Design category
Design category Wind force (Beaufort scale) Significant wave height (H 1/3, metres) A - ‘Ocean’ B - ‘Offshore’ C - ‘Inshore’ D - ‘Sheltered waters’ exceeding 8 up to, and including, 8 up to, and including, 6 up to, and including, 4 exceeding 4 up to, and including, 4 up to, and including, 2 up to, and including, 0,3
Definitions[edit]
A. OCEAN: Designed for extended voyages where conditions may exceed wind force 8 (Beaufort scale) and significant wave heights of 4 m and above but excluding abnormal conditions, and vessels largely self-sufficient.
B: OFFSHORE: Designed for offshore voyages where conditions up to, and including, wind force 8 and significant wave heights up to, and including, 4 m may be experienced.
C: INSHORE: Designed for voyages in coastal waters, large bays, estuaries, lakes and rivers where conditions up to, and including, wind force 6 and significant wave heights up to, and including, 2 m may be experienced.
D: SHELTERED WATERS: Designed for voyages on sheltered coastal waters, small bays, small lakes, rivers, and canals when conditions up to, and including, wind force 4 and significant wave heights up to, and including, 0,3 m may be experienced, with occasional waves of 0.5m maximum height, for example from passing vessels.
Craft in each Category must be designed and constructed to withstand these parameters in respect of stability, buoyancy, and other relevant essential requirements listed in Annex I, and to have good handling characteristics.
For Design Category A, unlimited wind and wave conditions apply as they reflect that a vessel engaged on a long voyage might incur any conditions and should be designed accordingly. The amended Directive now states that this is ‘excluding abnormal conditions’, which was added to make it clear that some extreme conditions need not be considered, such as a hurricane. In practice this still means that a Category A boat should be designed to be able to survive being caught out in gale and storm force winds at sea.
Most large sailing yachts that are designed for blue water cruising are, out of necessity, designed to be able survive such conditions and therefore Category A may be applicable. Very few motor cruisers are designed with such conditions in mind and most large offshore motor cruisers are therefore assigned to Category B.
For category D the wording has been changed slightly by the amendments to the Directive. The maximum significant wave height is now 0.3m, but allowance must be made for waves of passing vessels up to a maximum wave height of 0,5 m.
It is important to note that the design category parameters are intended to define the physical conditions that might arise in any boat category for design evaluation. They are not intended for limiting the use of the recreational craft in any geographical areas of operation after it has been put into service.
The Commission has issued some additional guidance on the physical conditions, i.e. sea state, that should be considered from a design perspective for each category. It states that the physical conditions for each category are determined by the maximum wind strength and wave shapes, where the shape of the waves are consistent with waves generated by wind blowing at the maximum stated strength for a prolonged period, subject to limits of the implied fetch and the maximum stated wave heights, and excluding abnormal factors such as sudden change in depth or tidal races.
Put simply this means that that waves in Category D will be not only be small, but also of fairly regular shape, i.e. breaking waves are not envisaged, but for Category A the combination of severe winds and tall seas may result in very steep and even breaking waves.
