Offshoreonly.com - Prop rotation on Single

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- - Prop rotation on Single (https://www.offshoreonly.com/forums/general-q/154103-prop-rotation-single.html)

mats	03-22-2007 09:41 AM

Well, I disagree. A left spinning engine (as seen from the stern) rolls the boat to starboard. When the burning fuel pushes the pistons down and push on the crank it will create a force in the opposite direction and hence lead to a right spinning torque on the engine block and the boat which the engine block is bolted to (as seen from the stern).

Pat McPherson

03-22-2007 10:35 AM

Quote:

Originally Posted by mats (Post 2067119)

A left spinning engine (as seen from the stern) rolls the boat to starboard.

Well, I could be wrong, and it would not be the first time, but engine rotation is viewed from the front of the engine. A left hand engine turns CCW as viewed from the front.

mats	03-22-2007 01:20 PM

Well, this may be the miscommunication, I think you should view the engine from the flywheel end of it when defining what is right (CW)and left (CCW). http://www.propowermarine.com/faq-rotate.htm

Anyway, since the torque of the prop is stronger than that from the engine, the end result will be as you describe it, the boat will roll to port.

Pat McPherson

03-22-2007 01:56 PM

Your are correct...
http://www.perfprotech.com/home/Repowering.

Noise Pollution

03-22-2007 08:37 PM

If you are running a lot of power you will be putting more stress on the top bearning cap turning a left hand prop. Something worth considering.

throttleup

03-23-2007 05:26 AM

Another interesting characteristic with single engine boats is the tendency to list in the opposite direction as the rotation of the prop when the motor is near it's torque peak.

Many applications when run at 3500-4000 (depending on the torque peak of the motor) will list to the port, with a RH prop. As the speed and RPM increases the boat will level out. This is because as the engine RPM gets above the torque peak there is less torque at the prop which will allow the boat to level out.

kennyo

03-23-2007 07:52 AM

Quote:

Originally Posted by Pat McPherson (Post 2067048)

Not true...

A left hand spinning engine rolls a boat to port unless you mount the engine in backwards.
A right hand prop also rolls a boat to port.
A left hand prop rolls the boat to starboard; the opposite of the engine.

On my boat, I run with a right hand prop. With just one person in the boat, she run nice and level with no tab. The extra weight from the helm and driver on the starboard side offsets the roll to port from the engine and right hand prop.
If I add a passenger riding on the port side, I do need to lower my port tab to keep the boat running level.

You need to screen your passengers a little better!

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