for physical damage. Repair if the spindle is worn or if the wheels are out of alignment Drain Channels and Non-Return Valves Clean coaming tops and cross-joint channels by removing any loose scale or cargo residue by brushing or hosing. Clean coaming drain holes and check that the nonreturn valve is functioning Greasing Wheel spindles, cleat spindles, hinge pins, hydraulic cylinder protective sheaths, cleat wedges, drive chain sprockets, toothed rack and cylinder spherical bearings need to be kept well-greased. Re-grease every month if necessary, and always apply new grease after the ship has passed through heavy weather.
65 Painting Corrosion occurs mainly at the panel ends along the cross-joint or where access is difficult, but it can also occur on the underside of a panel, especially along hatch beams. Regular painting will be necessary Inert Gas Hatch covers with a double skin, in the form of a closed box, are filled with inert gas. After structural repair, the inner spaces must be re-inerted. This is done by inserting special tablets (available from the hatch cover manufacturer) into the space and welding shut. Never allow water to penetrate the box construction Hydraulic Systems and Components The cleanliness and viscosity of hydraulic oil must be checked. Samples of the oil should be sent to a chemist for testing (use the same company that checks and tests your fuel and lubricating oil). The hydraulic system is provided with bleed points from which samples can be taken. Hydraulic oil should be changed every five years or after there have been significant repairs, such as piping or cylinder replacement. Hydraulic oil filters should be changed every twelve months. Do not contemplate repairing the hydraulic system without the proper components and skilled fitters Use of Sealing Tape and Foam Fillers The use of sealing tape and foam fillers should be limited to: Emergency use. When hatches are known or thought to be leaking and there is insufficient time to complete permanent repairs; Charterers requirement. Charterers may require owners to apply sealing tape when highly water-sensitive cargoes are carried; Fumigation tape is usually applied to hatch covers during fumigation. The tape is not heavy duty and should be removed when fumigation has finished. Foam fillers can be used to fill the air space which is formed along the crossjoint of two closed panels. In heavy weather foam fillers may be washed away, their use should never be solely relied upon to prevent water ingress.
66 54 CHAPTER 5-SINGLE PULL MACGREGOR TYPE HATCH COVER DESIGN The hatch cover must be safe to operate, and it must be cost effective, both as an initial investment and in service, i.e. the maintenance cost has to be low and the service lifelong. Furthermore, the design of the hatch cover must suit the various general arrangements of vessels. Figure 5.1: Single Pull MacGregor Type Hatch Cover Source: Internet Single pull cover 1. Rising track. 2. Panel side chains. 3. Falling track (behind coaming). 4. Balancing roller. 5. Eccentric wheel. 6. Screw cleat. 7. Wheel guide rail. 8. Compression bar. 9. Coaming bar, Coaming stiffener. 10. Coaming hatch stay.
67 Coaming. 12. Sheave. 13. Cross joint cleat. 14. Panel top plate. 15. Backhaul wire. 16. Wire to winch or crane hook; bull wire. 17. Rubber gasket. 18. Stowage bay. The model of MacGregor single pull hatch cover is obtained from the ship named M V IRAN owned by Islamic Republic of Iran Shipping. This was a bulk carrier which was used to carry sacks of cement in bulk.there were 4 cargo holds in this ship using MacGregor single pull hatch cover. Team selected the first cargo hold and its dimensions and reduced to a convenient ratio of 1:25 to make the project. DESIGN BASIS NAME : M V IRAN OWNER : ISLAMIC REPUBLIC OF IRAN SHIPPING GENERAL CHARACTERISTICS CLASS AND TYPE : BULK CARRIER TONNAGE : 44,468 DWT LENGTH : METER BEAM : 30 METER DRAUGHT : 11 METER DEPTH : 16.0 METER INSTALLED POWER : 8238 KW PROPULSION : ONE FIXED PROPELLER SPEED : KNOTS CAPACITY : 54237M³ NO OF HOLDS 4 HOLD DIMENSION IN METERS HOLD NO 1 : HOLD NO 2 : HOLD NO 3 :
68 56 HOLD NO 4 : HATCH OPENINGS IN METER : NO OF PANTOONS : 4 TYPE : SINGLE PULL MACGREGOR TYPE NOTE : SACK CARRIER 5.1 PARTS DESIGN After studying all the hatch covers and their safety and operational aspects, team which comprise of six persons decided to design a working model of a single pull MacGregor type hatch cover. The various design aspects are given in this chapter Hold Design The hold design was selected from the cargo hold no 1 of the M V IRAN ship. The model was made in a convenient ratio 1: 25. Figure 5.2: Hold Design Source: Team Length of the hold: 150cm Width of the hold: 120cm Depth of the hold: 63.3cm Plate thickness: 1.5cm Hatch Opening Dimensions The hatch opening dimension was exactly followed from cargo hold no 1. Length: 74.6cm
69 57 Breadth: 44.5cm Figure 5.3: Hatch Opening Dimensions Source: Team Hatch Coaming Design The hatch coaming design is made from the ship after looking the minimum requirements stated in the load line convention. Figure 5.4: Hatch Coaming Design Source: Team Height: 10.3cm Height of hatch coaming stay: 8.3 Width of hatch coaming stay: 2cm Thickness of hatch coaming stay: 1cm Supported area: 14.3cm
70 58 Number of coaming hatch stay in end coaming: 3 Number of coaming hatch stay inside coaming: 4 Support for coaming (inside): cm square Number of supports in end coaming (inside): 3 Number of support in side coaming (inside): 4 Thickness of the support: 2cm Length between supports: 20cm Thickness of rubber gasket: 1cm Hatch Cover Design The model consists of four Pantoons whose design was taken from the ship Pantoons design. Figure 5.5: Hatch Cover Design Source: Team Length: 58cm Width: 23cm Thickness at middle: 3cm Thickness at edge: 2cm
71 59 Slope: 1cm Total number of panels: 4 Numbers of sliding wheels: 4 in each panel Diameter of sliding wheels: 2cm Wheel to wheel length: 19cm Numbers of balancing rollers: 2 in each panel Diameter of balancing rollers: 3cm Length between balancing roller: 20.3cm Type of connection in between two panel: Chain Chain length between two panel: 20.3cm Chain size: 0.7cm Size of chain connector: 4.5cm Track 1 Design The tracks design was taken from the Design features of the MV IRAN ship. Figure 5.6: Track Design Length: 85cm Width: 2.54cm Source: Team
72 Rising Track Design (Track 2) The rising track design was taken from the ships track design of MV IRAN. Figure 5.7: Rising Track Design Source: Team Overall length: 66.5cm Slanting height: 14 cm Straight length: 46.5 cm Peak height from the deck: 16cm Jack Design Since the eccentric wheel is not available for the model size, alternate arrangement for lifting the track was made using hydraulic jack. Since the team were not designing the hydraulic jack, the same of appropriate size and adequate power was brought from the market as per the instructions from project guide and team decision Figure 5.8: Jack Design Source: Team
73 61 Height of jack while normal condition: 15cm Height of jack while lifted condition: 18cm Lift of jack: 3cm Capacity of jack: 2000kg Crane Space Design The design of the crane space was taken directly from the ship. Figure 5.9: Crane Space Design Source: Team Height: 35.5cm Length: 50cm Breadth: 12.3 cm Pulley height from weather deck: 32.5cm Angle of pulley fitted related to base: 40 degree Motor Casing The motor casing was designed according to the motor dimensions. Length: 24.5cm Height: 25cm
74 62 Breadth: 10.7cm Motor Specifications The motor was selected according to the power required to roll the pantoons over the track and to pull the pantoons back to position. The motor selection was made after several trials. Voltage: 240 V Current: 12mA Phase: single phase Frequency: 50 Hz Power: HP Torque: 3.5cm Capacitor:.82 K Shaft diameter: 1cm Forward reverse switch: 240 V; 5 Ampere Push button: 240 V; 5 Ampere Pulley Design The pulley was selected according to the dimension of wire rope and the power required for opening and closing the hatch cover. Pulley fitted to the motor: Diameter: 8cm Numbers: 2 Width: 3cm
75 63 Pulley for rope Diameter: 2cm Width: 1cm Numbers: Rope The rope was selected according to the safe working load of the model. Length: 300cm Diameter: 3mm Reduction Gear Design The selected motor was 60 rpm speed and for the correct working of the hatch cover, the team designed the reduction gear to reduce the speed into 13 rpm. Number of teeth in bigger gear: 66 Number of teeth in smaller gear: 13 Actual speed: 60 rpm Reduced speed: 60=11.81(12rpm) Ladder Design The ladder design was taken from the MV IRAN Ship. Height: 36cm Width: 4.7cm Numbers of steps: 11 Gap between steps: 3.5cm
76 64 Figure 5.10: Ladder Design Source: Team Bulwark Design The design of the hand rail was taken according to the convenience. Figure 5.11: Bulwark Source: Team
77 65 Height from the deck: 7.2cm Height to the first cross bar: 3.2cm Gap between bars: 4cm Cross bar diameter: 0.4cm 5.2 MATERIAL SELECTION The material was selected according to the availability in the market and for the easy fabrication process. The material was also chosen by considering economic limits. After all discussions with the team members and project guide, for the successful fabrication of the model the team decided to choose the following materials: Cargo hold : Ply Wood Hatch Coaming : Wood Hatch Stay : Wood Pantoons : Wood Sliding Wheels : Plastic Balancing Wheels : Mild Steel Chain : Metallic Chain Connector : Galvanised Sheet Track : Aluminium Rising Track : Mild steel Rope : Iron Track Support : Cast Iron Motor Casing : Ply Wood Pulley : 2 Plastics, 2 Copper Supports : Steels & Aluminium
78 66 Hand rail : Galvanised Iron Ladder : Galvanised iron Hold supports : Ply woods Side dog : Wooden Gaskets : Rubber Gear : Harden steel Motor shaft : Polished steel
79 67 CHAPTER 6 - FABRICATION The design was made with the specific dimensions and was submitted to project guide for approval. After making necessary changes as directed by the project guide, the design was approved. After the approval, team started the fabrication work which is explained in this chapter. 6.1 FABRICATION OF CARGO HOLD Ply wood material dimensions brought into workshop: 8 ft 6 ft: One piece 6 ft 4 ft: Two pieces 4 ft 4 ft: One piece Figure 6.1: Cargo Hold Source: Team Placed on the work table and marked the dimensions as follows: 120 cm 63.3 cm (bulkhead separation forward) 120 cm 63.3 cm (bulkhead separation aft) 150 cm 63.3 cm (side plate starboard) 150 cm 63.3 cm (side plate port)
80 cm 120 cm (weather deck plate) 150 cm 120 cm (bottom plate) Marked dimensions were cut accordingly. These parts were joined together in the shape of cuboid with the help of nail and gum. Sander machine was used to get the surface finish. The final hold dimensions: 150 cm 120 cm 63.3 cm 6.2 FABRICATION OF HATCH WAY Hold space was marked and removed using wood cutter from the cuboid made above. The dimensions were: 74.6 cm along the longitudinal axis of the hold cm vertical to the longitudinal axis. Edges were well polished with sander machine. Figure 6.2: Hatch Way Source: Team
81 HATCH COAMING FABRICATION Brought the wooden piece to the work table which having the dimensions: Length: 300cm Breadth: 12cm Thickness: 2.8cm Length of 300 cm was divided into four parts as follows: 80cm: Two piece 50cm: Two piece All the four pieces were planed and polished. New dimensions of pieces were: Length: 80cm Breadth: 11.8 cm Thickness: 2.6 cm Length: 50cm Breadth: 11.8cm Thickness: 2.6cm All the four pieces were joined together with the help of nails and hatch coaming was made. Figure 6.3: Hatch Coaming Source: Team
82 HATCH STAY FABRICATION Brought wooden reaper of dimension: Length: 400cm Breadth: 2cm Thickness: 1cm 14 pieces were made having length 7.6 cm each and 28 pieces were made having length 3cm each. These pieces were made into the shape (14 pieces) as shown below: Figure 6.4: Hatch Stay Source: Team 6.5 FABRICATION OF SIDE & END DOG Dimensions of wooden piece which was used: Length: 320cm Width: 10cm Thickness: 2cm
83 71 Using wood cutter length of 320 cm were cut into four pieces Length: 88 cm (two pieces) Breadth: 10cm Thickness: 2cm Length: 66cm (two pieces) Breadth: 6cm Thickness: 2cm Length of 80cm and breadth of 2.7cm was removed from the 88cm pieces as shown in the figure 6.5. Figure 6.5: Side and End Dog Source: Team All the parts were plain with planner machine and dog was fabricated. 6.6 FABRICATION OF HATCH COVER Dimension of the cylinder wooden piece which was taken to the mill: Length: 70cm Diameter: 38cm
84 72 Figure 6.6 Pantoons Source: Team From the above, four pieces of similar dimensions were made which having the dimensions: Length: 7cm Width: 25cm Thickness: 3cm The pieces obtained were taken to the work table. After the plaining and chisel work the final dimensions of hatch cover were: Length: 58cm Width: 22cm Thickness at middle 3cm Thickness at the edge: 2cm For keeping all four hatch covers in line with each other, locking arrangement were made throughout the length by using wooden reaper. Hatch cover 1: Locking arrangement at the aft end. Hatch covers 2 & 3: Locking arrangement at both ends. Hatch cover 4: Locking arrangement at the forward end.
85 73 Plastic wheels (16 pieces), metallic wheel (8 pieces) and the fitting arrangement were brought to the working table. Plastic wheels were fitted at each corners of the hatch cover as shown in figure 6.7. Figure 6.7 : Pantoons and wheels Source: Team Metallic wheels were also fitted according to the balancing dimensions. Figure 6.8: Metallic Wheels on A Pantoon Source: Team Washers were provided on both side of the metallic wheels for the smooth operation. 6.7 SLIDING TRACK FABRICATION Z-section was welded to the jack top as shown in the figure 6.9. The dimensions of Z-section were:
86 74 7.5cm toward the hold 10.5cm towards the deck 4cm towards the hold again Width of the plate was 2.56cm and thickness 0.3cm. The other end of Z section was welded to the iron plate as shown in the figure A wooden piece was screwed to the iron plate and having dimensions: Length: 80cm Width: 2.5cm Thickness: 2cm Figure 6.9 Sliding Track Source: Team Figure 6.10: Hydraulic Jack and Sliding Track Source: Team
87 75 At the top of the iron plate, rail was fitted for the sliding wheels. 6.8 FABRICATION OF RISING TRACK Material used: Mild steel Two pieces i.e. rectangular & triangular were made separately and then joined together to get the final shape as shown in the figure 6.11 Prepared for both i.e. port and starboard side Dimensions of triangular piece: Base: 12cm Perpendicular: 6.5cm Hypotenuse: Thickness: 1.cm Figure 6.11: Rising Track Source: Team Dimension of rectangular piece Length: 47cm Height: 6.5cm Width: 1.5cm Two supports were provided for the rising track.
88 76 The dimensions were: Height: 15.7cm Width: 3.2cm Thickness: 1.5cm Four L angles were fitted with the supports as shown in the figure FABRICATION OF CRANE SPACE Dimensions were marked on the wooden piece as Length: 50 cm Height: 35.5 Thickness: 1.5cm Two pieces of above dimensions were made Again marking was done as Height: 35.5 Breadth: 12.3cm Thickness: 1.5cm Two pieces of above dimensions were made These all four pieces were joined together by using nails and gum to form a rectangular box. Top platform dimensions: Length: 53cm Breadth: 14cm Thickness: 1.5
89 77 Figure 6.12: Crane space Source: Team Top platform made was fixed at the top of the rectangular box made above as shown in the figure. A pulley was then fitted at the middle at a height of 32.5cm from the weather deck 6.10 MOTOR REDUCTION GEAR PULLEY FABRICATION Motor shaft and the smaller gear shaft were coupled together and bearing is provided. Bigger gear is engaged to the smaller gear and bearing is provided at each end. Pulley was fitted to the bigger gear shaft. Motor and gears were covered with casing for safely purpose FABRICATION OF BULWARK 10m of iron rods of diameter 4mm were brought to the work table. Four pieces of 150 cm length each were cut by using hack saw. Two rods were taken and kept parallel to each other at a distance of 3.2cm. Nails were taken and welded as shown in the figure 6.13.
90 78 Figure 6.13: Bulwark Source: Team Distance between the nail: 7cm Repeat the same process for the remaining two rods. Rails were provided around the top platform too as shown in the figure FABRICATION OF LADDER Two iron rods of length 36cm and diameter 5mm each were brought to the work table. These rods were kept parallel 4.7cm apart. 11 steps were welded 3.6cm apart. Figure 6.14: Ladder Source: Team
91 79 CHAPTER 7-ASSEMBLY OF FABRICATED PARTS After the fabrication work the team collected the fabricated parts together and assembled them as per the design stated in the chapter 5. Different parts which was fabricated separately: Cargo hold Hatch coaming Hatch stay Side & end dogs Hatch cover Sliding track Rising track Crane space Motor assembly Hand rail Ladder Figure 7.1 Assembly of fabricated parts Source: Team 7.1 ASSEMBLY BETWEEN CARGO HOLD AND HATCH COAMING
92 80 These parts were fabricated separately and assembled together by using nails and for extra support iron L-angles are provided. Figure 7.2 Cargo hold and Hatch coaming Source: Team Hatch comaing at port and starboard were provided with four L- angles and at aft forward were provided with three L-angles each. These L-angles were screwed well into the hatch coming and cargo hold. finally it was assured that the assembled part is rigid. 7.2 ASSEMBLY OF HATCH STAY ON COAMING After fitting the coaming hatch stays were provided for additional rigidity of coaming. 14 hatch stays were fabricated separately and were assembled as: 4 at port & starboard each 3 at aft & forward each Hatch stays were fitted using nails and gum. Figure 7.3 Hatch stay on coaming
93 81 Source: Team 7.3 ASSEMBLY OF SIDE DOGS AND END DOGS ON COAMING For the beading arrangement as well as fitting of sliding track side and end dogs were provided. These were fitted perpendicular to the coaming. Figure 7.4 Side dogs and end dogs on coaming source: Team Again this assembly was done by using nails.
94 ASSEMBLY OF SLIDING TRACKS Sliding tracks were fabricated separately and was welded with hydraulic jacks. Hydraulic jacks well positioned and screwed into the weather deck such a way that lifting and dropping action of tracks takes place effectively without interruption. Figure 7.5 Sliding track Source: Team 7.5 ASSEMBLY OF RISING TRACK Rising tracks were fabricated and they were fitted according to the position of balancing wheels. Supports provided for the rising tracks were fitted to the weather deck with the help of screws. Figure 7.6 Rising track Source: Team
95 ASSEMBLY OF HATCH COVER All the four hatch covers were fitted with plastic sliding wheels at the four bottom corners. Also metallic balancing wheels were provided at port & starboard ends. All the hatch covers were made in line above the sliding track. Bottom wheels were checked for alignment with the tracks. Figure 7.7 Hatch cover Source: Team Chain is attached to each hatch cover s metallic balancing wheels at both port and starboard ends. These metallic wheels were checked for their correct alignment with the rising track. Figure 7.8 Hatch cover Source: Team
96 ASSEMBLY OF CRANE SPACE INTO CARGO HOLD Separately fabricated crane space was fitted over the weather deck at the specific position as shown in the figure by using nut and bolt arrangement. Figure 7.9 Cargo space into cargo hold Source: Team 7.8 ASSEMBLY OF MOTOR PULLEY GEAR ARRANGEMENT INTO CARGO HOLD Motor was bolted into the weather deck with the help of nut and bolt arrangement. The roller bearings supports were too bolted to the weather deck. 7.9 Assembly of Bulwark Holes were drilled into the weather deck using drilling machine and positions were adjusted according to the nail position welded. Figure 7.10 Bulwark Source: Team
97 85 The whole bulwark is placed over the drilled holes and forces inside to make it tight and rigid. The whole bulwark is placed over the drilled holes and forces inside to make it tight and rigid. Same procedure was followed for the crane top platform and bulwark fitting. Figure 7.11 Bulwark Source: Team 7.10 ASSEMBLY OF LADDER This is provided to connect weather deck and crane top platform. Top of ladder is attached to the platform and bottom to the weather deck. Both ends were fitted permanently. Figure 7.12 Ladder Source: Team
98 ASSEMBLY OF LOCKING ARRANGEMENT For this purpose grooves were provided at each corner of the coaming such a way that the hatches can lock well during normal voyage. This arrangement will helpful for avoiding unnecessary sliding of hatch covers. Figure 7.13 Locking arrangement Source: Team 7.12 ASSEMBLY OF WIRE ROPE Wire is provided for pulling hatch covers fore and aft direction with its wheel rolling between guides on the top of the coaming. For this purpose two eye bolts were provided to the furthest panel as shown in the figure Figure 7.14 Wire rope Source: Team
(1986) (Rev 1 1996) (Corr.1 June 2000) (Rev.2 July 2005) (Corr.1 Oct 2005) Hatch cover securing and tightness 1. Application 1.1 The following recommendations apply to steel hatch covers that are fitted
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