Water jet propulsion boat and marine vessel

Abstract

To provide a water jet propulsion boat that facilitates smooth turning, even with improved seaworthiness and straight-running stability.SOLUTION: The water jet propulsion boat 10 comprises a hull 20, and at the front of a keel 26 in the hull, a cavity 29 penetrating in the left-right direction is formed.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The technology disclosed in this specification relates to water jet propulsion boats and ships. [Background technology]

[0002] A water jet propulsion boat has a hull and generates a propulsive force for the hull by generating a water current flowing toward the rear of the hull. Known vessels have a keel extending from the bow to the stern of the hull, which is provided at the center of the width of the bottom surface of the hull (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 4169543 Summary of the Invention [Problem to be solved by the invention]

[0004] Generally, the sharper the keel, the better the boat's seakeeping ability and straight-line stability, but it tends to make it more difficult to turn smoothly.

[0005] This specification discloses a technique that can solve the above-mentioned problems. [Means for solving the problem]

[0006] The technology disclosed in this specification can be realized, for example, in the following forms.

[0007] The water jet propulsion boat disclosed in this specification includes a hull, and a cavity penetrating the hull in the left-right direction is formed in a front portion of a keel.

[0008] When the water jet propulsion boat turns, the water around the bottom of the hull passes through the cavity, reducing the water resistance acting on the bottom of the hull during turning, making it easier to turn smoothly.

[0009] The techniques disclosed in this specification can be realized in various forms, such as a water jet propulsion boat, a ship, a method for manufacturing a water jet propulsion boat, a method for manufacturing a ship, etc. [Effects of the Invention]

[0010] When the water jet propulsion boat turns, the water around the bottom of the hull passes through the cavity, reducing the water resistance acting on the bottom of the hull during turning, making it easier to turn smoothly. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a side view schematically illustrating a water jet propulsion boat 10 according to an embodiment. [Figure 2] FIG. 1 is an explanatory diagram showing a cavity 29 and its surroundings in an embodiment. [Figure 3] 3 is a cross-section of the hull 20 of the embodiment taken along the line III-III in FIG. [Figure 4] Cross section of the hull 20 at position IV-IV in FIG. [Figure 5] FIG. 10 is an explanatory diagram showing a cavity 29a and its surroundings in another embodiment. [Figure 6] 3 is a cross-section of a hull 20b of another embodiment taken along the line III-III in FIG. [Figure 7] FIG. 10 is a side view schematically illustrating a water jet propulsion boat 10c according to another embodiment. [Figure 8] FIG. 10 is a side view schematically showing a modified water jet propulsion boat 10d. DETAILED DESCRIPTION OF THE INVENTION

[0012] FIG. 1 is a side view that schematically illustrates a water jet propulsion boat 10 according to an embodiment. Arrows indicating various directions relative to the position of the water jet propulsion boat 10 are appropriately shown in each of the following figures. More specifically, arrows indicating the forward, rearward, leftward, rightward, upward, and downward directions are appropriately shown in each figure. The forward-backward, leftward, rightward, and upward (vertical) directions are perpendicular to one another. FIG. 1 also illustrates the waterline W of the water jet propulsion boat 10 when it is planing.

[0013] The water jet propulsion boat 10 in this embodiment is, for example, a personal watercraft (PWC) and includes a hull 20, a drive unit 30, a jet propulsion mechanism 40, a jet flow adjustment mechanism 50, a displacement mechanism 60, a steering device 70, and a control unit (ECU) 80.

[0014] The hull 20 is the main structure of the water jet propulsion watercraft 10. The hull 20 has a keel 26 extending from bow to stern at the center of the bottom in the transverse direction. The keel extends from bow to stern at the centerline of the hull at the bottom. The keel is connected to the bow and stern members. The keel corresponds to the backbone of the hull. In this specification, the term "keel" may also include part of the stem of the hull. As will be described in detail later, a cavity 29 is formed in the front part of the keel 26 of the hull 20.

[0015] The hull 20 has a hull main body 27 and a plate 28. The hull main body 27 has a hull 21, a deck 22, and a seat 23. The hull 21 forms the bottom of the hull 20. The deck 22 forms the upper part of the hull 20. The seat 23 is located approximately in the center of the hull 20 in the fore-and-aft direction. An operator (crew member) (not shown) can sit on the seat 23. The plate 28 is a plate connected to the lower part of the hull main body 27. The plate 28 is located forward of the keel 26.

[0016] The drive unit 30 is disposed below the hull 20. The drive unit 30 has an engine 31, a crankshaft 32, and a coupling 33. The engine 31 is a spark-ignition multi-cylinder internal combustion engine. The crankshaft 32 is a rotating shaft that outputs the drive torque generated by the engine 31. The crankshaft 32 extends rearward from the engine 31. The coupling 33 connects the crankshaft 32 to an impeller shaft 45, which will be described later. The coupling 33 transmits the drive torque of the crankshaft 32 to the impeller shaft 45.

[0017] The jet propulsion mechanism 40 is provided in the rear portion of the hull 21 of the body 20. The jet propulsion mechanism 40 has an impeller housing 43, an impeller 44, an impeller shaft 45, stator vanes 46, and a nozzle 47. The jet propulsion mechanism 40 also has a flow path 41 formed therein.

[0018] The flow path 41 is formed in the rear portion of the hull 21 of the hull 20, in the center portion in the left-right direction. One end of the flow path 41 opens downward from the hull 21 as a water intake 42 for sucking in water. The flow path 41 extends rearward from the water intake 42. The other end 49 of the flow path 41 opens rearward from the hull 21.

[0019] The impeller housing 43 is a generally cylindrical body extending in the front-to-rear direction. The impeller housing 43 is arranged to protrude rearward from the other end 49 of the flow path 41. The impeller 44 is accommodated within the impeller housing 43. The impeller 44 is connected to the rear end of the impeller shaft 45. The impeller 44 rotates integrally with the impeller shaft 45 around the central axis of the impeller shaft 45. The stator vanes 46 are arranged rearward of the impeller 44 within the impeller housing 43. The nozzle 47 is cylindrical. The nozzle 47 is fixed to the rear end of the impeller housing 43. The rear end of the nozzle 47 opens as an outlet 48 for spraying water.

[0020] When the driving torque from the engine 31 is transmitted to the impeller shaft 45 and the impeller 44 rotates accordingly, water is drawn into the flow path 41 from outside the hull 20 via the water intake 42. The water drawn into the flow path 41 is supplied from the impeller 44 to the stator vanes 46. The water supplied by the impeller 44 is rectified as it passes through the stator vanes 46. The rectified water passes through the nozzle 47 and is ejected from the ejection port 48 toward the rear of the hull 20. In this way, the jet propulsion mechanism 40 can generate a jet flow toward the rear of the hull 20.

[0021] The jet flow adjustment mechanism 50 has a deflector 51 and a reverse gate 52. The displacement mechanism 60 has a deflector moving mechanism 61 and a reverse gate moving mechanism 65.

[0022] The deflector 51 is substantially cylindrical (frusto-conical) and is formed so that its inner diameter decreases toward the rear. The deflector 51 is disposed rearward of the nozzle 47. The deflector 51 covers the outlet 48 of the nozzle 47. The jet flow emitted from the outlet 48 passes through the deflector 51 and is emitted from an outlet 53. The deflector 51 is rotatable about a vertical axis and a horizontal axis behind the outlet 48. Depending on the rotation position of the deflector 51, the left-right direction and the up-down direction of the jet flow emitted from the outlet 48 toward the rear of the hull 20 can be changed. The deflector moving mechanism 61 displaces the deflector 51 in response to operation by the ship steering device 70.

[0023] The reverse gate 52 is disposed on the rear side of the deflector 51. The reverse gate 52 is provided so as to be displaceable among a forward position, a neutral position, and a reverse position. The forward position is a position where the reverse gate 52 does not cover the discharge port 53 of the deflector 51. The neutral position is a position where the reverse gate 52 covers part of the discharge port 53 of the deflector 51. The reverse position is a position where the reverse gate 52 covers the entire discharge port 53 of the deflector 51.

[0024] The steering device 70 has, for example, a steering handle. The operator of the water jet propulsion boat 10 can rotate the steering handle by grasping grips provided on both ends of the steering handle. When the operator rotates the steering handle, the deflector 51 can be rotated left and right via the displacement mechanism 60. The steering device 70 also has multiple controls (not shown). By operating the controls, the operator can start and stop the engine 31, rotate the deflector 51 up and down, or rotate the reverse gate 52.

[0025] The ECU 80 is, for example, a CPU, a multi-core CPU, or a programmable device (such as a Field Programmable Gate Array (FPGA) or a Programmable Logic Device (PLD)). The ECU 80 operates the deflector moving mechanism 61 and the reverse gate moving mechanism 65 in response to an operation of the ship steering device 70, for example.

[0026] FIG. 2 is an explanatory diagram showing a cavity 29 and its surroundings in an embodiment. FIG. 2 shows the cavity 29 and its surroundings as viewed in the left-right direction. As shown in FIG. 2, the hull 20 has a cavity 29 that penetrates in the left-right direction. The cavity 29 is formed in the front portion of the keel 26 of the hull 20. In other words, the cavity 29 is located near the underside of the hull 20. In this embodiment, the cavity 29 has a shape that extends in the front-to-rear direction. With the water jet propulsion boat 10 of this embodiment, when the water jet propulsion boat 10 turns, water located around the bottom of the hull 20 passes through the cavity 29. Therefore, the water jet propulsion boat 10 can turn more smoothly by reducing the water resistance acting on the bottom of the hull 20 during turning.

[0027] The cavity 29 is the space between the hull main body 27 and the plate 28. As shown in FIG. 2 , the plate 28 has a front end 281, an aft end 282, and an intermediate portion 283. The front end 281 is the forward end of the plate 28. The aft end 282 is the rear end of the plate 28. The intermediate portion 283 is located between the front end 281 and the aft end 282. The front end 281 and the aft end 282 of the plate 28 are connected to the lower part of the hull main body 27. When viewed in the left-right direction, the contour line of the upper side of the plate 28 is curved. Also, when viewed in the left-right direction, the contour line of the lower side of the plate 28 is curved. In other words, when viewed in the left-right direction, the plate 28 has a curved shape such that the intermediate portion 283 protrudes downward. Because the plate 28 has this structure, the intermediate portion 283 of the plate 28 is spaced apart from the hull main body 27 in the up-down direction. This creates a space between the hull main body 27 and the plate 28.

[0028] In the water jet propulsion watercraft 10, the cavity 29 is formed by attaching the plate 28 to the hull main body 27, so there is no need to form the cavity by, for example, penetrating a portion of the hull main body from side to side. As a result, manufacturing the water jet propulsion watercraft 10 does not require a process of penetrating a portion of the hull main body from side to side, making it relatively easy to manufacture the water jet propulsion watercraft 10. Furthermore, because there is no need to penetrate a portion of the hull main body 27, the cavity 29 can be formed without reducing the strength of the hull main body 27.

[0029] The plate 28 is attached to the hull main body 27, for example, with bolts. In other words, the plate 28 is removably connected to the hull main body 27. This makes it possible to replace the plate 28 with another plate having a different shape, for example, and to change the characteristics of the water jet propulsion boat 10 as needed.

[0030] 1, at least a portion of the cavity 29 is located below the waterline W when the water jet propulsion boat 10 is planing. A portion of the front side of the cavity 29 is located above the waterline W when the water jet propulsion boat 10 is planing. Because a portion of the front side of the cavity 29 is located above the waterline W, the water jet propulsion boat 10 can reduce water resistance acting on the bottom of the hull 20 when traveling straight, thereby improving propulsion efficiency.

[0031] 2, in a left-right view, the angle θ1 formed between the rear end 282 of the plate 28 and the hull main body 27 is smaller than the angle θ2 formed between the front end 281 of the plate 28 and the hull main body 27. In other words, the distance between the hull main body 27 and the plate 28 is shorter at the rear side of the cavity 29 than at the front side of the cavity 29. This structure makes it possible to prevent the water jet propulsion boat 10 from turning more than intended during a turn.

[0032] Figure 3 shows a cross section of the hull 20 of this embodiment taken along the line III-III in Figure 2. Figure 3 shows a cross section intersecting the fore-and-aft direction of the hull 20. Figure 3 also shows a centerline CL, which is the centerline of the hull 20 in the left-right direction.

[0033] A cross section of the plate 28 intersecting the fore-and-aft direction is bounded by a straight line portion L1, a curved line portion C1, and a curved line portion C2. The straight line portion L1 extends in the left-right direction and faces the hull main body 27 in the up-down direction. The left end of the straight line portion L1 is located to the left of the center line CL, and the right end of the straight line portion L1 is located to the right of the center line CL. The left end of the curved line portion C1 intersects with the left end of the straight line portion L1. The right end of the curved line portion C1 is located below the left end of the curved line portion C1 and near the center line CL. The intermediate portion from the left end to the right end of the curved line portion C1 is curved so as to protrude downward and to the left. The right end of the curved line portion C2 intersects with the right end of the straight line portion L1. The left end of the curved line portion C2 is located below the right end of the curved line portion C2 and near the center line CL. The intermediate portion from the left end to the right end of the curved line portion C2 is curved so as to protrude downward and to the right. The right end of curved section C1 and the left end of curved section C2 intersect near the center line CL, and the intersection of the right end of curved section C1 and the left end of curved section C2 forms corner E1. That is, a cross section of the plate 28 intersecting the fore-and-aft direction has a central portion located near the center line CL that juts out downward. More specifically, a cross section of the plate 28 intersecting the fore-and-aft direction has a generally triangular shape with corner E1 located near the center line CL and jutting out downward. This structure of the plate 28 enables the water jet propulsion boat 10 to improve its wave-riding ability when traveling straight.

[0034] Figure 4 shows a cross section of the hull 20 taken along line IV-IV in Figure 2. Figure 4 shows a cross section of the hull 20 intersecting the vertical direction. The cross section shown in Figure 4 shows a portion of the hull main body 27 that forms the rear profile 290 of the cavity 29. Figure 4 also shows a centerline CL, which is the centerline of the hull 20 in the left-right direction.

[0035] In a vertical view, the rearward contour line 290 of the cavity 29 has a central portion located near the lateral centerline CL of the hull 20 that juts out forward. More specifically, in a vertical view, the rearward contour line 290 of the cavity 29 has a corner E2 that is located near the lateral centerline CL of the hull 20 and juts out forward. In other words, the portion of the hull 20 that forms the rearward contour line 290 of the cavity 29 continuously narrows in width in the lateral direction toward the front. Because the hull 20 has this structure, the water jet propulsion boat 10 can reduce water resistance acting on the bottom of the hull 20 when planing forward, thereby improving propulsion efficiency.

[0036] 5 is an explanatory diagram showing a cavity 29a and its surroundings in another embodiment. In the following, in the hull 20a of another embodiment, parts common to the hull 20 of the embodiment described above are designated by the same reference numerals and descriptions thereof will be omitted as appropriate.

[0037] The hull 20a of another embodiment differs from the hull 20 in the shape of its plates. Specifically, when viewed in the left-right direction, the upper contour line of the plate 28a has a shape that includes a portion that bends at an angle greater than or equal to 90 degrees and less than 180 degrees. When viewed in the left-right direction, the upper contour line of the plate 28a has a corner E3 that bends at an angle θ3 and a corner E4 that bends at an angle θ4. Because the plate 28a has this structure, similar to the hull 20, the middle portion 283 of the plate 28a is spaced apart from the hull main body 27 in the up-down direction. This creates a space between the hull main body 27 and the plate 28a. Both the angles θ3 and θ4 are greater than or equal to 90 degrees and less than 180 degrees. Because the angles θ3 and θ4 are both greater than or equal to 90 degrees and less than 180 degrees, the plate 28a can have a more gently curved shape compared to, for example, an embodiment in which the angle θ3 or the angle θ4 is less than 90 degrees. This reduces the water resistance acting on the bottom of the hull 20a when the water jet propulsion boat is traveling straight, thereby improving propulsion efficiency.

[0038] Water jet propulsion boats including the hull 20a of the other embodiments also achieve the same effects as the water jet propulsion boat 10 of the embodiment. That is, according to the water jet propulsion boats of the other embodiments, when the water jet propulsion boat turns, water located around the bottom of the hull 20a passes through the cavity 29a. This reduces the water resistance acting on the bottom of the hull 20a when turning, making it easier for the water jet propulsion boat to turn smoothly.

[0039] Figure 6 shows a cross section of a hull 20b of another embodiment taken along line III-III in Figure 2. In the following, parts of the hull 20b of another embodiment that are common to the hull 20 of the embodiment described above are designated by the same reference numerals, and descriptions thereof will be omitted where appropriate.

[0040] In the hull 20b of another embodiment, the shape of the cross section of the plate intersecting the longitudinal direction differs from that of the hull 20. Specifically, in the hull 20b, the cross section of the plate 28b intersecting the longitudinal direction is surrounded by curved portions C1, C2, and C3. The curved portion C3 extends in the left-right direction and faces the hull main body 27 in the up-down direction. The left end of the curved portion C3 is located to the left of the center line CL, and the right end of the curved portion C3 is located to the right of the center line CL. The curved portion C3 is curved so that the intermediate portion from the left end to the right end protrudes upward. The left end of the curved portion C1 intersects with the left end of the curved portion C3. The right end of the curved portion C2 intersects with the right end of the curved portion C3. In other words, in the hull 20b, the cross section of the plate 28b intersecting the longitudinal direction has a central portion located near the center line CL that protrudes upward.

[0041] Water jet propulsion boats including the hull 20b of the other embodiments also achieve the same effects as the water jet propulsion boat 10 of the embodiment. That is, according to the water jet propulsion boats of the other embodiments, when the water jet propulsion boat turns, water located around the bottom of the hull 20b passes through the cavity 29b. This reduces the water resistance acting on the bottom of the hull 20b when turning, making it easier for the water jet propulsion boat to turn smoothly.

[0042] 7 is a side view showing a water jet propulsion boat 10c according to another embodiment. In the following description, parts of the water jet propulsion boat 10c according to another embodiment that are common to the water jet propulsion boat 10 according to the above-described embodiment are designated by the same reference numerals, and their description will be omitted where appropriate.

[0043] The water jet propulsion boat 10c of this embodiment differs from the water jet propulsion boat 10 in the structure of its hull. Specifically, the water jet propulsion boat 10c includes a hull 20c. A plurality of cavities 29c aligned in the fore-and-aft direction are formed in the front portion of the keel 26 of the hull 20c. The hull 20c includes a hull main body 27 and a plate 28c. The plate 28c is connected to the lower part of the hull main body 27 so that no gap is formed between the plate 28c and the hull main body 27. The plate 28c has a plurality of cavities 29c that penetrate in the left-right direction. The plurality of cavities 29c are circular when viewed in the left-right direction.

[0044] The water jet propulsion boat 10c of the other embodiment also provides the same effects as the water jet propulsion boat 10 of the embodiment. That is, according to the water jet propulsion boat 10c of the other embodiment, when the water jet propulsion boat 10c turns, water present around the bottom of the hull 20c passes through the cavity 29c. Therefore, the water jet propulsion boat 10c can turn more smoothly by reducing the water resistance acting on the bottom of the hull 20c when turning.

[0045] The technology disclosed in this specification is not limited to the above-described embodiments, and can be modified into various forms without departing from the spirit thereof, for example, the following modifications are also possible.

[0046] 8 is a side view showing a modified water jet propulsion boat 10d. In the following, parts of the modified water jet propulsion boat 10d that are common to the water jet propulsion boat 10 of the above-described embodiment are designated by the same reference numerals, and descriptions thereof will be omitted where appropriate.

[0047] The modified water jet propulsion boat 10d differs from the water jet propulsion boat 10 in the hull structure. Specifically, the water jet propulsion boat 10d includes a hull 20d. The hull 20d includes a hull main body 27 and an attachment 128. The attachment 128 is connected to the lower part of the hull main body 27 so that no gap is formed between the attachment 128 and the hull main body 27. The attachment 128 is located in the front part of the keel 26. In other words, the modified water jet propulsion boat 10d includes the attachment 128 instead of the plate 28 of the water jet propulsion boat 10 of the embodiment. The attachment 128 has multiple cutouts formed from the front end to the rear end in a left-right view. Therefore, the outline of the lower side of the attachment 128 has a shape in which convex portions and concave portions alternate from front to rear in a left-right view. In other words, a gap 129 is formed in the attachment 128 where the concave portions are located.

[0048] The water jet propulsion boat 10d of the modified example also achieves the same effects as the water jet propulsion boat 10 of the embodiment. That is, with the water jet propulsion boat 10d, when the water jet propulsion boat 10d turns, water located around the bottom of the hull 20d passes through the gap 129. This reduces the water resistance acting on the bottom of the hull 20d when turning, making it easier for the water jet propulsion boat 10d to turn smoothly.

[0049] In the above embodiment, the engine 31 is exemplified as the drive source of the drive device 30. However, an electric motor or the like may be provided together with the engine 31 or instead of the engine 31.

[0050] In the above embodiment, a portion of the front side of the cavity 29 is located above the waterline W when the water jet propulsion boat 10 is planing, but this is not necessarily limited to this; for example, the entire cavity may be located below the waterline W when the water jet propulsion boat is planing.

[0051] In the above embodiment, the hull 20 of the water jet propulsion boat 10 has the plate 28, but this is not necessarily limited to this, and the hull of the water jet propulsion boat may have a cavity formed by other methods.

[0052] In the above embodiment, the contour line of the upper side of the plate 28a has the corners E3 and E4 when viewed in the left-right direction, but there may be one corner or three or more corners.

[0053] The shape of the plate in the water jet propulsion boat is not limited to the above embodiment, and various modifications are possible.

[0054] In the above embodiment, a PWC is given as an example of an application of the technology disclosed in this specification, but the technology disclosed in this specification can be applied to watercraft in general, such as sports boats. [Explanation of symbols]

[0055] 10, 10c, 10d: Water jet propulsion boat 20, 20a-20d: Hull 21: Hull 22: Deck 23: Seat 26: Keel 27: Body 28, 28a-28c: Plate 29, 29a-29c: Cavity 30: Drive unit 31: Engine 32: Crankshaft 33: Coupling 40: Jet propulsion mechanism 41: Flow path 42: Water intake 43: Impeller housing 44: Impeller 45: Impeller shaft 46: Stator vane 47: Nozzle 48: Jet outlet 49: Other end 50: Jet flow adjustment mechanism 51: Deflector 52: Reverse gate 53: Discharge port 60: Displacement mechanism 61: Deflector movement mechanism 65: Reverse gate movement mechanism 70: Ship steering device 80: ECU 128: Attachment 129: Gap CL: Centerline W: Waterline

Claims

1. A water jet propulsion boat, Equipped with a hull, The water jet propulsion boat has a cavity formed in a front portion of the keel of the hull, the cavity penetrating in the left-right direction.

2. The water jet propulsion watercraft according to claim 1, At least a portion of the cavity is located below a waterline when the water jet propulsion watercraft is planing.

3. The water jet propulsion watercraft according to claim 2, A front portion of the cavity is located above the waterline when the water jet propulsion watercraft is planing.

4. The water jet propulsion watercraft according to claim 1, The cavity is located near the underside of the hull.

5. The water jet propulsion watercraft according to claim 1, The hull is The hull body and a plate, wherein a front end and a rear end of the plate are connected to a lower part of the hull main body, and an intermediate portion of the plate located between the front end and the rear end is spaced apart from the hull main body in the up-down direction; The cavity is a space between the hull body and the plate.

6. The water jet propulsion watercraft according to claim 5, In the water jet propulsion watercraft, when viewed from the left and right, the contour line of the upper side of the plate has a curved shape or a shape having a portion that bends at an angle of 90 degrees or more and less than 180 degrees.

7. The water jet propulsion watercraft according to claim 5, In the water jet propulsion watercraft, a contour line of a lower side of the plate is curved when viewed in the left-right direction.

8. The water jet propulsion watercraft according to claim 5, In a cross section of the plate intersecting the fore-and-aft direction, a central portion located near the center line of the hull in the transverse direction protrudes downward.

9. The water jet propulsion watercraft according to claim 8, In the water jet propulsion boat, a cross section of the plate intersecting the fore-and-aft direction is located near the center line of the hull in the transverse direction and has a generally triangular shape with corners that protrude downward.

10. The water jet propulsion watercraft according to claim 5, the angle formed between the rear end of the plate and the hull main body is smaller than the angle formed between the front end of the plate and the hull main body when viewed in the left-right direction.

11. The water jet propulsion watercraft according to claim 5, The plate is removably connected to the hull body.

12. The water jet propulsion watercraft according to claim 1, The water jet propulsion watercraft, wherein a central portion of a rear side contour line of the cavity, located near a center line in the left-right direction of the hull, protrudes forward when viewed in a vertical direction.

13. The water jet propulsion watercraft according to claim 12, The water jet propulsion watercraft has a rear contour line of the cavity that is located near a center line of the hull in the left-right direction when viewed from above and has a corner that protrudes forward.

14. The water jet propulsion watercraft according to claim 1, The cavity has a shape that extends in the front-to-rear direction.

15. The water jet propulsion watercraft according to claim 1, In the water jet propulsion watercraft, a plurality of the cavities are formed in a front portion of a keel of the hull, and are aligned in a longitudinal direction.

16. A vessel, Equipped with a hull, A vessel, wherein a cavity penetrating in the left-right direction is formed in the front part of the keel of the hull.

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