Daggerboards: profiles, planforms, paranoia

Originally posted by ChrisB14 I will probably be painting the board to allow it to be as smooth as possible while still being able to take the odd bump or scratch.

- white so that you can more easily spot any weed: slower than the slowest planform and section!

Hi Chris,
It's interesting that I went through the same dilemmas for my Farr, but ended in similar decisions. I settled for NACA 0009 daggerboard and 0012 rudder. They seem to work ok, although when I get round to it I'll do need to refinish the daggerboard as a season of use and an imperfect case means it's looking a bit shabby now. I think we'll need to use slot gaskets on the Farr's as the tapered case results in gushers of water through when planning
Dave

Nice little story from Sailing Anarchy:

Yacht designer lives by a marina and knows an engineer living on a boat. He goes down to ask him to do some structural calculations on a keel for him, it turns out he actually is a rocket engineer/scientist

He gives the engineer the data and goes back to his office.

A few days later the engineer comes back "can't do it......too many variables".

As a pevious poster said, make what you can make well.  Try it out, if it don't work make another.

Design, make, review.

Hi Chris,

My build is still in progress but I made a reasonable amount of progress over the summer and am now filling and fairing the hull (Or at least I will when I get back home from Uni at Xmas)

With regards to foils, I am using a 0009 section for the daggerboard and a 0011 section for the rudder. I would have gone for a thicker section for the daggerboard but the daggerboard case ended up being only 22mm thick. This was because the lengths that made up the thickness of the girder were only 22mm thick. If you haven't made up the girder yet then I would suggest trying to pack this up with filler to get a thickness closer to 24mm (Max. thickness in the class rules AIUI) at that point. I had originally planned to make a foam core board but I thought 22mm was too narrow to do this easily. Instead I am using spruce.

In terms of planform, I agree that a reasonable amount of rake is fast with the 3.7 because the rig has a fair amount of rake. Having looked at a few aeroplane wings that are swept back I noticed that they almost all have tip that is parallel to the centre line. I was also planning on using virtually no fore-aft taper because I want to get maximum power out of the rig (I have gained a reasonable amount of weight since I started the build!).

I think that turbulent 00XX sections are the way to go with the 3.7 because it is so twitchy and hence angle of attack can vary quite a lot as the helm corrects for gusts, waves etc. As I understand it you need to have a fairly perfect finish to keep flow attached long enough for laminar sections to really come into their own.

There are some resources on the NZ website for foil design as well which are oldish but the physics haven't changed.

Regards and good luck,
Max D

Originally posted by ChrisB14 Originally posted by Medway Maniac What I'd do at the tip would depend upon how confident I was that I could predict the angle of flow to the tip. Hard to do that. My understanding is that on the pressure side the flow at tip will be partially downward, sweeping around the tip and upward on the low-pressure side. Thus my thoughts about squaring off the leading edge. Not my idea, of course, but gathered from "Principles of Yacht Design"