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Daggerboard - symmetric or asymmetric?

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Joined 2014-03-01

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I’m about to start shaping a daggerboard from a blank made of spruce strips glued together, and I’m thinking about making it asymmetric.

Does anyone have practical experience using asymmetric foils? Do they offer an advantage, and more importantly, are there any drawbacks?

Is there an ideal foil section? Should I leave one side completely flat, or should it be shaped with some curvature?

I’m also wondering whether to shape the daggerboard case to fit the (asymmetric) foil section, which will mean I cannot switch to a symmetric section in the future, or whether to leave it rectangular, and to leave the daggerboard rectangular in section above the point where it exits the hull when fully lowered…

All thoughts welcome!

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cuica - 18 August 2014 06:05 AM

I’m about to start shaping a daggerboard from a blank made of spruce strips glued together, and I’m thinking about making it asymmetric.

Does anyone have practical experience using asymmetric foils? Do they offer an advantage, and more importantly, are there any drawbacks?

Is there an ideal foil section? Should I leave one side completely flat, or should it be shaped with some curvature?

I’m also wondering whether to shape the daggerboard case to fit the (asymmetric) foil section, which will mean I cannot switch to a symmetric section in the future, or whether to leave it rectangular, and to leave the daggerboard rectangular in section above the point where it exits the hull when fully lowered…

All thoughts welcome!

I can’t really comment on the asymmetric aspect, all my foils to date have been symmetric based on the idea that just a little (necessary) leeway gives you a reasonable angle of attack and when you don’t require a lateral force, foil is balanced.

If you are using foil on a shunting craft, Tom Speers P3xxxxxx series foils would be hard to beat, there are both symmetric and asymmetric sections in the family. Having a rectangular trunk where possible is better IMO, less tendency to bind up and it is more versatile.

Best Wishes,
Skip

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cuica - 18 August 2014 06:05 AM

I’m also wondering whether to shape the daggerboard case to fit the (asymmetric) foil section, which will mean I cannot switch to a symmetric section in the future, or whether to leave it rectangular, and to leave the daggerboard rectangular in section above the point where it exits the hull when fully lowered…

 

You can make the daggerboard case rectangular and slightly oversize. Then, use solid wood templates (for want of a better word), say 20mm thick, top and bottom, cut out to the shape of the foil. These can be be easily matched fairly close to the shape of the foil to give a good seal with little turbulence. If you you change the shape of the foil later, just cut out the templates and glue in a new set shaped for the new foil. Another thing you do is to make the template oversize and glue a fabric material to the face, which reduces wear on the foil (as long as you can keep sand out of the fabric). Suitable fabrics might be nylon webbing or the fibrous side of Velcro.

Mal.

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which reduces wear on the foil (as long as you can keep sand out of the fabric)

You can always glue a couple of very thin strips of some slippery plastic material on the inside of the daggerboard trunk. Sand does not stick (as good) to slippery plastic, and it has less friction the wood or fabric.

Cheers,
Johannes

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