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post #17 of Old 01-28-2010
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Smile Great Explanation

It's interesting modifying rudder shapes etc. and seeing the huge difference to the way the boat feels Jeff. We have a 25 foot trailer yacht and the standard rudder blade is approx. 38mm thick but a poor approximation to say a modified NACA section. When I redesigned the blade (with the assistance of a designer I might add) I couldn't believe the difference it made! The new one is around 42mm thick and approximates an 0012 with the concave exits. Upwind now there is way less windward helm and the boat sits way better "in the trim groove" and heels less. Downwind there is less drag too (no longer trying to hold onto 3 dead Buffalos) - We also brought the blade's leading edge closer to the gudgeon pivot axis which means it's no longer acting as a brake when going through turns (old position was 40mm aft). Looking forward to going through the same process on the keel. Need to seal up the keel / hull interface (layup some carbon and form a template that attaches to the bottom of the boat), then look at the shape characteristics. As you correctly point out Jeff, sails & foils are inter-related and are critical to how a boat performs. Now I'm starting to discover just how everything works by playing around with things. Thanks for your article
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