SP, I am glad to hear you are sticking around. It would have not been the same around here without you.
But on this subject, I will have to agree to disagree with you here. I would like to think that this guy knew what he was talking about (though maybe I put my trust in the wrong people?).
I will quote:
"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."
Maybe it is just a bit of both here as he does mention "low speed wander" and "Prop torque only exacerbates the problem". It does sound like a form of vortex shedding to me though