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Dustin Laurence
07-07-2001, 01:16 PM
Hello folks, I have become the startled owner of a small 13' sloop-rigged
sailing dinghy. The boat is not of interest for Wooden Boat types
(fiberglass, bermuda rig, hollow aluminum spars, all the usual moral
failings) but my question at least pertains to wood. The only piece of
honest wood on the boat is the daggerboard, which is in very bad shape; a
~2 mm split running the entire length a couple of inches behind the
leading edge, warping, parts separating, etc. I don't really understand
why it hasn't snapped it off from a mild bump in the sand or two. The
boat hasn't been made for over 20 years so a new one is unlikely, but it
seems to be a fine boat for my kids to learn to sail while I read Arthur
Ransome to them and try to brainwash them that traditional hulls/rigs are
Good Things. (Have I sucked up enough yet to get some advice on a plastic
boat?) And it was free, so I can't complain about much of anything.

I'm reasonably handy, so with enough guidance I might be able to repair or
replace the darn thing myself. My first thought was to just learn how to
shape a new one, but I'm not sure I have the knowledge to make it come out
passably. Advice on how one goes about getting the curves right and the
lines straight would be welcome. I supose a Real Man would just do it by
eye with a hand plane, but I'm not too confident about that (not having
any experience--yet--with a hand plane).

Another thought I had recently was to go ahead and epoxy the split back
together, and then take a hand plane and carve away everything that is
warped until it is symmetrical again. I'd end up with a somewhat smaller
board, but maybe one that would still work since mostly just the leading
edge is warped (i.e. I would end up tapering back the leading edge but not
losing length). Then, since I suspect repeated wetting/drying cycles are
why it warped and split in the first place (I imagine the daggerboard has
been stored dry in between sails for 20 years, and for all I know left in
the sun), I thought I might cover it in epoxy and glass to more or less
stabilize the moisture content and (hopefully) keep it from warping any
more (oops, there goes any goodwill I might have built up). Or, if
someone dissuades me from that, just varnish and hope for the best.

Any and all advice on the advisability and actual technique of the above
fixes or better ones I didn't think of are most welcome. My knowledge of
woodworking is very modest (though I do have access to a shop with machine
tools). The hull will need work eventually, but she sails fine (I had her
outside the Long Beach breakwater aimed at Hawaii on the 4th and she
behaved herself well) and I don't have the courage to broach that subject
on a Wooden Boat forum. :)

Dustin

no1likhim
07-07-2001, 04:48 PM
I see two fixes. Having just constructed my daggerboard for the 8 foot dinghy I built, I could easily say to build one.

I used 3/4 cabinet grade oak ply. Shaped and sanded the edges and gave it a "spit coat" of varnish, steel wooled it and then followed wuit with 3 more coats like that.

Or, you could repair. Sand down the bad boy, and give it a spit coat of epoxy, fill in the split with thick epoxy and glass the thing. Fiberglass will give excellent strength.

Mike

htom
07-07-2001, 06:19 PM
Given the model name, etc, we might be able to come up with a pointer to some other owner whose board hasn't warped and cracked, and you might then be able to make a copy of their daggerboard. It shouldn't be that hard.

Failing that (or after you get a tracing of that non-failed board), a chunk of marine ply the same thickness as the failed board, trace the shape, cut out with a coping saw, (saber saw, jig saw, bandsaw ... what have you) then bash it with a power sanding device until the curves match approximately. You're not restoring a 12-Meter to competion status, after all.

You can do this.

paladin
07-07-2001, 06:46 PM
It should be quit easy. Trace an outline of the original board. Then..across the chord..the front edge to the back edge...measure it, then divide into thirds. There should now be two lines vertically on the drawing of your board, dividing it into three. Pick the first line aft (back of) the leading edge of the board. That point shall be the thickest part of the board as measured from the original board. If your lumber is not thick enough, you can use marine plywood epoxied to the correct thickness.
On a clead piece of paper draw a lon straight line, exceeding the fore and aft width of the board. Place dots where the leading edge of the board should be, measure over and add another dot where the maximum chord should be (the first vertical line), continue measuring and add the second line and the dot where the trailing edge (back of the board) should be.
Now, after measuring the thickness of the board, divide by 2, and draw a second line parallel to the main line that you just drew, equal to half the thickness of the board. Carefully impose a dot exactly equal to the dot indicating the half chord mark.
Now...you will need a batten, a piece of wood at least twice in length to the maximum fore and aft measurement of the board. It must be very limber, a 1 inch wide piece of three feet long formica might work.
Secure one end of the batten several inches in front of the dot indicating the leading edge of the board, up past the mark on the second parallel line indicating the maximum airfoil width (Tape the drawing or do this on an old piece of wood or ply and drive a nail for the maximum width dot on the second line) and continue on past the dot indicating the trailing edge of the board. This should give you a very smooth airfoil shape, for half the board. Now do the same thing to the other side of the drawing and you should get a symmetrical airfoil.
If you don't understand my ramblings, e-mail me and I will draw this out and e mail it back to you...Good Luck......

Dustin Laurence
07-07-2001, 09:08 PM
The boat is a Chrysler Pirateer, made in May
of 1978. I suppose I knew better to leave
that out, but I wasn't sure there would be
much interest in the problem in the first
place.

You can do this.

Thanks for the vote of confidence.

Dustin Laurence
07-07-2001, 09:15 PM
Originally posted by paladinsfo: ....If you don't understand my ramblings, e-mail me and I will draw this out and e mail it back to you...Good Luck......

No, that made sense, thanks. My question is about the next step; at that point we have a cross-section and a profile drawing. But how is the shape accurately reproduced in 3-d in wood? I could do it by eye, but then I'm not sure I'd actually be using the drawing to any appreciable extent.

I suspect this is a rather elementary question, so feel free to tell me to go read a book on the standard method instead. Feel free to tell me which of the many books....

Will
07-07-2001, 10:03 PM
Dustin ,I don't dought that Paladin's approach is Best ,but there's many a parralel sided daggerboard and centerboard in this world with just the edges rounded ( actually brought to an ellipse ) . The thinner the plate the less difference it makes .I've never seen a boat that small with fully shaped underwater foils ,it's just not worth it most people have decided .

Ed Harrow
07-07-2001, 10:37 PM
What will said. Is the original made of ply or boards? In any case I don't doubt you'd get acceptable service from one made out of Marine ply, using the existing as at least an indicator to the profile.

Rounding the fore and aft edges would be useful, and epoxying a glass strip around would likely prolong its life.

Note that, if you use ply, the piece that will go across the top of the board to keep it from falling thru, must be mounted to either side of the ply, not to the top (ply won't hold screws driven in from the edges). I'd suggest you simply drill right thru, have a suitable strip on either side and bolt, not screw, the assembly together. A bit of glue or epoxy would be useful.

Then go sailing http://media5.hypernet.com/~dick/ubb/smile.gif

Dustin Laurence
07-08-2001, 01:18 AM
Originally posted by Ed Harrow:
What will said. Is the original
made of ply or boards?

The original is grown wood, not ply. (This point confused me when I first got the boat, because someone appears to have once "fixed" the leading-edge split by cutting a slot several inches deep from the leading edge to more than half-way back, then glueing in a strip of wood. So it looks a bit like three-layer ply from the bottom.)

And, believe it or not, it has the airfoil shape rather than being straight-sided, though distorted now by the warping. That's why I'd imagined making a new one with that shape, in slavish imitation of the original.

Dustin

bainbridgeisland
07-08-2001, 03:32 AM
Don't worry too much about fixing or replacing the board. The performance difference between a really good foil shape and simply rounding off the leading edge and tapering the trailing edge for 2-3 inches is hard to measure. In fact, if fore and aft length (chord length) is more than 12 times the thickness (chord thickness), even a lab has trouble measuring much difference.

Simply rounding off the front of the board and reinforcing it a little would likely not change performance noticably.

If you choose to build a new board and the original board was not plywood, you may want to laminate a blank to make the board from. Most woods that glue well are suitable. I prefer spruce or fir but have also used luan and mohagany. White pine and W.R. cedar are too soft and weak except for the smallest dinghy.

The size of the laminations depend on finish and service. If you think you can seal out most of the moisture for the life of the board, use large laminations, say 3.5 inches forward and aft and full depth and thickness of the board. However if the wood gets wet, swelling may split the joints.

Most people are better off being safe and using small laminations. This way if the wood gets wet, the board will likely survive without splitting seams. For a 1" thick board, 1" thick laminations works well. For a 1 1/4" board use 1 1/4" and so forth.

Blanks are easy to make. You just lay them on a flat surface as they are edge glued and then clamp with bar clamps of pipe clamps. The hardest part is cleaning off excess glue.

After the blank is made, copy the shape from the original board.

Dale Harvey
07-08-2001, 09:57 AM
Go find a supplier who sells cut lengths of Starboard. Just remember that if you leave this stuff unsupported in the hot sun too long, it can bend. It can also be bent back. Cuts just like wood, grinds easily, no finish required.

TomRobb
07-09-2001, 12:36 PM
Just a thought....
Half of the plys in plywood are going the wrong way to do much for the beam stiffness of the dagerboard. Real World, in a little boat, probably not a big deal. But if such anal compulsiveness is your bag, you could laminate the board into home-made plywood yourself with your favorite goop, but instead of the laminations at 90 degrees, make them more like 5 or 10 degrees and odd numbers of laminates perhaps.

Naah. Just use some decent marine ply & fuhgegaboudit.

[This message has been edited by TomRobb (edited 07-09-2001).]

[This message has been edited by TomRobb (edited 07-09-2001).]

Scott Rosen
07-09-2001, 06:20 PM
Built one for my Nutshell. It's easy. Use the existing board for the basic shape. Transfer it to a sheet of marine ply of the same thickness as the existing board. Cut it out with a sabre saw or a coping saw, whichever you have handy. Round the edges, or taper it by eye. If all you're going to do is round the edges, you can probably get by with nothing more than sandpaper. If you're going to try for the foil shape, you'll need to mark the board as described above and cut with a hand plane. Make the cap of solid lumber. Use the newly cut board to mark the width and thickness of the board onto the cap. Cut a slot through the cap the witdth and thickness of the board, sort of like a through mortice. You can use a hand saw or sabre saw for the sides and a chisel to cut the end square. Then glue the board to the cap and clamp on the sides of the cap. You shouldn't need any mechanical fastenings, as there is very little stress at the cap/board joint. I wouldn't waste the time and effort to glass the board. You may want to add a chaffing strip on the bottom edge of the board to prevent damage in a grounding. Copper or bronze sheeting, bent to shape and riveted should do the trick.

Francois van Wyk
07-10-2001, 01:10 AM
I was in a very similar situation. I have a fibreglass boat, 13.5 feet, with wood trim and mast. The daggerboard was warped and split. First I traced the outline onto glued up 3/4 RED OAK, glued it up and boy what that a mistake. That red oak swelled up so much I had to circle around around just off the jetty trying to raise the damn dagger board - it was jammed tight into the center board case. Next step was to redo the whole project: traced the outline, glued up white oak 3/4 boards with polyurethane glue, basic shaping, used cpes and varnish, and works like a dream. Minimal woodworking skills required.
And I have been sailing off Marina del Rey and Cabrillo Beach.
Don't hassle over it, just go for it and learn as you go.

Dustin Laurence
07-11-2001, 01:10 PM
Thanks for the advice, guys. You've convinced me that trying to make a foil shape would only be worth it as a woodworking exercise (which, granted, I could really use). I'll probably just make a flat one so I can get back to sailing, as someone suggested.

Dustin