I don't know if the Cape Horn will behave differently than a Monitor but I cannot use our Monitor while the engine's running. The prop wash causes the vane to overcompensate and it will not settle into a course.
I have, but I have a 2-blade prop and kept the speed
down to 5 knots to minimize prop wash. And assuming
its light wind conditions, it helps alot to have the light-
air wind vane.