Abstract:
A watercraft ( 10 ) having two sources of ( 22, 32 ) of cooling water ( 28, 34 ) for injection cooling of hot exhaust gas ( 30 ) being conveyed through an exhaust pipe ( 16 ) upstream of muffler ( 54 ). The first water source ( 22 ) may be an active apparatus such as the engine cooling apparatus ( 22 ). The second source of water ( 32 ) may be a passive apparatus such as a Pitot tube ( 38 ) formed in the stern drive ( 20 ) of the watercraft ( 10 ). By providing two independent sources of cooling water, the probability of exhaust component failures is significantly reduced.

Description:
BRIEF DESCRIPTION OF THE DRAWINGS 
     The features and advantages of the present invention will become apparent from the following detailed description of the invention when read with the accompanying drawing in which a watercraft is illustrated as having an exhaust pipe having connections to a first supply of water and to a second supply of water. 
     DETAILED DESCRIPTION OF THE INVENTION 
     The FIGURE illustrates a watercraft  10  having a hull  12  with an internal combustion engine  14  disposed within the hull. The engine  14  has an exhaust pipe  16  passing through a transom  18  to the exterior of the hull  12 . The engine  14  is connected to a stern drive  20  as is known in the art of inboard/outboard marine craft. Although illustrated herein as embodied as an inboard/outboard powered watercraft, the present invention may be embodied in any style of watercraft, including inboard, outboard and inboard/outboard applications. 
     Watercraft  10  is equipped with an engine cooling apparatus  22  which includes a pump  24  and associated water jacket  23  and piping  25 . Engine cooling apparatus  22  is operable to draw water from a body of water  42  exterior to the hull  12 , to circulate the water through various engine cooling passages (not shown) and water jacket  23  to remove heat from the engine  14 , and to return the heated water to the exterior of hull  12 . Engine cooling apparatus  22  is an active apparatus in the sense that pump  24  provides the motive force for the circulation of coolant through the cooling apparatus  22 . As used herein, the term “active apparatus” is meant to include only those components or collection of components which generate their own movement to accomplish their intended design function. Engine cooling apparatus  22  is an active apparatus because pump  24  must be operated in order to circulate coolant there through. As used herein, the term “passive apparatus” is meant to include only those components or groups of components which can perform their intended design function without self generated motion. In addition to providing an engine cooling function, engine cooling apparatus  22  is connected to the exhaust pipe  16  by a first fluid connection such as conduit  26 . Conduit  26  is operable to direct a first flow of water  28  from the engine cooling apparatus  22  into exhaust pipe  16  to cool exhaust gas  30  and downstream portions of pipe  16 . 
     The FIGURE also illustrates an auxiliary water supply  32  operable to provide a second flow of water  34  into the exhaust pipe  16  upstream of muffler  54 . As illustrated in the figure, the auxiliary water supply  32  includes a tube  38  having a funnel shaped opening  36  disposed on a forward facing surface of the stern drive  20 . As the watercraft  10  is moved forward through body of water  42 , tube  38  functions as a Pitot tube operable to force water through conduit  40  and into exhaust pipe  16 . The auxiliary water supply  32  is a passive apparatus since its functioning to deliver cooling water  34  to exhaust pipe  16  does not require the self generated movement of any of the components of the water supply  32 . The second flow of water  34  augments the cooling capability of the first flow of water  28  to further reduce the temperature of the exhaust gas  30 . Opening  36  is preferably funnel shaped in order to increase the flow of water through conduit  40  as the watercraft is moved through the body of water  42 . One may appreciate that the opening  36  of tube  38  may be disposed on any forward facing surface of watercraft  10  as long as it is located at a point below the water line  44  during the operation of the watercraft  10 . In order to prevent exhaust gas from flowing out of opening  36  when engine  14  is running but watercraft  10  is stationary or moving very slowly, a check valve  46  may be connected in conduit  40  in order to pass fluid flowing into the exhaust pipe  16  but to block fluid from flowing out of exhaust pipe  16  into tube  38 . In order to further increase the volume of the second flow of water  34 , a plurality of openings  36  may be provided at different locations on the exterior of watercraft  10  below waterline  44 . It is desirable that the connections of both conduit  26  and conduit  40  are located on an upstream portion of exhaust pipe  16  in order to minimize the uncooled length of exhaust pipe  16 . In one embodiment the outlet  48  of conduit  40  is disposed on the exhaust pipe  16  at a location proximate the outlet  50  of the conduit  26 . Such proximate locations may include, for example, the outlets  48 ,  50  being located on a single flanged insert  52  which is adapted to be installed as part of exhaust pipe  16 . By using such an insert  52 , one can envisioned the auxiliary water supply  32  being installed as a back-fit kit on an existing watercraft that is already equipped with a connection between the engine water jacket  23  and the exhaust pipe  16 . 
     A method of cooling the exhaust pipe  16  of a watercraft  10  includes the steps of directing a first flow of water  28  from an engine cooling apparatus  22  into the exhaust pipe  16  of an engine  14 . A second flow of water  34  may then be. directed from an auxiliary water supply  32  into the exhaust pipe  16 . The means for directing the second flow of water  34 , such as auxiliary water supply  32 , is preferable a passive apparatus which is operable independent of the means for directing the first flow of water  28 , such as engine cooling apparatus  22 . By disposing the inlet end  36  of a conduit  40  below a waterline  44  of the watercraft  10 , a flow of water  34  will be forced through conduit  40  as the watercraft  10  is moved through a body of water  42 . Thus even upon failure of an engine cooling apparatus  22 , a continued source of cooling water  34  will be supplied to exhaust pipe  16 , thereby preventing damage to the exhaust pipe  16  and associated downstream components such as muffler  54 . Furthermore, the risk of injury to an occupant of the watercraft  10  during periods of continued engine operation following the failure of cooling apparatus  22  is significantly reduced. 
     In one embodiment, engine coolant apparatus  22  may be designed to provide a flow rate of 30 gpm of water through conduit  26  into exhaust pipe  16  at full throttle operation. With no other cooling flow,this amount of water will cool the. exhaust gas from approximately 1,400 degrees Fahrenheit to 160 degrees Fahrenheit. Auxiliary water supply  32  may be designed to provide a flow rate of 10 gpm of water through conduit  40  into exhaust pipe  16  at full throttle speed. With no cooling flow  28  from the engine cooling apparatus  22 , this auxiliary water supply  32  will cool the exhaust gas to approximately 200 degrees Fahreheit, which is sufficiently low to protect downstream components such as muffler  54 . With both systems operating, the exhaust gas will be cooled to approximately 130 degrees Fahrenheit. While less than optimal for long term operation of engine  12 , the flow of cooling water  34  provided by the auxiliary source of cooling water  32  is adequate to prevent component damage and dangerously high exhaust pipe temperatures for short periods of operation of engine  12  without exhaust cooling flow  26 . A higher flow rate may be provided through the auxiliary water supply  32  by increasing the size of the conduit  40 , and the specific component sizes and resulting temperatures may be selected on an application specific basis using analytical or empirical techniques known in the art. 
    
    
     While the preferred embodiments of the present invention have been shown and described herein, it will be obvious that such embodiments are provided by way of example only. Numerous variations, changes and substitutions will occur to those of skill in the art without departing from the invention herein. Accordingly it is intended that the invention be limited only by the spirit and scope of the appended claims.