Bre keel

[TimLM]

Whilst developing dinghy foils I was advised by the moth guys that the humming came from the trailing edge of the foil and to stop it - it disturbs the flow - they slice the trailing edge square this worked for me. So maybe something to try?

[Matthew P]

After discussing the sensitivity of the foil nose shape to imperfections the chapter on Keel and Rudder Design in Lars Larsson's "Principles of Yacht Design" has a couple of interesting (to me, anyway) pages on trailing edges.  In conclusion they should be knife sharp but this is not practical.  Surprisingly it is better to have a square cut-off (note: we're only talking millimetres here) than rounded.  A rounded trailing edge apparently induces "fluctuating separation" (Mr Larsson's expression, not mine) and this can cause "severe vibrations and noise in the hull at speeds where resonance occurs".

I have read elsewhere of roughened surface at the leading edge to promote micro-vortices that cause the flow to stick better near the surface of the foil and delay separation. Personally I think this is like wearing a moustache - it could be an advantage but the potential benefit is offset by the risk of a bad mistake, so better to keep smooth if you are unsure.  Of course, all the Swallow Yacht sailor's I know with moustaches are people of impeccable taste and discernment and having a moustache is an enhancement. 

Even more exciting is the subject of tip shape.  Mr Larsson and others have written on this and the conclusions are again surprising.  A squared-off shape is superior to round unless you have a fancy elliptical shape designed by a Master Fluid Dynamicist .  Or winglets - but let's not go there.

Matthew
Gladys BR20     

[Rob Johnstone]

Winglets now there's an idea.. Thet could be mounted in a pivot at the end of the centreboard with some sort of parallel motion to keep them horizontal when the cb is lifted and lowered....
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