Boat Speed Under Power – Mainsheet May 2005

Title:Boat Speed Under Power
Author:Jim Jaeschke
Date: 5/1/2005
Hull #: 73

Boat Speed Under Power – Engine/Transmission/Propeller Performance There has been a few lively discussions on the Sailnet C380+ list about how fast and at what RPM our boats will move under engine power. The bottom line is that your boat should cruise at 7+ knots at engine rev’s that promote long life. I’ll try to help you get there by discussing prop characteristics, tying in engine performance and, for the practical side: tachometer and boat speed instrumentation.

Instrumentation In order to know our boat’s motoring performance, we need reasonably accurate instrumentation. It has been reported that the tachometer on some boats has not been calibrated, resulting in erroneous RPM readings. It is important, not only for this discussion but also for engine life, that the tach indicate engine RPM correctly. If you suspect a problem, have your boat yard

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