Thread: Stay sail
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Old 04-13-2016, 07:32 PM   #19
koliver
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City: Saltspring Island
Country: BC, canada
Vessel Name: Retreat
Vessel Model: C&L 44
Join Date: Nov 2007
Posts: 3,045
Typically, a steadying, or "staysail" on a trawler is smaller than the sail for a small dinghy, say eg a Laser. The effect on a Laser is to make this dinghy, weighing 150 lb all in, go fairly well. To translate that to a trawler weighing upwards of 20 tons, or more than 250 times as much, is to get roughly 1/250 times the speed a Laser is able to get, from the wind. So if a Laser gets to 6 knots in a certain wind, your trawler will get a benefit of 1/250 x 6 = 0.02 knots, less deductions for a less efficient hull shape.

To use the sail for steadying, is to align it with the centerline of the boat and when the boat wants to roll, the sail is there to resist.

To use the sail for wind cocking while at anchor, the sail must be aft of the pivot point of the boat, or for best results, at the stern, where the sail will offer windage when the boat swings, that will pull the stern back, tightening the anchor rode and keeping the boat pointed closer to straight ahead. While pointing straight ahead, the sail offers no windage, so there will be some falling off and hunting for direction.

Unless your trawler has a good location for a sail, hoisting will be a total waste of resources. Boats set up for sails, like Mark's, allow the hoisting of a large enough sail area to offer measurable help if downwind in the trades, mounted out in front, where they pull the boat, but can't be used for steadying or for wind cocking.

The small sails sometimes seen on GBs and similar boats are generally too small to offer any assistance travelling, too far forward to help holding position in an anchorage, and too small to do an effective job of dampening roll.
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