Section 1 General

1.1.1 These Guidance Notes are on certification of rigs of sailing vessels. It is not intended to give design guidance. It does not provide a prescriptive method of assessment.

It should be noted that for the correct application a basic knowledge of sailing technology is beneficial. Also, there may be a need for unified approach and interpretation. This appendix gives Sections with technical information that may be useful during the certification process.

It is emphasised that the approach described below is a minimum design approach that is in no way mandatory for the certification process.

1.2.1 The design loads for the various sailing conditions can be derived from model tests or from established calculation models, and take account of the weather window for that sail setting.

There are in general two ways to approach this:

1. By reaction of the vessel: For vessels and cases where the wind acting on the rig causes a significant moment of heel, and does so in a more or less static way (e.g. constant sailing at a constant angle), one can assume the effects of inertia to be small and therefore the heeling moment equals the sum of: The result of the action of the wind on sails and other rigging components. The effect of gravity on the inclined rig. The stability cross curve of the vessel is, in a way, used as a measuring device. The rig manufacturer and yacht builder can specify the maximum angle of heel which the vessel and the rig were designed for. This angle is usually chosen, as is appropriate for the vessel size and type, and acts as a natural maximum. The skipper can see to it that this angle is not exceeded and should reduce sail or adjust course if necessary to comply. For design purposes, the total moment is to be determined from loads of the sail set and other elements exposed to wind as well as gravity loads. Appropriate factors for wind force components are to be applied. Levers are to be measured to the centre of lateral force in the tangential, axial and radian direction as appropriate.
2. By quantification of action: There are vessels and cases where the load from the rig is not expected to result in a significant angle of heel and there is no natural maximum for the forces in the rig. This can occur when the vessel is very stable (e.g. trimaran; swath-type catamaran) or when the vessel is very large with respect to the rig.

1.2.2 The rigging can then be designed for wind conditions consistent with the maximum advised mean apparent wind speed appropriate for each combination of sails (Large Yacht Code paragraph 11.2.2.2.3). Wind loads are to be taken as derived from wind tunnel tests or from aerodynamic theory.

1.2.3 Wind speeds used in the calculation of sail loads are the greater of apparent wind speeds or real speeds.