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Old 08-30-2009, 04:42 AM   #13
FF
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Join Date: Oct 2007
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30 Horspower Saab Diesel with a variable pitch prop

"Take the cubic inches of the old engine and multiply by the usual cruise RPM ..."

"If memory serves, the term for that kind of calculation is aruspicy."

Actually its a measure of WORK ,the swept volume (displacement) of the engine times the RPM.

A thought that has not yet put forward is to keep the usually efficient and trouble free CPP and just stick in a replacement motor.

A bellhousing adapter might be needed to be Mfg , but that's hardly a problem.

At only 5500lbs the boat is nice and light , only about 2 1/2 tons or so.

With 10hp to 15hp per ton the wake drag will probably be really high but well above displacement speed may be possible.

The usual problem is the stern will sink further and further , although Herrishof used a retrofitted mounted set of horizontal fins to counter this on his canoe sterned , overpowered boats.

Might work for your boat?

3 cyl are* balanced by their design ,
to get a 4 cyl smooth usually takes a special counter shaft and operation with certain speeds restricted.

So an Aquadrive and soft mounts are a needed* addition to a 4 banger ,

but hardly needed on a smoother 3.

We installed Volvo MD3B is various boats and the soft mounts were no smoother (but they were* quieter) than the workboat style bolted down.


-- Edited by FF on Sunday 30th of August 2009 05:47:40 AM
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