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Author Topic: Prop clearance from keel - advice needed.  (Read 1371 times)

tigertiger

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Prop clearance from keel - advice needed.
« on: July 14, 2009, 01:56:09 PM »

Prop clearance.

I am modifying a sailing boat to take a prop for auxiliary drive. I have been advised to have a cut-out rudder, so that if I stuff the prop I will damage the rudder and not the keel. I am ready to increase the rudder area if needed.

In the figure I have place the prop and tube where I think it should go. The wood has been cut now so I committed on the angle of attack.

My main question is, have I left enough clearance between the keel and the prop to allow drive? Or does the prop need to be further out.
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Liverbudgie

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Re: Prop clearance from keel - advice needed.
« Reply #1 on: July 14, 2009, 02:33:36 PM »

Tiger,

You will need to make the opening in the rudder larger, say x one half.  I know it is too late now or maybe not, but vessels with this arrangement had an aux prop fitted to one side or the other, just ahead of the rudder. If you google classic boats you might find some pitures which illustrate this.

LB
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tigertiger

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Re: Prop clearance from keel - advice needed.
« Reply #2 on: July 15, 2009, 02:33:58 AM »

Thanks LB
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amdaylight

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Re: Prop clearance from keel - advice needed.
« Reply #3 on: July 16, 2009, 12:35:46 AM »

Tiger,

If you look at the attached link ( http://memory.loc.gov/cgi-bin/query/D?hh:3:./temp/~ammem_pMYU:: ) you will find a set of drawings and photos for the fishing schooner "Lettie G. Howard", while this shows a different method of giving room for the prop ahead of the rudder it should show you how much space you need. All of the boats that I have seen have the stern post cut out to clear the prop, not the rudder. If they cut out the rudder it would weaken it to the point that it would fail. But as this is a pre-built boat that you are trying to convert it may be the only way to go. If they were adding auxiliary power after the boat was built then they would run the shaft out the side and have the prop just ahead of the rudder along side of the stern post.

Andre :-))
over yonder in Portland Oregon
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