Foam daggerboard?

Thread starter #1
I've done some searching on and off this site for anyone who has done a home made daggerboard using foam and fiberglass.

I currently have an original 1983 mahogany daggerboard that has seen better days. I will eventually restore it, but since my primary use of the boat is for club racing, I want to go with the more competitive, longer foiled shape. It would be easy and probably cheaper to just go buy one of the Intensity boards and be done with it, but I like to make stuff whether it makes economic sense or not.

One of my other hobbies is RC aircraft, and I have made plenty of super stronger, high performance sailplane wings using foam, reinforcing spars, and fiberglass. I can send one of my 12 foot wings up a winch line at full power and barely get it to bend. That got me thinking about building a daggerboard using the same techniques. I have a hot wire bow that I use to cut wing cores. I can either make a carbon fiber/kevlar composite or a set of steel spars, and then cover the hole mess with bi-directional fiberglass and epoxy. Of course, I'd follow the class dimensions, etc.

Thoughts? Has someone already done this? Bad idea?

I am not sure you can get enough strength with a foam core for a board that is only 3/4" thick. You might be better off making a solid wood core and then glassing it.

Alan Glos
Cazenovia, NY


Active Member
The strength will depend on the glass-cloth-weight along with any type
of reinforcement used internally. I'd say you are already very experienced in
this type of construction and I would be interested to see how
your project comes out. Note that the daggerboard slot is too
narrow for a proper NACA airfoil unless you can figure out
a way to get around that. Dagger board area should be somewhere
around 4% of the total sail area roughly.


Well-Known Member
Water is ~800 denser than air—plus—the board has to support the weight of the skipper. I'd like a board made of cast aluminum! :eek:

Kevlar is amazing stuff: I just discovered thin Kevlar cords are infused into overhead wires carrying fiber-optics.

Once your foam core is "hot-knifed", perhaps secure dozens of Kevlar cords lengthwise. (But I don't know how "stretchy" Kevlar is for this application). Wait for member mixmkr's input, who has experience with home-made daggerboards.
Thread starter #6
Thanks for the replies so far. I've also thought of many of these concerns as well as the surface 'hardness' of the board. My wings don't need a high amount of hardness to prevent dings or hitting stuff underwater (I do sail on the Ohio River so that is inevitable). The de-turtling weight of me standing on the board is also a concern. I could use all carbon and kevlar weave and make the thing literally bullet proof, but at that point I'd be constructing a $500 daggerboard and that makes no sense at all despite my initial comments about economics.

I think the board would do it's job under sailing conditions but may be too fragile to really hold up to the abuse that I can dish out under weekly racing conditions. I've been known to haul the boat up out of the water and have forgotten to pull the board up. I may destroy a foam board on the first week since none of the strength will really be on the leading or trailing edges.....
The daggerboard from Intensity Sails is $170+ shipping.
I'd buy that one and spend your time and creativity on something else.


Well-Known Member
PA110100-002.JPG Wow...'Glad I reduced it! :confused:

I actually do own an aluminum billet, 7-inches in diameter. My understanding is that, as a raw aluminum alloy, it is on the "soft" side. Although, if you hit it with a hammer, it rings like a bell. A local metal recycler offered 25¢ per pound—and it's maybe 75 pounds—so I still own it. :rolleyes:

"Machining" would not be necessary. The trick would be to use a hot wire bow (as above), form Styrofoam to a proper NACA foil shape, pack it in "green sand", and pour molten aluminum into the Styrofoam mold. Since it would come out of the mold with a rough surface, the cheap way to finish it would be a belt sander.

This casting process has been known even before Biblical times, and is named "The Lost-Styrofoam Method". ;) Yeah, it would be heavy as blazes, but the weight would be in an especially good spot heading upwind. :)

Wanting a cast aluminum daggerboard makes me wish I'd saved all my beer cans! :D
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Thread starter #11
I happen to be on the board of our local club, so I asked the question tonight at our Board meeting if anyone minded if I made my own wood board as long it matched class dimensions. I got mild laughter with a comment that half the club has made their own daggerboards.....

We have a very strong local racing scene with 17-20 boats every Tuesday night, but very few do any ‘official Sunfish class regattas’, so following the monopolistic rules to the book is not required. 90% of the fleet is also using Intensity sails at this point too.


Well-Known Member
I have a Super Sunfish daggerboard made of carbon fiber. As far as I can tell it is hollow and very light but stiff. I always think it is cool to experiment so I would offer the suggestion of building your own even if you buy an Intensity in the mean time. The SSF board is a little different than the wood daggerboards but not as long as the current race daggerboard.

Your fellow club members will only start complaining after you start winning all the races.


Active Member
I extended my original 69 wood board...then extended it again. It's now 50"... way past legal length....but I don't race and am goofing around. I also got the Intensity board just recently so will compare this upcoming season... The first pic shows what it was...and the 1st extension....with the cardboard cutout showing the 2nd extension to be done. I ran aluminum flat bar (with a slight L shape....cut off on side of the "L" a bit), to stiffen and just fiberglassed the heck out of it. It's been in 20 knot winds and didn't bust!


Thread starter #16
That thing looks like a weapon!

Yep, I saw your original thread too. Would like to here the comparison between the Intensity board and your extended one. I’ll be watching your original thread.