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Converting 100-ton steel ketch to diesel-electric

My dead old engine was overpowered and now removed. I calculate with my 36" diameter 28" pitch prop that I can cruise at 4 knots in dead calm turning at 200RPM, which requires about 40HP. I have a spare 32kW generator that I am re-purposing to 60Hz 3-phase and am dedicating to an induction motor. I got a 30HP motor for very cheap so will experiment with that and expect 3 knots, if that works well I will then obtain a 40HP motor and keep the smaller one as a backup "get me home" drive. I am planning chain drive with an 800RPM motor which requires a 4:1 gear ratio and cheap and easy to change ratios for optimum speed.

Detractors can't believe that I am prepared to accept only 4 knots, but I know my boat after sailing about 6,000nm, (2,500nm of which with no engine at all); I am totally at ease with 100nm per day and anyway most of the time will be motor-sailing, so 40HP down the shaft is perfectly adequate for that application.

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