Curious rudder question - SailNet Community
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post #1 of 7 Old 03-27-2012 Thread Starter
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Curious rudder question

Just a curious question for those out there that know a lot about marine architecture.
If you have a fin keeled, spade ruddered boat, and decided to remove the spade rudder and install a transom mounted rudder (keeping in mind all of the transom beefing up stuff), would it significantly change the sailing characteristics of the boat? At least to the point where it would change enough that a boat wouldn't be sailable?
I'm not really planning on doing this, but am thinking of fabricating an emergency rudder and building in mounting spots. I am just curious, from a general architecture standpoint, if changing the rudder location would have a major effect on how all the other hull balancing acts work out since I assume in all the math and modeling the rudder location, size, and shape is factored big is that factor?
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post #2 of 7 Old 03-27-2012
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Re: Curious rudder question

I would think if it works on a 70' volvo ocean racer it would work on most boats.

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post #3 of 7 Old 03-27-2012
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Re: Curious rudder question

Many windvanes steer spade-ruddered boats in much similar manner to what you're contemplating (Hydrovane, for one, uses it's own rudder)

I'd expect the boat would still handle OK as long as you took care to balance the new rudder as well as the original. Depending on the transom/counter arrangement it may end up an odd looking duck....


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post #4 of 7 Old 03-27-2012
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Re: Curious rudder question

Agree with Faster. Also rather than building an emergency rudder, many windvanes can perform the same function, so this is an alternative.

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post #5 of 7 Old 03-27-2012
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Re: Curious rudder question

I'm no nautical engineer, but it seems the further back the rudder is, the more leverage it would have. It may be more efficient, not less. Probably best to check with someone who actually knows what that are talking about here.

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post #6 of 7 Old 03-27-2012
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Re: Curious rudder question

I wouldn't bother unless you are planning on offshore use. The Cirrus rudder is pretty far aft to start with. As posted it would be slightly more efficient. If you do this the transom will have to be beefed up to handle the loads.
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post #7 of 7 Old 03-27-2012
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Re: Curious rudder question

I did that on my first boat , moving the rudder 6 feet further aft. I took it off the trailing edge of the keel and hung it on a skeg. Altho I didn't hang it off the transom, I should have. There was minimal change in balance, but a huge improvement in down wind control.
Had I hung it off the transom, I would have drastically simplified and improved self steering, with a trimtab on the trailing edge of the rudder.
A reversed transom, with the rake, would make such a rudder far less efficient than a vertical or slightly raked forward rudder. If such a move would mean a vertical or slightly raked forward rudder, I would highly recommend it, before heading offshore.
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