Life is a funny thing. I never thought that I would be designing a foil whilst being concerned that it would be compatible with a boat that I have never owned, but that is exactly where I find myself at the moment.

My desire to keep my current foil compatible with my Bladerider foil and making the two interchangeable has me re-designing my 2010 foil yet again to include an accurate rendering of a Bladerider centreboard attachment, something that I thought I would do in a non-virtual space, but checking revealed that my bulb needed to be bigger, so, as I needed to re-do the entire design, I decided to add the plug hole for the vertical.

Now this sounds easy, but when you are trying to be accurate it requires a significant amount of work to try and make things as compatible as possible, including moulding and measuring my current BR foil. Whilst doing this third design iteration the irony was not lost on me that I am trying to make things as compatible as possible with a boat that I have never owned. The second irony is that, if I do this job right, then my new foil should be a bolt on upgrade or replacement that would work on any Bladerider.

Well it’s 2:30am as I write this but I have just finished putting my foil into mould form in Rhino. This process can be very finicky as it involves pushing one object into another, and if your surfaces aren’t 100% it will most likely fail.

Anyway it’s done now which means that we can start cutting … well actually no … we can start creating tool paths and spending a few hours on that process, then we can produce come g-code then start cutting.

Well I sent the Rhino file of my 2010 foil to my mould maker (aka my brother) to start the mould construction process again, this time for the “Belmont” foils. Andrew has decided to embark on a rather small construction job, making Farrier F22 for himself, so the CNC machine has been getting a good workout lately. The cut time for a farrier float frame is about 15 mins, so it is heaps quicker than doing it all manually.

The design for my next foil is 100% mine, and has been heavily influenced by the current top of the pops, the Mach 2, combined with what I have learnt from sailing with my current foil. So what is changing and why ?

I have changed The foil planform to allow a flap that is significantly wider in the middle compared to the tips, which has been a feature of all Amac’s foils. My current foil has a flap that is pretty much rectangular ( i.e. the same width in the middle as the tips). Having it much wider in the middle and smaller in the tips should give better control with lower flap drag as the flap can achieve the same effect moving through a smaller angle.

I am no longer using the NACA 63-412 section, but I am keeping it “in the family” so to speak, by using a lower drag NACA section. In the computer it has 10% less drag for only a 3% lift loss at 15kts, so hopefully that will translate into a real on-the water gain.

I have designed two versions of this foil, a bulbed and non-bulbed version. Whilst I am still a not a true believer in the bulb like Amac, the bulbed version will allow me to swap between my BR horizontal and this foil, for back-to-back testing and vertical re-use. If this foil works really well, I will probably make the bulb-less one above.

Not to be left out in the cold, by current foil is be getting some tweaks for this weekend, so hopefully the wether will behave.

I really liked Adam May’s the foiling guide, and like my how to make a Moth part 1 it alludes to a more parts that are “yet to come”, as a teaser the last line of the document is “[Wand and cable section still to come to complete this section]” but it never came …

with a recent post over on Sailing Anarchy complaining that people never put information out there I rolled up my sleeves and wrote Magic wands – Wand control systems on Hydrofoil moths.

This is my understanding of how this all works, if you don’t agree then let the debate start …

Finally, here is the long awaited part 2 of how to home build a moth. This one covers how to construct your own hydrofoils

Home Building a Carbon Moth Part 2 – Foils