Dear Bertrand,
Good to hear that the latest iteration of your rig is working well. It raises some interesting points:
- How does it compare to the previous hinged versions, particularly to windward? Which is better, the smoothness of a full double sided sail with a small amount of beneficial asymmetrical wing shape (due to panel bulging) , or the full asymmetric wing shape of the hinged version with the single sided rear flap (David has noted turbulence at the join of the flap)?
- It is often shown that, for the same wind resistance, a wing section can be many times wider than a circular section (ie mast). This takes some believing, especially when you see that for your sail it is wide enough to climb up inside! Of course a fabric wing is not going to be as good as a solid wing from which the data taken.
So, is it the case that the sail, when fully raised, has more or less resistance to the mast with the sail dropped? With your bi-plane rig this can be readily tested, by mooring from the centre of the front beam, with only one sail up, then see how the boat lies. Ideally the test would be carried out in different wind speeds.
cheers Mark