I wish I could make a competitive fin for a U.S.O.M out of nothing but a piece of wood. I know it can be done with carbon fairly easily, and I’ve seen the P.D.F. all about how to do it, but I just don’t have the patience do deal with laying up layers of carbon cloth.
The pine one could be the same thickness but wider in profile. Might be close to competitive.
(Note to self:give it a try)
Comments?
thanks
John,
A pine fin on a USOM might be ok but a little thick to get stiffness. You could fairly easily laminate a fin by using thin marine plywood sandwiched around carbon cloth and maybe an outer skin of carbon(after you shape it). Another idea would be aluminum but that would take longer and would be relatively heavy. I would really try the plywood carbon fin, I used one a couple years ago on a USOM that went upwind pretty damn well. That is your best bet other than buying one.
John, I don’t know much about wood but I doubt you could build a thin enough foil out of it. The t/c(thickness /chord) ratio should be around 6-7%. You might check around for premade carbon laminates that include un directional and woven fabric-try Aerospace Composites. Then you could use a grinder and shape it. Carbon grinds as easily as fiberglass but is equally to more nasty.You’d need a respirator and to coverup well.I’m not sure you can find a laminate like this but it might be worth a try. Good Luck!
Doug Lord
–High Technology Sailing/Racing
how about sitka spruce with one layer of carbon? great strength to wieght ratio… used in full size boats quite often.
just repaired my boats spare DB using sitka. board is (was) hollow core, all carbon. broke it almost in two on a particularlyt windy day. bought some sitka, laminated to 1x6’s to make up the section thickness and then shaped it to slip inside. the last 2 1/2" of trailing edge, my taper ran to about an 1/8" thick. nice tight grain…it was no problem. inserted it, layed up some layers of carbon over it, cut to length and faired…voila, new board.
i would think it should work for r/c applications…but i could be wrong
cheers
I don’t know how fast they are, but I just hack a keel out of a hardwood plank you get at the hardware store. While I haven’t had any personal experience, my brother swears by laminating two thin sheets of plywood or balsa with epoxy. I know he’s made at least one skinny blade 20" long with 4 lbs on the tip for his 36/600. Don’t know about the bend, but he seems to like it.
Graham
I was thinking a wooden fin with nothing but a layer of carbon cloth skin would be stiff. Trouble is I have to buy a huge piece of the stuff and throw away the rest. Mahogany might work well. I’ve got some 1/4 inch.
I was also thinking a piece of aluminum flashing folded in half the long way, and filled with resin might be stiff enough.
Thanks for the Ideas all.
Cheers
John
I don’t know if this is going to help or not. I used to sail marbleheads a few years ago and what we did was make up a male "mould out of a piece of pine etc.
The best way we found to do this was shape the “pine” but leave the “centre” of the now mould thicker than the centreboard should be.
Hot glue a piece of ply to this section. Then wax up the “two sides”, and fibreglass them, remember to go at least 1/2 inch on to the ply with the glass.Now, before the fibreglass begins to “tack” off, attach some shaped pieces of ply etc to the two sides of the “mould” (these are used to support the mould once it has cured). When it’s cured(about 3-5 days depending on conditions etc)peel of the two sides of your mould, wax them up. Now get your bulb and drill two holes into it large enough to take 2, 3/16 stainless steel rods, these will need to be glued(don’t use epoxy) into the bulb. The rods need to be at least the length of the centreboard. Then the next step. The two halves of the mould need to be joined. The easiest way of doing this is just clamp the two halves together then drill through the flange. Place small nuts and bolts through these holes and tighten. get some chop strand mat and pull it apart, cut up the pieces into small bits about the size of a sewing pin(length). Then make up a resin put these bits of mat into it and stir it in well, place the mould over the rods making sure that they are positioned in the centre of the moulds, then just pour the resin mix into the mould. It’s handy to have a small hole at the bottom of the centreboard to allow the air to escape while the resin is going in. Once the resin starts to seep out through this hole,cover it up. Have with you a thin but stiff piece of wire, this is used to push into the resin to help the trapped air escape.
Once the mould is full just leave it to cure. When it has cured remove the bolts and peel the sides off and you have a stiff light weight centreboard(keel). For extra protection glass the keel to the bulb with some 225 chop strand mat.
I hope this wasn’t difficult to understand but if you like I can do up some rough pictures to give you a better idea.
Peter
In the USOM construction guide you can a nice way to build wooden keels, you need some plywood, balsa and unidirectional carbon for stiffness. I have seen keels build utilizing this method and they seem to do their job.
Gio