Investigation of Factors leading to Dynamic Instabilities in High-Speed, Shallow Draft Boats

This paper summarizes portions of a multi-year collaborative study on the dynamic stability of high-speed, shallow draft recreational boats, in which the author has played a small role. These boats are powered by outboard engines, and sometimes fitted with propeller tunnels to permit raising the outboard to reduce draft. Some of these boats have been known to exhibit a dynamic instability referred to as “swapping ends” or “spinout,” in which the boat enters into a moderate turn and then suddenly completes a 180-degree turn in a few seconds, pivoting about a location somewhere near the middle of the boat. During these incidents, occupants sitting in the boat can be ejected and then struck by the boat. Some other shallow-draft, high-speed boats have also been shown to have limited or intermittent helm control, also leading to passenger ejection. The danger of intermittent controllability is compounded by the lack of railings, lifelines, or well-defined seating on these boats to prevent ejection.