What is the recommended propeller rotation speed?

Hello, I have a 9,3m (30ft) steel boat with a OM636 diesel engine. I want to replace the engine with an electric engine. Did it on cars before but never on boats. I am worried because I don’t know how fast the propeller is spinning. I can imagine that spoinning timo fast to sufddent can cause damage. Is there a way to calculate safe limits of both rpm of propeller and also for acceleration.

Bubba Gubbins

2 easy ways to determine prop rpms. The first is the easiest- get a wheelspeed tachometer and measure the transmission output shaft rpms. The second- find the transmission ratio (info should be located on the transmission ID tag). With this you will be able to determine the output rpms at any given engine rpm.


Simpler still - look at the engine tacho while cruising at your preferred speed. Look at the performance curve for the electric motor you plan to use.. Are they the same? If not what gearing change do you need to make? The gear ratio of the existing gearbox should be on the rating plate. Note: Work out how much battery storage you 'll need for the desired speed & range of your usage of the boat. , the costs of the batteries & the charging setup you'll need. Dont forget the motor controller. All this needs to be marinised as moisture (& salt) will always find their way on board.