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The drogue is deployed from
the stern and attached to the boat with a bridle. The bridle performs two
functions; it provides a turning moment to keep the boat stern to the
wave, and it divides the total load and feeds the load into strong points
at the corners of the transom. The attachments at each side of the transom
should be designed to take 70% of the design load.
Figure 26 shows recommended
towline diameter vs. displacement. Since this is a once or twice in a
lifetime load, the diameters are based on 60 to 75% of the minimum
breaking strength of double braid nylon line. The working load under storm
conditions will be on the order of 10% of the minimum breaking strength
and well within the fatigue limit.
All elements of the
equipment must be carefully selected. For example, the sheet metal thimble
commonly used for an eye splice would not be adequate for this service.
Reinforced thimbles are available and should be used. All shackles, eyes
and swivels must be rated above the design load.
An anchor is used as a
weight at the end of the towline. The type of anchor or the weight of the
anchor is not critical. For smaller boats a 25 lb. anchor is adequate. For
large boats a 35 to 50 lb. anchor is preferable.
The construction and
attachment of the 5-inch diameter cones is shown on Figures 17 and 18. The
1-1/2 ounce rip stop dacron material is suitable for boats with a
displacement under 30,000 lbs. Above this displacement, a heavier material
is preferable.
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