Abstract: A number of embodiments of personal watercraft having catalytic exhaust systems for treating and purifying the exhaust gases. In all of the embodiments, the catalyst is positioned and disposed so as to be protected from water. In addition, arrangements are provided for cooling the catalyst, for circulating ventilating air across it, for isolating it from other components such as the fuel tank, and for permitting its flushing with fresh water after operating in a salt water environment.

Abstract: A number of embodiments of personal watercraft having catalytic exhaust systems for treating and purifying the exhaust gases. In all of the embodiments, the catalyst is positioned and disposed so as to be protected from water. In addition, arrangements are provided for cooling the catalyst, for circulating ventilating air across it, for isolating it from other components such as the fuel tank, and for permitting its flushing with fresh water after operating in a salt water environment.

Abstract: A number of exhaust systems for watercraft propelled by a propulsion unit contained within a tunnel formed in the underside of the hull. This tunnel has an opening through the side of the hull and exhaust gases are delivered to the tunnel from the engine through an exhaust system having an exhaust opening communicating with the tunnel. Various flow controlling arrangements are provided for controlling the flow through one or all of the openings so as to assist in exhaust silencing without significantly increasing back pressure.

Abstract: Two embodiments of exhaust systems for small watercraft that include cooling jackets circling a portion of the exhaust conduit. At least a portion of the water from the cooling jacket is mixed with the exhaust gases but at a point spaced substantially downstream of the cooling jacket so as to reduce the likelihood of water entering the engine through the exhaust system. In one embodiment, an additional cooling jacket is provided to which the coolant from the first cooling jacket is introduced and then discharged into the exhaust conduit. The second cooling jacket is disposed substantially downstream of the first cooling jacket.

Abstract: An arrangement and structure for running a marine engine for a brief period of time after the engine cooling jacket has been depleted of water so as to insure complete purging of water and water vapor from within the engine. In the illustrated embodiment, this operation is initiated by actuation of the starter switch and a timer is started to run only in the event the coolant is not in the engine for shutting of the engine after the lapse time has run.

Abstract: Two embodiments of water jet propulsion units having an improved bearing arrangement for supporting the impeller shaft where it passes through the hull for connection to the engine. In each embodiment, a gravity feed oil system supplies lubricant to the bearing.

Abstract: A water jet propulsion unit in which water is drawn off of the jet propulsion unit through a tap for other purposes, such as pumping the bilge with a jet pump or delivering coolant to the engine. A filter element which can be easily serviced is positioned in the conduit for precluding small particles which could clog the conduit from entering the conduit.

Abstract: A data processing apparatus includes a register, an access time counter, a comparator, and a bank waiting time counter. The register calculates a minimum period of time required to access all elements which constitute vector data when the vector data is accessed. The access time counter counts the time which has lapsed after access for the vector data is started. The comparator compares a value calculated by the register with a value obtained by the access time counter. The bank waiting time counter is incremented in accordance with a comparison result obtained by the comparator. The bank waiting time counter thus stores the waiting time due to the bank conflict.