Sketch and describe
(a) Deep framing
(b) Frame spacing
(c) Frame numbering
- Shell plating and decks are supported by framing, and it consist of
- Bars arranged transversely with longitudinal girders, or
- Bars arranged longitudinally with transverse deep beams and frames. Sometimes use in both
- Transverse frames mainly resist racking forces due to rolling
- Longitudinal frames contribute to longitudinal strength,
Both systems experience the following forces:
(1) Crushing forces, due to the inward water pressure on shell
(2) Upward pressure due to grounding, docking on bottom
(3) Concentration of heavy internal loads such as machinery and cargo etc.
(4) Forces due to deck loads, e.g. winches, thrust from derrick posts and masts etc.
(a) Deep Framing
- Deep framing is name given to a system, every frame is made deeper and stronger than normal, over a given area of shell plating, to provide extra local strength.
- Web frames are heavy plate frames, fitted in certain parts of a ship to give local strength.
- Fitted in engine rooms and at every 4th frame space in ‘tween’ decks abaft the after peak bulkhead.
- A modification of the web frame, called a ‘cantilever frame”, is used in some types of bulk carrier.
(b) Frame spacing
- In the main body of the ship, generally the frame spacing may exceed 1 m.
- Between the collision bulkhead and a point 1/5 of the ship’s length abaft the stem, it must not exceed 700 mm.
- In peak tanks and cruiser sterns, it must not exceed 610 mm.
(c) Frame Numbering
- Frames are usually numbered from aft to forward.
- Frame No. 1 being the first one forward of the sternpost.
- The frames in cruiser stern are usually lettered from the sternpost, aft.
(a) Sketch and describe double bottom tank construction. Why double bottom tanks are constructed? How to construct double bottom tank onboard?
(a) Double Bottom tank construction
- Vertical transverse floors are fitted in a cellular double bottom. Most commonly used are watertight or oil tight floor, solid floor & bracket floor
- Tanks divided transversely by watertight floor and bottom shell and tank top are supported by solid floor.
- Constructed with centre girder, side girder and margin plate meet the shell.
- Floors connected to side frame with margin bracket.
- Margin plate forming bilge space, water drain and provide bilge suction arrangement.
- Solid floor is continuous plate, side girder is broken at each side of the plate said intercostals
- Solid floors have large lightening holes, small air release and drain holes.
- Solid floors fitted heavy loaded places such as under bulkheads, boiler, machinery oom
- If solid floor attached centre girder and margin plate to large brackets known as bracket floor.
- Bracket floors fitted at intermediate frame spaces.
- Remaining bottom supports are transverse framing and longitudinal framing.
- Tank consists of vent, watertight manhole door, suction and filling pipe.
- Tank overflow pipe usually extends above weather deck.
1. Tank top being continuous increases the longitudinal strength.
2. To act as platform for cargo and machinery.
3. Used for storage of fuel, fresh water, ballast, etc. and for correcting list, trim and draught.
4. Double hull, in event of SW ingress.
5. Protection of shell in the events of damage to bottom shell.
6. Reduce oil pollution in the event of collision.
(a) How do you understand ‘Tank stabilizers’?
(b) Discuss with the aid of diagrammatic sketches following anti-rolling tanks regarding how to stabilize the ship.
(1) Passive tank
(2) Controlled passive tanks
(3) Active controlled tanks.
(a) Tank stabilizer
Roll damping system utilizing free surface tanks. There are three basic types;
(1) Passive Tanks
(2) Controlled Passive Tanks
(3) Active Controlled Tanks
Do not depend upon forward movement of ship, suitable for vessels such as drill ships.
When loading ship, reduction stability considered.
(b) Anti-rolling tanks
(1) Passive tanks
- Two wing tanks connected by a duct having a system of baffles.
- The tanks partially filled with water.
- When ship rolls, water moves across system in direction of roll.
- Ship reaches its maximum angle and start to return, water, slowed by baffles.
- Moment is created, reduce momentum of ship, decrease angle of subsequent roll,
- Depth of water in tanks is critical & depends upon metacentric height.
- Tank tuned for any loaded condition
- By adjusting water level, cross sectional area of duct
- If not adjusting, movement of water synchronize, create dangerous rolling condition
(2) Controlled passive tanks
- Air control valves control transverse movement of water.
- Valves use to restrict flow of water in U-tube system, or flow of air in fully enclosed system
- Control system same as fin stabilizer such as gyroscope system.
- Mass of water required in system about 2%to 2 1/2% of displacement of ship.
(3) Active controlled tanks
- Water is positively driven across ship in opposition to roll.
- Direction of roll and direction of water changes rapidly.
- Used uni-directional impeller in conjunction with series of valves.
- Impeller runs continually.
- Direction of water controlled by valve, valve activated by gyroscope system.
(a) Sketch the mid-ship construction of the Ore/Oil bulk carrier.
(b) Explain about how to construct the bulk carrier for carrying the Ore cargo.
(a) Ore oil bulk carrier
- Iron ore vessel has a small hold capacity, ore is heavy.
- A deep double bottom fitted, together with longitudinal bulkheads and maintain a high centre of gravity
- Ship designed to carry bauxite, requires more volume space for cargo and have a normal height of DB and longitudinal bulkheads used to restrict ore space.
- A bulk carrier carry any type of bulk cargo, have restricted volume for an iron ore cargo,
- For light grain, which requires three times volume of the ore.
- One method of overcoming this difficulty is to design the ship to load ore in alternate holds.
- The design of bulk carriers will vary considerably.
- Fig. (Ore/Oil carrier) shows cross-section of ore oil bulk carrier carry an alternative cargo of oil in wings and double bottom.
- Structure is similar to oil tankers, having longitudinal framing at deck, bottom and side shell, longitudinal bulkhead and tank top.
- These longitudinal framings are supported by transverse webs 2.5 m apart.
- Supporting members fitted in tanks rather than ore space, to get enough space for discharging of cargo with grabs.
- Using grabs needed to increase the thickness of the tank top that required by the Classification Societies.
Sketch & describe the construction of a stern frame.
What problem will be occurred if the connection of stern frame to the hull structure is not strong enough?
- The shell plating at the after end is terminated by the stern frame.
- Use casting, but fabrications and forgings
- Single-screw ships stem frame has boss on centreline for tail shaft and enough size of boss’s hole is provided for propeller to operate in.
- The lower part of the stern frame may provide a support for the rudder post.
- An overhanging section provide gudgeons for the rudder upper-pintles.
- The upper side of stem frame provide connecting points to the floors of the after end construction.
- The transom post and vibration post are ensure that vibrations caused by propeller are kept to a minimum.
- Larger stern frame, particularly those of cast construction, are manufactured in two parts and bolted together. After careful alignment, welded.
- If the connection of stem frame to the hull structure is not strong enough, serious vibrations set up in the after end of the ship by turning of propeller.
- Frames in cruiser stern are usually lettered from the sternpost, aft.
(a) What is Bulbous bow?
(b) Explain with the aid of Sketch how it is constructed and why such an arrangement is used?
(c) Sketch and describe the construction of a bulbous bow and briefly comment on the advantages and disadvantage of fitting this bow to certain vessels.
(a) Bulbous bow
- Improves forward buoyancy, reduce pitching of ship
- To reduce ship’s resistance under certain circumstances.
- Arrangements from a casting plated into forward end to a fully radiuses plated structure, or cylindrical shape plated into the forward end.
(b) Construction arrangement of bulbous bow
- Formed by steel plate.
- Supported by centerline welded stiffener and breast hook 1 m apart.
- Outer bulb plating thicker than normal shell plating.
- To resist high water pressure.
- To avoid damage by anchor and cables.
- Reduce width at waterline cause by bulb
- Horizontal stringers consist perforated plates, fit width and length of bulb
Advantages of fitting bulbous bow:
- Increases buoyancy forward, ship speed
- To reduces the pitching, wave making resistance.
Disadvantage of fitting bulbous bow:
- Increase frictional resistance
- Increase wetted surface area of ship.