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Old 05-12-2014, 09:41 AM   #15
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Join Date: Oct 2007
Posts: 19,833
The old MD 1 was claimed to be 15HP, the Md 2 was sold as 25 HP and the MD3 was 35 hp.

All used the same cylinders so the ratings were very easy to obtain.

A prop is sized to the boat for about a 50% slip ratio, so if the boat is a 5K boat the prop will expect 5K of water and be pitched for 10K (if there were no slip like a screw in wood).

Unless the prop suffers from marginal blade area the attempt to spin a prop set for 10k of thrust production will alkways overload the engine.

Tied stationary the tiny skinney blades used on sail boats may simply cavitate , which unloads the prop , so no black smoke is seen.

AS an aside we use an MD3B in our 33.3 ft 90/90 which is 28LWL.

It runs on about 13 hp , 3/4 GPH for thousands of hours, so far.

On the AICW it is grand to run to full throttle (only 2300 as we are >overproped< to cruise at 1600-1800) which probably produces 40 hp or so.

With a Maurice Griffiths hull, wide transom , of course the stern sinks as the boat can not climb up on her own bow wave.

This produces a HUGE stern wave , sent as a kiss when one of the imbecile passers is at a long ICW dock.

Great fun as they never believe a tiny sail boat can create a wave that size!!
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