Ship

Abstract

A ship (100) comprises: an acoustic measurement device (12) which has an underwater transducer (S) on the ship bottom (11); and a bow appendage (20) which is fixed to the outer surface of a bow part of the marine vessel. The bow appendage (20) has a function, when the ship is traveling forward, for deflecting, outward in the width direction of the underwater transducer (S), a streamline (F) that passes from the vicinity of the sea surface at the bow part and along the outer surface of the hull, near the underwater transducer (S).

Description

Ship

[0001] The present invention relates to a ship provided with acoustic measurement equipment inside a hull.

[0002] In tankers and container ships, acoustic measurement equipment for detecting water depth, the position and speed of underwater objects is sometimes provided to improve navigation safety. The acoustic measurement equipment includes, for example, echo sounders that identify water depth and the position of objects, and Doppler sonars that measure the movement of objects (e.g., the speed of ships and fish).

[0003] The above-mentioned acoustic measurement equipment includes an underwater transducer provided on the bottom of the hull. The underwater transducer transmits ultrasonic waves into water from the transducer and receives the reflected ultrasonic waves. However, if bubbles generated near the bow water surface flow around to the bottom of the ship and the ultrasonic waves transmitted and received by the underwater transducer are blocked by the bubbles, the acoustic measurement equipment cannot obtain highly reliable signals.

[0004] To avoid this problem, for example, Patent Document 1 has been proposed.

[0005] The "Bubble removing device and ship construction method" in Patent Document 1 is provided with a water flow generator that blows water out from the side surface of the hull. The water flow generator is located forward of the hull relative to the acoustic measurement device, and is configured to blow away bubbles generated by air entrained in the bow wave generated by the hull before the bubbles reach the vicinity of the acoustic measurement device.

[0006] Japanese Unexamined Patent Publication No. 2011-116220

[0007] The "bubble removing device" of the above-mentioned Patent Document 1 has the following problems.

[0008] (1) The bubble removal device (water flow generator) is installed in the underwater portion of the hull's side, positioned forward of the acoustic measurement device, and is a device that sprays water outwards from the surface of the hull. Therefore, it requires a large-scale device (water flow generator). (2) The bubble removal device (water flow generator) must be installed at a specific location forward of the acoustic measurement device. Therefore, it directly affects the hull structure or design and reduces the ship's cargo capacity. (3) In the case of large ships such as tankers and container ships, the bottom of the hull where the underwater transducer is installed reaches a depth of, for example, 20m or more. Therefore, the water pressure of the water discharged by the water flow generator is high, and the power required for the bubble removal device is large. (4) The pressure and flow rate of the water discharged by the bubble removal device (water flow generator) must be variably controlled according to the ship's navigation conditions. Therefore, the control becomes complex and maintenance is required.

[0009] This invention was devised to solve the problems described above. In other words, the objective of this invention is to provide a vessel that can prevent the underwater transducer of an acoustic measuring instrument from being obstructed by bubbles generated near the water surface at the bow, does not require large-scale equipment, has little impact on the hull structure or hull design, and does not reduce the cargo capacity.

[0010] According to the present invention, a ship is provided that comprises an acoustic measuring instrument having an underwater transducer on the bottom of the ship, and a bow appendage fixed to the outer surface of the bow of the ship, wherein the bow appendage has the function of diverting streamlines that pass from near the sea surface at the bow along the outer surface of the hull and near the underwater transducer outward in the width direction of the underwater transducer when the ship is moving forward.

[0011] According to the above-described configuration of the present invention, the bow appendage has the function of diverting streamlines that pass from near the sea surface at the bow along the outer surface of the hull and near the underwater transducer to the outside in the width direction of the underwater transducer when the ship is moving forward. This prevents the underwater transducer from being obstructed by bubbles generated near the water surface at the bow.

[0012] Furthermore, since the bow appendage is fixed to the outer surface of the bow of the ship, it does not require large-scale equipment, has little impact on the ship's hull structure or design, and does not reduce the ship's carrying capacity. In addition, since the bow appendage is simply fixed to the outer surface of the bow of the ship, it does not require control or maintenance.

[0013] This is a perspective view of the bow section of the hull of the embodiment described later. This is an explanatory diagram of the hull shape of Figure 1, a half-width plan view of the bow as seen from below. This is an explanatory diagram of the hull shape of Figure 1, a side view of the bow as seen from the side. This is a simulation result showing the streamlines flowing along the hull when the draft substantially coincides with the boundary between the curved surface and the vertical surface. This is a simulation result showing the streamlines flowing along the hull when the draft is approximately 7 m and the sea surface substantially coincides with the lowest waterline. This is a diagram of the principle of the present invention. This is a supplementary explanatory diagram of the principle of the present invention. This is a diagram showing an example of the shape of a bow appendage. This is an explanatory diagram of the mounting position of the bow appendage. This is a side view of the bow section of the bow appendage used in the embodiment described later. This is a view along the line B-B in Figure 8A. This is a simulation result showing the streamlines flowing along the hull having a bow appendage when the fixing position of the bow appendage is 1 m from the bottom of the hull. This is a simulation result showing the streamlines flowing along the hull having a bow appendage when the fixing position of the bow appendage is 3 m from the bottom of the hull. This is a simulation result showing the streamlines flowing along a hull with a bow appendage, when the fixed position of the bow appendage is 6m from the bottom of the hull. This is the same simulation result as Figures 9A-9C when the bow appendage is linear (Type I) as shown in Figure 6E. This is the same simulation result as Figures 9A-9C when the bow appendage is triangular as shown in Figure 6F. This is a simulation result calculating the increase in hull resistance.

[0014] Embodiments of the present invention will be described below with reference to the drawings. Common parts in each figure are denoted by the same reference numerals, and redundant explanations are omitted.

[0015] Figure 1 is a perspective view of the bow section of the hull 10 of the embodiment described later. In this figure, 1 is the upper deck sideline, 2 is the bottom plate line, 3 is the hull centerline, 7 is the waterline for normal ballast, and 8 is the waterline for design full. Also, 20 is a bow appendage described later.

[0016] The waterline 7 for normal ballast (hereinafter referred to as "minimum waterline 7") refers to the minimum draft required for navigation. The waterline 8 for design full (hereinafter referred to as "maximum waterline 8") refers to the draft position when fully loaded according to the design specifications.

[0017] The vessel 100 in Figure 1 is, for example, the largest vessel capable of passing through the Strait of Malacca, with a total length of approximately 300m, a total width of approximately 60m, and a draft of approximately 20m. In this example, the draft at the highest waterline 8 (maximum draft) is set to approximately 20m, and the bow draft at the lowest waterline 7 (minimum bow draft) is set to approximately 7m.

[0018] Figures 2A and 2B are explanatory diagrams of the hull shape of Figure 1. In these figures, Figure 2A is a half-width plan view of the bow of the hull 10 as seen from below, and Figure 2B is a side view of the bow as seen from the side of the hull.

[0019] In Figure 2A, 4 is the Fore Perpendicular (F.P.) position. Also, the side of the bottom plate line 2 on the hull centerline side (inside) is the horizontal hull bottom 11. In Figure 2B, 5 is the buttock line of the hull centerline 3, and 6 is the baseline (Base Line) that coincides with the hull bottom 11.

[0020] In this example, the buttock line 5 of the hull centerline 3 is formed as a gently curved surface 5a from the baseline 6 to above the minimum waterline 7, and above that, including the maximum waterline 8, is formed as a vertical surface 5b. In Figure 2A, the curved surface 5a and vertical surface 5b of the hull 10 as viewed from below are also composed of gently curved surfaces (not shown).

[0021] In Figures 2A and 2B, the symbol ● represents the underwater transducer S of the acoustic measuring instrument 12. The acoustic measuring instrument 12 is either an echo sounder or a Doppler sonar.

[0022] An echo sounder is a device that uses sound waves to explore underwater objects and terrain, and is used to measure water depth and locate schools of fish. Specifically, it emits sound waves (ultrasound), measures the time it takes for these sound waves to reflect off underwater objects or the seabed and return, calculates the distance from that time, and determines the water depth and the location of the object. A Doppler sonar is a device that uses sound waves to measure the position and speed of objects, utilizing the Doppler effect to measure the movement of objects (for example, the speed of a ship or fish).

[0023] The underwater transducer S is located inside the bottom plate line 2 in Figure 2A, near the bow, less than 1 m (approximately 1.7% of the hull width) from the hull centerline 3, and is installed flush with the bottom 11 so as not to protrude. The position of the underwater transducer S is within 6 m (2% of the total hull length) from the tip of the bottom 11. Although this figure shows one underwater transducer S, there may be two or three or more underwater transducers S.

[0024] Figures 3A and 3B show simulation results illustrating the streamlines F flowing along the hull. These figures are half-width plan views of the bow of the hull 10 viewed from below, with the starting point of the streamlines F being the sea surface 5 m ahead of the bow end position 4 (on the right side in the figure). In these figures, Figure 3A shows the case where the draft substantially coincides with the boundary between the curved surface 5a and the vertical surface 5b, while Figure 3B shows the case where the draft is approximately 7 m and the sea surface substantially coincides with the minimum draft line 7.

[0025] In the case of Figure 3A, the streamlines F located away from the hull centerline 3 flow in the width direction along the gentle curve of the hull side, as the hull at sea level is a vertical plane 5b, and there is almost no flow that dips below the sea surface. Similarly, since the buttock line 5 of the hull centerline 3 is a vertical plane 5b, the streamlines F close to the hull centerline 3 also flow near the sea surface along the gentle curve of the hull side, and there is little flow that dips below the sea surface. Therefore, there are no streamlines F that reach the underwater transducer S at the bottom of the hull 11 from the sea surface, and the phenomenon of bubbles b generated at the sea surface flowing along the streamlines F and reaching the underwater transducer S hardly occurs.

[0026] In the case of Figure 3B, the streamlines F located away from the hull centerline 3 dive below the sea surface at the curved section 5a of the hull at sea level, and flow along the gentle curve of the hull side below the sea surface. Similarly, since the buttock line 5 of the hull centerline 3 is also a curved section 5a, the streamlines F close to the hull centerline 3 also dive below the sea surface at the curved section 5a, creating a flow that reaches the bottom of the hull 11 below the sea surface. Therefore, streamlines F are generated that reach the underwater transducer S at the bottom of the hull 11 from the sea surface, and there is a possibility that bubbles b generated at the sea surface will flow along the streamlines F and reach the underwater transducer S.

[0027] In actual vessels, the acoustic measuring instrument 12 always functions normally when the draft is close to the maximum waterline 8, but may become unstable when it is close to the minimum waterline 7. This is thought to be because, as shown in Figure 3B, bubbles b generated on the sea surface flow along the streamline F that reaches the underwater transducer S. The present invention was conceived based on the above-mentioned perspective.

[0028] Figure 4 is a schematic diagram of the present invention. In this figure, the bow appendage 20 is fixed to the bow of the hull and has the function of diverting the flow from the vicinity of the sea surface at the bow outwards in the width direction when the ship 100 is moving forward. In this figure, the flow from the vicinity of the sea surface at the bow flows from right to left.

[0029] In this example, the bow appendage 20 has a V-shape when viewed from the outside of the hull, and has a widthwise center 20a and a pair of widthwise ends 20b. The widthwise center 20a is located towards the bow compared to the pair of widthwise ends 20b. The front surface 20c (bow side) of the bow appendage 20 is smoothly formed from the widthwise center 20a to the pair of widthwise ends 20b so as not to disrupt the streamline F. Furthermore, the thickness of the bow appendage 20 from the front surface 20c to the rear surface 20d (stern side) is formed to be substantially constant.

[0030] In Figure 4, the flow that reaches the front surface 20c is divided in the width direction at the center 20a, and forms a vortex at the width direction end 20b, drawing in the bubbles b contained in the flow. The formation of this vortex suppresses the flow from the outside to the inside in the width direction of the bow appendage 20, as will be shown in the embodiments described later.

[0031] Figure 5 is a supplementary explanatory diagram of the principle of the present invention. In this figure, the vessel 100 equipped with acoustic measuring instrument 12 has an underwater transducer S on its hull bottom 11. The vessel 100 also has a bow appendage 20 fixed to the outer surface of its bow. The bow appendage 20 has the function of diverting the streamlines F that pass from near the sea surface at the bow along the outer surface of the hull and near the underwater transducer S outward in the width direction of the underwater transducer S when the vessel 100 is moving forward. "Near the underwater transducer S" refers to the area near the underwater transducer S exposed on the outer surface of the hull and affected by bubbles b. This area is set according to the performance of the underwater transducer S, and is, for example, within about 1.0 m in the direction of sound wave transmission and reception from the underwater transducer S.

[0032] In Figure 5, the streamline F that runs from near the sea surface at the bow along the outer surface of the hull and passes near the underwater transducer S will be referred to below as the "virtual streamline Fi". The streamline F that is deflected outward in the width direction of the underwater transducer S by the bow appendage 20 will be referred to below as the "actual streamline Fr".

[0033] In this example, the bow appendage 20 has a widthwise central part 20a that coincides with the virtual streamline Fi, and a pair of widthwise ends 20b spaced widthwise from the virtual streamline Fi. In the embodiment described later, the virtual streamline Fi is set to the hull centerline 3.

[0034] The overall width B of the bow appendage 20 is set such that the streamlines F passing outside the widthwise end 20b do not reach the underwater transducer S. Therefore, the overall width B of the bow appendage 20 is set so that the underwater transducer S is located inside a pair of parallel streamlines F passing outside a pair of widthwise end 20b.

[0035] In the embodiment described later, the underwater transducer S is located within 1 m of the hull centerline 3. In this case, the total width B of the bow appendage 20, whose widthwise center 20a is located on the hull centerline 3, is preferably 2 m or more.

[0036] In this example, the widthwise end 20b is located downstream (towards the stern) of the widthwise center 20a, and is designed to deflect the streamline F located near the widthwise center 20a toward the widthwise end 20b.

[0037] The gradient θ with respect to the plane perpendicular to the virtual streamline (hull centerline 3) from the widthwise center 20a to the widthwise end 20b is, for example, 20° or more and 40° or less, preferably 30°. If the gradient θ is less than 20°, the increase in hull resistance may become excessive. Also, a larger gradient θ can reduce the increase in hull resistance, but if it exceeds 40°, the vortex formed at the widthwise end 20b mentioned above may weaken, and the effect of drawing bubbles b into the vortex may decrease.

[0038] Due to the configuration of the bow appendage 20 described above, the streamline F (actual streamline Fr) deflected outward in the width direction at the front 20c of the bow appendage 20 flows outward from the bow appendage 20. In addition, the bubbles b accompanying the actual streamline Fr rise due to buoyancy, and after separating from the bow appendage 20, they move (float) above the actual streamline Fr. Therefore, it is possible to prevent the bubbles b accompanying the actual streamline Fr from exceeding the hull centerline 3 of the bottom plate line 2 and reaching the bottom of the hull 11, and as a result, it is possible to prevent the bubbles b from reaching the underwater transducer S located near the hull centerline 3 on the bottom of the hull 11.

[0039] The total height H of the bow appendage 20 from the hull surface is preferably such that the underwater transducer S is not affected by bubbles b, and in the example described later, it is 0.3 m. A larger total height H is more effective, but increases the resistance of the hull.

[0040] Figures 6A to 6F are diagrams showing examples of shapes of the bow appendage 20. In this figure, Figure 6A is the basic shape shown in Figures 4 and 5. Further, Figure 6B is similar to the basic shape, but differs in that the width-direction end portions 20b are curved toward the downstream side. Further, Figure 6C differs in that the front face 20c is V-shaped, while Figure 6D differs in that the front face 20c is U-shaped or elliptical. It is assumed that the same effect can be obtained with any of the bow appendages 20 of Figures 6A to 6D.

[0041] In this figure, Figure 6E is an example where the shape viewed from the outside of the hull is linear (type I), and Figure 6F is an example of a triangular shape. The bow appendages 20 of Figures 6E and 6F generate actual flow lines Fr that flow over the bow appendage 20 without being deflected thereby, so the effect of the present invention was not obtained in the examples described later.

[0042] Figure 7 is an explanatory diagram of the attachment position of the bow appendage 20. As shown in this figure, the fixed position of the bow appendage 20 is preferably the curved surface portion 5a of the bow and below the lowest waterline 7. Note that in the examples described later, the bow appendage 20 is positioned on the hull center line below the lowest waterline 7.

[0043] Further, it is preferable that the entire bow appendage 20 is positioned rearward (toward the stern side) of the bow end position 4 and above the base line 6. This is because if it is positioned forward of the bow end position 4, the overall length of the hull, which is the principal dimension of the ship, changes, which affects the basic design. Further, if it is positioned below the base line 6, the increase in hull resistance becomes excessive.

[0044] Figures 8A and 8B are explanatory diagrams of the bow appendage 20 used in the examples described later. In this figure, Figure 8A is a side view of the bow, and Figure 8B is a view taken along arrow B-B in Figure 8A.

[0045] In Figures 8A and 8B, the total width B of the bow appendage 20 is 2 m, and the total height H is 0.3 m. Further, the angle formed by the front face 20c with respect to the hull surface is 90° (vertical). Note that the angle formed by the front face 20c with respect to the hull surface is preferably an acute angle less than 90°. This is because if it exceeds 90°, actual flow lines Fr that flow over the bow appendage 20 without being deflected thereby are generated.

[0046] (Example 1) Figures 9A to 9C are simulation results showing streamlines F flowing along a hull provided with a bow additional member 20. In this example, the bow additional member 20 is fixed on the hull centerline below the lowest waterline 7 at heights (installation heights) of 1 m, 3 m, and 6 m from the ship bottom 11, respectively. The hull is the ship 100 shown in Figure 1, having a total width of about 60 m, a draft of about 20 m, and a minimum bow draft of about 7 m.

[0047] In this figure, the fixed position of the bow additional member 20 from the ship bottom 11 is 1 m in Figure 9A, 3 m in Figure 9B, and 6 m in Figure 9C. The simulation conditions for the streamlines F are the same as those in Figure 3A and Figure 3B.

[0048] Furthermore, the bow additional member 20 is the one shown in Figure 6A (and Figures 8A and 8B). In this case, the reference position of the bow additional member 20 is the position (height) where the front surface of the center portion 20a in the width direction contacts the hull.

[0049] From a comparison between Figures 9A to 9C and Figure 3B, it can be seen that when the bow additional member 20 is fixed at positions 1 m, 3 m, and 6 m from the ship bottom 11, the flow from the water surface is diverted outward in the width direction in all cases, and flows outside the underwater transducer S provided on the ship bottom 11 in the width direction.

[0050] With respect to the minimum bow draft of about 7 m, the positions 1 m, 3 m, and 6 m from the ship bottom 11 correspond to installation heights of approximately 14%, 43%, and 85% of the minimum bow draft, respectively. Therefore, it is preferable that the installation height of the bow additional member 20 from the ship bottom 11 is within a range of from about 14% to about 85% of the minimum bow draft. Furthermore, with respect to the minimum bow draft of about 7 m, the total width B and total height H of the bow additional member 20 correspond to approximately 29% and approximately 4.3% thereof, respectively.

[0051] (Example 2) Figures 10A and 10B are simulation results similar to those of Figures 9A to 9C for the case of the bow additional member 20 of Figures 6E and 6F. In this figure, Figure 10A corresponds to the case where the bow additional member 20 has the linear shape (type I) of Figure 6E, and Figure 10B corresponds to the case of the triangular shape of Figure 6F.

[0052] From Figures 10A and 10B, when the bow appendage 20 is linear (I-shaped) or triangular, vortex formation becomes unstable, and actual streamlines Fr are generated that flow over the bow appendage 20 without being deflected. Therefore, the effects of the present invention were not obtained in the case of a linear (I-shaped) or triangular shape.

[0053] (Example 3) Figure 11 shows the simulation results of calculating the increase in hull resistance in Example 1. In this figure, the horizontal axis is the installation height of the bow appendage 20 from the bottom of the hull 11 (m), and the vertical axis is the rate of increase in hull resistance (%). The underlined line in the figure represents the case of the minimum draft (waterline with normal ballast), and the upper line represents the case of the maximum draft (waterline with design full).

[0054] This figure shows that the increase in hull resistance is approximately 0.5% or less regardless of whether the installation height of the bow appendage 20 is 1m, 3m, or 6m. Furthermore, the lower the installation height of the bow appendage 20, the greater the increase in resistance tends to be, and the increase in resistance may be excessive if it is less than 1m. Conversely, the higher the installation height of the bow appendage 20, the smaller the increase in resistance tends to be, and the increase in resistance was smallest at 6m. Therefore, from the viewpoint of suppressing the increase in resistance, it is preferable that the installation height of the bow appendage 20 be as close to the minimum draft as possible.

[0055] According to the above-described embodiment of the present invention, the bow appendage 20 has the function of diverting the streamlines F that pass from near the sea surface at the bow along the outer surface of the hull and near the underwater transducer S outward in the width direction of the underwater transducer S when the ship 100 is moving forward. This prevents the underwater transducer S from being obstructed by bubbles b generated near the water surface at the bow.

[0056] Furthermore, since the bow appendage 20 is fixed to the outer surface of the bow of the ship, no large-scale equipment is required, and there is virtually no impact on the ship's hull structure or design, and the ship's carrying capacity is not reduced. Moreover, since the bow appendage is simply fixed to the outer surface of the bow of the ship, no control or maintenance is required.

[0057] It should be noted that the present invention is not limited to the hull 10 described above, and other hulls may also be used. For example, the bow portion of the hull 10 is preferably composed of the curved surface portion 5a and the vertical surface 5b described above, and the waterline portion is curved, but it may also be a bulbous bow with a spherical projection at the bow below the waterline. Furthermore, the hull 10 is preferably a single-hull, but it may also be a twin-hull.

[0058] Furthermore, it is preferable that the virtual streamline Fi described above coincides with the hull centerline 3 and the bow appendage 20 is located on the hull centerline, but even if the virtual streamline Fi does not coincide with the hull centerline 3, it is acceptable as long as the bow appendage 20 is located on the virtual streamline.

[0059] It should be noted that the present invention is not limited to the embodiments described above, and various modifications can be made without departing from the spirit of the invention.

[0060] B Overall width, b Air bubbles, F Streamlines, Fr Actual streamlines, Fi Virtual streamlines, H Overall height, S Underwater transducer, θ Slope, 1 Upper deck sideline, 2 Bottom plate line, 3 Hull centerline, 4 Bow end position, 5 Buttock line of hull centerline, 5a Curved section, 5b Vertical surface, 6 Baseline, 7 Minimum waterline (waterline with normal ballast), 8 Maximum waterline (waterline with design full), 10 Hull, 11 Bottom, 12 Acoustic measuring equipment (echo sounder or Doppler sonar), 20 Bow appendage, 20a Center in width direction, 20b End in width direction, 20c Front, 20d Back, 100 Ship

Claims

1. A ship comprising an acoustic measuring instrument having an underwater transducer on the bottom of the hull, and a bow appendage fixed to the outer surface of the bow of the ship, wherein the bow appendage has the function of diverting streamlines that pass from near the sea surface at the bow along the outer surface of the hull and near the underwater transducer outward in the width direction of the underwater transducer when the ship is moving forward.

2. The vessel according to claim 1, wherein the underwater transducer is located in the bottom of the hull near the bow, and the bow appendage is located in the bow below the minimum draft.

3. The vessel according to claim 2, wherein the bow section is formed as a gently curved surface from the baseline to above the minimum waterline, and the fixing position of the bow appendage is the curved surface.

4. The vessel according to claim 1, wherein the underwater transducer is located near the centerline of the hull at the bottom of the vessel, and the bow appendage is located in front of the underwater transducer and on the centerline of the hull.

5. The vessel according to claim 1, wherein the fixing position of the bow appendage is within a range of approximately 14% to approximately 85% of the minimum draft at the bow from the bottom of the hull.

6. The vessel according to claim 3, wherein the entire bow appendage is located aft of the bow end and above the baseline.

7. The vessel according to claim 1, wherein the bow appendage has a widthwise central part located along the outer surface of the hull from near the sea surface of the bow portion and coincides with a virtual streamline passing near the underwater transducer, and a pair of widthwise ends spaced widthwise from the virtual streamline, the widthwise central part is located towards the bow compared to the pair of widthwise ends, the front surface of the bow appendage is smoothly formed so as not to disturb the streamline from the widthwise central part to the pair of widthwise ends, the widthwise ends are located towards the stern compared to the widthwise central part and are configured to deflect the streamline located near the widthwise central part toward the widthwise ends.

8. The vessel according to claim 7, wherein the overall width of the bow appendage is set such that the streamlines passing outside the widthwise end do not reach the underwater transducer.

9. The ship according to claim 7, wherein the gradient with respect to a plane perpendicular to the virtual streamline from the center in the width direction to the end in the width direction is 20° or more and 40° or less, and the thickness of the bow appendage from the front to the back is substantially constant.

10. The vessel according to claim 1, wherein the rate of increase in hull resistance is approximately 0.5% or less.

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