Exhaust system for small watercraft and personal watercraft

1. An exhaust system for a small watercraft, comprising:

an exhaust chamber having a predetermined volume, within which an exhaust gas discharged from an engine flows, the exhaust gas containing water supplied at a position of the exhaust system; and

an exhaust pipe configured to allow an inside of the exhaust chamber and an outside of the watercraft to communicate with each other, and having an upstream end portion in a flow passage of the exhaust gas, which is connected to the exhaust chamber and a downstream end portion in the flow passage of the exhaust gas, which is connected to a body of the watercraft so as to open outside the watercraft, the exhaust pipe being configured to discharge the exhaust gas from the exhaust chamber outside the watercraft,

wherein the upstream end portion of the exhaust pipe is configured to protrude into the exhaust chamber to a vicinity of a lower end of the exhaust chamber and has an upstream opening end face that opens substantially downward in the exhaust chamber so as to be spaced apart a predetermined distance from an inner surface of the exhaust chamber which is opposed to the upstream opening end face,

and wherein the predetermined distance between the inner surface of the exhaust chamber and the upstream opening end face satisfies a formula represented by:

D /3 ≦L≦D

where L is a distance between the upstream end face of the exhaust pipe and the inner surface of the exhaust chamber which is opposed to the upstream opening end face, and D is an inner diameter of the upstream end portion of the exhaust pipe.

2. The exhaust system for a small watercraft according to claim 1 , wherein the upstream opening end face of the exhaust pipe is substantially horizontal.

3. The exhaust system for a small watercraft according to claim 1 , further comprising:

a water jet pump configured to extend in a longitudinal direction of the watercraft and to propel the watercraft;

wherein the exhaust chamber comprises a first exhaust chamber provided on one side of the water jet pump to be located on an upstream side in the flow passage of the exhaust gas and a second exhaust chamber provided on an opposite side of the water jet pump to be located on a downstream side in the flow passage of the exhaust gas and configured to communicate with the first exhaust chamber through a pipe member provided to extend in a lateral direction of the watercraft over the water jet pump, and the upstream end portion of the exhaust pipe is connected to the second exhaust chamber.

4. The exhaust system for a small watercraft according to claim 1 , wherein the upstream opening end face of the exhaust pipe opens obliquely downward, and the upstream opening end of the exhaust pipe is spaced substantially equally apart from the inner surface of the exhaust chamber which is opposed to the upstream opening end face, over an entire periphery of the upstream opening end.

5. A water-jet propulsion personal watercraft, comprising:

a water jet pump configured to extend in a longitudinal direction of the watercraft and to propel the watercraft;

an engine configured to drive the water jet pump;

a first exhaust chamber and a second exhaust chamber, each having a predetermined volume, within each of which an exhaust gas discharged from the engine flows, the exhaust gas containing water supplied at a position of an exhaust system equipped in the watercraft, the first exhaust chamber being provided on one side of the water jet pump to be located on an upstream side in the flow passage of the exhaust gas, and the second exhaust chamber being provided on an opposite side of the water jet pump to be located on a downstream side in the flow passage of the exhaust gas and configured to communicate with the first exhaust chamber through a pipe member provided to extend in a lateral direction of the watercraft over the water jet pump; and

an exhaust pipe configured to allow an inside of the second exhaust chamber and an outside of the watercraft to communicate with each other, and having an upstream end portion in a flow passage of the exhaust gas, which is connected to the second exhaust chamber and a downstream end portion in the flow passage of the exhaust gas, which is connected to a body of the watercraft so as to open outside the watercraft, the exhaust pipe being configured to discharge the exhaust gas from the second exhaust chamber outside the watercraft,

wherein the upstream end portion of the exhaust pipe is configured to protrude into the second exhaust chamber to a vicinity of a lower end of the second exhaust chamber and has an upstream opening end face that opens substantially downward in the second exhaust chamber so as to be spaced apart a predetermined distance from an inner surface of the second exhaust chamber which is opposed to upstream opening end face, and

wherein the predetermined distance between the inner surface of the second exhaust chamber and the upstream opening end face satisfies a formula represented by:

D /3 ≦L≦D

where L is a distance between the upstream end face of the exhaust pipe and the inner surface of the second exhaust chamber which is opposed to the upstream opening end face, and D is an inner diameter of the upstream end portion of the exhaust pipe.