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Old 07-10-2013, 04:21   #1
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rudder rebuild kit/plans

Does anyone have a good source for a nice rudder rebuild kit or plans for the like?

This will be for an externally mounted rudder that will basically hang from the transom via a captured pintle/gudgeon arrangement (with bearing).

I'm hoping to use fiberglass pole (due to the ease of fiberglass fabrication for the remainder of the rudder), but plans call for aluminum or stainless would fine too.

Length would be about 1.5 meters below the water line with a ~600mm cord (leading to trailing edge) length and a 120mm to 160mm thickness (depending on structural/material requirements).

Any sources would be greatly appreciated...
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Old 07-10-2013, 04:55   #2
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Re: rudder rebuild kit/plans

What kind of boat?
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Old 07-10-2013, 05:16   #3
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Re: rudder rebuild kit/plans

Typically rudders on production boats have a stainless steel tube running the length of the rotational axis to which flat bar stock is welded to in the shape of a frame.

A mold is made from which the rudder halves are layed up in fiberglass. The halves are bonded together around the stainless steel frame and the void filled with foam.

Alternately, with custom boats I have seen a bulk of plywood laminated around the welded rudder stock and frame.

This mass is sculpted into shape using a planer and rasps to get close to the final shape, then coated with epoxy and fiberglass before a final fairing to get to the finished form.

The second method saves on the labor of making plug (usually foam) and a mold, but the first allows for a much more accurate finished form.

Either way, most are using templates of the profile to gauge the shape, make two sets where one is slightly oversized. This oversized set will help you see where you need to remove material. The one that is the right size is for checking your results and/or adding material if you removed too much.

Good luck, show us some progress photos!
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Old 07-10-2013, 05:25   #4
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Re: rudder rebuild kit/plans

Foss rudders in Fl.
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Old 07-10-2013, 05:59   #5
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Re: rudder rebuild kit/plans

One thing to consider about the first method I mentioned, if you look at the Foss website rudder construction page, is that the rudder remains in the mold while it is filled with foam. To achieve the desired density, the expanding foam must be held captive by a structure able to resist significant pressure.

If, as I suspect, the OP is on a budget or a devoted DIYer the second method will be the way to go. Price for replacement rudder for my (production, not custom) boat is $4,000.00.
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Old 07-10-2013, 08:54   #6
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Re: rudder rebuild kit/plans

If I understand the OP correctly, he is designing a transom hung rudder. These rudders do not typically get driven by twisting on a rudder post as is the case with spade or skeg mounted blades, rather they typically are driven by a directly mounted tiller. This simplifies the design considerably.

I've only built one such rudder myself, and that for an auxiliary rudder wind vane, but the methodology should be the same. I used four layers of 3/4 inch marine ply epoxied together as a base and shaped it to a NACA 0018 foil shape. I got the shape by making a lot of longitudinal cuts with a table saw, about 1/4 inch apart and with the depth adjusted so that the bottoms of the cuts followed the NACA shape, working from both sides of the 3 inch thick slab. When all the cuts were done, it was easy to remove the remaining "lands" between the cuts with a chisel, leaving a somewhat rough surface of the correct foil shape. Careful sanding and checking with a template resulted in a smooth and accurate foil. A layer of glass cloth set in epoxy to finish, and a very strong rudder was completed.

Don't know if this technique appeals to the OP but relieves him of the need for a "kit".

Cheers,

Jim
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