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Sealing system between the hull and the foil arm?


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Hello everybody,

is someone here who can show me more information / details about the sealing system between the foil arm and the hull on the AC75 boats?

The background is: I plan to build a functional scale model in the scale 1: 13.5. I am very grateful for any information and pictures.

ViewCapture20210320_205000.thumb.jpg.09ae9c1cc56e8076b515e293de9a2d8a.jpg

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3 hours ago, Hydroptere said:

Hello everybody,

is someone here who can show me more information / details about the sealing system between the foil arm and the hull on the AC75 boats?

The background is: I plan to build a functional scale model in the scale 1: 13.5. I am very grateful for any information and pictures.

ViewCapture20210320_205000.thumb.jpg.09ae9c1cc56e8076b515e293de9a2d8a.jpg

5 .00 shows foil arms to hull bearing not a huge amount of detail though.

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02780108-FDC0-46E2-A389-C5D56439E83A.jpeg.16c7417cee0621ddc145ca38cf764215.jpeg

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The real boats don't seal the foil penetration. They use a wetbox inside the hull, which must self-drain:

From the Class Rule:

11.16      The enclosed volume of the hull surface, including the volumes required by Rule 11.8 
must be watertight except for penetrations:
....
 (b)      inside regions defined by cylinders of length 1.600 m and diameter 1.250 m centred on each 
foil cant reference point and whose axes are aligned with the foil cant axes, in order to permit 
foil cant, providing that the volumes inside the hull surface exposed by these penetrations shall:
(i)         be entirely above MWP;
(ii)        be entirely within the cylinder described;
(iii)       be separated from the remainder of the enclosed volume by a watertight boundary which 
need not satisfy Rule 11.19;
(iv)       have a total combined volume of no more than 450 litres; and
(v)        be self draining, and have drain area of at least 0.100 m2 per 1.000 m3 of floodable volume;
 

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The wet box concept has been well understood for quite some time and I imagine their solutions would not be too different from modern canting keel offshore yachts. The basic concept is a sealed box with a flexible boot around the hydraulic cylinder (not the shaft). As mentioned above for a model yacht a piece of neoprene would probably suffice. On offshore canting keeling boats one important detail is a vent above the waterline to release pressure from the water being pushed into the box, probably less of a concern on a boat where the wet box spends most of it's time out of the water. In the early days this was not always implemented and resulted in a few exploding wet boxes from the pressure build up from water being forced up into the box. Another advantage of the wet box is it gives another version of the old left handed screw driver with nippers being sent to bail out the wet box.....

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