MEO Orals on Naval Architecture Function 3 Part 2

Duct Keel

• An internal passage of water tight construction (two longitudinal girders spaced not more than 2.0 m apart) running same distance along the length of the ship, often from the forepeak to the forward machinery space bulkhead.
• To carry the pipe work, and an entrance is at forward machinery space via a watertight manhole.

Bulbous bow

• A bulb shaped under water bow which is designed to reduce wave making resistance and any pitching motion of the ship.

Camber

• Curvature given to a deck transversely.
• It is measured by the difference between the heights of the deck at side and centre.
• The camber amidships is frequently one fiftieth of the breadth of the ship.

Carving note

• Form completed by the owner of the ship under construction.
• Gives details of tonnage, name, port of registry, etc.

Cofferdam 

• Narrow void space between two bulkheads or floors that prevents leakage between the adjoining compartment.

Coffin plates

• They are used to connect stern frames to the flat plate keel.
• The stern frame is extended forward far enough, two or three frame spaces, to provide a good connection with a flat plate keel.
• The aft most plate of the keel, coffin plate is dished around the extension.

CRP

• Contra – rotating propeller.
• A propulsion arrangement with two propellers rotating in opposite direction on the same shaft.

Freeboard

• Vertical distance from the load water line to the top of the freeboard deck.
• Freeboard has considerable influence on sea worthness of the ship.
• The greater the freeboard larger is the above water volume of ship.
• This provided reserve buoyancy assisting the ship to remain afloat in the event of damage.

Types of keel

• Bar keel, Duct keel, Flat plate keel.

Freeing port  

• An opening in the lower portion of a bulwark, which allows deck water to drain overboard.
• Some freeing ports have hinged gates that allow water to drain overboard but that swing shut to prevent seawater flowing in board.

Dead light

• A hinged steel cover, which is part of a port or scuttle.
• It is used to cover the glass in heavy weather.

Dead rise

• Athwartship rise of the bottom from the keel to the bilge.
• Also known as ‘ Rise of floor ‘.

Deep tanks

• Tanks extending from the bottom or inner bottom up to or higher than the lowest deck.
• They are often fitted with hatches so that they also may be used for dry cargo in lieu of fuel oil, ballast water of liquid cargo.

Devil’s claw  

• A stretching screw with two heavy hooks or claws.
• It is used to secure the anchor in the hawse pipe.

Displacement

• A ship floating freely displaces a mass of water equal to its own mass and this mass is known as the ship’s displacement.

Light displacement

• It is the displacement of the ship complete & ready for sea but no crew, passengers, baggage, stores, fuel, water, cargo on board. Boilers, if any, are filled with water to working level.

Load displacement  

• It is at the maximum permissible draught and is made up of the light displacement and the dead weight.

Docking plug

• A brass screw fitted in the garboard strake of the shell plating at the bottom of each compartment to drain the water, which remains in the ballast tanks while the vessel is in dry dock.

Flare

• The spreading out of the hull form from the centre vertical plane usually in the fore body above waterline.

Floodable length

• The length of the ship that may be flooded without sinking below her safety or margin line.

Floors

• They are transverse vertical plates those run across the bottom of the ship from the centre girder to the bilge.
• Watertight or oil tight floors are used to divide the double bottom space into suitable tanks.

Flush deck ship

• A ship constructed with an upper deck extending through out her entire length without a break or a super structure such as forecastle, bridge or poop.

Free surface

• Liquid in a partially filled tank that tends to remain horizontal as the vessel heels or rolls

Garboard strake

• The strake of the bottom shell plating adjacent to the keel plate.

Intercostals

• These are plates, angles, etc., fitted down between others or cut to allow other parts to pass through them. Side girders, parallel to the centre girder & fitted between the floors, are intercostals.
• Vessels of up to 20 meters in breadth must have one intercostal side girder on each side.
• Vessels of greater are to have two such girders on each side.  

Kort nozzle

• A shroud or duct fitted around a propeller in order to increase thrust at low speeds.
• It is often fitted to tugs and trawlers.

Length overall

• The extreme length of a ship measured from the foremost point of the stem to the aftermost part of the stern.

Length between perpendiculars

• The length of a ship between the forward and after perpendiculars.
• The forward perpendicular is a vertical line at the intersection of the fore side of the stem and the summer load waterline.
• The after perpendicular is a vertical line at the intersection of the summer load waterline and the after side of the rudder post or stern post, or the centreline of the rudder stock if there is no rudder post or stern post.

Gross tonnage

This is the total of the under deck tonnage and the tonnage of the following spaces.

1. Any tween deck space between the second and upper decks.
2. Any enclosed spaces above the upper deck.
3. Any excess of hatchways over 0.5 % of the gross tonnage.
4. At the ship owner’s option and with the surveyor’s approval, any engine light and air space on or above the upper deck.

Exempted space

These are spaces, which are not measured for the gross tonnage calculation.

1. Wheel house, chart room, radio room, navigation aid room.
2. Spaces for machinery & condenser, stability tanks
3. Safety equipment and battery spaces.
4. Gallery, washing & sanitary.
5. Sky lights, domes & trunks.

Deducted space

• The tonnage of these spaces must be measured first and may then be deducted from the gross tonnage of the ship to give the net tonnage. 

1. Master & crew accommodation, provision store.
2. Chain locker, steering gear space, anchor gear and capstan space.
3. Workshop, storerooms.
4. Donkey engine & donkey boiler space, pump room. (Outside the machinery space)
5. Water ballast tanks. (maximum limit of 19 % of the gross tonnage is imposed)
6. Propelling power allowance.

Propelling power allowance (PPA) 

This is the largest deduction and is determined according to certain criteria, as follows:

If the machinery space tonnage is

1. Between 13% to 20% of gross tonnage PPA = 32% of gross tonnage.
2. Less than 13% of gross tonnage PPA = proportion of 32% of gross tonnage.
3. More than 20% of gross tonnage PPA = 1.75 times the machinery space tonnage.

Maximum limit of 55% of the gross tonnage for the PPA.

Net tonnage

• This is the tonnage value obtained by deducting from the gross tonnage the total value of the deducted spaces.
• The net tonnage is considered to represent the earning capacity of the ship.

Reference:

Oral Guide by – MIN ZAR TAR

MEO Orals on Naval Architecture Function 3 Part 2