Define the following
(a) Displacement and Deadweight
(b) Gross tonnage and Net tonnage
(c) Deducted space
(d) Exempted space
(e) Freeboard
(f) Propelling power allowance
(a) Displacement and Deadweight
- Displacement equal to relevant mass of water displaced by the ship.
- Displacement = lightweight + deadweight
- Lightweight is without cargo, fuel, lube oil, ballast water, fresh water and fresh water in tank, consumable stores, passengers and crew and their affects.
- Deadweight equal to the ship’s loaded capacity, including bunkers and other supplies necessary for ship’s propulsion.
Deadweight = displacement – light weight
(b) Gross Tonnage and Net Tonnage
- GT means measure of overall size of a ship, due to provision of present convention.
- NT means measure of useful capacity of a ship, due to provision of present convention.
- Measurements as GT and NT.
- one ton = 100 cubic feet = 2.83 cubic meter.
- Measurements express size of internal volume of the ship in accordance with the give rule.
- Used for calculating harbor and canal dues / charges.
Gross Tonnage
- Calculate using formula, account ship’s volume in cubic meter.
- Below main deck, enclosed spaces above main deck.
- Function of moulded total volume of all enclosed spaces
- (international tonnage convention 1969, regulation 3)
GT=K1XV
V= total volume of all enclosed spaces in m³
K1= 0.2+0.02xLog10(V)
Net Tonnage
- Non-dimensional number.
- Describe total volume of all cargo space
- Function of total volume of all enclosed cargo space (VC)
where: Vc = total volume of cargo spaces in m3
K2 = 0.2 + 0.02 log10Vc
K3=1.25x(GT+10,000)/10,000
D = moulded amidships in meters
d = moulded draft amidships in meters
N1= number of passengers in cabins with not more than & berths
N2 = number of other passengers
(c) Deducted space
Measure first, deducted from gross tonnage
Deducted spaces are
1. Master’s accommodation.
2. Crew accommodation & an allowance for provision stores.
3. Pump men, electricians, carpenter and boatswain workshops and store rooms
4. Pump room, outside machinery space.
5. Safety equipment and batteries space below upper deck
6. Chain locker, steering gear space, anchor gear and capstan space.
7. Water ballast tanks, exclusive carriage of water ballast; a maximum limit of 19% of gross tonnage Imposed.
8. Propelling power allowance
(d) Exempted space
Not measured in gross tonnage calculation
1. Wheelhouse, chart room, radio room and navigation aids room.
2. Safety equipment and battery spaces.
3. Washing and sanitary accommodation forming part of crew accommodation.
4. Galley spaces
5. Stability tanks and machinery
6. Spaces fitted with and for the use of machinery.
7. Skylight, domes and trunks.
(e) Freeboard
The vertical distance from summer load waterline to the top of the freeboard deck plating, measured at the ship’s side amidships.
Minimum freeboard allowable-in conjunction with an overall
- Adequate structure and stability
- hull essentially watertight from keel to freeboard deck, weathertight- above this deck
- Working platform, high enough from water surface, safe movement on exposed deck in heavy seas.
- has enough reserve buoyancy to avoid danger of foundering or plunging in a heavy seaway.
(f) Propelling Power Allowance
largest deduction
- If the machinery space tonnage is between 13% and 20% of the gross tonnage, the propelling power allowance (PPA) is 32% of the gross tonnage.
- If the machinery space tonnage is less than 13% of the gross tonnage, the PPA is the amount expressed as a proportion of 32% of the gross tonnage.
- If the machinery space tonnage is more than 20% of the gross tonnage, the PPA is
- 1.75 times the machinery space tonnage.
- Maximum limit for PPA is 55% of the gross tonnage.
(a) What are the local stresses and structural stresses throughout the length of the ship?
(b) Express the preventive measures taken for compensating these stresses.
(a) Stresses on Ship’s Structures
The separate stresses to which ship’s structure is subjected divided as follows
(a) Structural – those affecting the whole ship.
(b) Local – those affecting the particular part of the ship.
(1) Structural Stresses
(1) Longitudinal Stresses in still water
(2) Longitudinal Stresses in sea way causing Hogging and Sagging
(3) Shearing stresses
(4) Racking stresses
(5) Water pressure
(6) Dry docking
(2) Local Stresses
(1) Panting
(2) Pounding
(3) Localized loading
(4) At the end of superstructures
(5) Deck opening
(6) Other local regions of stress
(b) Preventive measures taken for compensating these stresses
To overcome Longitudinal Stresses
(1) Longitudinal bulkheads
(2) Deck and Bottom longitudinal
(3) Double bottom structure
(4) Deck girders
(5) Deck plating
(6) Side shell plating
(7) Hatch coamings, etc. being fitted.
To preserve the transverse form
(1) Transverse bulkheads, and
(2) Deep transverses, being fitted.
To stiffen the plating against compressive stresses
(1) Frames
(2) Beams and
(3) Floors, etc. being securely bracketed together.
To resist the water pressure, a major stress on the hull
1. The bottom structure is made much heavier
2. Side framing reducing in size with height
To prevent the various stresses causing deformation or possible fracture
1. Increasing the sizes of material used.
2. A careful deposition of the material.
3. Paying careful attention to the structure design.
(a) How do you understand freeboard?
(b) What are the items to be prepared for the load line survey?
(a) Freeboard
It is the vertical distance from the summer load waterline to the top of the freeboard deck plating, measured at the ship’s side amidships.
(b) Items to be prepared for a load line survey
- The surveyors inspect ships -load line regulations obeyed, conditions of assignment maintained onboard.
- Usually expect- weather-tight integrity and crew protection from the sea on the external decks are kept to required standards.
(1) Hatches
- Cover must be weather tightness
- Rubber seals of steel hatches in good condition
- Closure arrangements should be satisfactory.
- Hatch coamings have no excessive corrosion.
(2) Ship’s side doors
All closing and securing mechanisms below the freeboard deck functioning correctly.
(3) Internal weather tight doors
Function properly both by local and remote control.
(4) Superstructure doors and side scuttles
- Rubber seals in good order
- Close arrangements satisfactorily
- steel rims have no excessive corrosion
- Scuttles fitted with appropriate toughened glass, Deadlights satisfactory closure.
(5) Deck penetrations such as ventilator trunks, tank air pipes etc.
- Around any pipe or trunk on expose deck no excessive corrosion.
- minimum height clearance of vents and air pipes above the deck.
(6) Non-return valves and extended spindles
Good working order and extended spindles well lubricated.
(7) Side railings
No significantly damaged sections, not to be weakened, not have excessive corrosion.
(8) Underdeck walkways
Adequately light, well ventilated & effectively gas tight seal
(9) The Approved Stability Booklet
Approved stability booklet updated for any significant modifications made to the vessel.
(a) What is Load Line and Where are Load lines locating at ship?
(b) What is Freeboard Deck?
(c) Sketch with dimensions.
(d) Explain the Load line markings.
(e) Summer Load Line, Winter Load Line
(a) Load line
Load line marks located amidships on both side of ship, showing maximum draught to which vessel loaded in summer and winter and in salt and fresh water.
Purpose-
- Storage of cargo, ballast, etc. to assure sufficient stability
- To avoid excessive structural stresses.
(b) Freeboard Deck
The uppermost continuous deck exposed to weather and sea which permanent closing all opening.
(c) Load Line
- When loading, minimum freeboard requires to ensure ship is sea worthy.
- Top of deck line is level with top surface of freeboard deck.
- TF – Tropical zone load line in fresh water
- F – Summer Freeboard in fresh water
- T – Tropical Zone load line in sea water
- S – Summer load line in sea water
- W- Winter load line in sea water
- WNA – Winter North Atlantic zone load line. This is required for ships of 100 m or less in length.
- F and TF – Deducting from the summer (S) or tropical (T) freeboard.
Deducting value is the result from below formula.
Fresh Water Allowance = Displacement in sea water (tones)/4 x TPC (mm)
Where TPC is the tones per centimeter immersion in sea water at the summer load line.
(e) Summer Load Line – passes through center of ring and marked.
Winner Load Line – add to summer freeboard (1/48 X summer freeboard) of summer draught.
(a) How do you understand “Framing”?
(b) Sketch one type of framing system.
(c) Describe about framing systems used in ship construction, indicating in which ships they are used.
(a) Framing
- The 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.
(b) Transverse framing
(c) Transverse Framing
- It is generally adopted in dry cargo and passenger ships.
- Consists of vertical stiffeners, and bulb plate or deep-flanged web frames,
- Attached to deck beams and floor structure by brackets.
- Particular locations, ends of the hatches, require frames of increased scantlings frames.
- Very deep web frames are often used in the machinery space.
- Frame spacing is generally not more than 1 m
- Spacing reduced in the pounding region ends at the fore and aft ends in the peak tank regions.
Longitudinal framing
- It is generally adopted in oil tankers.
- Longitudinal framing of side shell employs horizontal bulb plates and increased scantlings towards lower side shell.
- Longitudinal frames are support by transverse webs to against compressive loadings on both side and bottom.
Combined system
- Used particularly in tankers, less than 200 meter in length.
- Consists of transverse side frames and longitudinal bottom frames.
- A number of longitudinal stringers are fitted, depending on the depth of the tank.
- Brackets and knees are used to tie the side frames, the underside of the deck, the bottom plating and stringers.
(a) Describe, with the aid of the sketches, about an anchor cable arrangement? Anchor cable termination detail.
(b) Explain the method of locking in stowed position, with the aid of a sketch. Anchor cable releasing mechanism for emergency use.
(a) Anchor Cable Arrangement
- Windlass raises and lowers anchor and cable.
- Anchors are housed against forward side shell,
- Anchor cable passes through hawse pipe on to forecastle deck and travels over bow stopper and windlass cable lifter drum.
- It also passes through spurling pipe into chain locker and drops vertically down.
- Hawse pipe fitted to smooth running of anchor cable and to maintain water tightness of forecastle.
- Spurling pipe made of heavy plate with chafing ring on lower edge.
- Cable or bow stopper used to hold anchor cable in place while ship at anchor or anchor is fully housed.
- windlass is freed and isolated from any shocks or vibrations.
- Chain locker is normally fitted forward of collision bulkhead.
- It sizes adequate to house all anchor cable and still leave empty space above.
- Reduce height of centre of gravity of considerable mass of cables.
- A perforated floor or grating is fitted at bottom to provide drainage well and out of mud and water.
- The forecastle deck forms top of locker with spurling pipe at centre.
(b) Method of locking in stowed position
- Final link of anchor cable is secured to ship’s structure by clench pin.
- An insert heavy plate pocket is fitted into chain locker side with vertical pin holding final link of anchor cable.
- A hand-wheel assembly on deck is used to raise the pin and release the link.
- If the safety of the ship does not allow time to raise the anchor.
- By releasing the clench pin, all the cable can quickly pass out of the chain locker,
- Ship free leaving out of danger
