Section 6 Definitions

6.1.1 The following definitions apply except where they are inappropriate or where specifically defined otherwise.

6.2.1  Rule length, L _R, is the distance, in metres, on the summer load waterline 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 _R is to be not less than 96 per cent, and need not be greater than 97 per cent, of the extreme length on the summer load waterline. In craft without rudders, the Rule length, L _R, is to be taken as 97 per cent of the extreme length on the summer load waterline. In craft with unusual stem or stern arrangements the Rule length, L _R, will be specially considered.

6.2.2  Length between perpendiculars, L _pp, is the distance, in metres, on the summer load waterline 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 craft 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 summer load waterline with the fore side of the stem. The after perpendicular, A.P., is the perpendicular at the intersection of the summer load waterline with the after side of the rudder post or to the centre of the rudder stock for craft without a rudder post.

6.2.3  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 craft 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.

6.2.4  Length of the hull, L _H, is the distance, in metres, measured parallel to the static load waterline from the foremost part of the stem to the aftermost part of the stern or transom, including all structural and integral parts of the craft, such as wooden, plastic or metal stems or sterns, bulwarks and hull/deck joints and excluding removable parts that can be detached in a non-destructive manner and without affecting the structural integrity of the craft, e.g. spars, bowsprits, pulpits at either end of the craft, stemhead fittings, rudders, outdrives, outboard motors and their mounting brackets and plates, diving platforms, boarding platforms, rubbing strakes, fenders and other projections. Detachable parts of the hull acting as hydrostatic or dynamic support to the craft when at rest or underway are not excluded. In case of multi-hull craft, the length of each hull shall be measured individually and L_H shall be taken as the longest of the individual measurements.

6.2.5  Length waterline, L _WL, is the distance, in metres, measured on the static load waterline from the foreside of the stem to the after side of the stern or transom.

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

6.2.7  Breadth, B, is the greatest moulded breadth, in metres, or, for craft of composite construction, the extreme breadth excluding rubbing strakes or other projections. For multi-hull craft it is to be taken as the sum of the breadths of the individual hulls.

6.2.8  Depth, D, is measured, in metres, at the middle of the Rule length, L _R, 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 at side.

6.2.9  Draught, T, is the summer draught, in metres, measured from top of keel. Where a deeper ‘scantling draught’ has been specified by the designer, this is to be used instead.

6.2.10  Block coefficient, C _b, is the moulded block coefficient at draught T corresponding to summer load waterline, based on Rule length L _Rand moulded breadth B, as follows:

6.3.1 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 thereof, and below which all openings in the sides of the craft are fitted with permanent means of watertight closing. It is the deck from which the freeboard is measured.

6.4.1 Bulkhead deck is the uppermost deck up to which the transverse watertight bulkheads are carried.

6.5.1 Strength deck is normally the uppermost continuous deck. Other decks may be considered as the strength deck provided that such decks are structurally effective.

6.6.1 A weather deck is a deck which is exposed to sea and weather loads.

6.6.2 The weather deck is the lowest continuous deck exposed to sea and weather loads, and is not to be taken lower than the bulkhead deck for the determination of the requirements for closing appliances from Pt 3, Ch 4 Closing Arrangements and Outfit.

6.7.1 A wet deck is the lower most exposed surface of the cross-deck structure, connecting the hulls of a multi-hull craft.

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

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

6.9.1 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.

6.9.2 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.

6.10.1 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.

6.11.1 For hull reference purposes, the craft 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.

6.12.1 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.

6.13.1 A superstructure is defined as a decked structure on the freeboard deck, extending from side to side of the craft, or with the side plating being less than four per cent of the breadth, B, inboard of the shell plating.

6.13.2 An enclosed superstructure is a superstructure with:

1. Enclosing bulkheads of efficient construction;

2. Access openings, if any, in these bulkheads fitted with doors complying with the requirements of Pt 3, Ch 4, 6.5 Companionways, doors and accesses on weather decks;

3. All other openings in sides or ends of the superstructure fitted with efficient weathertight means of closing.

6.13.3 The standard height of superstructure for L_L of 75 m or less is to be taken as 1,8 m, and for L_L of 125 m or greater is to be taken as 2,3 m. Intermediate values are to be determined by linear interpolation.

6.14.1 A deckhouse is in general defined as a decked structure on or above the freeboard deck with side plating being four per cent or more of the breadth, B, inboard of the shell plating.