Dr. Strangefoil or: How I Learned to Stop
Worrying and Love Hydrofoils
Abelin - I14 USA 1090
The milled cores from
decided that I needed a lifting t-foil rudder for my International
14, I knew I had my work cut out for me. While there are
off-the-shelf t-foil rudders available, I decided to save a few
bucks and design my own and find someone to build it. Wanting
to support my SA friends, I began talking with Phil of Philís
Foils. Phil had done some work on lifting foils for other
14ís, so he was familiar with the designs and knew what kinds of
forces the foils would have to deal with. He gave me some good
design tips and some ballpark figures of the costs, which were very
The first step in the design process was to select a
shape for the main rudder. If you look around the boatyard
itís apparent that almost every rudder shape is unique, especially
in development classes such as the I14. Itís not difficult to
come up with a reasonable rudder shape based on what other boats and
other fleets are using. You may not win a world championship
with your own design, but if you put some time into it, it will
likely perform well.
important aspect of design is the structure of the foils.
Rather than taking the time to figure out how much carbon and/or
glass of what weight to lay up on the foils and what kind of wood to
use as a core, I simply told Phil to make it very strong, figuring
heíd have much better idea of what to use than I would. I also
let Phil select the contour shape for the main rudder from his
Internet I assembled the data to select a hydrofoil shape for the
lifting foils. I selected a thin asymmetric foil section that
should have acceptable performance characteristics and (hopefully)
be strong and durable. I was also able to glean enough
operational data to deal with the intricacies of the design.
When I was satisfied with the shapes I sent Phil my hand drawn
designs with the contour data for the lifting foils.
beginning I was a bit concerned about the core milling process for
the lifting foils. Generally construction of very thin foils
is done using molds. While molds can makes construction
easier, building a mold is time consuming and too expensive for a
one-off project such as this.
The Finished Product
section I had selected had a finished thickness of only 1.0 cm at
its thickest point. This made the carbon skin a significant
proportion of the overall thickness of the foil and required milling
the core to only a few millimeters thickness in some spots.
The cores would be tricky to produce, but Phil was confident he
could do it.
I was quite
pleased when Phil emailed me with pictures of the finished
cores. The milling had gone very well and he was soon starting
the process of lying up carbon fiber matt around the cores and
putting on the clear epoxy finish. The whole process was
very timely and I soon had a box from Canada at my doorstep.
The results are very impressive and show considerable skill in
Now I have to construct all of the control
mechanisms, the mounts, and get everything adjusted properly.
Hopefully the design will perform as anticipated. And why did
I go with the clear epoxy finish as opposed to the simpler and
cheaper paint finish? Because it just looks freaking cool,
thatís why! Thanks Phil!