New daggerboard

[Captain Kidd]

I made my daggerboard out of a piece of cheap plywood I had picked up. I didn't realize it when I bought it used but I found out when I built the board. I figured at some point I would have to build another and the time has come. The board has delaminated and will no longer fit in the trunk due to swelling.

I've pondered how to make a new one - plywood? I don't have any more marine ply. Use something from the box stores? I looked at a piece of rough milled oak that a guy was selling. That would make a one piece board. It had a little twist in it. Not bad. But did I really want to be planing and sanding oak? Then there is the strip method. The problem there is that my board is only 7/8" thick. Why so thin? When I made the first one, I mistakenly and foolishly left out a layer of ply! Shame on me. Anyway, I'm not going to tear the trunk apart (which was built to the thickness of the daggerboard) and rebuild it.

Well, I decided to go the strip route. I went to Lowes today and picked out a 2x8x10 that was clear, straight, and had fairly tight grain (for a box store). I cut nine 7/8" strips out of it this evening. Laid on their side they will give me the necessary dimensions for the board.

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I haven't worked with epoxy since finishing Disciple Ship over two and a half years ago. I had some left over but the epoxy had mostly hardened. I heard that if you warm it up, it will liquify again. So I turned a ceramic heater on it and after a while it did the trick! I had bought some cheap measuring cups to pour what I could for measurement, but turns out it was unnecessary because even the epoxy that was up in the pump liquified.

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I laid out the strips and coated them with 100% epoxy so that they wouldn't be epoxy "starved" and then came back and coated them with thickened epoxy. I clamped them together and laid my train track on them and did my best to make sure they are on "plane".

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Hopefully the epoxy will cure properly and give me a strong board. After shaping it, I may cover it in glass. I think I have enough epoxy to do it. I'm not going to be able to get the nicest foil shape with it, since it is so thin; but I'll round the front edge and feather the aft edge.

[Doug SC]

That is an investment in time. I hope the epoxy will hold up as I haven't heard of heating it. Which part hardened the resin or hardener or both? I use MAS and it hasn't ever done that. However, I did have some West System G/flex toughened 650 go bad a number of years ago. I think it might have hardened but don't recall exactly.

[Spot]

I have had to 'dethaw' (uncrystalize) the epoxy/part A side of multiple brands of resin.
The hardener portion usually does not heat and is recommended not to be heated before use.
I used a water bath, getting the epoxy to 140F or 60C for a half hour or so.

Looking good so far! You reminded me of this that came up on another forum:

https://www.pdracer.com/keel/

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(I worked on the shape for #4 to make it more like a 'true' airfoil)

[Riley Smith]

Nice! (And I'm totally OUT Of epoxy). I haven't laminated anything in a while. What you have done is called "high grading" the lumber and is a legitimate tactic to get a better product. You can make some really good stuff selecting the wood for a consistent grain. I might add that if you alternate the growth rings it is very stable and not prone to move as much. I've been jonesing for a wood project but with summer mowing, I usually have bits and pieces of grass cutting machinery all over the shop. As well as the machines themselves, so not much else gets done. The train track is great!

[Captain Kidd]

Doug, the epoxy was almost totally crystallized. Hardener was fine.

Spot, I'm shooting to get as close to #4 as possible. The board is thin but I'll work at it.

[Spot]

Advise if you need help with the foil layout
Once you know thickness and length, there are online calculators for NACA00XX foils
0009 shown as example, done with XFLR software and Rhino3D for notes

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[Captain Kidd]

Advise if you need help with the foil layout
Once you know thickness and length, there are online calculators for NACA00XX foils
0009 shown as example, done with XFLR software and Rhino3D for notes

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PM sent

[Krusen]

The advantage of going all the way to #4 is only worth it for all out racing. 

There is a strong advantage for #3, the dagger board stays inline with the hull much better, and any twist relative to the overall lines of your vessel will decrease the advantage.

#4 requires a very tight fit in the well, and any aquatic growth or mud will tend to jam the board.  #4 is also easily broken on he trailing edge, and the wood will carry water by capillary action far into the wood strips.  Thus, you will need to cut out a larger section to repair a relatively minor break.

Save present and future work, go #3.

[Charles Brennan]

Dale, That's gonna be a challenge!! 
"Great Minds Think Alike  . . . . . . .  But Fools Seldom Differ!" 
I was on the same track as Spot, tracking down a NACA foil generator. 

Your dimension are going to be a challenge.

I cut nine 7/8" strips out of it this evening.

OK, 9 strips X 1½' thickness glued together gives us 13.5 inches X ⅞" thick.
13.5" / ⅞" gives a 15% chord to length thickness, which would suggest a NACA 0015 foil.
EXCEPT!!  When you plot the foil using those numbers, it ends up being twice as thick as your dagger board measurements.   
Spots estimate of a NACA 0009 foil is much closer, but will STILL be thicker than your dagger board thickness of ⅞"

Think if it was me, I'd get out the Shinto Rasp and round off the front end of it. Then I'd get out the block plane and move three block plane widths from the trailing edge.  I'd take a swipe clear down the length, then move over 1 plane width closer to the trailing edge and take two swipes.  Move over to the trailing edge and take three swipes with the block plane, then evaluate how it looks.

I ran a couple foils full size, according to your dimensions and they all came out too thick, to be useful, using NACA curves.
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(NACA 10 pictured.)

Food for thought,
Charles Brennan

[Captain Kidd]

Dale, That's gonna be a challenge!!   

Think if it was me, I'd get out the Shinto Rasp and round off the front end of it. Then I'd get out the block plane and move three block plane widths from the trailing edge.  I'd take a swipe clear down the length, then move over 1 plane width closer to the trailing edge and take two swipes.  Move over to the trailing edge and take three swipes with the block plane, then evaluate how it looks.

I ran a couple foils full size, according to your dimensions and they all came out too thick, to be useful, using NACA curves.
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(NACA 10 pictured.)

Food for thought,
Charles Brennan

Yep, I'm with you. Spot sent me a PM with a dimension for max thickness. I'll work from there. Round off front and taper to the rear.

[Spot]

The 7/8 x 13 1/2" numbers would be between a 0006 and 0007

So I would use the 0006 and creep the tail towards the nose to what the trunk allows, making for a rounded trailing edge and ever so slightly 'beefier' blade.

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A #3 style board in a trunk would not be a deal-breaker either.

PS moving the wide point a little forward 1/4" or 3/8" could have merit too.
PPS I am not a professional at foil design

[Charles Brennan]

Spot, DOHHHH!!!   
How did I manage to invert the arithmetic, so badly? 
What happens, when you whip out your calculator, before engaging your brain. 
Good catch.

Charles Brennan

[Captain Kidd]

Let's throw a monkey wrench into our calculations (not that I think it's going to make any huge difference in how I shape my board).

Let's say the daggerboard is slanted, which mine is. It drops into the water at an angle. Wouldn't that make the width of the board longer? The water is going to be running across a greater distance (admittedly not a lot, but still a bit).

With the question posed, let me go ahead and post a pic or two on my work tonight. I did some rough sanding on the board.

Here is one side after removing clamps.

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Here are the two sides after rough sanding.

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One side has a couple low spots.

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I'll try and position the board so that they are either planed/sanded down or at the top of the board which remains in the trunk.

Here is a shot that shows the grain in the wood and my effort to get it all on an even plane. The grain was a lot tighter in this plank than most of the ones I had to choose from. And the plane looks pretty good I think.

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It's obvious from that last pic that attempting to get an accurate foil shape is going to be very difficult due to the thickness (or rather thinness) of the board.

[Spot]

Nice words and pictures, thanks for bringing us along.

What are you thinking for finish on the final product?

If it is going to be painted, then building up and fairing any defects becomes less of a cosmetic issue.

Perhaps thinking about a #3 foil with a more elliptical entry and the trailing edge tapered as far as practical is a good way to go.

[Captain Kidd]

Nice words and pictures, thanks for bringing us along.

What are you thinking for finish on the final product?

If it is going to be painted, then building up and fairing any defects becomes less of a cosmetic issue.

Perhaps thinking about a #3 foil with a more elliptical entry and the trailing edge tapered as far as practical is a good way to go.

I think you're right. It is just too thin to do much else. That's basically what I did with my first daggerboard.

As far as finish, I painted my first board. Likely will do the same. I can't see much need in keeping it bright. I have both products on hand (Glidden Porch & Deck Enamel and Helmsman Spar Urethane) so it's a toss up. I'm not worried about a picture perfect finish.