6.4 Boat Design
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        With a drogue deployed, a well-designed and properly constructed fibreglass boat should be capable of riding through a Fastnet type storm with no structural damage. Model tests indicate that the loads on the hull and rigging in a breaking wave strike should not be excessive.

        There are three areas that require special attention:

  1. The attachment fittings for the bridle of the drogue towline at the corners of the transom must be capable of carrying 70% of the towline design load. For a 7500 lb. displacement boat each fitting must be capable of carrying 5300 lbs. Many yachts are equipped with a Genoa track which runs aft to the transom. Such a structure, which distributes load along the hull, could be provided with a special eye at the transom for attaching the bridle.

        If the nylon towline is led through a chock instead of attaching directly to an eye, experience suggests that chafing may occur even with good chafing gear installed. Consideration should be given to the use of a short length of wire cable running through a stainless steel chock before attaching to the nylon line.

  1. Many sailors are reluctant to deploy a drogue from the stern because they fear that the boat may suffer structural damage if the breaking wave strikes the flat transom, the cockpit and the companionway doors. The model tests do not show this to be a serious problem. The boat is accelerated up to wave speed and the velocity of the breaking crest is not high relative to the boat. The stern is actually more buoyant than the bow, and will rise with the wave. However, the boat may be swept from the stern. The cockpit may f ill and moving water may strike the companionway doors. The structural strength of the transom, the cockpit floor and seat, and the companionway doors should be checked at a loading corresponding to a water jet velocity of approximately 15 ft./sec.
  2. When a boat is riding to a drogue no action is required of the crew. The cockpit may not be habitable and the crew should remain in the cabin with the companionway closed. In a severe wave strike the linear and angular acceleration of the boat may be high. Safety straps designed for a load of at least 4g should be provided for crew restraint. All heavy objects in the cabin should be firmly secured for negative accelerations and drawers and lockers should be provided with latches or ties which will not open even with significant distortion of the hull structure.

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