Fin and rudder construction (questions)

After reading threw the US1M construction manaul (One manual I recommend) I am some what confused as to the best method for fin and rudder construction.

What would be the easiest method (short of buying) to build the fin and rudder???

On page 19 of the US1M manual it shows a laminated keel. This is the one I am leaning towards.

Is there other methods that you have used that produce a good keel?



have a look at this topic might help you a little

Never hold your farts in.
They travel up your spine, into your brain,
and that’s where sh*+y ideas come from.

I’ve used epoxy plating, from the electronics shop (normally for making custom electronic circuits.)
it’s about 1,5mm thick, just big enough to make rudders and it is superstrong.

My keel is made of a plate of 5mm aluminium

I’m theorising (havn’t tried it) that you could make a pretty good fin shaped from a 1/4 inch piece of mahogany, and covered with carbon cloth and resin but I’ve always wondered how to make the sharp trailing edge that way. I suppose you can’t really sand the carbon cloth, so maybe a metal insert if some kind. Maybe a thin sheet of brass sandwiched between two pieces of 1/16th hardwood, then covered. Hmmmmmm…

Do you have a photo or two of your rudder and keel?

The epoxy plating or circut boards I have seen all have little holes in them Can you get them with out all the holes?

Once you have shaped the rudder are you covering it with fiberglass?


Edit— Menno With a Aluminnun keel of 5mm would there not be a lot of deflection bow to stern and left to right? I would be looking at a keel length of around 14 1/2 inches(apx)for a keel for the US1M hull. (measured bottom of hull to bottom of bulb) Jeff

In the case of the EC-12 we use a foam core (Clegicel)with a 3 oz glass C laminate. The foam floats, i.e. a positive bouyancy (helps that sagging fantail on the EC-12) but that is probably not a concern for you, but it DOES produce an extremely lightweight part that you can drive a truck over it.

Even a balsa core would be very light and the glass provides the strength. Hollow epoxy graphite would probably be the most desireable if serious racing is where your headed. A lot of manufacturers will make you a custom rudder.


Larry, I would check carefully the EC-12 rules, especially the following:

7.1 Rudders shall be constructed of wood and/or fiberglass.

It is my understanding that foam core is not a permitted material in an EC-12.

If in doubt, I would request advice from the EC-12 class secretary.

Doug Hale

The fiberglass/epoxy plates that Menno referrs to can be purchased in blocks up to 1" thick in just about any length and width. This is sometimes referred to as “G10 epoxy”. It is a very common material for making windsurfer fins. It is common for a fin “shaper” (the windsurfing name for the guy who comes up with the airfoil and planform shape of the fin) to use a grinder to turn a 15" by 6" by 3/4" block of G10 into a windsurfer fin. Even for mass production the fin is reproduced with templated out of similar blocks of this material. It is very strong and easy to shape.

  • Will

Will Gorgen


Here is a link to a supplier of G10 sheet:

Here is a link to FinWorks (one of the top end windsurfing fin companies). They use G10 epoxy blocks to form their fins…

<blockquote id=“quote”><font size=“1” face=“Verdana, Arial, Helvetica” id=“quote”>quote:<hr height=“1” noshade id=“quote”>Originally posted by Albertaclipper

Is there other methods that you have used that produce a good keel?
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Jeff, I?m not sure I might help, or if it’s going to work or not, but have you seen this web site: ? They produce and sell foam cores for model RC airplanes wings, it shouldn?t be too difficult for them to make a core for a NACA fin. At that point it?s just a matter to cover it (vacuum bagging) with CF for strength and stiffness. I haven?t checked for price or if it?s feasible (I?m planning too but I?m to busy right now), but I?m not expecting it to bee too expensive… at least not as much as a ?professionally? made fin. It might be worth the try.

Let me know if it works out for you.



The epoxy plate i used is not G10

However, it doesn’t have these tiny holes in it. It had a copper film on one side but i sanded that away with the sanding machine.
Because the plating is superthin i covered the upper part with 1,5 mm balsa and finished it with epoxy. This also gave enough ‘body’ for the rudder shaft.

The 5mm aluminium is strong enough to hold the 2,4 kg IOM bulb. Measured from the bottom of the hull to the bottom of the bulb the keel is approx. 14,5" (36,5cm)

I’ll post some pictures as soon as i have them.