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Americas Cup AC75 Arm build

What is a AC75 Arm and why build one?


The foil arms are the wing like structures protruding from the side of the boat.
The Right hand one, or Starboard, is up and the left hand one, or Port, is down. The starboard side also shows the foil on the end of the arm.


Here you can see the construction of the foil arm with the internal structure and the outer layer.

We have an AC75 boat, kindly loaned by BAR, (Ben Ainslie Racing), but we don't have any foils for it.
If we are going to have the boat on display in the future it really needs foils!

Here is a video describing the operation of the arm and foil.


Our next problem, should we guess or find some proper drawings?

Suprisingly there is not a full set of plans on the internet to build your own AC75!
There is however a set of rules for AC75 boats setting out the parameters each team are expected to build by.
One of these parameters was a diagram of the arm which we took and tried to get meaningful data from.


The diagram, left, shows the relationship between the boat hull and the fin.

A word of caution!

Even the experts can get this wrong.

The foil arms are all built by one company to provide consistancy, but the outer shape of the arm is down to each team.

The following video shows the stress testing of the arm, to destruction in this case.

The next stage of the story is making the formers for the two sides of the arm.

Click here to continue to the next section

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