Abstract: A blade design for a counter-rotating propeller system improves the performance of the outboard drive on which is it employed when the propellers are run partially exposed. The propeller system includes a pair of counter-rotating propellers that rotate in opposite directions about a common axis. The rear propeller has a smaller diameter--about 92% of the front propeller--and a total blade face surface area of about 85% of the total blade face surface area of the front propeller. The blades of the front and rear propellers desirably have the same camber and generally the same pitch. The rear propeller pitch is between 90% and 110% of the front propeller pitch. These blade parameters improve the efficiency of the rear propeller over prior designs when the propellers run partially exposed in order to maximize the thrust produced by the propulsion system.

Abstract: A marine propulsion device improves the handling characteristics and the responsiveness of the watercraft on which it is used. The propulsion device includes a pair of counter-rotating propellers. At least the blades of the front propeller each have a mean camber line in cross-section which has a generally constant radius of curvature. This blade shape reduces cavitations and permits the rear propeller to be mounted closer to the front propeller, and consequently closer to the steering axis of the outboard drive. As a result, steering torque is reduced. The blades of the rear propeller also are not more than thirty percent smaller than the blades of the front propeller, and the average pitches of the propellers do not differ by more than one to four percent. These blade configurations of the front and rear propellers improve the stability of the watercraft when turning, thereby reducing chine walk, as well as improve the responsiveness of the watercraft.

Abstract: A propulsion system for a marine drive, which includes a pair of counter-rotating propellers, provides improved acceleration from idle or low speeds. Engine exhaust from an engine which powers the marine drive is conveyed to the water about each of the propellers. The exhaust gases aerate the water about each propeller to reduce drag resistance on each propeller. Several embodiments of the propulsion system are disclosed which convey the exhaust gases to both propellers for this purpose.

Abstract: A tandem propeller assembly for use with a marine propulsion unit is disclosed wherein a single shock-absorber assembly is utilized to assure damping effects for both propellers so as to protect the propulsion system from being damaged when either propeller is obstructed by drifting wood or other debris. Each of the preferred embodiments disclosed provides a simple structure for absorbing impacts upon either propeller in a tandem propeller assembly while minimizing any increase in the surface area of contact with the water which would increase the propulsion resistance and would result in speed loss.

Abstract: A fish line and weed cutting arrangement for a marine propulsion lower unit wherein the cutting member may be formed from sheet metal or the like and is positioned between the propeller and thrust taking member. The propeller is formed with a recess that receives and rotatably couples the fish line and weed cutting member and which does not interfere with the axial positioning of the propeller on the drive shaft.

Abstract: Several embodiments of propeller constructions employing an improved fish line and weed cutting device that extends into a recess formed in the lower housing. In each embodiment, the cutting member is disposed radially inwardly of the recess to define a gap and one or more projections extend outwardly from the cutting member to fill the gap and define a narrow area that will prevent the entry of fish lines into the opening of the lower unit that defines the recess.