The keel is parallel for the top half, then tapers a little toward the bottom, very similar to the plan, although a bit more aggressive on the foil shape. I traced the profile on each end, set up a Skilsaw for various depths, and cut depth indicating grooves about 1/16" shy of the finished shape.
Then, it's headphone time as the planer shaves it down to the saw kerfs.
I tried 50 grit on a belt sander, but it wasn't working for me. So the rest was shaped with a block plane, working as fast as the blister on my thumb would re-heal.
I left the trailing edge pretty sharp, and I'll soften that eventually, a little. I was happy that the edges stayed very straight.
And, the build area is now covered and mostly cleared. I still have a 16"ΓΈ x 10' cypress log if anybody needs some material for a boom, or?
Lastly, I built a building jig/platform which will have supports from frame 18 and back.
My plywood comes on Thursday, and I can't wait to get some boat-shapes going.
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Foil is looking good. On the trailing edge there was an excellent thread on foils humming on SBA on SA. The net of the discussion was you want to have 2 sharp corners for the flow to release from and you want one side aft of the other. The hum happens when the foil oscillates from side to side if it's symetrical. I think a 15 degree angle was the recommend angle. I just used the sander to create that angle after I glassed my foil, but I allowed for it in my core so I was sanding glass and epoxy, not wood.
ReplyDeletecheers, Kevin.
p.s. I think I'll stick to my carbon boom :-)
Yes, exactly. My core is a bit smaller than the 13.75" max to allow for sheathing thickness and then an 1/8" or so bevel. I did a bunch of foil research, with help from the SA crowd too, before templating the keel of my prior boat, and that was the advice there as well.
ReplyDeleteNice work! You are putting forward some very interesting ideas. I really like the weight saving tip as I am using Iroko (heavy!).
ReplyDeleteNow, this tip about the 2 sharp corners ... Can you please explain?
Thanks! George.
While I think the holes are helpful and not detrimental to strength due to the max-thickness area being reenforced with carbon uni, this design hasn't been tested on the water yet. So copy as you please, but use your own judgment.
ReplyDeleteThere is a pic here of trailing edge options:
http://forums.sailinganarchy.com/index.php?showtopic=23515&view=findpost&p=480364
Basically, you want two square edges at the trailing edge, with as small a flat as your build method will allow- I'll shoot for 1/16", and go from there. Even better is a slight bevel, usually about 30 degrees from square. Most glass/resin/paint constructions won't tolerate much sharper than this. Biggest thing is to avoid rounding back there, to the point of occasionally "sharpening" your bevel with a block sander (hopefully pretty rarely if you're careful with it).
Hello,
ReplyDeleteThanks for the info!
George.
Chad,
ReplyDeleteAre you also using cut outs on your rudder?
I was toying with the idea of making the rudder more efficient in line with philsfoils.com tips. Then I saw your design which does exactly that! Now, do you thing there will any significant turbulence created at the point where the rudder 'hugs' the hull? Also, if mounted on pins as usual, you will have to be able to mount it at an angle of 90 degrees. Or have you thought of s/thing else?
George.
Hi George,
ReplyDeleteI wasn't going to do any holes in the rudder core- it's already a bit thinner than Chris' design, and it won't have the uni tapes the way the keel did, just a carbon cloth wrap.
I added the "lip" under the hull to give the rudder some balance, and I think it helps reduce down-surface ventilation. There shouldn't be any additional drag there if the gaps are kept reasonable. Mounting will be with transom and rudder gudgeons (each has just holes) and a continuous pin that gets dropped in from the top.