Length over all ( Loa) = Horizontal distance over the extremities between bow and stern

Length between perpendiculars ( Lbp) = distance from aft perpendicular ( centre of rudderstock) to forward perpendicular ( intersection of waterplane and bow at design draft)

Load line length ( Lll) = length as used in freeboard calculation

Beam ( breadth) ( B) = width of the hull usually measured inside shell plating ( moulded)

Depth ( H) = height from baseline to uppermost deck at side measured inside the plating

Draught ( T) = underwater depth of a vessel

  • Draught at the stern ( Ta) is the vertical distance between water line and keel plate ( immersion in water of the vessel) measured on the aft perpendicular;
  • Draught forward ( Tfwd) is the vertical distance between water line and keel plate ( immersion in water of the vessel) measured on the forward perpendicular.


It is the difference between the draught at stem ( forward) and the draught at the stern;

A vessel could be:

  • Down and trimmed by the head, i. e. the draught at forward is larger than the one at the stern;
  • Down and trimmed by the stem, i. e. the draught at the stern is larger than the one at the forward.
  • Even keel is the situation where the trim equals zero, i. e. the draught at the stern equals the draught at the stem.


  • L/ B- The ratio of length and breadth: L/ B can differ quite significantly depending on the type of vessel. Common values are 6- 8 for passenger ships; 5- 7 for cargo ships; and 3- 5 for tug boats. A larger value of L/ B is favourable for speed, but unfavourable for manoeuvrability.
  • L/ D– The length/ depth- ratio varies between 10 and 15. This relation plays a role in the determination of the freeboard and the longitudinal strength.
  • B/ T– The breadth/ draught- ratio varies between 2 and 4. 5. A larger breadth in relation to the draught ( a larger B/ T value) gives a greater initial stability.
  • B/ D– The breadth/ depth ratio varies between 1 and 2. If this value becomes larger, it will have an unfavourable effect on the stability ( because the deck edge will be emerged when the vessel heels) and on the strength.

Moulded dimensions

Distance measured a tin side of the shell plating ( i. e. distance measured between 2 points excluding the plate thickness)

Base Line

Measured imaginary horizontal lenght of the upper part of the spine plate.

Deck Line

Horizontal line marked usually at the top of the main deck/ free board deck at the ship’ s side

Load Line

Waterline of a vessel immersed in water:

  • Light water line is the water line of a vessel carrying only her regular inventory
  • Deep waterline/ summer water line is the water line of a vessel at the maximum draught in salt water
  • Construction ( scantling) water line is the water line used as the limit to which the structural components of a vessel are designed.

Air draught

Vertical distance between the water line and the highest point of the vessel

Freeboard Mark

Shows the maximum allowed value of a sinking ship, leaving enough space for safety. Lloyd’ s Register of British and Foreign Shipping was the first to introduce loading recommendations in 1835.

In 1860 Samuel Plimsoll ( 10 February 1824 – 3 June 1898) , a British politician, took up the load line cause after more and more vessels were lost due to overloading. His efforts against what was called at the time “ coffin ships” ( unseaworthy, overloaded vessels, often heavily insured, in which owners risked the lives of their crew) were paid off when in 1876 the United Kingdom

Merchant Shipping act  has mandated the marking load line. The location of the loading line mark is not connected to the 1894 law.
In the 1930 Load Line Convention, the application of load line regulations became international. Later on, in 1966 during the Load Line Convention held in London, the rules of 1930 were re- examined and amended.

  • The free board is marked according to the result of the freeboard calculation ( which takes into account the main parameters such as length, beam ( breadth), sheer, length of superstructures etc. ) ; the scope of the freeboard calculation is to establish the summer freeboard in salt water;
  • The load line markings must be permanently visible on the shell plating of the vessel;
  • The abbreviations of the marked load lines have to be in the language of the flag state of the vessel;
  • When a vessel carries timber cargo on deck and certain demands are met, the ship is allowed to have more draught ( less freeboard) . The mark used for such cases is known as the Timber Mark;