Marine Kit 4 Marine Kit 4 Sail Smooth, Sail Safe Includes Basic ship Terminologies and Investigation Check list
Index 1. Ship Terminology 03 2. Motions of a Floating Body...09 3. Ship Stability.10 4. Free Surface Effect..13 5. Effect of Water Density on the Draft 15 6. Displacement of Ship..16 7. Loading of Ship...17 8. Tanker Ships....19 9. Speed of Ship....20 10.Ship Power Plant..21 11.SONAR 23 12.Unit Conversions.26 2
1. Ship Terminology Starboard Stern Bow Port Bow : Front part of the ship Stern : Rear part of the ship Starboard : Right side of the ship Port : Left side of the ship 3
Hull Hull is a body of a ship Most of the modern vessels have double hull to prevent flooding in case of accidents. Ship Hull Tankers have double hull to prevent oil spilling in case of hull damage. Double hull also serves as ballast tanks in the partial loaded or unloaded condition to keep the center of gravity as low as possible for stability. Double Hull 4
Various terms used to define hull cross section fore is the front part aft is the rear part Keel Keel of the ship is the principal structural member of a ship running lengthwise along the center line from bow to stern, to which the frames are attached. http://web.nps.navy.mil/~me/tsse/navarchweb/1/module2/introductio n.htm# 5
Cross section of ship Beam Waterline Freeboard Draft Draft of a ship is the vertical distance between the waterline and the bottom of the hull Freeboard of a ship is the vertical distance above the waterline Beam of a ship is the width of a ship at any cross section 6
Deadrise: Deadrise is an angle measured upward from a horizontal plane at the keel level. Deadrise Flat bottomed vessels have 0 (zero) deadrise. Deadrise for V shaped hull varies from bow to stern. Deadrise is very important feature in the stability of the vessel. A flat bottomed boat rises on a plane quickly and provides a stable comfortable ride in calm water but will pound heavily in rough water. A vessel with deadrise provides greater stability and comfort in rough conditions. Ocean going big ships are never flat bottomed in the fore and aft hull sections, may be almost flat bottomed in the mid ship section. Ocean going vessel with full flat bottomed hull may capsize easily in the heavy seas 7
Bulkheads Bulkheads Bulkhead: Bulkhead is a upright wall like structure within the hull of a ship. Bulkheads increase structural rigidity of the vessel Bulkheads create watertight compartments to prevent flooding in case of hull breach or leak. Longitudinal Bulkheads are used to create watertight compartments in case of ship capsize. It also divides cargo into different sections and thus helps improve stability of ship by creating different center of gravities for different sections. (More on this in free surface effect) 8
2. Motions of a floating body Any floating body has three motions namely Roll, Pitch and Yaw Roll: Rolling is the motion of a floating body about the longitudinal axis ( axis along the length of the body) Pitch: Pitching is the motion about the transverse axis of the body (i.e axis along the width of the ship. Yaw: Yawing is the motion of a floating body about the vertical axis. Control of all the three motions is very important for ship stability and ride comfort. 9
3. Ship Stability Center of Gravity (G), Center of Buoyancy (B), and Metacenter (M) play very important role in stability of the ship. The center of buoyancy, is the center of gravity of the volume of water which the hull displaces. This point is referred to as B in naval architecture. The center of gravity of the ship itself is known as G in naval architecture. When a ship is upright, the center of buoyancy is directly below the center of gravity of the ship. 10
Center of Gravity is the point where all the weight of the object can be considered to be concentrated Center of Buoyancy is the center of mass of the immersed part of ship or floating object Metacenter is the point where lines of action of upward buoyancy force intersect When the ship is vertical, it lies above the center of gravity and so moves in the opposite direction of the heel as ship rolls Relationship between G and M G under M: ship is stable G = M: ship neutral G over M: ship unstable M G G B M B Stable Unstable 11
When the cargo in the ship are evenly distributed, the ship will be upright. The sum of the gravity forces of cargo and the ship will be acting at one point - the Center of Gravity, G, acting downwards. Similarly, the Center of Buoyancy of the ship will be acting at one point B, acting upwards. What is stable equilibrium? A ship is said to be in Stable Equilibrium if on being slightly inclined, tends to return back to the original position. However, a ship will be in Unstable Equilibrium when she tends to move further from that original position on being tilted slightly. A ship in Neutral Equilibrium will tend to neither return nor move further from that position. 12
4. What is the free surface effect? This effect proves fatal in partially filled ocean going vessels in the heavy seas. Wave Force of wave heels the ship to the starboard. Center of gravity of oil shifts. Oil acts as a single mass, hence the change in the center of gravity is drastic Force of wave and change in the center of gravity heels the ship more and more without giving it a chance to come to its upright position. As the ultimate effect of wave force and big change in center of gravity ship capsizes. 13
How to minimize the free surface effect? Ship is fitted with compartments, i.e. (longitudinal bulkheads) Now the liquid in the tank acts as different masses and center of gravity of individual mass changes. But effect of changing all the center of gravities does not shift the center of gravity of the ship as significantly as before. The other way to minimize the free surface effect is to fill the tanks nearly full. This does not give the liquid room and hence minimizes the free surface effect. Tanker ships never sail partially filled 14
5. Effect of change in density of water on the draft of a ship Density of Fresh Water = 1000 kg / m 3 Average Density of Sea Water = 1030 kg / m 3 Draft of ship changes with the change in density of water Keeping the load same, change in the draft can be calculated by following equation New Draft OldDraft OldDensity NewDensity Fresh water draft is more than salt water draft Ships transiting between sea water and fresh water have to consider this change in draft to avoid a danger of running aground 15
6. Displacement of ship The word "displacement" arises from the basic physical law, discovered by Archimedes, that the weight of a floating object equates exactly to that of the water displaced Displacement = actual total weight of the vessel Unit of Displacement = long ton or metric ton How to calculate Displacement of ship? 1. Volume of submerged part (cu. Feet) = length * Beam * Draft 2. Multiply this by block coefficient of hull 3. Multiply this figure by 64 to get weight of ship in pounds or divide by 35 to calculate weight in long tons 4. Using SI or metric system: displacement (in tons) is volume (in cubic meters) multiplied by the specific gravity of sea water (nominally 1.025) 16
Plimsoll line or International Load Line the mark on the hull of a ship that shows where the waterline is when the ship is loaded to full capacity according to the condition of the water at the point of loading. Lightship weight is the displacement of the ship only with no fuel, passengers, cargo, water, etc. on board. Full Load Displacement: Displacement when ship is loaded with cargo or people to the point that it is submerged to its load line Deadweight Tonnage (DWT) is full load displacement minus the lightship weight. It includes the crew, passengers, cargo, fuel, water and stores etc. A ship can carry cargo weighing roughly 90% of its deadweight tonnage 17
7. Loading of Ship Cargo should be always evenly distributed Uneven distribution makes ship unstable Uneven distribution also creates stresses on the ship structure Cargo should be properly secured (e.g.in case of cargo like cars) Stowage Factor = Volume of cargo Mass of cargo Proper care should be taken to distribute the load evenly when carrying high density cargo with stowage factor above 0.56 18
8. Tanker Ships Tankers are used to carry liquid and gaseous cargo All the tanker ships have double hull in order to prevent oil leakage Partially filled tankers are highly unstable in heavy seas because of the free surface effect General Arrangement of Cargo and Ballast Tanks for Tankers Slop tanks are provided for storage of dirty ballast residue and tank washings from the cargo tanks 19
9. Speed of ship Speed of a ship is measured in knots Modern ships are powered by diesel engines Some ships are powered by steam turbines also Nuclear power is used in defense naval ships Propeller shaft Propellers Power Source (Diesel Engine / Steam Turbine/ Nuclear power) Loss of propulsion system can prove fatal, especially in heavy seas as ship loses control over direction 20
10. Ship Power Plant Most new ships today are powered by diesel engines, though a few older ships are still powered by steam turbines and reciprocating steam engines Propeller shaft Power Plant (Engine/ turbine) Propeller 21
Power plant and propulsion system are the most critical systems in any ship It gives the ship the force required to move Failure of power plant or propulsion system could be fatal as ship loses control on the direction Loss of power or propulsion in heavy seas or near the shore is very dangerous since ship may stray with the direction of winds and waves and may run aground 22
11. SONAR SONAR (Sound Navigation and Ranging) SONAR is a technique that uses sound propagation under water (primarily) to navigate, communicate or detect other vessels Principle of SONAR: Reflection of sound waves 23
A transmitter is used to transmit the signal A receiver is used to catch the reflection (echo) The time from transmission of a pulse to reception is measured Speed of sound in water is known Distance Using the formula Speed = Time we can calculate the distance of the object from the source of the pulse (transmitter) Distance d Time t SEA BED 24
Speed of sound in water is calculated using following equation Speed of Sound (feet /s) = 4388 + (11.25 temperature (in F)) + (0.0182 depth (in feet) + salinity (in parts-per-thousand)). 1 foot = 0.3048 meters Distance from the object is calculated using formula Distance = Speed of sound x time between transmission and reception 2 25
12. Unit Conversions 1 Metric ton = 2204.62 pounds = 1000 kilogram 1 long ton = 2240 pounds = 1016.05 kilogram 1 meter = 3.281 feet 1 knot = 1.151 miles / hour = 1.852 kilometer / hour 1 nautical mile = 1.151 miles = 1.852 kilometer 746 horsepower = 1 Watt = 1 Joule / second 26