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Old 17-11-2010, 23:43   #1
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Boat: 1973 Formosa 41 Foot
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Wink Formosa 41 Engine Revs Under Load

Hi All,
I rebuilt my 4.108 Perkins myself and that included the doing up the injector pump and injector nozzles.

I think the pitch of the prop is 18-it's supposed to be the standard size for this boat I think.

The engine in nuetral seems to rev out to about 4,000 RPM.
Under load the maximum revs is about 1800 and the boats doing about 6 knots or so.

When under load it's easy to reach 1800 rpm at not much throttle but when I push the throttle to maximum there's no difference at all?

I then loosened of the injector adjustment by 1/4 of a turn to give it a little more fuel and lower the pressure to open the nozzles but still no difference.

Is this normal or do you think the prop size is to big?

Anyone else have what I've got as far as engine, prop and boat go at all?

Cheers

Alan B
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Old 18-11-2010, 00:38   #2
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Gearing and diameter?

I had the pitch of my propeller reduced from about 18" down to (about) 12.5" and the diameter reduced from 22" down to about 20".

Running my John Deere 4045D (85hp) with 2:1 reduction this lifted my max revs from about 1800 to 2500 (max) with everything clean. Dirty I only get 2300 so I'm guessing I'm still a bit over pitched.

You don't say what your propeller diameter is or what sort of reduction gear you're using.

Most of the propeller people should be able to make recommendations.

My experience has been that some calculations and tables indicate a slightly oversized propeller for my boat, so if getting a prop for a big heavy boat you may want to keep this in mind.
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Old 18-11-2010, 00:50   #3
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Quote:
Originally Posted by Alan B View Post
Hi All,
I rebuilt my 4.108 Perkins myself and that included the doing up the injector pump and injector nozzles.

I think the pitch of the prop is 18-it's supposed to be the standard size for this boat I think.

The engine in nuetral seems to rev out to about 4,000 RPM.
Under load the maximum revs is about 1800 and the boats doing about 6 knots or so.

When under load it's easy to reach 1800 rpm at not much throttle but when I push the throttle to maximum there's no difference at all?

I then loosened of the injector adjustment by 1/4 of a turn to give it a little more fuel and lower the pressure to open the nozzles but still no difference.

Is this normal or do you think the prop size is to big?

Anyone else have what I've got as far as engine, prop and boat go at all?

Cheers

Alan B
i believe there is someone in leaky teaky yacht club who has just been thru this -- is a yahoo group used to be called formosa owners group. is excellent resource for formosa owners. come on over-- someone knows this answer
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Old 18-11-2010, 01:14   #4
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It could be one of many things. People really spent a lot of energy talking about being over proped when I went thru this.

Check your exhaust system for restrictions. Cheap place to start and if nothing has changed with your prop (aside from the possibility of being fouled with growth), I'd say it's more likely a power loss somewhere.

More than one person has found the problem to be in the exhaust system. Don't a$k me how I learned thi$.
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