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Shunda77

Wide sport boats and the effect of heel on keel flow.

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I am puzzled about something to do with the trend of wider sport boats, particularly in the stern sections with chines etc.

After drawing a few lines plans myself I realized that it is possible to get fairly narrow, symmetrical heeled waterlines if the hull volume is carefully balanced fore and aft.
But one thing I am not sure about is the tendency for those heeled water lines to start at the bow and end in the extreme aft quarter well to the side (and at a not insignificant angle) to the center line of the boat.
Now while this heeled water line shape looks fast, the keel is of course still on the center line of the hull, would this not cause problems with maintaining a correct angle of attack to keep the foil lifting effectively up wind? or are there other factors such as the heeled angle of the foil that mitigate this to some extent?
It would  seem to me that the heeled waterline shape would effectively shift the angle of attack of the foil which would increase leeway, but I am not sure if I have included all the dynamics of the situation, does anyone have any understanding of this?
 

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It's the keel that defines your course, not the hull! Basically, the keel will assume the angle of attack that balances the sideforce from the sails and the hull just follows. Thus, you should worry about the angle of attack of your hull, as it will NOT move along it's heeled centerline.

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Search for Diagonal Heeling. I recall an interview with G. Verdier where he talks about it. 

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11 hours ago, neuronz said:

It's the keel that defines your course, not the hull! Basically, the keel will assume the angle of attack that balances the sideforce from the sails and the hull just follows. Thus, you should worry about the angle of attack of your hull, as it will NOT move along it's heeled centerline.

Yes, that could be the factor that I wasn't properly considering, it is the lift dynamics of sails and keel that would determine heading. So how is it that these boats sail to weather well at all? the heeled waterlines are well off the center line, basically any boat that has a lot of the windward side of the stern in the air when it heels is doing this. These boats obviously do sail to weather without seemingly pushing the hull sideways through the water, perhaps as the displacement wave dynamics develop there is not much of an issue?
The wide boats with a chine aft would have that chine immersed at a considerably different angle to the keel line.

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You sail a VX1 flat, (optimum heel angle is 6 degrees according to the designers). Hike hard and play the main/jib a lot. Should be able to hold 6kts upwind. In 12-15.

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Direction of incoming flow is the result of heel and leeway - algebra maths

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