Does motor height have an effect on torque steer?

[XcellR8]

I've been reading some of the posts wrt boat setup and proper motor height. Will raising the motor higher on the transom lessen the amount of effort required to turn left (ie - the amount of torque steer)?

 

[rodbolt]

Re: Does motor height have an effect on torque steer?

usually<br /> not always<br /> trim and motor height do funny things with steering torque

 

[umblecumbuz]

Re: Does motor height have an effect on torque steer?

Imagine a leg, say, ten metres long, hanging down underneath your boat, with a prop on it.<br /><br />When you accelerate, the prop tries to drive your boat forward, but because it is a screw, it also tries to swing the leg sideways. So your boat would lean, or list, as you accelerate, and this lean turns your boat into its own rudder (it assumes an assymetric profile in the water).<br /><br />So in theory, the distance from the waterline to the prop will make a difference to the torque forces acting on your boat. In practice, other factors come into the picture, which can modify or cancel out any torque-steer.

 

[XcellR8]

Re: Does motor height have an effect on torque steer?

Originally posted by rodbolt:<br /> usually<br /> not always<br /> trim and motor height do funny things with steering torque

Heres my situation:<br /><br />Right now my cavitation plate is about even with the bottom of the boat (motor is mounted in the second hole from the top). When I bought the boat it was over propped with a 13.75 x 21p 4-blade SS prop (90 hp Merc - it was only turning 4400 rpm at WOT). With this prop I found it was really difficult to turn left unless you were trimmed way up or going very slow. I borrowed a 13 x 19p 3-blade aluminum prop to try and this really woke the boat up along with a noticeable reduction in torque steer (5200 rpm at WOT). It's still there just not as bad, just wondering if there's room for further improvement (both in the handling/performance dept. and steering effort)?

 

[XcellR8]

Re: Does motor height have an effect on torque steer?

Originally posted by Stillfishing:<br /> Imagine a leg, say, ten metres long, hanging down underneath your boat, with a prop on it.<br /><br />When you accelerate, the prop tries to drive your boat forward, but because it is a screw, it also tries to swing the leg sideways. So your boat would lean, or list, as you accelerate, and this lean turns your boat into its own rudder (it assumes an assymetric profile in the water).<br /><br />So in theory, the distance from the waterline to the prop will make a difference to the torque forces acting on your boat. In practice, other factors come into the picture, which can modify or cancel out any torque-steer.

Makes sense to me. Theory wise I was thinking the same as you, just wasn't sure if "the other factors" were powerful enough to diffuse the theory ... <br /><br />I realize trial and error is the best solution but unfortunately I don't have as much spare time as I would like so before I make such a change I'm trying to learn more about it and hopefully avoid having to put it back!

 

[Chris1956]

Re: Does motor height have an effect on torque steer?

Xcel, You should be able to adjust the zinc trim tab to counteract most of the torque of the motor. On my Merc Inline, I have the motor mounted so high on the transom, the trim tab has little effect.