INTERNATIONAL MARITIME ORGANIZATION E IMO SUB-COMMITTEE ON SHIP DESIGN AND EQUIPMENT 48th session Agenda item 6 DE 48/6/1 17 November 2004 Original: ENGLISH ANCHORING, MOORING AND TOWING EQUIPMENT Shipboard fittings and supporting hull structures associated with anchoring, towing and mooring Executive summary: Action to be taken: Paragraph 5 Submitted by the Republic of Korea SUMMARY This paper provides revised draft MSC circular on Shipboard fittings and supporting hull structures associated with anchoring, towing and mooring which will provide uniform requirements under the proposed new SOLAS regulation II-1/3-8 on Anchoring, towing and mooring equipment. Related documents: DE 47/8/2; DE 47/25 (paragraph 8); DE 47/WP.10 and NAV 50/19 (paragraph 6) Background 1 The Sub-Committee, at its forty-seventh session, prepared a draft new SOLAS regulation II-1/3-8 on Anchoring, mooring and towing equipment and submitted it to MSC 79 for approval with a view to adoption. In this regard, the Sub-Committee also prepared a related draft MSC circular on Shipboard fittings and supporting hull structures associated with towing and mooring based on IACS UR A2 and agreed to finalize it at DE 48. In the mean time, IACS informed in its submission DE 47/8/2 that the Unified Requirement UR A2 will be implemented by all its Member Societies for new ships contracted for construction after 1 January 2005. Proposal 2 Pending the introduction of new SOLAS regulation II-1/3-8, finalization of the relevant draft MSC circular and anticipated implementation of IACS UR A2 by IACS societies in the near future, the Republic of Korea has carefully reviewed the said draft circular and the UR A2 as provided in DE 47/WP.10, annex 3, and DE 47/8/2 respectively. The draft MSC circular as prepared by DE 47 is basically identical to UR A2 and the main areas of concern identified by the Republic of Korea on the two documents are as follows: For reasons of economy, this document is printed in a limited number. Delegates are kindly asked to bring their copies to meetings and not to request additional copies.
- 2 -.1 Both the draft circular and UR A2 define the applied forces as twice the maximum breaking strength of the tow/mooring line anticipated to be used throughout the service life of the ship and the safety factor as design load which is two times the rope maximum breaking load (MBL). These applied forces and safety factor as defined are excessively higher than the values actually required during the normal operation of the vessels. It is to be considered that the shipowners normally select the mooring ropes on board which have higher strength than required mooring force to consider local damage, wear down and increased lifespan etc. Therefore, the drafted circular is requiring strength that is about 3 to 4 times the strength that has been normally used in the industry so far without any reported problem. This redundancy in strength requirement will merely bring increased shipbuilding costs without achieving further safety benefits. For instance, in 7,000 to 8,000 TEU class container vessels, the mooring ropes with about 120 ton MBL (e.g. Atlas rope 78 mm in diameter) are normally supplied on board by the request of the shipowner due to the reasons stated above, although the required mooring rope tension based on IACS Recommendation No.10 is about 54.7 ton each with 12 line mooring. In this case, the applied force (design load) will then be 240 ton instead of normally applied 54.7 ton if we follow the draft circular. Presently, there is no industry standard listing such a large force - for example, the biggest standard bollard of ISO 3913 has 100 ton SWL (single rope maximum loading) for nominal size 800..2 In the draft circular, the requirements for towing are also used for mooring. It is necessary, however, to describe the requirements for towing equipment and those for mooring equipment separately to use different safety levels, considering the fact that the acting forces to the towing and mooring fittings are from different sources..3 Ships applicable to this circular should be defined in the proposed SOLAS regulation II-1/3-8 first. It is necessary to clearly state the vessels that are exempted from the SOLAS regulation and this draft circular. 3 Based on this review, the Republic of Korea has prepared a revised draft MSC circular on Shipboard fittings and supporting hull structures associated with [anchoring,] towing and mooring as provided in annex 1 to this document. The proposal, therefore, was prepared based on the original purpose of the intended circular, inter alia, to provide uniform standards for the design and construction of the fittings and hull structures and on practical practices which have been verified through the industry application. The background information of the proposed revised draft circular is also provided in annex 2 to this document. 4 Although DE 47 decided to also include in the draft circular the provisions of IACS UR A1 for Anchoring, Mooring and Towing Equipment, the revised draft and the background information mainly deals with towing and mooring issues only, due to the practical reasons and considering the relevant decision of NAV 50 that recommends MSC 79 not to include the word anchoring in the proposed SOLAS regulation II-1/3-8 (NAV 50/19, paragraph 6.3, refers). Action requested of the Sub-Committee 5 The Sub-Committee is invited to consider the revised draft MSC circular and background information in the annexes to this document and take action as appropriate. ***
ANNEX 1 REVISED DRAFT MSC CIRCULAR SHIPBOARD FITTINGS AND SUPPORTING HULL STRUCTURES ASSOCIATED WITH [ANCHORING,] TOWING AND MOORING 1 Application 1.1 Under regulation II-1/3-8 of the 1974 SOLAS Convention, as amended by resolution MSC. [ ] in 2005, new displacement type vessels except high speed craft, special purpose vessels and offshore units shall be provided with arrangement, equipment and fittings of sufficient safe working load to enable the safe conduct of all [anchoring,] towing and mooring operations associated with the normal and emergency operations of the ship. The arrangement, equipment and fittings shall meet the appropriate requirements of the Administration or an organization recognized by the Administration. 1.2 The present Guidance is intended to provide standards for the design and construction of shipboard fittings and supporting hull structures associated with [anchoring,] towing and mooring which Administrations are recommended to implement. The Administrations, however, are recommended not to use this Guidance to certain special purpose vessels such as FPSO, barge, dredger, etc. if, in the opinion of the Administrations, the application of this guidance is unreasonable. 2 Definitions For the purpose of this circular: 2.1 Shipboard fitting means: [anchoring equipment such as anchors and chains, and] bollards and bitts, fairleads, stand rollers, chocks used for the normal mooring of the vessel and the similar components used for the towing and emergency towing of the vessel. Other components such as [cable lifters,] capstans, winches, etc. are not covered by this circular. Any weld, bolt or other fastening connecting the shipboard fitting to the supporting hull structure is part of the shipboard fitting and subject to any industry standard applicable to such fitting. 2.2 Supporting hull structures mean that part of the ship structure on/in which the shipboard fitting is placed and which is directly submitted to the forces exerted on the shipboard fitting. The supporting hull structure of [cable lifters,], capstans, winches, etc. used for the [anchoring,] towing, emergency towing and mooring operations mentioned above is also subject to this Guidance. 2.3 Industry Standard means international standard (ISO, etc.) or standards issued by national associations such as DIN, KS or JIS, etc. which are recognized in the country where the ship is built subject to the approval of the Administration. [3 Anchoring - The requirement for calculation of Equipment Number. - The selection of anchor and chain grade (size and strength).]
ANNEX 1 Page 2 4 Towing 4.1 Strength The strength of shipboard fittings used for normal or emergency towing operations at bow, sides and stern and their supporting hull structures should comply with the requirements of this circular. 4.2 Arrangement Shipboard fittings for towing are to be located on longitudinals, beams and/or girders, which are part of the deck construction so as to facilitate efficient distribution of the towing load. Other equivalent arrangements may be accepted (for Panama chocks, etc.). 4.3 Load considerations 4.3.1 The design load used for normal towing operations at bow and stern should be applied as specified below:.1 twice the breaking strength of the tow line according to the [MSC/Cir. xx] [paragraph xx] IACS Recommendation No.10 Equipment for the ship s corresponding Equipment Numeral (EN) is to be applied. 4.3.2 The design load used for normal towing operations at ship sides should be applied as specified below:.1 1.25 times the intended maximum towing load. 4.4 Shipboard fittings The selection of shipboard fittings is to be made by the shipyard in accordance with an industry standard (e.g. ISO 3913 Shipbuilding Welded Steel Bollards) accepted by the Administration. When the shipboard fitting is not selected from an accepted industry standard, the fittings should be of equivalent to recognized Industry standard if in compliance with design load as per 4.3 above. 4.5 Supporting hull structure Arrangement 4.5.1 The arrangement of the reinforced members (carling) beneath shipboard fittings should consider any variation of direction (laterally and vertically) of the towing forces (which is to be not less than the Design Load as per 4.3) acting through the arrangement of connection to the shipboard fittings. Acting point of towing force 4.5.2 The acting point of the towing force on shipboard fittings should be taken at the attachment point of a towing line or at a change in its direction.
ANNEX 1 Page 3 Allowable stresses 4.5.3 Allowable bending stress: 100% of the specified yield point for the material used; allowable shearing stress: 60% of the specified yield point for the material used; no stress concentration factors being taken into account. 4.6 Safe Working Load (SWL) 4.6.1 The SWL should not exceed one half of the design load as given in 4.3.1 and 80% of the design load as given in 4.3.2. 4.6.2 The SWL of each shipboard fitting is to be marked (by weld bead or equivalent) on the deck fittings used for towing. 4.6.3 The SWL with its intended use (for normal and/or emergency conditions) for each shipboard fitting referred to in paragraph 4.6.2 above, is to be noted in the towing and mooring arrangement plan or other information available on board for the guidance of the Master. 4.6.4 The above requirements on SWL apply for a single post basis (no more than one turn of one line). 4.6.5 The arrangement plan mentioned in paragraph 4.6.3 above is to define the method of use and characteristics of towing lines. 4.7 Emergency towing arrangements Ships subject to SOLAS regulation II-1/3-4 are to comply with that regulation and resolution MSC.35(63) as may be amended. 5 Mooring Application Equipment that is used for both towing and mooring is to be in accordance with paragraph 4. However when equipment is only used for mooring, ensuing paragraphs should be applied. 5.1 Strength The strength of shipboard fittings used for mooring operations at bow, sides and stern and their supporting hull structures should comply with the requirements of this circular. 5.2 Arrangement Shipboard fittings for mooring are to be located on longitudinals, beams and/or girders, which are part of the deck construction so as to facilitate efficient distribution of the mooring load. Other equivalent arrangements may be accepted (for Panama chocks, etc.).
ANNEX 1 Page 4 5.3 Load considerations The design load used for mooring operations should be applied as specified below. If shipboard fittings are also used for normal towing operations, the design load should also be applied as specified in 4.3.2..1 For shipboard fittings: 1.25 times the breaking strength of the mooring line according to the [MSC/Cir. xx] [paragraph xx] IACS Recommendation No.10 Equipment for the ship s corresponding Equipment Numeral (EN) should be applied. For individual mooring lines with breaking strength above 490 kn (50,000 kg) the breaking strength of the mooring lines may be reduced with corresponding increase of the number of the mooring lines and vice versa, provided that the total breaking load of all lines aboard ship is not less than the required value. The number of lines is not to be less than 6 and no one line is to have a strength less than 490 kn (50,000 kg). For the fittings with rotating device such as roller fairlead, stand roller etc., 55% of load stated above should be applied..2 For supporting hull structures for capstans, winches etc.: 1.25 times the breaking strength of the mooring line according to subparagraph.1 above or maximum hauling in force, whichever is greater, should be applied. 5.4 Shipboard fittings The selection of shipboard fittings should be made by the shipyard in accordance with industry Standard (e.g. ISO 3913 Shipbuilding Welded Steel Bollards) accepted by the Administration. When the shipboard fitting is not selected from an accepted industry standard, the fittings should be of equivalent to recognized industry standard in compliance with design load as per paragraph 5.3. 5.5 Supporting hull structure Arrangement 5.5.1 Arrangement of the reinforced members (carling) beneath shipboard fittings should consider any variation of direction (laterally and vertically) of the mooring forces (which should be not less than the Design Load given in 5.3) acting through the arrangement of connection to the shipboard fittings. Acting point of mooring force 5.5.2 The acting point of the mooring force on shipboard fittings should be taken at the attachment point of a mooring line or at a change in its direction. Allowable stresses 5.5.3 Allowable bending stress: 100% of the specified yield point for the material used; allowable shearing stress: 60% of the specified yield point for the material used; no stress concentration factors being taken into account.
ANNEX 1 Page 5 5.6 Safe Working Load (SWL) 5.6.1 The SWL should not exceed the 80% of design load given in 5.3. 5.6.2 Refer to paragraph 4.6.2 with understanding that towing is to read to mean mooring. 5.6.3 Refer to paragraph 4.6.3 with understanding that towing is to read to mean mooring. 5.6.4 Refer to paragraph 4.6.4. 5.6.5 Refer to paragraph 4.6.5 with understanding that towing is to read to mean mooring. ***
ANNEX 2 BACKGROUND ON REVISED DRAFT MSC CIRCULAR ON SHIPBOARD FITTINGS AND SUPPORTING HULL STRUCTURES ASSOCIATED WITH [ANCHORING,] TOWING AND MOORING The background information on each paragraph of the revised draft MSC circular as proposed by the Republic of Korea in annex 1 is provided hereunder. The revised draft circular was prepared using the draft circular in annex 3 of DE 47/WP.10 as base texts and new additions or modifications from original texts have been italicized for ease of reference. To summarize the proposal of the Republic of Korea, proposed applicable loads, SWL, design loads and safety factors at design loads for each mooring and towing condition have been listed at the end of this annex in Table 1 - Summary of key factors of proposed draft circular. 1 Application The application part has been detailed in a similar way that the reslution MSC.35(63) describes in connection with emergency towing arrangements under SOLAS regulation II-1/3-4. This description, however, has been made on the condition that applicable/non-applicable ships are mentioned in the proposed SOLAS regulation II-1/3-8. The Republic of Korea considers that the applicable ship should be defined in the SOLAS regulation first. Special purpose vessels such as FPSO may be additionally mentioned in the circular as vessels that are exempted. 2 Definitions 2.1 Equipment for anchoring have been included. 2.2 Equipment for anchoring have been included. 2.3 KS (Korean Industrial Standard) is recommended to be included as an example of the industry standards. KS has been continuously evaluated and updated to accommodate changes in technology. Strength of mooring fittings in the KS has been completely evaluated through strength analysis and sample tests under the Joint Committee of Mooring fittings organized by the Korea Shipbuilders Association and Members of Korean Ship Builders together with major classification societies. KS is now commonly being used to the vessels built in major shipyards in the Republic of Korea. 3 Anchoring Requirements for anchoring equipment may be included in the circular based on IACS UR A1 as decided by DE 47. The requirement to be included in this guidance, however, should be limited to the requirements for decision of particulars of anchoring equipment and should not contain detailed procedures such as manufacturing, test, etc. It would be better for this guidance to contain basic requirements only, leaving the detailed specific requirements on class requirements and industry standards. For this purpose, Table 1 of IACS UR A1 and Table 5 of IACS Recommendation No.10 should be combined and included as a single table in the circular. This part on anchoring, however, should be handled in accordance with the decisions of MSC 79 in response to the recommended deletion of the word anchoring in the proposed SOLAS regulation II-1/3-8 (NAV 50/19, paragraph 6.3, refers). The word anchoring and anchoring related terms have been included in square brackets throughout the revised draft circular.
ANNEX 2 Page 2 4 Towing Considering that the towing and mooring fittings have different load applications from each other, they have to be described separately. Paragraph 4, therefore, should be applied to towing fittings only. 4.1 Strength No change has made to the draft circular prepared by DE 47. 4.2 Arrangement No change has made to the draft circular prepared by DE 47. 4.3 Load considerations The load considerations for towing fittings on bow/stern and for those at sides should be separately applied considering different usage and towing forces. Paragraph 4.3 has therefore been divided into 4.3.1 and 4.3.2 accordingly. 4.3.1 For towing fittings on bow and stern, it is not possible to apply twice the maximum breaking strength of the tow line anticipated to be used throughout the service life of the ship because the tow line is normally provided by the towing vessel being used during the towing operation and therefore its maximum breaking strength can not be estimated in advance. It is also considered prudent that an IMO circular not directly refer to external standards such as IACS Recommendation No.10 Equipment. It is suggested, therefore, that the IACS document be reproduced as an MSC circular or included in this circular and referred to accordingly. 4.3.2 For towing fittings at sides, it is not possible to apply twice the maximum breaking strength of the tow line anticipated to be used throughout the service life of the ship because the tow line is normally provided by the towing vessel being used during the towing operation and therefore its maximum breaking strength can not be estimated in advance. In addition, the IACS Recommendation No.10 Equipment for the ship s corresponding Equipment Numeral (EN) can not be applied for normal towing from ship s sides (for instance, assistance of berthing, canal transit etc.) and is applicable for towing from bow and stern only. Therefore, the towing load (force), in other words the intended maximum towing load, should be decided by intended maximum tug boat pull capacity which are agreed between shipowner and shipbuilder (designer). Considering the fact that the towing force is restricted by tugboat pull capacity and intended towing load has been applied without any strength problem so far, it is considered sufficient to apply 1.25 times of intended towing load. 4.4 Shipboard fittings If based design load as of paragraph 4.3 is complied with, the recognized standards fittings having equivalent strength with Industry standard should be accepted. 4.5 Supporting hull structure No change has been made to the draft circular prepared by DE 47.
ANNEX 2 Page 3 4.6 Safe Working Load (SWL) In accordance with paragraph 4.3, the SWL should be determined as proposed. 4.7 Emergency towing arrangements No change has been made to the draft circular prepared by DE 47. 5 Mooring A separate set of requirements is necessary for mooring operation because of the reasons stated in 5.3 and 5.4 below. Therefore, new paragraphs have been inserted as in annex 1. 5.1 Strength As stated in 4.1. 5.2 Arrangement As stated in 4.2. 5.3 Load considerations 5.3.1 The mooring rope provided onboard is normally of considerably higher grade than the required mooring force according to IACS Recommendation No.10 Equipment. In addition, the maximum breaking load is decided through an actual rope breaking test which is conducted at final building stage. It is therefore not possible to predict, at ship design stage, the strength of ropes to be used by ship s operators throughout the whole ship s lifespan. As a result, it is considered unreasonable to apply twice the maximum breaking strength of the mooring line anticipated to be used throughout the service life of the ship. The mooring ropes are normally provided onboard with margins for wear down, local damage and increased lifespan etc. which are well beyond the safety factor of the rope. The rope strength in accordance with IACS Recommendation No.10 contains the rope safety factor already. Therefore, regardless of how big the ropes being used onboard are, the required force to be applied should be decided by a reasonable method and the restrictions for the use of mooring fittings should be clearly marked. If design load is to be applied with twice of MBL of rope being used, existing provision and reinforcement should also be strengthened about 3 to 4 times accordingly. This is considered to be quite excessive and will increase the hull weight and shipbuilding cost. Because the breaking strength of the mooring lines according to IACS Recommendation No.10 is sufficient from the view point of mooring force, it is not necessary to apply design load twice of this force. Therefore, it is proposed to apply 1.25 times the rope strength in accordance with IACS Recommendation No.10 as design load considering strength margin. In addition, the strength of fitting with rotating device can be reduced considering minimized friction between the rope and the fittings - for example, 55% as recommended by OCIMF. Because the load according to IACS Recommendation No.10 contains the rope s safety factor (say 2.5), 55% is still higher than required rope tension for mooring. For example, if a wire rope is provided, the suggested SWL 0.55 [applicable load], in other words [applicable load]/1.82, is still higher than the required rope MBL of IACS Recommendation No.10 without the rope safety factor [applicable load]/2.5.
ANNEX 2 Page 4 5.3.2 Considering the mooring winches are designed based on design load of 80% rope MBL according to classification societies rules, 125% rope MBL as design load for supporting hull structure has 56% margin. Capstans will not have holding power, so the maximum hauling in force should be applied. 5.4 Shipboard fittings The design load applied by industry standards is not twice the acting force (breaking strength of the mooring lines). Therefore, the circular should accept equivalent strength of shipboard fittings as industry standard. 5.5 Supporting hull structure Arrangement 5.5.1 Reinforcement of mooring fittings and design load should be as given in 5.3. Acting point of mooring force 5.5.2 As stated in 4.5.2. Allowable stresses 5.5.3 As stated in 4.5.3. 5.6 Safe Working Load (SWL) 5.6.1 The SWL should not exceed 1.25 times the design load given in 5.3. 5.6.2,.3,.4 and.5 As stated in 4.6.2 through 4.6.5.
ANNEX 2 Page 5 Table 1 Summary of key factors of proposed draft circular Item Normal towing on bow and stern Normal towing at ship s sides for tug points for assistance of berthing, canal transit etc. Emergency towing Normal mooring Capstans, mooring winches Applicable Load (Reference Load) [AL] SWL [B] Design Load Safety Factor at Design Load (Combined stress) Fittings The breaking strength of the tow line according to the [AL] 2 [AL] As per Standard [IACS Recommendation No.10 Equipment] for the ship s Bending 100%, Shear 60% of Reinforcement corresponding EN. [AL] 2 [AL] Yield Fittings Intended towing load: to be decided by intended tug boat [AL] 1.25x [AL] As per Standard pull capacity by agreement between ship operator and ship Bending 100%, Shear 60% of Reinforcement builder. [AL] 1.25 [AL] Yield Fittings [AL] 2 [AL] 1 / Ultimate strength As per SOLAS Reg. II-1/3-4 Reinforcement [AL] 2 [AL] Fittings Reinforcement Capstans, mooring winches Reinforcement The minimum breaking strength of the mooring line according to the [IACS Recommendation No.10 Equipment ] for the ship s corresponding EN. For individual mooring lines with breaking strength above 490 kn (50,000 kg), the breaking strength of mooring lines may be reduced with corresponding increase of the number of the mooring lines or vice versa, provide that the total breaking load of all lines aboard ship is not less than the Rules value. The number of lines is not to be less than 6 and no one line is to have a strength less than 490 kn (50,000kg). Not covered by the circular. (Reference : if follow the requirement of Classification Societies, mooring winches is to design with 80% of rope nominal breaking loads) The minimum breaking strength of the mooring line as mentioned above for Normal mooring fittings/reinforcement or maximum hauling in force, whichever is greater [AL] 0.55 [AL] Note: #1) Ditto 1.25x [AL] 0.55 1.25x[AL] Note: #1) Ditto Bending 100%, Shear 60% of Yield As per Standard [AL] [AL] As per Class. [AL] 1.25 [AL] Bending 100%, Shear 60% of Yield Bending 100%, Shear 60% of Yield Note #1) 0.55 [AL] should be applied to rotating fittings such as fairleads, stand rollers etc. Because the reference load [AL] contains rope s safety factor (Wire rope 2.5, Manila rope 3.25, Fiber rope 3.8), 0.55 [AL] is still higher than required rope MBL for mooring (e.g. the suggested SWL 0.55 [Applicable Load], in other words [Applicable Load]/1.82, is still higher than the required rope MBL of IACS Recommendation No.10 without the rope safety factor [Applicable Load]/2.5)