Surface drives and prop torque

[Orbit`]

Is prop torque increased or decreased when comparing surface drives and sterndrives?

Also any experiences with the differences noticed by people who have gone form prop drive to stern drive?

ORB.

[terry taylor]

HI. Next question please thanks.

[194264]

Propshaft torque or propeller torque as you call it, is a product of engine torque and the gear ratio in the drive. The fact that it is a surfacing drive or a sterndrive has nothing to do with torque.

[Orbit`]

When observing from behind a boat, the propeller turns clockwise when underway with a normal right-hand propeller. As water resists the clockwise rotating propeller, it causes the boat to roll slightly in the opposite direction (counterclockwise) or down on the left (port) side and up on the right (starboard) side. To offset this slight imbalance, the driver's seat is placed on the starboard (right) side. Boats differ significantly in the degree of their reaction to prop torque.


So with that in mind, different sized props have differnt effects, not just the engine's torque....
So with surface drive props being larger but only in the water for half a revolution, i was wondering the differences in prop torque experienced.

[flabum1017]

What you are describing is called Torque Roll. To answer that question, yes it is different from submerged props to surfacing props. Surfacing props have less torque roll and more prop walk (the tendancy of a prop to cause the stern of the boat to "walk" to the right.)

Some stern drives such as the Blackhawk and all race drives are set up high and can be called a surface drive just as an outboard can be set up either deep in the water or at the surface.

[terry taylor]

HI. Great question and answer . This process is very evident in hi-po. dragsters at launch, it,s so much the boat is forced to one side and the supporting weight is used to chuck it back straight thanks.

[Orbit`]

Intresting!

Are there any numbers to directly compare the level of torque between the two systems?

I wouldn't call most hi/po stern drives surface drives....the props really are quite differnt...but yes i'll give that they can definatly be called semi-surface props
I have a really good article explaining the differnt props somewhere. I"ll track it down.

I wonder though, With a twin surface drive are all the issues associated with prop walk solved?

ORB.

Edit - this is the article http://www.simplicity-marine.com/surfprop.htm

[flabum1017]

Twin surface drives running opposite rotations will cancel eachother out, thus eliminating prop walk. just as they would cancel the effect of torque roll with submerged drives. There will, however, be a certain degree of torque roll in a twin sterndrive setup from the engines.

[Orbit`]

Thanks for clearing that up.