Let’s build some foils

Published on January 26th, 2013

Two weeks ago I started the new boat build. I decided that I should tackle the difficult things first and then move on to more familiar territory and do the hull last. I also chose to work like this so that I could keep the space in the limited confines of the garage. Once the hull is started it will take up a lot of room so it was on to the biggest job… the foils.

I have taken on board all that I have learned over the last couple of years with the latest foil building techniques and materials and went for high modulus carbon as the stiffness is in another world compared to standard modulus. I’ve also opted for a 3mm pushrod to run the flap as anything smaller seems to either snap off at the thread or buckle under the loads experienced in race mode.

First task was to cut and trim the cloth which took the best part of 1 day per each part (ie. rudder vertical half, rudder horizontal half etc.). Then prepping the moulds and preparing the vacuum bag before laying up was done.

I started with the rudder vertical to find my feet and apart from being really time intensive, was relatively straightforward. Particular attention to the edges is essential to ensure a clean join and no sanding prior to joining. The routine was, while one part was in the oven, I would prep then next part to keep the momentum going.

Once I had popped the two rudder vertical halves, I glued them together using epoxy/ silica/ fibres effectively creating a solid vertical. The end result is a vertical that I cannot bend with all of my weight on it.

The rudder horizontal was a different beast as it is soooo tiny we are talking just a few layers in the tips. However, again with patience and attention to detail I was able to create a really stiff horizontal as well. I think it is possibly the smallest moth rudder in the world!

The main foil vertical was a little trickier as it has the inclusion of the pushrod and bell crank assembly to consider. Again the same method of joining was used (epoxy/ silica/ fibres) with the addition of Spa bond on the leading and trailing edges creating a solid foil. Again, I couldn’t bend the thing with all of my body weight on it!

While the vertical was curing, I laid up the main foil horizontal which was also a little trickier as it include the flap and hinge detailing of course. However, taking time and going slowly will ensure a good finish.

Last job was to add an oversized tiller stock to take the Maguire tiller mechanism which in a word is the Rolls Royce of adjustable tillers and well worth having.

To build and assemble all of the parts took 12 days pretty much full time. To then set up the flap, pushrod and bellcrank took another two days. Lots of putting together, checking, taking apart, trimming, re assembling etc. etc.

The end result is I now have an incredibly stiff set of foils with a smooth kevlar hinge that all fit together really nicely.

There is no rocket science in making foils assuming you have moulds and a decent vacuum pump however, it is incredibly time consuming and when you add up the cost of the carbon and materials plus labour time, I can easily see how builders can justify charging in excess of £3000 for a set.

I am happy with these foils and hope I have over engineered them to last.

Now that these are done and awaiting final sanding and durepoxing, I am going to lay up the hull over the next few days. I covered the plug in brown parcel tape this evening and will be building up the release wax tomorrow and may get to laying up the inner skin in the afternoon.

Then there will be a switch back as I need to build a mould for the deck and foredeck before final assembly.


  1. Posted by gerald on May 31st, 2013, 07:43

    Were can I get detailed drawings of foils? I would like to set up foils for my sailing model.

  2. Posted by admin on June 14th, 2013, 20:57

    You’ll have to find a hydrodynamic expert, pay them to design the foils, get them cut in a CNC machine as the whole process is very involved. Anyone who has foil designs is unlikely to supply information as it’s a very time consuming process.

    Good luck!

  3. Posted by Klaus on August 18th, 2014, 11:35

    What’s the layup/strength of the lower rudder connection? How did you integrate it into the rudder?


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