ChuckieTodd wrote:We experienced the same feeling on our first trip back from Horn Island. Headed north with 12kts or so out of the southwest with maybe 2-3 foot seas. This was a VERY uncomfortable ride. I felt as though I had no control whatsoever. Being the first trip, I was quite anxious - too anxious to slow down but too nervous to speed up. At 9kts, I was in that "middle ground" that mastreb spoke of. I've since learned to slow to 6, drop the boards and take my time.
I "knew" about the problem of semi-planing, being above displacement speed but below planing speed, from an engineering standpoint, but I'd thought of it as simply being inefficient. Then I actually got caught in these conditions outside of Dana Point and really felt it.
Because the boat hasn't flattened out on a plane, wave action causes it to wallow side to side, which changes its drag continuously as the hull rotates. This constantly changing coefficient of drag at above displacement speeds causes side-to-side yawing as the resistance to motion through the water changes abruptly. The boat is also continually changing from plane to displacement, which causes the prop to ventilate and sets up kind of a periodic oscillation in pitch.
So you wind up in a place where the boat is simultaneously rotating, turning, and pitching all at the same time. It's a recipe for both seasickness and poor handling.
The theoretical displacement speed of these boats is 6.5 knots. Consider that a transition point to planing, pull boards up, and go WOT to get up on a plane. Ease back once you're on a plane to 90% throttle for best fuel consumption, and stay there while you're on a plane. If for whatever reason you can't stay on a plane, drop down to 6.5 knots, drop boards, and stay in displacement mode.