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Americas Cup AC75 Arm build

The first arm

Lower mould.jpg

Having built the first former, two sheets of 3mm ply were screwed to the former.


The aerofoils shape was roughly cut from 18mm ply and attached to 9mm MDF formers. 

These were then routed to shape.


The aerofoils cut to shape from 18mm ply are positioned on the former.

The leading edge, left hand side on the photo are all in a line while the trailing edge reduces as it gets to the fin end.

The first and last aerofoil are doubled up for strength.

The aerofoils are screwed to the temporary uprights which are then screwed to the stringers.

Once in position the aerofoils are epoxied to the 3mm ply.

first strip.jpg

Once the epoxy has cured the first strip of batten is fixed.
The batten is 22 x 3mm. Initially the strips are screwed to the aerofoils.


Once the first strip is fitted they are built up ensuring each is fitted tight to the next.

The battens are knot free ensuring less chance of breakage.

7More strips.jpg

More strips are added.

6Tapering off.jpg

As we add the strips to the trailing edge the width of the arm reduces.

Now that the first layer is fitted and screwed down, we left it for three days covered in water soaked rags to help the wood dry 'into' the shape we wanted.

The next stage is to remove ten of the strips, carefully keeping the order, and epoxy them down to the aerofoils and to the edge of it's neighbour.

They were then screwed back down.

The last job of the day was to back off the screws one turn to hopefully remove them fully when the epoxy had cured.

After the screws and any excess epoxy were removed, the second layer of battens were fitted and the process was repeated.

Final shaping.jpg

More shaping to get the final profile of the arm, you can see the templates used to get the final shape.

Lift off.jpg

The first half being released from the former.

The excess 3mm ply will be cut off.


This photo gives a perspective on the size of the arm.

This is the upper half of the arm, the lower half was next built.

The next stage, the "coming together", can be seen by clicking here

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