Re: Engine-Prop matches -- CCSSC - Chris Craft Sea Skiff Club

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Date Posted: 15:54:49 11/03/02 Sun
Author: Alan
Author Host/IP: cache-rl05.proxy.aol.com / 152.163.189.101
Subject: Re: Engine-Prop matches
In reply to: Bob Durand 's message, "Engine-Prop matches" on 11:32:25 11/03/02 Sun

>With out knowing what Horse power at what rpm you have and what rpm you are now running it is very hard to guess what props to use. Michigan wheel is another place to look for info. There may be some one else who has repowered and can help. We run a three blade 14x11 prop on our 22' "SmithSkiff" and we have repowerd to a V8.

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[> [> Re: Engine-Prop matches -- Alan, 16:40:51 11/03/02 Sun (cache-dp01.proxy.aol.com/205.188.209.101)

Sorry, Faye typed it wrong, it is a 14x14 prop with a cup that we run on SmithSkiff. Do you run a reduction gear? that will make a major difference in prop speed.

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[> [> [> Re: Engine-Prop matches -- bob durand, 18:22:03 11/03/02 Sun (cache-mtc-am01.proxy.aol.com/64.12.97.6)

>Sorry, Faye typed it wrong, it is a 14x14 prop with a
>cup that we run on SmithSkiff. Do you run a reduction
>gear? that will make a major difference in prop speed.
hello Alan,The engines are 225hp each and new this year. they replaced 1965 Chrysler 318s rated at 190hp but operating very inefficiently. Currently, the boat operates well with crusing speed of 19mph@2850rpms and max rpms of 4300 yeild 34mph.My question iin consideration of noticable vibration in the area between the rudder post and the strut fastenings. engine (s)alignment is fine having been checked 3 times. shafts are new and checked as are cutless bearings. both sides have this vibation. it is most noticable at 3000 revs and above.could it be that cupped props wouldhelp? the props have both been checked twice by henry Smith Co. Thanks

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[> [> [> [> Re: Engine-Prop matches -- Alan, 08:13:09 11/05/02 Tue (cache-mtc-am01.proxy.aol.com/64.12.97.6)

.
>Bob. Your RPM sounds fine. On my 22skiff I did not like the sound or feel when I let the engine run much above 4000 rpm so I over wheeled to get 38/3900 rpm. I did loose some top speed put 34MPH is just fine with me. I cruse 19 to 20 mph @ 2000 rpm. It may be that your clearance between prop and rudder is not enough which could cause your problem. The second thing that could cause this is prop to bottom clearance. I am sorry, but I can't rember how to figure this clearance. I do rember the prop hub to strut should me 1 to 1 1/2 times the shaft dia.. The third thing is strut and rudder supports.. Cups should dropmrpm appox 200 rpm

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[> [> [> [> [> Re: Engine-Prop matches -- Bob, 07:21:17 11/07/02 Thu (cache-mtc-am01.proxy.aol.com/64.12.97.6)

>Alan, Thanks for the info.I have contacted Michigan Wheel and await their reply.Some of the dimensions involved are:
Prop shaft end to rudder-4 in,strut to shaft taper-aft end- 4 3/4 in.,prop tip to hull-2 1/2 in.,shaft dia-1 1/2 in.I dont know what these figures mean.In my exploring I did find that the tube steering yoke on one side is worn enough toallow the rudder to flutter quite noyicably. Does a cupped prop reduce the impact of the propwash on the hull? It seems that that clearance is close to me. Thanks,Bob

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[> [> [> [> [> [> Re: Engine-Prop matches -- Alan, 09:06:42 11/09/02 Sat (cache-rl05.proxy.aol.com/152.163.189.101)

Bob, Any slop in the steering system can set up all kinds of noise and shakes and can sound and feel like some else and some place else. In other words, slop is bad. prop hub to strut should be i to 1/2 tines the shaft dia. In other words the clearance along the shaft between strut and prop hub should be 1.5 to 2.25". There again the less clearance is better, less wip.

Cuped wheels. I may be wrong on this, but here goes. Cuped wheels are usely used on higer speed boats. They seem to give better out of the hole speed as the engine can come up to rpm faster and as boat speed/engine rpm get up the cup gives the effect of appox. 2" of pitch.

Alan

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