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Old 09-06-2011, 12:49   #1
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Lightbulb Prop Speed Question.

I am seeking info regarding engines in sailboats.
Some specifications, and discussions I have seen here, mention engine figures like 3000 rpm for a max speed.

My question is, "Is that engine speed also the speed of the prop?"

In other words, if my engine is cranking 3000 rpm is my prop also spinning at that rate?

Thanks
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Old 09-06-2011, 13:05   #2
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Re: Prop Speed Question.

Generaly not...most transmissions reduce the speed...my engines 85 HP is rated at 2200 RPM..my transmision reduces that by over half, so Max, max my prop would ever turn is less than 1100 RPM....I generaly run the engine at around 1600, so the prop is less then 800 RPM.
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Old 09-06-2011, 13:09   #3
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Re: Prop Speed Question.

Quote:
Originally Posted by Gunkhole57 View Post
I am seeking info regarding engines in sailboats.
Some specifications, and discussions I have seen here, mention engine figures like 3000 rpm for a max speed.

My question is, "Is that engine speed also the speed of the prop?"

In other words, if my engine is cranking 3000 rpm is my prop also spinning at that rate?

Thanks
Maybe, but unlikely, as that high speed prop is inefficient for slow boats. Most transmissions have gear reduction, it should be on the spec. plate on the tranny. If you have a v-drive the reduction might be there. My boat is apparently unusual as Walter says the reduction is preferably in the v-drive but since Yanmar only makes reduction transmissions, the 2.3:1 reduction happens at the tranny and my v-drive is 1:1.

Also max rpms for engines vary depending on the manufacturer, under 2000 to 4000 is what I believe I've seen so far.

JOhn
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Old 09-06-2011, 13:18   #4
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Re: Prop Speed Question.

Engine RPM is not prop RPM. My Yanmar comes with three available transmissions, to suite different customer's prop RPM needs.

M.
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Old 09-06-2011, 18:00   #5
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Re: Prop Speed Question.

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Old 09-06-2011, 23:27   #6
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Re: Prop Speed Question.

Thanks to all that have replied! I have an idea that may change the safety issues for sailboat engines, and you folks have helped me tremendously. When I work out the bugs I will post my idea...

Again, many thanks.
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