Small size vessel and exhaust manifold for small size vessel

Abstract

To provide a small size vessel capable of effectively cooling the periphery of an exhaust hole unit formed by merging a plurality of exhaust hole units by a water jacket.SOLUTION: A small size vessel 100 includes a hull 101, an engine E, and the exhaust manifold. An exhaust manifold 103 includes: four upstream side exhaust hole units 1; one downstream side central exhaust hole unit 2 arranged on the downstream side of the four upstream side exhaust hole units 1 in an exhaust flow direction and formed by joining the two central upstream side exhaust hole unit 1 among the four upstream side exhaust hole units 1; two downstream side adjacent exhaust hole units 3 arranged on the downstream side of the four upstream side exhaust hole units 1 in the exhaust flow direction and adjacent to one downstream side central exhaust hole unit 2 with spacing on both sides; and a water jacket 5. The water jacket 5 is provided in the exhaust manifold 103 so that coolant flows in between the downstream side central exhaust hole unit 2 and the downstream side adjacent exhaust hole unit 3.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] This invention relates to small ships and exhaust manifolds for small ships.

Background Art

[0002] Conventionally, ships equipped with an engine and an exhaust manifold provided with a water jacket have been known (see, for example, Patent Document 1).

[0003] Patent Document 1 discloses a small ship equipped with a four-cylinder engine and an exhaust manifold having a water jacket. The exhaust manifold is configured to be cooled by the water jacket in order to suppress the temperature rise due to the flow of exhaust gas from the engine. The cooling water flows through the water jacket in a direction opposite to the exhaust gas flow direction and flows into the cylinder head.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Here, although not specified in Patent Document 1, there is an exhaust manifold that merges a part of a plurality of exhaust hole portions at an intermediate position before gathering the plurality of exhaust hole portions into one. In such an exhaust manifold, since a large amount of exhaust gas flows through the exhaust hole portion on the downstream side in the exhaust gas flow direction formed by the merger, the vicinity of the merged exhaust hole portion tends to become particularly hot. For this reason, in the field of exhaust manifolds provided in small ship engines, it has been desired to effectively cool the vicinity of the exhaust hole portion formed by merging a plurality of exhaust hole portions in the middle by a water jacket.

[0006] The present invention has been made to solve the above-described problems, and one object of the present invention is to provide a small ship and an exhaust manifold for a small ship capable of effectively cooling the vicinity of an exhaust hole portion formed by merging a plurality of exhaust hole portions by means of a water jacket.

Means for Solving the Problems

[0007] In order to achieve the above object, a small ship according to a first aspect of the present invention includes a hull, a four-cylinder engine provided in the hull, and an exhaust manifold provided in the engine. The exhaust manifold includes four upstream exhaust hole portions each connected to four exhaust ports of the engine, one downstream central exhaust hole portion disposed downstream of the four upstream exhaust hole portions in the exhaust flow direction and formed by merging two central upstream exhaust hole portions among the four upstream exhaust hole portions, two downstream adjacent exhaust hole portions disposed downstream of the four upstream exhaust hole portions in the exhaust flow direction and adjacent to the one downstream central exhaust hole portion with a space therebetween on both sides, and a water jacket formed to extend along the exhaust flow direction and flowing cooling water in a direction opposite to the exhaust flow direction toward the engine. The water jacket is provided in the exhaust manifold so that the cooling water flows between the downstream central exhaust hole portion and the downstream adjacent exhaust hole portions.

[0008] In the small ship according to the first aspect of the present invention, as described above, in the exhaust manifold, one downstream central exhaust hole portion formed by merging the two central upstream exhaust hole portions out of the four upstream exhaust hole portions, two downstream adjacent exhaust hole portions adjacent to both sides of one downstream central exhaust hole portion with a space therebetween, and a water jacket formed to extend along the exhaust flow direction and flowing cooling water in a direction opposite to the exhaust flow direction toward the engine are included, and the water jacket is provided in the exhaust manifold so that cooling water flows between the downstream central exhaust hole portion and the downstream adjacent exhaust hole portion. As a result, it is possible to provide the water jacket at a position between the downstream central exhaust hole portion and the downstream adjacent exhaust hole portion, which is a position adjacent to the downstream central exhaust hole portion where exhaust gas flows in from both of the two central upstream exhaust hole portions and is particularly likely to become high temperature, and is also adjacent to the downstream adjacent exhaust hole portion. Further, the water jacket can be disposed on each of one downstream adjacent exhaust hole portion side and the other downstream adjacent exhaust hole portion side with respect to the downstream central exhaust hole portion. That is, the water jacket can be disposed so as to sandwich the downstream central exhaust hole portion. As described above, the vicinity of the downstream central exhaust hole portion formed by merging a plurality of upstream exhaust hole portions can be effectively cooled by the water jacket.

[0009] In the small ship according to the first aspect, preferably, the exhaust manifold includes a flange portion provided with three outlet openings through which exhaust gases corresponding to one downstream central exhaust hole portion and two downstream adjacent exhaust hole portions flow out, and the water jacket is provided in the flange portion so that cooling water flows between the downstream central exhaust hole portion and the downstream adjacent exhaust hole portion. With such a configuration, a water jacket can be provided in the flange portion disposed at the most downstream position in the exhaust gas flow direction, between the downstream central exhaust hole portion and the downstream adjacent exhaust hole portion. For this reason, compared with the case where there is no water jacket in the flange portion between the downstream central exhaust hole portion and the downstream adjacent exhaust hole portion, the exhaust manifold can be cooled by the water jacket from a more downstream side in the exhaust gas flow direction. Therefore, the vicinity of the downstream central exhaust hole portion formed by the confluence of a plurality of upstream exhaust hole portions can be more effectively cooled by the water jacket.

[0010] In this case, preferably, on the exhaust gas outflow surface where the three outlet openings of the flange portion are located, the three outlet openings are arranged spaced apart from each other, and on the exhaust gas outflow surface, the water jacket is not provided between the three outlet openings, and a plurality of water jackets are provided around the three outlet openings so as to surround the three outlet openings. With such a configuration, since the three outlet openings are spaced apart from each other on the exhaust gas outflow surface, compared with the case where the three outlet openings are connected to each other, a water jacket can be provided on a more downstream side in the exhaust gas flow direction approaching the three outlet openings at a position between the downstream central exhaust hole portion and the downstream adjacent exhaust hole portion. Also, the vicinity of the downstream central exhaust hole portion can be more effectively cooled by the water jacket surrounding the three outlet openings.

[0011] In the small ship according to the first aspect, preferably, a plurality of water jackets are provided around the downstream central exhaust hole portion so as to surround the downstream central exhaust hole portion. With such a configuration, the vicinity of the downstream central exhaust hole portion can be more effectively cooled by the water jacket surrounding the downstream central exhaust hole portion.

[0012] In the small ship according to the first aspect, preferably, the three outlet openings through which the exhaust gases corresponding to one downstream central exhaust hole portion and two downstream adjacent exhaust hole portions flow out have substantially the same area as each other. With such a configuration, it is possible to equalize the exhaust gas flow between the plurality of exhaust hole portions and suppress the pulsation and exhaust interference at the plurality of exhaust hole portions.

[0013] In this case, preferably, the three outlet openings are arranged in a straight line in a row, and in the orthogonal direction orthogonal to the arrangement direction of the three outlet openings and the exhaust gas flow direction when passing through the three outlet openings, the outlet opening of the downstream central exhaust hole portion is formed in an elongated shape in which the opening length is larger than the opening length of the outlet opening of the downstream adjacent exhaust hole portion. With such a configuration, since the downstream central exhaust hole portion can be formed to be elongated in the orthogonal direction, it is possible to secure a larger separation distance for forming a larger water jacket between the downstream central exhaust hole portion and the downstream adjacent exhaust hole portion.

[0014] In the configuration in which the outlet opening of the downstream central exhaust hole portion is formed in an elongated shape, preferably, the outlet opening of the downstream adjacent exhaust hole portion is formed in a circular shape, and the outlet opening of the downstream central exhaust hole portion is formed in an oval shape extending in the orthogonal direction. With such a configuration, it is possible to secure a larger separation distance between the downstream central exhaust hole portion and the downstream adjacent exhaust hole portion by the downstream central exhaust hole portion having an oval-shaped outlet opening extending in the orthogonal direction.

[0015] In the small boat according to the first aspect, preferably, the engine is an in-line four-cylinder engine, and the four inlet openings of the exhaust manifold into which exhaust flows from the in-line four-cylinder engine are arranged in a straight line in a row, and the three outlet openings through which the exhaust corresponding to one downstream central exhaust hole portion and two downstream adjacent exhaust hole portions flows out are arranged in a straight line in a row. With this configuration, in the exhaust manifold provided in the in-line four-cylinder engine, the vicinity of the downstream central exhaust hole portion formed by the confluence of a plurality of upstream exhaust hole portions can be effectively cooled by the water jacket.

[0016] In this case, preferably, the arrangement direction of the four inlet openings and the arrangement direction of the three outlet openings are the same direction. With this configuration, compared with the case where the arrangement direction of the four inlet openings intersects the arrangement direction of the three outlet openings, the size of the exhaust manifold in the direction orthogonal to the arrangement direction of the four inlet openings can be suppressed.

[0017] In the small boat according to the first aspect, preferably, between the downstream central exhaust hole portion and the downstream adjacent exhaust hole portion, the width of the water jacket in the arrangement direction of the downstream central exhaust hole portion and the downstream adjacent exhaust hole portion is larger than the thickness of the exhaust manifold forming the downstream central exhaust hole portion and the downstream adjacent exhaust hole portion. With this configuration, between the downstream central exhaust hole portion and the downstream adjacent exhaust hole portion, a relatively large width of the water jacket can be ensured.

[0018] In the small boat according to the first aspect, preferably, the minimum separation distance between the downstream central exhaust hole portion and the downstream adjacent exhaust hole portion is 10 mm or more. With this configuration, between the downstream central exhaust hole portion and the downstream adjacent exhaust hole portion, it is possible to avoid the thickness of the exhaust manifold becoming too small and the width of the water jacket becoming too small.

[0019] In the small boat according to the first aspect, preferably, the engine is disposed within the hull, and includes the engine and an impeller driven by the engine to generate a water flow, and is provided with a jet propulsion unit that generates a propulsion force by the water flow. With this configuration, in a jet propulsion boat equipped with a relatively high-output engine and in which the engine is likely to become hot, the vicinity of the downstream-side central exhaust hole portion formed by the confluence of a plurality of upstream-side exhaust hole portions can be effectively cooled by the water jacket.

[0020] The exhaust manifold for a small boat according to the second aspect of the present invention includes four upstream-side exhaust hole portions each connected to four exhaust ports of a four-cylinder engine provided in the small boat, and is disposed downstream of the four upstream-side exhaust hole portions in the exhaust flow direction, and is formed by merging the two central upstream-side exhaust hole portions among the four upstream-side exhaust hole portions. One downstream-side central exhaust hole portion, two downstream-side adjacent exhaust hole portions disposed downstream of the four upstream-side exhaust hole portions in the exhaust flow direction and adjacent to both sides of the one downstream-side central exhaust hole portion at intervals, and formed to extend along the exhaust flow direction, and flowing cooling water in a direction opposite to the exhaust flow direction toward the engine. And a water jacket, and the water jacket is provided so that cooling water flows between the downstream-side central exhaust hole portion and the downstream-side adjacent exhaust hole portion.

[0021] In the exhaust manifold for a small ship according to the second aspect of the present invention, as described above, in the exhaust manifold, one downstream central exhaust hole portion formed by merging two of the four upstream exhaust hole portions in the center, and two downstream adjacent exhaust hole portions adjacent to both sides of one downstream central exhaust hole portion with a space therebetween, and a water jacket formed to extend along the exhaust flow direction and flowing cooling water in a direction opposite to the exhaust flow direction toward the engine are included, and the water jacket is provided in the exhaust manifold so that cooling water flows between the downstream central exhaust hole portion and the downstream adjacent exhaust hole portion. As a result, it is a position adjacent to the downstream central exhaust hole portion where exhaust flows in from both of the two upstream exhaust hole portions in the center and is particularly likely to become extremely hot, and is also a position adjacent to the downstream adjacent exhaust hole portion. A water jacket can be provided at a position between the downstream central exhaust hole portion and the downstream adjacent exhaust hole portion. Further, the water jacket can be disposed on each of one downstream adjacent exhaust hole portion side and the other downstream adjacent exhaust hole portion side with respect to the downstream central exhaust hole portion. That is, the water jacket can be disposed so as to sandwich the downstream central exhaust hole portion. As described above, it is possible to provide an exhaust manifold for a small ship that can effectively cool the vicinity of the downstream central exhaust hole portion formed by merging a plurality of upstream exhaust hole portions by a water jacket.

[0022] In the exhaust manifold for a small ship according to the second aspect, preferably, a flange portion is provided with three outlet openings through which exhaust gases corresponding to one downstream central exhaust hole portion and two downstream adjacent exhaust hole portions flow out. The water jacket is provided in the flange portion so that cooling water flows between the downstream central exhaust hole portion and the downstream adjacent exhaust hole portion. With this configuration, a water jacket can be provided in the flange portion disposed at the most downstream position in the exhaust gas flow direction between the downstream central exhaust hole portion and the downstream adjacent exhaust hole portion. Therefore, unlike the case where there is no water jacket in the flange portion between the downstream central exhaust hole portion and the downstream adjacent exhaust hole portion, the exhaust manifold can be cooled by the water jacket from a more downstream side in the exhaust gas flow direction. Thus, the vicinity of the downstream central exhaust hole portion formed by the confluence of a plurality of upstream exhaust hole portions can be more effectively cooled by the water jacket.

[0023] In this case, preferably, on the exhaust gas outflow surface where the three outlet openings of the flange portion are located, the three outlet openings are spaced apart from each other. On the exhaust gas outflow surface, the water jacket is not provided between the three outlet openings, and a plurality of water jackets are provided around the three outlet openings so as to surround the three outlet openings. With this configuration, since the three outlet openings are spaced apart from each other on the exhaust gas outflow surface, a water jacket can be provided on a more downstream side in the exhaust gas flow direction approaching the three outlet openings at a position between the downstream central exhaust hole portion and the downstream adjacent exhaust hole portion as compared with the case where the three outlet openings are connected to each other. Also, the vicinity of the downstream central exhaust hole portion can be more effectively cooled by the water jacket surrounding the three outlet openings.

[0024] In the exhaust manifold for a small ship according to the second aspect, preferably, a plurality of water jackets are provided around the downstream central exhaust hole portion so as to surround the downstream central exhaust hole portion. With this configuration, the vicinity of the downstream central exhaust hole portion can be more effectively cooled by the water jacket surrounding the downstream central exhaust hole portion.

[0025] In the exhaust manifold for small ships according to the second aspect, preferably, the three outlet openings through which the exhaust gases corresponding to one downstream central exhaust hole portion and two downstream adjacent exhaust hole portions flow out have substantially the same area as each other. With this configuration, it is possible to equalize the exhaust gas flow among the plurality of exhaust hole portions and suppress the pulsation and exhaust interference at the plurality of exhaust hole portions.

[0026] In this case, preferably, the three outlet openings are arranged in a straight line in a row, and in the orthogonal direction orthogonal to the two directions of the arrangement direction of the three outlet openings and the exhaust gas flow direction when passing through the three outlet openings, the outlet opening of the downstream central exhaust hole portion is formed in an elongated shape having a larger opening length than the outlet opening of the downstream adjacent exhaust hole portion. With this configuration, since the downstream central exhaust hole portion can be formed in an elongated shape in the orthogonal direction, it is possible to secure a larger separation distance for forming a larger water jacket between the downstream central exhaust hole portion and the downstream adjacent exhaust hole portion.

[0027] In the configuration in which the outlet opening of the downstream central exhaust hole portion is formed in an elongated shape, preferably, the outlet opening of the downstream adjacent exhaust hole portion is formed in a circular shape, and the outlet opening of the downstream central exhaust hole portion is formed in an oval shape extending in the orthogonal direction. With this configuration, it is possible to secure a larger separation distance between the downstream central exhaust hole portion and the downstream adjacent exhaust hole portion by the downstream central exhaust hole portion having an oval-shaped outlet opening extending in the orthogonal direction.

[0028] In the exhaust manifold for a small ship according to the second aspect, preferably, the engine is an in-line four-cylinder engine, and the four inlet openings through which exhaust flows from the in-line four-cylinder engine are arranged in a straight line in a row. The three outlet openings through which exhaust corresponding to one downstream central exhaust hole portion and two downstream adjacent exhaust hole portions flows out are arranged in a straight line in a row. With this configuration, in the exhaust manifold provided in an in-line four-cylinder engine, the vicinity of the downstream central exhaust hole portion formed by the confluence of a plurality of upstream exhaust hole portions can be effectively cooled by the water jacket.

Advantages of the Invention

[0029] According to the present invention, as described above, it is possible to provide a small ship and an exhaust manifold for a small ship capable of effectively cooling the vicinity of the exhaust hole portion formed by the confluence of a plurality of exhaust hole portions by a water jacket.

Brief Description of the Drawings

[0030]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Mode for Carrying Out the Invention

[0031] Hereinafter, embodiments will be described with reference to the drawings.

[0032] [Embodiment] (Configuration of Small Ship) With reference to FIGS. 1 to 12, the configuration of a small ship 100 equipped with an exhaust manifold 103 for a small ship will be described.

[0033] As shown in FIG. 1, the small ship 100 is a so-called personal watercraft. The personal watercraft has a relatively small hull 101 and is configured to travel on water by obtaining a thrust that moves the hull 101 by jetting water.

[0034] The small ship 100 includes a hull 101 and a jet propulsion unit 102. The jet propulsion unit 102 includes a four-cylinder engine E and an impeller E4 provided in the hull 101. The jet propulsion unit 102 is configured to drive the impeller E4 by the engine E to generate a water flow. And the jet propulsion unit 102 is configured to generate a propulsion force that propels the hull 101 by the water flow. Note that the engine E is an in-line four-cylinder engine in which four cylinders E1 are arranged in series. Therefore, the exhaust ports E2 connected to the four cylinders E1 of the engine E are also arranged in series so as to line up in the same direction as the four cylinders E1.

[0035] In addition, the small ship 100 includes an exhaust manifold 103 for small ships provided in the engine E and a collecting pipe 104.

[0036] Here, in the drawings, the forward direction of the small ship 100 is indicated by FWD, and the reverse direction is indicated by BWD. Also, the arrangement direction of the four exhaust ports E2 is indicated by the A direction. Also, a predetermined orthogonal direction orthogonal to the A direction is indicated by the B direction.

[0037] Note that the exhaust outflow surface 40 of the flange portion 4 (to be described later) of the exhaust manifold 103 is a flat surface extending in the A direction and the B direction (see FIG. 7), and is the surface that contacts the collecting pipe 104. Exhaust gas flows from the exhaust manifold 103 to the collecting pipe 104 through the exhaust outflow surface 40. Also, cooling water flows from the collecting pipe 104 to the exhaust manifold 103 through the exhaust outflow surface 40.

[0038] (Configuration of Jet Propulsion Unit) As shown in FIG. 1, the jet propulsion unit 102 includes an engine E to which a drive shaft E3 extending in the front-rear direction is connected, an impeller E4 fixed to the rear end portion of the drive shaft E3, a nozzle E5, a deflector E5a, and a reverse gate E5b (bucket).

[0039] As shown in FIGS. 2 and 3, the engine E has a lid member E20 installed on the upper part of the cylinder head E1a. The lid member E20 is formed by combining a cross-shaped first housing part E21 and an annular polygonal (hexagonal) second housing part E22 in a plan view (when the engine E is viewed from above). In a plan view, the center position of the cross-shaped first housing part E21 and the center position of the annular polygonal second housing part E22 are substantially coincident. The cross-shaped first housing part E21 protrudes above the annular polygonal second housing part E22. Therefore, the annular polygonal second housing part E22 is divided into a plurality (four) by the cross-shaped first housing part E21 in a plan view. Inside the annular polygonal second housing part E22 and between the cross-shaped first housing part E21 and the annular polygonal second housing part E22, a plurality (four) of gaps E23 (through holes) are provided. Although it is an example, the first housing part E21 and the second housing part E22 are formed of a plant-derived cellulose nanofiber (CNF) reinforced resin. The plant-derived cellulose nanofiber reinforced resin is a high-strength material produced by kneading and dispersing plant-derived cellulose nanofibers, which are biomass materials utilizing wood resources, into a resin such as polypropylene. Note that the first housing part and the second housing part may be formed of other materials. Also, the first housing part and the second housing part may be formed of different materials from each other.

[0040] Referring to FIG. 1 again, the hull 101 is provided with a water channel 101a extending from the opening at the lower part of the hull 101 to the opening at the rear part of the hull 101. An impeller E4 is arranged in the water channel 101a. By driving the impeller E4, water is taken into the water channel 101a from the opening at the lower part of the hull 101.

[0041] The drive shaft E3 extends in the front-rear direction and is configured to rotate around a central axis extending in the front-rear direction by the crankshaft of the engine E.

[0042] The impeller E4 is configured to rotate together with the drive shaft E3 within the water passage 101a to generate a flow directed toward the rear nozzle E5 within the water passage 101a.

[0043] The nozzle E5 is disposed at the most downstream position on the rear side of the water passage 101a where the impeller E4 is disposed. The nozzle E5 functions as a water discharge port (jet port). That is, the nozzle E5 is configured to generate a propulsive force by ejecting water. A deflector E5a and a reverse gate E5b are installed on the nozzle E5.

[0044] The deflector E5a is configured to be rotatable in the left - right direction about an axis extending in the up - down direction. That is, the deflector E5a is configured to be able to change the direction of the water ejected from the nozzle E5 in the left - right direction. The reverse gate E5b is configured to be rotatable in the up - down direction about an axis extending in the left - right direction. That is, the reverse gate E5b is configured to be able to change the direction of the water ejected from the nozzle E5 in the up - down direction.

[0045] (Configuration of the collector pipe) The collector pipe 104 shown in FIGS. 4 and 5 is connected to the exhaust manifold 103 from the downstream side in the exhaust flow direction. Specifically, the collector pipe 104 is fixed to the flange portion 4 of the exhaust manifold 103 described later by fixing members. The fixing members are fastening members such as bolts and nuts.

[0046] The collector pipe 104 includes a single collecting hole 104b through which the exhaust passes. The collecting hole 104b is configured to collect the exhaust flowing in from one downstream - side central exhaust hole portion 2 and two downstream - side adjacent exhaust hole portions 3 of the exhaust manifold 103 into one flow.

[0047] In addition, the collecting pipe 104 includes a plurality of cooling water passages 104a. The cooling water passages 104a are arranged around the collecting hole 104b and extend along the exhaust flow direction of the collecting hole 104b. The flow direction of the cooling water flowing through the cooling water passages 104a and the flow direction of the exhaust passing through the collecting hole 104b are opposite to each other.

[0048] The cooling water passages 104a supply cooling water to the exhaust manifold 103 through the exhaust outflow surface 40 of the flange portion 4. The small ship 100 is provided with a cooling water pump (not shown) for pumping cooling water from the outside of the small ship 100. The small ship 100 is configured to supply the pumped cooling water from the collecting pipe 104 to the cylinder head E1a of the engine E through the exhaust manifold 103. That is, the cooling water pumped by the cooling water pump flows in the order of the cooling water passages 104a of the collecting pipe 104, a water jacket 5 (described later) of the exhaust manifold 103, and the cooling water passages E10 (see FIG. 6) in the cylinder head E1a.

[0049] (Configuration of Exhaust Manifold) The exhaust manifold 103 shown in FIGS. 4 and 5 is formed to be substantially symmetric with respect to a symmetry plane S extending in a direction orthogonal to the A direction. The exhaust manifold 103 is fixed to the cylinder head E1a of the engine E. The exhaust manifold 103 is located between the cylinder head E1a and the collecting pipe 104. The exhaust generated in the cylinder E1 of the engine E flows in the order of the exhaust port E2 of the cylinder head E1a, the exhaust manifold 103, and the collecting pipe 104.

[0050] The exhaust manifold 103 includes four upstream exhaust hole portions 1, one downstream central exhaust hole portion 2, two downstream adjacent exhaust hole portions 3, a flange portion 4, and a water jacket 5.

[0051] In addition, the exhaust manifold 103 includes four inlet openings 6 into which the exhaust corresponding to the four upstream exhaust hole portions 1 flows, and three outlet openings 7 through which the exhaust corresponding to one downstream central exhaust hole portion 2 and two downstream adjacent exhaust hole portions 3 flows out.

[0052] In short, the inlet opening 6 is the opening at the upstream end of the four upstream exhaust hole portions 1 in the exhaust flow direction, and is the opening through which exhaust gas flows from the engine E into the exhaust manifold 103. The outlet opening 7 is the opening at the downstream end of the one downstream central exhaust hole portion 2 and the two downstream adjacent exhaust hole portions 3 in the exhaust flow direction, and is the opening through which exhaust gas flows out from the exhaust manifold 103 into the collecting pipe 104.

[0053] (Configuration of the "Four Upstream Exhaust Hole Portions" of the Exhaust Manifold) The four upstream exhaust hole portions 1 are respectively connected to the four exhaust ports E2 of the four-cylinder engine E provided in the small ship 100. The four inlet openings 6, which are the openings at the upstream ends of the four upstream exhaust hole portions 1, are arranged in a straight line in the A direction. The four inlet openings 6 are spaced apart from each other at substantially the same interval in the A direction. The four upstream exhaust hole portions 1 are configured to approach each other as they go downstream in the exhaust flow direction.

[0054] That is, the four upstream exhaust hole portions 1 are configured such that the interval in the A direction gradually decreases as they go downstream in the exhaust flow direction. Also, the four upstream exhaust hole portions 1 are configured to approach the central position (symmetry plane S) of the exhaust manifold 103 in the A direction as they go downstream in the exhaust flow direction.

[0055] The cross section of the four upstream exhaust hole portions 1 perpendicular to the exhaust flow direction is formed by an arcuate surface. Specifically, the cross section of the four upstream exhaust hole portions 1 perpendicular to the exhaust flow direction is formed to be substantially circular.

[0056] (Configuration of the "One Downstream Central Exhaust Hole Portion" and the "Two Downstream Adjacent Exhaust Hole Portions" of the Exhaust Manifold) As shown in FIG. 4, one downstream central exhaust hole portion 2 is arranged on the downstream side of the four upstream exhaust hole portions 1 in the exhaust flow direction, and is formed by merging the two central upstream exhaust hole portions 1 among the four upstream exhaust hole portions 1.

[0057] Therefore, one downstream central exhaust hole portion 2 is connected to the two central upstream exhaust hole portions 1 from the downstream side in the exhaust flow direction. The exhaust hole connecting one downstream central exhaust hole portion 2 and the two central upstream exhaust hole portions 1 is formed in a Y shape. The downstream central exhaust hole portion 2 is arranged on the central position (symmetry plane S) of the exhaust manifold 103 in the A direction.

[0058] The cross section of one downstream central exhaust hole portion 2 perpendicular to the exhaust flow direction is formed by an arc-shaped surface (see FIG. 8).

[0059] The two downstream adjacent exhaust hole portions 3 are in a pair configuration. The two downstream adjacent exhaust hole portions 3 are arranged on the downstream side of the four upstream exhaust hole portions 1 in the exhaust flow direction, and are adjacent to both sides of one downstream central exhaust hole portion 2 in the A direction with a gap therebetween. That is, the two downstream adjacent exhaust hole portions 3 sandwich one downstream central exhaust hole portion 2 from both sides in the A direction.

[0060] Therefore, one downstream adjacent exhaust hole portion 3 and the other downstream adjacent exhaust hole portion 3 in the A direction are respectively connected to the upstream exhaust hole portion 1 at one end in the A direction and the upstream exhaust hole portion 1 at the other end from the downstream side in the exhaust flow direction. Each of the two downstream adjacent exhaust hole portions 3 is formed in an S shape. The two downstream adjacent exhaust hole portions 3 are formed to be substantially symmetric with respect to the central position (symmetry plane S) of the exhaust manifold 103 in the A direction.

[0061] The cross section of the two downstream adjacent exhaust hole portions 3 perpendicular to the exhaust flow direction is formed by an arc-shaped surface. Specifically, the cross section of the two downstream adjacent exhaust hole portions 3 perpendicular to the exhaust flow direction is formed to be substantially circular.

[0062] The three outlet openings 7 are arranged in a straight line in the A direction. Therefore, the arrangement direction of the four inlet openings 6 and the arrangement direction of the three outlet openings 7 are the same direction. On the exhaust outflow surface 40 where the three outlet openings 7 of the flange portion 4 are located, the three outlet openings 7 are arranged spaced apart from each other. Specifically, the three outlet openings 7 are arranged spaced apart from each other at substantially the same interval in the A direction. Note that the minimum separation distance W0 (see FIG. 8) between the downstream central exhaust hole portion 2 and the downstream adjacent exhaust hole portion 3 is 10 mm or more.

[0063] The three outlet openings 7 shown in FIG. 7 have substantially the same area as each other. The two outlet openings 7 corresponding to the two downstream adjacent exhaust hole portions 3 have the same shape as each other. The two outlet openings 7 corresponding to the two downstream adjacent exhaust hole portions 3 and the one outlet opening 7 corresponding to the one downstream central exhaust hole portion 2 have different shapes from each other.

[0064] The outlet opening 7 of the downstream central exhaust hole portion 2 is formed in a vertically long and slender shape. Specifically, in the arrangement direction (A direction) of the three outlet openings 7 and the orthogonal direction (B direction) orthogonal to the two directions of the exhaust flow direction when passing through the three outlet openings 7, the outlet opening 7 of the downstream central exhaust hole portion 2 is formed in a slender shape in which the opening length L1 is larger than the opening length L2 of the outlet opening 7 of the downstream adjacent exhaust hole portion 3.

[0065] Specifically, the outlet opening 7 of the downstream adjacent exhaust hole portion 3 is formed in a circular shape. Also, the outlet opening 7 of the downstream central exhaust hole portion 2 is formed in an oval shape extending in the orthogonal direction (B direction). Therefore, the width (length in the A direction) of the outlet opening 7 of the downstream central exhaust hole portion 2 is smaller than the width (length in the A direction) of the outlet opening 7 of the downstream adjacent exhaust hole portion 3.

[0066] (Configuration of the "flange portion" of the exhaust manifold) The flange portion 4 is disposed at the most downstream position in the exhaust flow direction of the exhaust manifold 103. The flange portion 4 is provided with a plurality of fixing member attachment portions 41 for attaching bolts which are fixing members. The plurality of fixing member attachment portions 41 are disposed around the downstream side central exhaust hole portion 2 and the two downstream side adjacent exhaust hole portions 3. The fixing member attachment portion 41 has a hole through which a bolt is inserted. Further, the flange portion 4 is provided with three outlet openings 7 through which exhaust corresponding to one downstream side central exhaust hole portion 2 and two downstream side adjacent exhaust hole portions 3 flows out.

[0067] (Configuration of the "water jacket" of the exhaust manifold) With reference to FIGS. 6 to 12, the water jacket 5 will be described. As shown in FIG. 6, the water jacket 5 is formed so as to extend along the exhaust flow direction. The exhaust flow direction and the flow direction of the cooling water flowing through the water jacket 5 are opposite to each other. That is, the water jacket 5 is configured to flow the cooling water in a direction opposite to the exhaust flow direction toward the engine E.

[0068] Here, as shown in FIG. 8, in the present embodiment, the water jacket 5 is provided in the exhaust manifold 103 so that the cooling water flows between the downstream side central exhaust hole portion 2 and the downstream side adjacent exhaust hole portion 3.

[0069] That is, the water jacket 5 is provided between adjacent exhaust holes (the downstream side central exhaust hole portion 2 and the downstream side adjacent exhaust hole portion 3) at a position closer to the collecting pipe 104 than the engine E. In short, the water jacket 5 is provided between adjacent exhaust holes on the downstream side in the exhaust flow direction of the exhaust manifold 103.

[0070] In detail, the water jacket 5 is provided on the flange portion 4 so that cooling water flows between the downstream central exhaust hole portion 2 and the downstream adjacent exhaust hole portion 3. In other words, the water jacket 5 is provided on the exhaust manifold 103 near the exhaust outlet surface 40 of the flange portion 4 so that cooling water flows between the downstream central exhaust hole portion 2 and the downstream adjacent exhaust hole portion 3.

[0071] 7, on the exhaust outlet surface 40 of the flange portion 4, the water jackets 5 are not provided between the three outlet openings 7, but are provided in multiple locations around the three outlet openings 7 so as to surround the three outlet openings 7. On the exhaust outlet surface 40, the multiple water jackets 5 are arranged in an annular row that extends in an elongated manner in the A direction so as to surround the three outlet openings 7.

[0072] In other words, the water jacket 5 between the downstream central exhaust hole portion 2 and the downstream adjacent exhaust hole portion 3 is not provided over the entire thickness direction of the flange portion 4. The water jacket 5 between the downstream central exhaust hole portion 2 and the downstream adjacent exhaust hole portion 3 is provided only on the side of the flange portion 4 opposite the exhaust outflow surface 40 in the thickness direction of the flange portion 4.

[0073] 8, between the downstream central exhaust hole portion 2 and the downstream adjacent exhaust hole portion 3, the width W1 of the water jacket 5 in the arrangement direction (direction A) of the downstream central exhaust hole portion 2 and the downstream adjacent exhaust hole portion 3 is larger than the thickness W2 of the exhaust manifold 103 that forms the downstream central exhaust hole portion 2 and the downstream adjacent exhaust hole portion 3. Between the downstream central exhaust hole portion 2 and the downstream adjacent exhaust hole portion 3, the water jacket 5 is formed to be at least larger than the minimum thickness of the exhaust manifold 103 that forms the downstream central exhaust hole portion 2 and the downstream adjacent exhaust hole portion 3.

[0074] Also, as shown in FIGS. 8 and 9, a plurality of water jackets 5 are provided around the downstream-side central exhaust hole portion 2 so as to surround the downstream-side central exhaust hole portion 2. Specifically, the water jackets 5 around the downstream-side central exhaust hole portion 2 are provided one each on one side and the other side of the downstream-side central exhaust hole portion 2 in the A direction. As shown in FIG. 8, the water jacket 5 is formed larger than the downstream-side central exhaust hole portion 2 in a direction orthogonal to the A direction.

[0075] Also, the water jacket 5 extends along the shape of the downstream-side central exhaust hole portion 2 and the shape of the downstream-side adjacent exhaust hole portion 3. Specifically, the water jacket 5 has an arcuate (arc-shaped) surface that extends along the shape of the downstream-side central exhaust hole portion 2 and the shape of the downstream-side adjacent exhaust hole portion 3.

[0076] Also, as shown in FIGS. 7 and 8, the downstream-side central exhaust hole portion 2 is configured to gradually change its shape so that the cross-sectional shape changes from an oval shape to a circular shape while maintaining the area of the cross-sectional shape as it goes upstream in the exhaust flow direction from the outlet opening 7. Note that the "cross-sectional shape" means the shape in a cross-section orthogonal to the exhaust flow direction.

[0077] Also, as shown in FIGS. 7 to 9, the water jackets 5 on the surface (exhaust outflow surface 40 or cross-section) where the downstream-side central exhaust hole portion 2 exists are configured to merge with each other and decrease in number as they go upstream in the exhaust flow direction from the outlet opening 7.

[0078] Also, as shown in FIGS. 10 to 12, the water jackets 5 in the cross-section where the upstream-side exhaust hole portion 1 exists are configured to branch and increase in number as they go upstream in the exhaust flow direction. As shown in FIG. 11, at an intermediate position of the upstream-side exhaust hole portion 1 relatively close to the engine E in the exhaust flow direction, the water jacket 5 becomes four and is formed in an annular shape surrounding each of the four upstream-side exhaust hole portions 1.

[0079] (Effects of the present embodiment) In this embodiment, the following effects can be obtained.

[0080] In this embodiment, as described above, the exhaust manifold 103 includes one downstream central exhaust hole portion 2 formed by merging two central upstream exhaust hole portions 1 out of the four upstream exhaust hole portions 1, two downstream adjacent exhaust hole portions 3 adjacent to both sides of the one downstream central exhaust hole portion 2 with a space therebetween, and a water jacket 5 formed to extend along the exhaust flow direction and flowing cooling water in a direction opposite to the exhaust flow direction toward the engine E. The water jacket 5 is provided in the exhaust manifold 103 such that cooling water flows between the downstream central exhaust hole portion 2 and the downstream adjacent exhaust hole portions 3. Thereby, the water jacket 5 can be provided at a position between the downstream central exhaust hole portion 2 and the downstream adjacent exhaust hole portions 3, which is a position adjacent to the downstream central exhaust hole portion 2 where exhaust gas flows in from both of the two central upstream exhaust hole portions 1 and is particularly likely to become high temperature, and is also adjacent to the downstream adjacent exhaust hole portions 3. Further, the water jacket 5 can be disposed on each of one side of the downstream adjacent exhaust hole portion 3 and the other side of the downstream adjacent exhaust hole portion 3 with respect to the downstream central exhaust hole portion 2. That is, the water jacket 5 can be disposed so as to sandwich the downstream central exhaust hole portion 2. As described above, the vicinity of the downstream central exhaust hole portion 2 formed by merging the plurality of upstream exhaust hole portions 1 can be effectively cooled by the water jacket 5.

[0081] In the present embodiment, as described above, the exhaust manifold 103 includes a flange portion 4 provided with three outlet openings 7 through which exhaust gases corresponding to one downstream central exhaust hole portion 2 and two downstream adjacent exhaust hole portions 3 flow out. The water jacket 5 is provided in the flange portion 4 such that cooling water flows between the downstream central exhaust hole portion 2 and the downstream adjacent exhaust hole portion 3. Thereby, a water jacket 5 between the downstream central exhaust hole portion 2 and the downstream adjacent exhaust hole portion 3 can be provided in the flange portion 4 disposed at the most downstream position in the exhaust gas flow direction. For this reason, unlike the case where there is no water jacket in the flange portion between the downstream central exhaust hole portion and the downstream adjacent exhaust hole portion, the exhaust manifold 103 can be cooled by the water jacket 5 from a more downstream side in the exhaust gas flow direction. Therefore, the vicinity of the downstream central exhaust hole portion 2 formed by the confluence of the plurality of upstream exhaust hole portions 1 can be cooled more effectively by the water jacket 5.

[0082] In the present embodiment, as described above, on the exhaust gas outflow surface 40 where the three outlet openings 7 of the flange portion 4 are located, the three outlet openings 7 are arranged spaced apart from each other. On the exhaust gas outflow surface 40, the water jacket 5 is not provided between the three outlet openings 7, and a plurality of water jackets 5 are provided around the three outlet openings 7 so as to surround the three outlet openings 7. Thereby, since the three outlet openings 7 are spaced apart from each other on the exhaust gas outflow surface 40, a water jacket 5 can be provided on a more downstream side in the exhaust gas flow direction approaching the three outlet openings 7 at a position between the downstream central exhaust hole portion 2 and the downstream adjacent exhaust hole portion 3 as compared with the case where the three outlet openings are connected to each other. Further, the vicinity of the downstream central exhaust hole portion 2 can be cooled more effectively by the water jacket 5 surrounding the three outlet openings 7.

[0083] In the present embodiment, as described above, a plurality of water jackets 5 are provided around the downstream-side central exhaust hole portion 2 so as to surround the downstream-side central exhaust hole portion 2. Thereby, the vicinity of the downstream-side central exhaust hole portion 2 can be cooled more effectively by the water jacket 5 surrounding the downstream-side central exhaust hole portion 2.

[0084] In the present embodiment, as described above, the three outlet openings 7 through which the exhaust gases corresponding to one downstream-side central exhaust hole portion 2 and two downstream-side adjacent exhaust hole portions 3 flow out have substantially the same area as each other. Thereby, the flow of the exhaust gas between the plurality of exhaust hole portions can be made uniform, and pulsation and exhaust interference at the plurality of exhaust hole portions can be suppressed.

[0085] In the present embodiment, as described above, the three outlet openings 7 are arranged in a straight line in a row, and in the orthogonal direction (B direction) orthogonal to the two directions of the arrangement direction of the three outlet openings 7 and the exhaust gas flow direction when passing through the three outlet openings 7, the outlet opening 7 of the downstream-side central exhaust hole portion 2 is formed in an elongated shape in which the opening length L1 is larger than the opening length L2 of the outlet opening 7 of the downstream-side adjacent exhaust hole portion 3. Thereby, since the downstream-side central exhaust hole portion 2 can be formed to be elongated in the orthogonal direction, a larger separation distance for forming the water jacket 5 larger can be secured between the downstream-side central exhaust hole portion 2 and the downstream-side adjacent exhaust hole portion 3.

[0086] In the present embodiment, as described above, the outlet opening 7 of the downstream-side adjacent exhaust hole portion 3 is formed in a circular shape, and the outlet opening 7 of the downstream-side central exhaust hole portion 2 is formed in an oval shape extending in the orthogonal direction. Thereby, a larger separation distance can be secured between the downstream-side central exhaust hole portion 2 and the downstream-side adjacent exhaust hole portion 3 by the downstream-side central exhaust hole portion 2 having the oval-shaped outlet opening 7 extending in the orthogonal direction.

[0087] In this embodiment, as described above, the engine E is an in-line four-cylinder engine E. The four inlet openings 6 of the exhaust manifold 103 into which exhaust flows from the in-line four-cylinder engine E are arranged in a straight line in a row, and the three outlet openings 7 through which the exhaust corresponding to one downstream central exhaust hole portion 2 and two downstream adjacent exhaust hole portions 3 flows out are arranged in a straight line in a row. As a result, in the exhaust manifold 103 provided in the in-line four-cylinder engine E, the vicinity of the downstream central exhaust hole portion 2 formed by the confluence of the plurality of upstream exhaust hole portions 1 can be effectively cooled by the water jacket 5.

[0088] In this embodiment, as described above, the arrangement direction of the four inlet openings 6 and the arrangement direction of the three outlet openings 7 are the same direction. As a result, compared with the case where the arrangement direction of the four inlet openings and the arrangement direction of the three outlet openings intersect, the size of the exhaust manifold 103 in the direction orthogonal to the arrangement direction of the four inlet openings 6 can be suppressed.

[0089] In this embodiment, as described above, between the downstream central exhaust hole portion 2 and the downstream adjacent exhaust hole portion 3, the width W1 of the water jacket 5 in the arrangement direction of the downstream central exhaust hole portion 2 and the downstream adjacent exhaust hole portion 3 is larger than the thickness W2 of the exhaust manifold 103 forming the downstream central exhaust hole portion 2 and the downstream adjacent exhaust hole portion 3. As a result, between the downstream central exhaust hole portion 2 and the downstream adjacent exhaust hole portion 3, the width W1 of the water jacket 5 can be ensured to be relatively large.

[0090] In this embodiment, as described above, the minimum separation distance W0 (see FIG. 8) between the downstream central exhaust hole portion 2 and the downstream adjacent exhaust hole portion 3 is 10 mm or more. As a result, between the downstream central exhaust hole portion 2 and the downstream adjacent exhaust hole portion 3, it is possible to avoid the thickness of the exhaust manifold 103 becoming too small and the width of the water jacket 5 becoming too small.

[0091] In this embodiment, as described above, the engine E is disposed within the hull 101 and includes the engine E and an impeller E4 that is driven by the engine E to generate a water flow, and is provided with a jet propulsion unit 102 that generates a propulsion force by the water flow. As a result, in a jet-propelled boat equipped with a relatively high-output engine E that is likely to become hot, the vicinity of the downstream-side central exhaust hole portion 2 formed by the confluence of the plurality of upstream-side exhaust hole portions 1 can be effectively cooled by the water jacket 5.

[0092] [Modification Example] The embodiment disclosed this time should be considered to be illustrative in all respects and not restrictive. The scope of the present invention is shown not by the description of the above embodiment but by the claims, and further includes all changes (modification examples) within the meaning and scope equivalent to the claims.

[0093] For example, in the above-described embodiment, an example in which a small ship is configured by a personal watercraft is shown, but the present invention is not limited to this. In the present invention, the small ship may be configured by a small boat or the like.

[0094] Further, in the above-described embodiment, an example in which a small ship is provided with a jet propulsion unit as a propulsion device is shown, but the present invention is not limited to this. In the present invention, the small ship may be provided with an outboard motor, an inboard engine, or the like as a propulsion device instead of a jet propulsion unit.

[0095] Further, in the above-described embodiment, an example in which the downstream-side central exhaust hole portion is formed in an oval shape is shown, but the present invention is not limited to this. In the present invention, the downstream-side central exhaust hole portion may be formed in an elliptical shape, a rectangular shape, or the like.

[0096] Further, in the above-described embodiment, an example in which a water jacket is provided in the flange portion at the most downstream position in the exhaust flow direction of the exhaust manifold is shown, but the present invention is not limited to this. In the present invention, a water jacket may not be provided in the flange portion at the most downstream position in the exhaust flow direction of the exhaust manifold.

[0097] In addition, in the above-described embodiment, an example in which two downstream adjacent exhaust hole portions are configured as a pair is shown, but the present invention is not limited to this. In the present invention, the two downstream adjacent exhaust hole portions do not have to be configured as a pair, such as having different shapes from each other.

[0098] In addition, in the above-described embodiment, an example in which the minimum separation distance between the downstream central exhaust hole portion and the downstream adjacent exhaust hole portion is set to 10 mm or more is shown, but the present invention is not limited to this. In the present invention, the minimum separation distance between the downstream central exhaust hole portion and the downstream adjacent exhaust hole portion may be less than 10 mm.

[0099] In addition, in the above-described embodiment, an example in which the arrangement direction of the four inlet openings and the arrangement direction of the three outlet openings are the same direction is shown, but the present invention is not limited to this. In the present invention, the arrangement direction of the four inlet openings and the arrangement direction of the three outlet openings may be different directions.

[0100] In addition, in the above-described embodiment, an example in which one downstream central exhaust hole portion and two downstream adjacent exhaust hole portions are arranged side by side in a straight line is shown, but the present invention is not limited to this. In the present invention, one downstream central exhaust hole portion and two downstream adjacent exhaust hole portions may be arranged side by side in a V shape or the like.

Explanation of Reference Numerals

[0101] 1 Upstream exhaust hole portion 2 Downstream central exhaust hole portion 3 Downstream adjacent exhaust hole portion 4 Flange portion 5 Water jacket 6 Inlet opening 7 Outlet opening 40 Exhaust outflow surface (of flange portion) 100 Small ship 101 Hull 102 Jet propulsion unit 103 Exhaust manifold E Engine E2 Exhaust port E4 Impeller Opening length of the outlet opening of the downstream-side central exhaust hole portion in the orthogonal direction (direction B) Opening length of the outlet opening of the downstream-side adjacent exhaust hole portion in the orthogonal direction (direction B) Minimum separation distance between the downstream-side central exhaust hole portion and the downstream-side adjacent exhaust hole portion Width of the water jacket between the downstream-side central exhaust hole portion and the downstream-side adjacent exhaust hole portion Thickness of the exhaust manifold forming the downstream-side central exhaust hole portion and the downstream-side adjacent exhaust hole portion between the downstream-side central exhaust hole portion and the downstream-side adjacent exhaust hole portion

Claims

1. A hull, a four-cylinder engine provided on the hull, and an exhaust manifold provided on the engine, wherein the exhaust manifold includes: four upstream exhaust hole portions each connected to four exhaust ports of the engine; one downstream central exhaust hole portion disposed downstream of the four upstream exhaust hole portions in the exhaust flow direction and formed by merging two of the central upstream exhaust hole portions among the four upstream exhaust hole portions; two downstream adjacent exhaust hole portions disposed downstream of the four upstream exhaust hole portions in the exhaust flow direction and adjacent to both sides of the one downstream central exhaust hole portion with a space therebetween; and a water jacket formed to extend along the exhaust flow direction and configured to flow cooling water in a direction opposite to the exhaust flow direction toward the engine, wherein the water jacket is provided on the exhaust manifold such that cooling water flows between the downstream central exhaust hole portion and the downstream adjacent exhaust hole portions. A small ship.

2. The exhaust manifold includes a flange portion provided with three outlet openings through which exhaust corresponding to the one downstream central exhaust hole portion and the two downstream adjacent exhaust hole portions flows out, wherein the water jacket is provided on the flange portion such that cooling water flows between the downstream central exhaust hole portion and the downstream adjacent exhaust hole portions. The small ship according to Claim 1.

3. On an exhaust outflow surface where the three outlet openings of the flange portion are located, the three outlet openings are spaced apart from each other, and on the exhaust outflow surface, the water jacket is not provided between the three outlet openings and is provided in plurality around the three outlet openings so as to surround the three outlet openings. The small ship according to Claim 2.

4. The water jacket is provided in plurality around the downstream central exhaust hole portion so as to surround the downstream central exhaust hole portion. The small ship according to Claim 1.

5. The three outlet openings through which exhaust corresponding to the one downstream central exhaust hole portion and the two downstream adjacent exhaust hole portions flows out have substantially the same area as each other. The small ship according to Claim 1.

6. The three outlet openings are arranged linearly in a row, In an orthogonal direction orthogonal to the arrangement direction of the three outlet openings and the direction of the exhaust flow when passing through the three outlet openings, the outlet opening of the downstream central exhaust hole portion is formed in an elongated shape with an opening length larger than the opening length of the outlet opening of the downstream adjacent exhaust hole portion. The small ship according to claim 5.

7. The outlet opening of the downstream adjacent exhaust hole portion is formed in a circular shape. The outlet opening of the downstream central exhaust hole portion is formed in an oval shape extending in the orthogonal direction. The small ship according to claim 6.

8. The engine is an in-line four-cylinder engine. The four inlet openings of the exhaust manifold into which exhaust flows from the in-line four-cylinder engine are arranged in a straight line in a row. The three outlet openings through which the exhaust corresponding to the one downstream central exhaust hole portion and the two downstream adjacent exhaust hole portions flows out are arranged in a straight line in a row. The small ship according to claim 1.

9. The arrangement direction of the four inlet openings and the arrangement direction of the three outlet openings are the same direction. The small ship according to claim 8.

10. Between the downstream central exhaust hole portion and the downstream adjacent exhaust hole portion, the width of the downstream central exhaust hole portion and the downstream adjacent exhaust hole portion of the water jacket in the arrangement direction is larger than the thickness of the exhaust manifold forming the downstream central exhaust hole portion and the downstream adjacent exhaust hole portion. The small ship according to claim 1.

11. The minimum separation distance between the downstream central exhaust hole portion and the downstream adjacent exhaust hole portion is 10 mm or more. The small ship according to claim 1.

12. The engine is arranged inside the hull. The small ship according to claim 1, comprising the engine and an impeller driven by the engine to generate a water flow, and a jet propulsion unit that generates a propulsion force by the water flow.

13. Four upstream exhaust hole portions respectively connected to the four exhaust ports of a four-cylinder engine provided in a small ship, One downstream central exhaust hole portion arranged downstream of the four upstream exhaust hole portions in the exhaust flow direction and formed by merging the two central upstream exhaust hole portions among the four upstream exhaust hole portions. Are arranged downstream of the four upstream exhaust hole portions in the exhaust flow direction, and two downstream adjacent exhaust hole portions adjacent to both sides of the one downstream central exhaust hole portion with a space therebetween, Comprises a water jacket formed to extend along the exhaust flow direction and flowing cooling water in a direction opposite to the exhaust flow direction toward the engine. The water jacket is provided such that cooling water flows between the downstream central exhaust hole portion and the downstream adjacent exhaust hole portion, an exhaust manifold for a small ship.

14. Comprises a flange portion provided with three outlet openings through which exhaust corresponding to the one downstream central exhaust hole portion and the two downstream adjacent exhaust hole portions flows out, The water jacket is provided in the flange portion such that cooling water flows between the downstream central exhaust hole portion and the downstream adjacent exhaust hole portion, the exhaust manifold for a small ship according to claim 13.

15. On the exhaust outflow surface where the three outlet openings of the flange portion are located, the three outlet openings are arranged spaced apart from each other, On the exhaust outflow surface, the water jacket is not provided between the three outlet openings, and a plurality are provided around the three outlet openings so as to surround the three outlet openings, the exhaust manifold for a small ship according to claim 14.

16. The water jacket is provided in plurality around the downstream central exhaust hole portion so as to surround the downstream central exhaust hole portion, the exhaust manifold for a small ship according to claim 13.

17. The three outlet openings through which exhaust corresponding to the one downstream central exhaust hole portion and the two downstream adjacent exhaust hole portions flows out have substantially the same area as each other, the exhaust manifold for a small ship according to claim 13.

18. The three outlet openings are arranged linearly in a row, In the direction orthogonal to the two directions of the arrangement direction of the three outlet openings and the exhaust flow direction when passing through the three outlet openings, the outlet opening of the downstream central exhaust hole portion is formed in an elongated shape in which the opening length is larger than the opening length of the outlet opening of the downstream adjacent exhaust hole portion, the exhaust manifold for a small ship according to claim 17.

19. The outlet opening of the downstream adjacent exhaust hole portion is formed in a circular shape, The outlet opening of the downstream-side central exhaust hole portion is formed in an oval shape extending in the orthogonal direction, the exhaust manifold for small ships according to claim 18.

20. The engine is an in-line four-cylinder engine, The four inlet openings into which exhaust flows from the in-line four-cylinder engine are arranged in a straight line in a row, The three outlet openings through which the exhaust corresponding to the one downstream-side central exhaust hole portion and the two downstream-side adjacent exhaust hole portions flows out are arranged in a straight line in a row, the exhaust manifold for small ships according to claim 13.

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