The CoB on the 6m R2AK boat cannot move very far to leeward because the stabiliser has limited buoyancy. The righting moment disappears at 7 degrees list corresponding to the CoB moving about 230mm leeward. That is the prime reason for the canted board. Essentially the canted board is big enough to keep the stabiliser off the water to eliminate its drag. The foil cant angle working range should be between 20 and 40 degrees off horizontal but it can be set more vertical for increased leeway prevention in light wind.
The "snappiness" as you describe is more likely related to losing attached flow or cavitation. Either can cause sudden loss of lift.
Kites are an effective means of eliminating heeling moment and producing reasonably efficient lift. Kite boards are combining the kite and foils these days. The foiling board is not necessarily faster but a lot softer riding. Kites have handling issues yet to be addressed for cruising boats.
We progressed a good way with the canted lifting sail but that idea still needs considerable development. I could write a book on the issues. There are some cruising proas with canted sails but they have only been successful when producing down force. Such a sail can increase stability as wind increases. A lifting sail needs some means of automatic, and preferably progressive, fusing of force once the windward hull starts to lift.
On 01/05/2016, at 2:11 PM, "lucsimard@ymail.com [harryproa]" <harryproa@yahoogroups.com.au> wrote:
Thanks Rick ! Been looking all over the web to figure why my thinking was incorrect (up to a point ... of max stability :-)).
So what I was doing incorrectly was to calculate the rolling forces/moments where the CB/metacenter moved all the way to leeward, at the angle of maximum stability. (same thing I used for calculating maximum forces in the beams).So I understand now foil lift help reduce heeling and please correct me if I am wrong but up to when the metacenter has moved past the center of lift on the foil, it's lift then start to help heel the boat.I guess this is why some foilers are so "snappy" when approaching the limit ? But as always some exeptions, one being when putting the foil all the way out of the boat to lw or special curved shape ... not simple.Starting to like big lifting foils less and like Rob's kite more !And now wondering about canted masts ... Vestas sailrocket style.Found this nice article for other novice whom's interested that explain basic stability in good details. (even if it is for mono, can relate to multi)
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Posted by: Rick Willoughby <rickwill@bigpond.net.au>
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