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Old 06-20-2017, 09:42 AM   #1
Seevee
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City: st pete
Vessel Model: 430 Mainship
Join Date: Sep 2016
Posts: 3,498
Thistle rudder again

I'd like to revisit the thistle (schilling or fishtail rudder). Looking at some of the old threads a lot of the links don't work any more.

Seems like quite a few folks have modified theres with great success for low speed handling.

I've got Boat Mechanical Systems Handbook, by Dave Geer on order, which has been mentioned several times as a good reference.

I like the idea of a bolt on addition, easy to install and remove if necessary.

Right now, I'm thinking of a two section rudder mod, one for the nose and one for the tail.

What I don't know is the dimensions that would work, but reading from others I'm guessing the following: Hopefully Dave's book will give some guidance.

X = 3 in
Y = 2 in.
Z = 3 or so, to fit shaft

As for the tail design, some leave it open on the end and some box it in. Why not a trailing diamond or curved shape, like in C and D below. The reasoning is to reduce turbulence in cruise, and give "some" effect in reverse, which would be better than a flat or open end.

Also, I'd figure out how to add a top and bottom plate.

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Thoughts?
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