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Old 04-12-2021, 02:13 PM   #12
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Originally Posted by DickR View Post
My own boat does that when the throttle lever is barely in gear. A quick search just now tells me this is called "low speed wander." From this reference:

"Roy Ellis, senior project manager of product development for Monterey Boats, said itís the result of water rushing aft along the sides of the boat and then collapsing into the hole behind it.

This creates swirling vortices of water that exert suction on each side of the transom, pulling the boat back to the right and then left, Ellis said. Prop torque only exacerbates the problem.

Inboard boats typically donít suffer from low-speed wander because their rudders have enough surface area to overcome the tendency to veer off course.

Sterndrives and outboards donít really have much of a rudder, relying more on directional prop thrust. At low speeds, prop thrust is not as effective as a rudder for maintaining a straight course. And thatís why sterndrives and outboards are more prone to low-speed wander."

Drives with two opposite-rotating props minimize or eliminate the effects of prop torque. I learned long ago that I could keep a mostly straight course at headway speed by anticipating the swings with small countering swings of the steering wheel.
Mr. Ellis statement may be the text book explanation, but personally I think there is more to it.

First, I have never had a significant problem with low-speed wander in any of my outboard powered boats. Not saying it doesnt happen, it just was not significant.

And with sterndrive boats, I have had less of a problem in boats with a full sharp V bottom. Hulls that "soften" at the keel and flatten at the stern seem to be worst offenders. My Carlson 23' was terrible to the point where I was going to add a fin to the bottom/rear to see if it helped. Sold it before I could try that out.

I also wonder if its worse with big ear 3 blade props vs smaller blade 5 blade props???

One thing for sure is when you have a boat badly afflicted with low-speed wander, its a royal pain to drive in the no wake zones.
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