Section 6 Definitions

6.1.1 Rule length, L, is the distance, in metres, on the waterline at draught T, from the forward side of the stem to the after side of the rudder post or to the centre of the rudder stock if there is no rudder post. L is to be not less than 96 per cent, and need not be greater than 97 per cent, of the extreme length on the waterline. For ships without rudders, the Rule length is to be taken as 97 per cent of the extreme length on the waterline. In ships with unusual stem or stern arrangements the Rule length, L, will be specially considered.

6.1.2 Amidships is to be taken as the middle of the Rule length, L, measuring from the forward side of the stem.

6.1.3 Breadth, B, is the greatest moulded breadth, in metres.

6.1.4 Depth, D, is measured, in metres, at the middle of the length, L, from top of keel to top of the deck beam at side on the uppermost continuous deck, or as defined in appropriate Chapters. When a rounded gunwale is arranged, the depth D is to be measured to the continuation of the moulded deck line.

6.1.5 Draught, T, is the scantling draught, in metres, measured from top of keel, and is not to be taken as less than the ‘summer draught’. Both of the draughts are to be indicated on the midship plan, irrespective of whether or not they are of the same value.

6.1.6 The block coefficient, C _b, is the moulded block coefficient at draught, T, based on Rule length, L, and moulded breadth, B, as follows:

6.1.7 Length between perpendiculars, L _pp, is the distance, in metres, on the waterline at draught T, from the fore side of the stem to the after side of the rudder post, or to the centre of the rudder stock if there is no rudder post. In ships with unusual stern arrangements the length, L _pp, will be specially considered. The forward perpendicular, F.P., is the perpendicular at the intersection of the waterline with the fore side of the stem. The after perpendicular, A.P., is the perpendicular at the intersection of the waterline with the after side of the rudder post. For ships without a rudder post, the A.P. is the perpendicular at the intersection of the waterline with the centreline of the rudder stock.

6.1.8 Load line length, L _L, is to be taken as 96 per cent of the total length on a waterline at 85 per cent of the least moulded depth measured from the top of the keel, or as the length from the fore side of the stem to the axis of the rudder stock on that waterline, if that is greater. In ships designed with a rake of keel, the waterline on which this length is measured is to be parallel to the designed waterline. The length L _L is to be measured in metres.

6.1.9 Load line block coefficient, C _bL, is defined as:

6.1.10 Maximum service speed, V, means the maximum ahead service speed, in knots, which the ship is designed to maintain, at the summer load waterline at maximum propeller RPM and corresponding MCR.

6.1.11 Bow reference height, H_b , is defined as:

For ships less than 250 m in length:

For ships 250 m or greater in length:

6.2.1 The freeboard deck is normally the uppermost complete deck exposed to weather and sea, which has permanent means of closing all openings in the weather part, and below which all openings in the sides of the ship are fitted with permanent means of watertight closing.

6.2.2 For the purposes of the Load Lines Conventions, as applicable, where the assigned summer freeboard is increased such that the resulting draught is not more than that corresponding to a minimum summer freeboard for the same ship, but with an assumed freeboard deck located a distance below the actual freeboard deck at least equal to the standard superstructure height, the related items for the conditions of assignment to the actual freeboard deck may be as required for a superstructure deck.

6.3.1 For a passenger ship the bulkhead deck is generally to be taken as the deck to which the main bulkheads and side shell are carried watertight.

6.3.2 For a cargo ship the bulkhead deck is generally to be taken as the freeboard deck.

6.4.1 A closing appliance is considered weathertight if it is designed to prevent the passage of water into the ship in any sea conditions.

6.4.2 Generally, all openings in the freeboard deck and in enclosed superstructures are to be provided with weathertight closing appliances.

6.5.1 A closing appliance is considered watertight if it is designed to prevent the passage of water in either direction under a head of water for which the surrounding structure is designed.

6.5.2 Generally, all openings below the freeboard deck in the outer shell/envelope (and in main bulkheads) are to be fitted with permanent means of watertight closing.

6.6.1 For the purpose of Load Line conditions of assignment, there are two basic positions of hatchways, doorways and ventilators defined as follows (see also Figure 1.6.1 Position 1 and Position 2):

Position 1:

• Exposed decks located abaft the forward 0,25 of the load line length, L_L, and less than one standard superstructure height above the freeboard deck.

• Exposed decks situated within the forward 0,25 of the load line length, L_L, and located less than two standard heights of superstructure above the freeboard deck.

Position 2:

• Exposed decks situated abaft the forward 0,25 of the load line length, L_L, and located at least one standard height of superstructure, but less than two standard heights of superstructure, above the freeboard deck.

• Exposed decks situated within the forward 0,25 of the load line length, L_L, and located at least two standard heights of superstructure, but less than three standard heights of superstructure, above the freeboard deck.

6.7.1 A passenger ship is a ship which carries more than 12 passengers.

6.8.1 For hull reference purposes, the ship is divided into 21 equally spaced stations where Station 0 is the after perpendicular, Station 20 is the forward perpendicular, and Station 10 is mid-L _pp.

6.9.1 Unless otherwise stated, the co-ordinate system is as shown in Figure 1.6.2 Co-ordinate system, that is, a right-hand co-ordinate system with the X axis positive forward, the Y axis positive to port and the Z axis positive upwards. Angular motions are considered positive in a clockwise direction about the X, Y or Z axes.

6.10.1 The equilibrium waterline is the waterline in still water when, taking account of flooding due to an assumed damage, the weight and buoyancy forces acting on a ship are in balance. This relates to the final floating position, see Figure 1.6.3 Damage heel angles, when no further flooding takes place or after cross flooding is completed.

6.10.2 The intermediate waterline is the waterline in still water, which represents the instantaneous floating position of a ship at some intermediate stage between commencement and completion of flooding when, taking account of the assumed instantaneous state of flooding, the weight and buoyancy forces acting on the ship are in balance. The deepest intermediate waterline corresponds to the maximum intermediate heel angle, see Figure 1.6.3 Damage heel angles.

6.10.3 The intermittent waterline is the waterline in still water, which represents the instantaneous floating position of a ship corresponding to the intermittently immersed heel angle. The intermittently immersed heel angle, see Figure 1.6.3 Damage heel angles, is the heel angle corresponding to the maximum range in the damage condition.