Abstract: A marine propulsion unit comprises a cylinder (1), a combustion chamber (2) extending from one end of the combustion chamber, a spark plug (8) provided in the combustion chamber (2), and a piston (5) mounted for reciprocating movement within the cylinder (1). A first port (9) is provided in the combustion chamber (2), and this is selectively openable independent of the position of the piston (5) within the cylinder (1). If the propulsion unit should be immersed in water so that the cylinder becomes flooded, the cylinder can be purged by opening the port (9) and moving the piston (5) so as to expel water through the port (9). Once all water has been expelled further movement of the piston causes gases in the cylinder to pass over the spark plug thus removing trapped water from the spark plug without the need to remove the spark plug from the engine to dry it.

Abstract: The present invention comprises an outboard motor (1) having a number of special features which prevent the ingress of water so that it can be operated underwater and a boat (10) also having a number of special features to be used together with the outboard motor (1). The features on the outboard motor (1) include a device for creating a water-tight seal on the carburetor shaft mountings (24, 26); a device for protecting the air intake of the carburetor against ingress of water (8, 9, 11, 13; 9, 14, 15); a bellows (28) coupled to and encapsulating the starter motor (5); a sealed housing (32) for the electrical system having a moisture-tight seal around each wire at the junction with the sealed housing; a one-way valve (22) disposed in the exhaust (6); and means for protecting the atmospheric vents (20, 21) against ingress of water. The features on the boat (10) include such an outboard motor (1) plus a ducted air intake (11, 15) for the carburetor (2 ) passing through an air sump (9).

Abstract: A replacement single tiller (1) has a cubical hollow base (4) from which throttle-operating cables (8a 8b) (etc) extend to different motor throttles for simultaneous throttle control. Within base (4) is rotary shaft (33) mounting pinions (30, 31) about the peripheries of which cables (8a 8b) are respectively moved by push-pull entrainment. Twist grip (3) on shaft (33) therefore controls both motors. Projection (5) fits between parallel arms of a motor bracket and is held therein by pin (18) in bore (14); such brackets are mutually interconnected by a transverse conducting rod for joint steering by the tiller.

Abstract: A vessel 1 has a transom 2 carrying a W-shaped (or two V-shaped) frames 3 symmetrically arranged about its median line. Thus varying sizes of outboard motors, mounted over the transom, for example in twos, can find equivalent arms of the frame 3 to abut against and are thus aligned and symmetrically mounted.

Abstract: A single tiller 7 is used to control two outboard motors mechanically connected to a manner know per se for simultaneous steering. Twist grip 8 turns drum 10 to wind on cables 11 and 12. Each of these cables enters a connector (13 or 14 respectively) where it is connected to two further cables (24,25 or 26,27 respectively) whereby cables 24, 26 are longer and 25, 27 are shorter. The longer cables 24, 26 are attached to the throttle control of the motor further from the tiller 7 and the shorter cables 25,27 to the nearer motor throttle control, in each case so that the throttle can be opened or shut by a positive pull-pull action, whereby lighter construction can be achieved. More motors and cables can be used if desired.

Abstract: An air intake installation for the carburetor system of an outboard motor is in the form of an elongate duct e.g. 9, 13a, so configured, located or equipped as to prevent water reaching the carburetor system even if the vessel capsizes. Preferably, a tube 9 (flexible to permit steering or tilting the motor) communicates with rigid under-deck elongate buoyancy spaces forwardly open at 14 and optionally gravity-valved at this open end to close on capsizing.

Abstract: A carburettor for a motor on a marine craft, with lower part 1 holding fuel 2 is provided with flexible piping 12 communicating at each end with openings 13, 14 both in the said lower part. The piping 12 preferably has an enlarged intermediate portion 16. If the carburettor is inverted e.g. upon vessel capsize, the fuel 2 drains into the piping 12/16, which is dimensioned to hold the fuel so that, when the vessel is righted the fuel drains back into the lower portion 1 without detrimental loss of contamination.

Abstract: A first tie rod 7 pivots at each end at 8 to respective steering brackets 3 for two outboard motors 1 and 2. Thus, whichever tiller 6 is moved (of either motor) the other will follow by interconnection. A second tie rod pivots at each end 11 to the upper ends respectively of two arms 12 attached one to each throttle grip 5. If either throttle grip 5 is twisted the other also moves by virtue of the tie rod interconnection 10 and arms 12.