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23/07/03 14:51:33Login ] [ Contact Forum Admin ] [ Main index ] [ Post a new message ] [ Search | Check update time | Archives: 1234567[8]910 ]
Subject: Re: Trapper 501 rudder


Author:
John Templar
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Date Posted: 24/11/03 16:50:46
In reply to: Frank Marsden 's message, "Re: Trapper 501 rudder" on 24/11/03 10:04:47

Frank
no I didnt keep the same prop, thats the point I was making. Those engines rotate in opposite directions! Thus we have opposite centifugal forces, one force taking the boat to starboard the other taking it to port!

Your prop is too big. it needs 15% of diameter as tip clearance 12 inch prop needs 1.8 ins and you aint got that much so we settle for about 1.4 the IDEAL diameter is 11 ins ...what it does do tho is increase cavitation (bet you have a 13 inch prop)

all yacht props are compromises, somewhere between maximum thrust ,, thats a 5 bladed full disc, ..and nil drag,, thats no blades at all ! if your happy with the lack of thrust from 2 narrow folding blades, go for it, personally I use a 12X10 3 bladed and dont notice it (always locked when the engine is off BTW)

With small helm movements little pressure is placed on the main part of the rudder blade. However, when you tack much larger forces are involved! Ergo, to reduce these forces you need additional area in front of the pivot line. Extra area at the BOTTOM 1/3 of the rudder would INCREASE the forces not decrease them ... look closely at the sweep of the rudder in relation to the pivot line!

what happens to the tiller when you are tied up is totally irrelevant to anything, its caused by turbulance

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Replies:
Subject Author Date
Re: Trapper 501 rudderFrank Marsden24/11/03 18:12:07


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