A trim tab control system is provided in which four buttons or switches are provided for the marine operator in which the operator can select to raise the bow, raise the stern, raise the port side of the boat, or raise the stern side of the boat in relative terms, and the system will automatically position the trim tabs to most efficiently achieve the operator's demanded change in position of the marine vessel.

A trim tab of resilient material affixed in a cantilever fashion at the stem of a boat and of a regressive flexural stiffness such that when deflected, the undersurface of the trim tab assumes the shape of a progressive curve in the direction of water flow. A trim tab of a progressive curve which has gas or liquid ejection to the undersurface to control the boundary layer. A trim tab located under a surface drive whereby the bite of the propeller is controlled relative to the trim tab and the trim tab is controlled to optimize the boat hull.

A propulsion system for a boat including a drive system and a propeller positioning system. The drive system may be of any type, such as outboard motors, inboard/outboard drives, surface drives, etc. The positioning system constrains movement of the propeller shaft to swing in a path generally parallel to the bottom surface of the boat. The boat has a hull with either a flat or a sloped bottom surface. Various positioning systems include bite bars, bite rams, cambered drives, jack boxes, jack plates and various linkage configurations. In one aspect a tie bar links multiple drives together. In another aspect, a four-bar steering linkage enables variations in immersion depths of multiple propellers while maintaining constant toe-in. In yet another aspect, yaw steering is achieved using differential immersion between multiple propellers.

A detachable planing enhancement system with two substantial planing surface areas attached symmetrically on the transom of an inflatable sportboat to provide a substantial lifting force thereon. The system includes a method of quick attachment and detachment to the transom of the inflatable sportboat and means to ventilate such planing surfaces with air to reduce drag at high planing speeds. The planing surfaces and attachment components are comprised of plastic compatible with the injection molding process of fabrication.

A trim tab shape control system for a boat with a transom according to an embodiment of the present invention includes a flexible plate and a trim tab control system. The flexible plate has a forward end attached to the transom, a rearward end, and an operative bottom surface. The trim tab control system includes a first force mechanism that is attached near the rearward end of the flexible plate and at least one second force mechanism interfacing the flexible plate between the transom and the first force mechanism. The force mechanisms are operative to deflect the operative bottom surface of the flexible plate in a controlled curve while in an up position, where the plate retains a shape in a down position which varies with force applied by the first and second force mechanisms and the operating conditions of the boat.