Daggerboard Design for a Dinghy

[Alan Cattelliot]

I really like to know how your trials will go. Thanks for the compliment, Serdar

 

[messabout]

Serdar you have gotten some very good information from several of our knowledgeable members. I will stick my oar in with some less sophisticated, but still practical, comments.

You have said that you are not a racer. I do not know what sort of dinghy that you have. If it is a hot rod like say...an RS Aero then, then you would probably want a sophisticated board and rudder. But what if you are never going to compete in fleet racing? If you have a simple dink that is intended for fun sailing, then don't sweat the board. A simple flat plate will work pretty well if it has only a little bit of help on the leading and trailing edge. No need for sophisticated foil sections. I am thinking of the Windmill class boat. Class rules specify that the board be three quarters thick and have the leading edge beveled at no more than one and one half inch back from the LE. The same specification for the trailing edge. Same deal for the rudder. I promise you That a well sailed, and properly rigged, Windmill will go to windward very efficiently. As high and as fast as some very fancy boats with more sophisticated foils.

None of that is to claim that flat boards are as good as perfect foil sectioned ones. But the difference is not all that big and does not matter very much for a casual sailor. You have mentioned the L/D ratio of a section at 16 to 26 degrees. I suspect that the foil will be stalled well before any of those incidence angles come into play. As for the trialing edge. a blunt edge of 2 or 3 mm ain't gonna matter enough to measure with seat of the pants data input. One of the more important design features is size. Make the board bigger than you think it needs to be. A bigger board makes a happier skipper when sailing in light airs.

 

[Alan Cattelliot]

None of that is to claim that flat boards are as good as perfect foil sectioned ones. But the difference is not all that big and does not matter very much for a casual sailor.

I agree with you. The gains with using a specific profile instead of a flat board should be balanced with the amount of work in building. If time and budget allow it, and if a specific profile is to be choosen, no matter what, finally, then It is also a good idea to first build a wooden daggerboard and test it, to check if the surface and the planform is ok. Then build, in a second time, the profiled daggerboard.

 

[serdar]

Serdar you have gotten some very good information from several of our knowledgeable members. I will stick my oar in with some less sophisticated, but still practical, comments.

You have said that you are not a racer. I do not know what sort of dinghy that you have. If it is a hot rod like say...an RS Aero then, then you would probably want a sophisticated board and rudder. But what if you are never going to compete in fleet racing? If you have a simple dink that is intended for fun sailing, then don't sweat the board. A simple flat plate will work pretty well if it has only a little bit of help on the leading and trailing edge. No need for sophisticated foil sections. I am thinking of the Windmill class boat. Class rules specify that the board be three quarters thick and have the leading edge beveled at no more than one and one half inch back from the LE. The same specification for the trailing edge. Same deal for the rudder. I promise you That a well sailed, and properly rigged, Windmill will go to windward very efficiently. As high and as fast as some very fancy boats with more sophisticated foils.

None of that is to claim that flat boards are as good as perfect foil sectioned ones. But the difference is not all that big and does not matter very much for a casual sailor. You have mentioned the L/D ratio of a section at 16 to 26 degrees. I suspect that the foil will be stalled well before any of those incidence angles come into play. As for the trialing edge. a blunt edge of 2 or 3 mm ain't gonna matter enough to measure with seat of the pants data input. One of the more important design features is size. Make the board bigger than you think it needs to be. A bigger board makes a happier skipper when sailing in light airs.

Dear Messabout,
"If you have a simple dink that is intended for fun sailing, then don't sweat the board"
My approach is to design best I can even for fun. Everyone aware of using just beveled plywood, no need to open thread for that approach here. I'm sure hundreds of people will read above mentioned valuable infos from Mr. Alan and will be happy, those are not easy to find on internet.

"L/D ratio of a section at 16 to 26 degrees. I suspect that the foil will be stalled well before any of those incidence angles come into play"
Sure, those performances are related to jibe&tack performances. Let me give you an example ; I designed my fins for windsurfing and gybe performances are increased much compared to well known brands.

" for the trialing edge. a blunt edge of 2 or 3 mm ain't gonna matter enough to measure with seat of the pants data input"
that part is the scary one... In case of capsize I will need to climb on it without cutting myself, I faced survivals cases in windsurfing with +30knts , high waves ....I know the risks and will stay in safe side forgiving some lift.