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IJCA Forums
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| Author |
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Jeff Jorgensen
Posts:3
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| 05/30/2008 9:29 AM |
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My skip is convinced that pinching upwind with the genoa is the best option in medium to heavy winds. I've suggested that keeping the telltales flying straight back is preferred and gives us superior speed and tactical options. I think he's getting the "rhumbline" bug. Any thoughts?
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Jeff Jorgensen
Posts:3
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| 07/26/2008 10:39 AM |
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It's hard to believe that after 380+ views, no one responded to my question. So I did some digging and here is what I have come up with:
1. Don't pinch! Gary Jobson in Championship Sailing writes the following: "If the wind overbends around the sail, there will be too large a vacuum and backwind will result. This forces a boat to "stall out". On the other hand, if too much wind is caught by the sail, the boat will heel beyond its designed lines and slip sideways...Your aim is to generate as much power in the sails while keeping the boat sailing on its lines." Page 166.
2. Maxamize lift! Chapman Piloting (1994) notes the following: "When sails are set at an efficient angle, air flows across their convex leeward surface and a low pressure area is created. The sail tries to move into it, impelled by the higher pressure on its windward side. This driving force created by the sails is transmitted to the hull throught the mast, sheets and sail attachments." Page 212.
3. Sail with a little weather helm! "Since most keels are rigidly attached to their hulls, the whole boat has to be aimed a couple of degrees to windward of the course it actually travels. While this may seem inefficient, it really is the fastest was to sail. Skippers call this "sailing with a weather helm." Chapman Piloting (1994) Page 213.
4. Find you angle of incidence! "Wind crossing the sail should nearly align with the leading edge at a small angle of incidence. Too large an angle of incidence will cause the air to separate from the sail creating large vortices. If the point of separation moves too far forward, the sail will loose its lift completely - it will be stalled. The boat will rapidly loose its speed. A turbulent trail of air will then minimize drive and increase heeling force. If a boat is pointing too high into the wind (small angle of incidence) the sail "back winds" and may flap in the area near the luff - it will be luffing. A good sail setting is to ease the sheet until the sail luffs and then trim it in again until it just stops. Note that it is more difficult to discover a stalled sail than one that is luffing as the appearance of the sail does not change. This is a common beginner's mistake. Generally we may say that the sails are most efficient when they are on the verge of luffing." Page 4 of Illustrated Sail and Rig Tuning by Ivar Dedekham 1999.
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