Abstract: A dual counterrotating propeller drive mechanism for a marine propulsion system incorporates a torque splitting device which consists of a differential gear means and a ratio gear means. The torque splitting device assigns a selectable fixed fraction of the engine torque to each propeller regardless of power, thrust, and speed conditions. The rear one of the two propellers adjusts its rotational speed relative to the front propeller in response to changes in the front propeller's wake and in this way maintains optimum propulsive efficiency over a wide range of operating conditions. Furthermore, precise matching of front and rear propeller parameters for a given application is no longer required.

Abstract: A marine stern drive unit is mounted aft of the boat transom on a rigid lift arm in a manner allowing the drive unit to be independently trimmed or moved vertically up or down. The drive unit is pivotally attached to the aft end of the lift arm for trimming movement about a generally horizontal axis and the lift arm is pivotally attached to the boat to rotate about a second horizontal axis such that the drive unit is moved generally vertically. The boat engine is preferably mounted transversely and power transmission from the engine to the drive unit is provided by a flexible drive belt which is supported by the rigid lift arm. Separate trim and lift movement is supplied to the drive unit by individual fluid cylinders. The trim cylinder operatively interconnects the drive unit with the boat hull or the forward end of the lift arm. The lift cylinder operatively interconnects the boat hull and the lift arm at a point aft of its pivotal connection to the boat.

Abstract: A system for optimizing the operating efficiency of a boat by balancing fuel consumption against cruising speed utilizes a comparison between engine speed and boat speed to effect automatic positioning of the drive unit. The measurements of boat and engine speed before and after an incremental change in vertical position or trim position are used to calculate the percent changes in boat speed and engine speed which, in turn, are used in conjunction with selected minimum and maximum incremental percentages to effect subsequent alternate control strategies. Depending upon the relative difference in the percent changes in boat and engine speeds, including adjustments based on the minimum and maximum incremental percents, the system will automatically continue incremental movement of the drive unit in the same direction, hold the drive unit in its present position, or move the drive unit an incremental amount in the opposite direction.

Abstract: A marine propulsion system includes a steerable lower gearcase portion and a drive mechanism including a chain drive for driving dual counterrotating propellers. The dual propellers are rotatably mounted to the lower steerable gearcase portion by means of inner and outer coaxially extending propeller shafts. A sprocket is mounted to each propeller shaft, and first and second chain portions extend between the propeller shaft sprockets and a pair of upper drive sprockets, preferably disposed above the water line during boat operation. Coaxially extending inner and outer drive shafts are interconnected with the engine output shaft, and are adapted for counterrotation in response to rotation thereof. The coaxial drive shafts are interconnected with the upper drive sprockets for driving such sprockets in opposite rotational directions, thereby resulting in movement of the first and second chain portions in opposite directions.

Abstract: A V-type four-stroke cycle internal combustion engine is provided with an exhaust manifold and an air intake manifold disposed in the valley of the V-engine, and arranged one above the other. The exhaust from the cylinders passes through exhaust passages formed in the cylinder heads which discharge exhaust into the valley of the V-engine for collection in a central exhaust cavity provided in the exhaust manifold. A single exhaust discharge outlet is in communication with the central exhaust cavity for discharging exhaust therefrom. The air intake manifold includes a series of air intake passages which supply air to the cylinders from within the valley of the V-engine. A series of cylinder head intake passages are provided with openings facing the valley of the V-engine for receiving air therefrom. The exhaust manifold is preferably water jacketed for cooling exhaust prior to its discharge from the engine, and the exhaust passages provided in the cylinder heads are also water jacketed.

Abstract: A system for optimizing the operation of a marine drive of the type whose position may be varied with respect to the boat by the operation of separate lift and trim/tilt means includes an automatic control system which stores preselected drive unit positions for various operating modes and is operative to return the drive unit to any pre-established position by pressing a selected operating mode positioning button. The various operating modes may include cruising, acceleration, trolling and trailering position, any of which may be selectively modified to accomodate changes in both operating or environmental conditions. This system may incorporate other optimization routines and/or automatic engine protection systems to provide virtually complete push button operation for complex marine drive unit positioning mechanisms.

Abstract: A transom extension assembly, particularly useful for smaller or auxiliary outboard motors, utilizes a pivotally connected 4-leg linkage and an operatively connected fluid power operator to lift the motor vertically with respect to the boat transom. The fluid power lift includes a mechanical latching apparatus by which the motor may be releasably held in its raised position and supported in its lowered position in a manner to relieve the hydraulic system from all other operating loads. The apparatus may include its own fluid pressure supply or may utilize fluid pressure from another boat system.

Abstract: A system for optimizing the speed of a boat at a paticular throttle setting utilizes sensed speed changes to vary the boat drive unit position vertically and to vary the drive unit trim position. The measurement of boat speed before and after an incremental change in vertical position or trim is used in conjunction with a selected minimum speed change increment to effect subsequent alternate control strategies. Depending on the relative difference in before and after speeds, the system will automatically continue incremental movement of the drive unit in the same direction, hold the drive unit in its present position, or move the drive unit an incremental amount in the opposite direction to its previous position. The alternate control strategies minimize the effects of initial incremental movement in the wrong direction, eliminate excessive position hunting by the system, and minimize drive unit repositioning which has little or no practical effect on speed.

Abstract: A transom extension assembly for mounting an outboard motor in a spaced relation to the boat transom includes a quadrilateral linkage assembly in which each of the functions to trim, tilt and lift the motor with respect to the transom is provided independently. Each function is provided by a separate hydraulic cylinder means, but operating fluid pressure is supplied by a single fluid pressure source which may be mounted directly on the transom extension linkage.