| Term | Definition |
| air draught |
the vertical distance measured from the ship's waterline to the highest point on the ship; usually comes into consideration when the ship has to sail under overhead bridges in the river
compare draught |
| ballast |
any weight in solid or liquid form taken on a ship to increase draught, to change trim, or to improve the stability; use of sea water is common |
| bar |
1. sand or silt forming a bank across the mouth of a river or harbour entrance; this build-up reduces the water depth and limits the draught of a ship which can cross it
2. of unit, 1 bar is equal to 1 atmosphere in pressure, i.e. 101.3 kpa |
| bar draught |
maximum draught which a ship can take to pass over a bar or sand bank |
| block coefficient |
the ratio of the underwater volume of a ship to the volume of a rectangular block having the length, breadth and draught of the ship
CB = immersed volume
L x B x H |
| deadweight |
total weight of cargo, stores, fuel and water needed to submerge a ship from her light draught to her maximum permitted draught; it is given by the difference between the load displacement and light displacement (also known as lightweight); DWT for short |
| design draught |
draught as used for design calculation before actual construction, which has a tendency to distort the final reading |
| draught marks |
figures welded on the bow, midship and stern of each side of a ship's shell plating to indicate draught; the distance is read from the lower edge of each number; draught measured at the bow is called forward draught and at the stern is called aft draught |
| draught survey |
survey carried out to determine the cargo weight on board by measuring the ship's draught |
| extreme draught |
draught measured to the lowest projecting portion of a ship |
| forced draught |
combustion air for boiler furnace supplied under pressure from a forced draught fan |
| hydrostatic curves |
a set of curves which plot the hydrostatic quantities such as displacement, centre of flotation, centre of buoyancy, transverse metacentre, etc against the draught; these curves are useful for quick assessment of the draughts and the initial stability in various loading conditions |
| keel cooler |
cooler designed to be built into the keel with the cooling water coming from the sea water flowing underneath the keel; generally used in vessels with shallow design draught for sailing in river, etc. |
| Laker |
a ship capable of transiting the St. Lawrence Seaway locks to trade in the Great Lakes between USA and Canada; the maximum beam and draught allowed in the lock is approximately 23.15 m and 26 feet fresh water respectively - this is equivalent to ship with a deadweight of about 20,000 tons |
| lightship draught |
draught when ship is empty and deadweight is zero |
| load lines |
the lines which are marked and painted amidships on each side of a ship to indicate the maximum permissible draughts of loading adjusted for various seasons and zones; also known as Plimsoll marks, so named after Samuel Plimsoll, a British Member of Parliament who introduced and promoted its widespread use in 1875
TF: Tropical Fresh water line; F: Summer Fresh water line; T: tropical load water line; S: Summer load water line; W: Winter line; WNA: Winter North Atlantic Line; the letters beside the circular marks indicate the assigning authority, e.g. AB refers to American Bureau of Shipping, etc.
|
| Malaccamax |
describe a maximum hull form capable of transiting the Straits of Malacca fully loaded; the maximum draught and beam allowed in the strait is approximately 21 metres and 60 metres respectively with a deadweight of 280,000~300,000 tons or in terms of TEU, not exceeding 12,000 |
| mean draught |
the average of forward and aft draughts of a ship |
| midship section coefficient |
the ratio of the midship section area of the underwater body of a ship to the rectangular area having the breadth and draught of the section; also known as midship coefficient
CM = midship section area
B x T |
| multi-cat |
a multi-purpose work vessel in the offshore industry which is built with a simple rectangular pontoon hull and a long open foredeck resembling a small pusher tug; its shallow draught is suitable for marine construction and harbour work |
| Panamax |
describe a class of ship size with the maximum dimension capable of transiting the Panama Canal; the maximum beam and draught allowed in the canal is approximately 32.3 metres and 12 metres fresh water respectively; equivalent to a ship with deadweight of about 55,000 tons |
| Post Panamax |
describe a vessel whose size do not allow it to transit Panama Canal unlike Panamax vessel; maximum size of this class built has a length overall, beam and draught of approximately 300 metres, 43 metres and 14.5 metres respectively |
| scantling draught |
the maximum draught which meets the strength requirements; this is usually used when the draught corresponding to the freeboard computed according to the Load Line Convention is greater |
| SSW |
Summer Salt Water, it refers to the draught of the ship in salt water when it is loaded to its summer loadline in the open sea |
| subdivision load line |
waterline used to determine the subdivision of vessel for compliance with SOLAS ; the deepest subdivision load line is the waterline which corresponds to the greatest draught permitted by subdivision requirements |
| Suezmax |
a large tanker capable of transiting the Suez Canal fully loaded; the maximum draught allowed in the canal is approximately 52 feet 6 inches salt water - this is equivalent to about 150,000 deadweight |
| summer draught |
the maximum permissible draught to which the ship may be immersed when arriving at any port located in the summer zone |
| tonnes per centimetre immersion |
number of tonnes required to change the draught of the vessel by one centimetre at a given draught; TPC for short; this is the metric equivalent to tons per inch immersion |
| tons per inch immersion |
number of tons required to change the draught of the vessel by one inch at a given draught; TPI for short; this is the non-metric equivalent to tonnes per centimetre immersion |
| trim |
indicates the difference between the forward and after draughts of a ship; when a ship is said to "trim by stern", the after end of the ship is deeper and when "trim by head", the ship is deeper in the forward end |
| waterline |
the line at a ship's side formed by the surface of water at a specific draught |
