VESSEL CONFIGURED FOR PITCH REDUCTION

Abstract

A vessel (30) comprising a hull (15) having an apparent centre of pitch (23) located at a position between about 10% and 35% of the length of the vessel (10) measured from the aftermost point (17) of the vessel on the design waterline. The hull (15) may be bare, or alternatively may be fitted with a damping system (31) located forwardly to provide damping forces to reduce the vertical motion at the bow and hence the vertical accelerations. In one arrangement, the vessel (10) may comprise a single hull vessel. In another arrangement, the vessel (10) may comprise a multi-hulled vessel.

Description

FIELD OF THE INVENTION

This invention relates to marine vessels particularly sea-going vessels primarily for commercial or military use.

BACKGROUND ART

The following discussion of the background art is intended to facilitate an understanding of the present invention only. The discussion is not an acknowledgement or admission that any of the material referred to is or was part of the common general knowledge as at the priority date of the application

A conventional sea-going vessel operating amongst waves is subjected to various motions associated with the six degrees of freedom, principally roll, pitch and heave and to a lesser extent yaw, surge and sway. It is difficult to modify, and hence control, surge and sway. Yaw is controlled principally by the rudder or other steering devices.

Comfort of persons on board a vessel operating in waves is affected by motion sickness (kinetosis). Whilst there are many known sources of kinetosis, one of the main drivers relates to the acceleration level and the frequency of changing accelerations.

Operation in waves does not generally produce large accelerations in yaw, surge and sway on a conventional vessel, and therefore the effect of these motions on comfort levels can be ignored.

Kinetosis is generally considered to be linked to the vertical accelerations and frequency of acceleration, relative to a person in a standing position. The effect of horizontal acceleration relative to a standing person is generally believed to be considerably less, although horizontal accelerations are not desirable because they can cause a loss of balance, as opposed to sickness.

If a person moves from the standing position to a supine or prone position (i.e. lying down) then the general belief is that kinetosis can be reduced.

The principal vertical accelerations experienced on a vessel operating in waves are the result of the vessel pitching or heaving. Therefore it is most desirable to reduce the amount of pitch and heave acceleration.

It is difficult to reduce the amount of heave when a vessel operates in waves. The forces generated by the changing buoyancy of the vessel in waves can be extremely large, and hydrodynamic aids such as foils and fins cannot produce sufficient force to mitigate heave without being impractically large.

The principal method by which heave can be reduced is through the implementation of a reduced “footprint” area at the sea surface, called the waterplane area. Vessels with this arrangement have greatly reduced stability characteristics, and are therefore generally designed as a catamaran and termed “Small Waterplane Area Twin Hull” craft, or SWATH. U.S. Pat. No. 3,623,444 (Lang) discloses such an arrangement in combination with large submerged fins. U.S. Pat. No. 3,447,502 (Leopold) also discloses a similar technology and suggests that the arrangement would offer very good sea keeping qualities. Unfortunately, despite the hopes at the time, few SWATH-type vessels have been constructed since the disclosure in U.S. Pat. No. 3,623,444 (Lang). The vessels which have been constructed have exhibited poor resistance characteristics and have therefore not achieved the anticipated high speed. However, the vessels, have demonstrated superior sea-keeping ability and high levels of comfort.

The cost to manufacture such a complex-shaped vessel is high relative to other types of craft. Further, such a vessel has little cargo capacity owing to the very factor that offers good sea-keeping; namely, the waterplane area is small, and consequently any weight placed on board will increase the draft of the craft substantially, which makes it unsuited to operation in shallow water. Propulsion arrangements also remain problematical, owing to the narrowness of the hull.

The vertical motion of a vessel on its longitudinal centreline can be considered to consist of two freedoms of motion. Translational motion where every point on the vessel moves up and down and known as heave, and rotational motion or pitch about somewhere near to the middle of the ship, with the bow going up when the stern goes down, and vice versa.

Accepting that heave motion can practically be very difficult to remove or even reduce, and that a very small waterplane area is not desirable because of the impact on cargo-carrying ability, then it is desirable to reduce the other component of vertical acceleration, namely pitch.

Pitch can be simplistically considered to be rotational motion about a point, called the Centre of Pitch, and at this point the vertical accelerations owing to pitch will be zero and any vertical motion and acceleration will be associated with Heave.

Further forward and further aft of the centre of pitch, the vertical motion and acceleration values will be increased by the pitching motion of the vessel.

In reality, the centre of pitch is not fixed, but moves as the vessel moves, and is dependent on a number of factors including the wave characteristics causing the ship motion and the shape of the vessel itself. The term “centre of pitch” can be used for descriptive purposes only. However, an apparent centre of pitch can be described as the longitudinal location at which the root-mean-square (RMS) average values of vertical accelerations are at a minimum. At this point all of the RMS accelerations can be attributed to heave.

The apparent centre of pitch is depicted in FIGS. 1, 2 and 3. FIG. 1 is a schematic side view of a vessel with a conventional hull configuration comprising a hull 1 having a bow 2 and an aft end (stern) 3. FIG. 2 is a schematic side view of a vessel similar to that shown in FIG. 1 but with a hydrodynamic damping device 4 mounted at or adjacent the bow 2. FIG. 3 is a schematic side view of a vessel with a conventional multi-hull configuration, incorporating a main hull 1 and side hulls 5, with the main hull 1 having a hydrodynamic damping device 4 mounted at or adjacent the bow 2. In FIGS. 1, 2 and 3, the design waterline of the respective hull is denoted by reference numeral 6 and the apparent centre of pitch is denoted by reference numeral 7. In the drawings, the water surface is represented by line 8. Three levels of the water surface 8a, 8b and 8c are depicted, and pitching motion of the respective hulls from the neutral position are depicted by broken lines.

Over a period of time in one sea state, and at a consistent vessel speed and heading, the distribution of vertical acceleration (RMS) at various longitudinal locations along the vessel 1 with the hull configuration depicted in FIG. 1 will be as illustrated in the diagram of FIG. 4. In this diagram, the minimum vertical acceleration occurs at about 40% of the length L of the vessel 1 measured on the design waterline from the after end 3, this location being the apparent centre of pitch 7. Aft of this location the acceleration values rise, and forward of this location the acceleration values also rise at a reasonably consistent rate. The region of lowest vertical accelerations extends to each side of the centre of pitch 7 over a length identified schematically in FIG. 1 by line 9. The greatest accelerations occur at the bow 5 (100% L). The apparent centre of pitch in this diagram is at 40% L from the after end 3, and this is reasonably typical of the pitching distribution of most sea-going ships.

Disclosure of the Invention

According to a first aspect of the invention there is provided a vessel comprising a hull having an apparent centre of pitch located at a position between about 10% and 35% of the length of the vessel measured from the aftermost point of the vessel on the design waterline.

According to a second aspect of the invention there is provided a vessel comprising a hull having an apparent centre of pitch located at a position between about 10% and 30% of the length of the vessel measured from the aftermost point of the vessel on the design waterline when the underwater hull shape is bare and devoid of any hydrodynamic force generators such as foils or fins, and without the assistance of any external force generators such as gyroscopic stabilisers.

According to a third aspect of the invention there is provided a vessel comprising a hull having an apparent centre of pitch located at a position between about 10% and 35% of the length of the vessel measured from the aftermost point of the vessel on the design waterline, the hull being fitted with a damping system located forwardly to provide damping forces to reduce the vertical motion at the bow and hence the vertical accelerations.

Preferably, the apparent centre of pitch in each of the abovementioned aspects of the invention is located at a position about 20% of the length of the vessel measured from the aftermost point of the vessel on the design waterline.

The damping system may comprise a hydrodynamic damping device such as a wing or foil mounted at, or close to, the bow. Preferably, the vessel designed for speeds of between 20 and 70 knots.

Preferably, the vessel has a length on the waterline of between 24 metres and 250 metres.

The vessel may comprise a single hull vessel or a multi-hulled vessel.

The multi-hulled vessel may comprise a trimaran having a centrally located main hull and two laterally spaced side hulls commonly known as amahs, in which case the main hull would constitute said hull in each of the abovementioned aspects of the invention.

The multi-hulled vessel may comprise a pentamaran having a centrally located main hull and four laterally spaced side hulls (two to each side of the main hull), in which case the main hull would constitute said hull in each of the abovementioned aspects of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood by reference to the following description of several specific embodiments thereof. The description will be made with reference to the accompanying drawings in which:

FIG. 1 is a schematic side view of a conventional hull configuration, illustrating the apparent centre of pitch; FIG. 2 is a schematic side view of a conventional configuration, illustrating the apparent centre of pitch, the hull configuration incorporating a hydrodynamic damping device mounted at or adjacent to the bow;

FIG. 3 is a schematic side view of a conventional multi-hull configuration, illustrating the apparent centre of pitch, the multi-hull configuration incorporating a main hull having a hydrodynamic damping device mounted at or adjacent to the bow;

FIG. 4 is a graph of vertical acceleration (RMS) versus distance from the after end of the conventional hull configuration as depicted in FIG. 1 as a percentage of the length L of the vessel measured on the design waterline;

FIG. 5 is a schematic side view of the hull of a vessel according to a first embodiment, illustrating the apparent centre of pitch;

FIG. 6 is a graph of vertical acceleration (RMS) versus distance from the after end of the hull configuration according to the first embodiment as a percentage of the length L of the vessel measured on the design waterline;

FIG. 7 is a schematic side view of the hull of a vessel according to a second embodiment, illustrating the apparent centre of pitch;

FIG. 8 is a graph of vertical acceleration (RMS) versus distance from the after end of the hull configuration according to the second embodiments as a percentage of the length L of the vessel measured on the design waterline; and

FIG. 9 is a schematic side view of the hull of a vessel according to a third embodiment, illustrating the apparent centre of pitch.

BEST MODE(S) FOR CARRYING OUT THE INVENTION

The first embodiment, which is shown FIG. 5, is directed to a vessel 10 comprising a high speed commercial or military vessel, such as a ferry, for passenger and cargo transport, including vehicle transport. In this embodiment, the vessel is designed for speeds between about 20 and 70 knots.

Typically, the vessel 10 has a waterline length between 24 metres and 250 metres, although it is of course not limited thereto.

The vessel 10 comprises an understructure 11 and a superstructure (not shown), both constructed primarily of aluminium. The actual waterline in relation to the understructure 11 is established by the water surface 13. The water surface rises and falls and under the influence of wave motion and is shown varying between three positions 13a, 13b and 13c. The pitching motion of the vessel 10 from the neutral position is depicted by broken lines 10a and 10b, with solid line 10c depicting the neutral position. The direction of pitching motion is depicted by the adjacent direction arrows 14.

The under structure 11 comprises a hull 15. In one arrangement, the vessel 10 may comprise a single hull vessel. In another arrangement, the vessel 10 may comprise a multi-hulled vessel. The vessel may, for example, comprise a trimaran having a centrally located main hull and two laterally spaced side hulls commonly known as amahs, in which case the hull 15 would be constituted by the main hull. Alternatively, the vessel 10 may, comprise a pentamaran having a centrally located main hull and four laterally spaced side hulls (two to each side of the main hull), in which case the hull 15 would be constituted by the main hull.

In the arrangement shown in FIG. 5, the vessel 10 is a single hull vessel. The hull 15 has a forward end terminating at a bow 17 and an aft end terminating at a stern 19. The bow 17 may incorporate a forwardly extending bulbous portion 21 below the waterline 13.

The design waterline of the hull 15 is denoted by reference numeral 20. The hull 15 has an apparent centre of pitch which is identified by reference numeral 23.

The hull 15 is configured to move the apparent centre of pitch 23 considerably further aft in comparison a conventional vessel design as discussed above and depicted in FIG. 1. This is generally not considered to be beneficial by those skilled in the art because such a hull shape is likely to increase the resistance of the vessel to forward motion and hence to reduce the speed of the vessel.

Specifically, the apparent centre of pitch 23 located at a position between 10% and 30% of the length L of the vessel measured from the aftermost point of the craft on the design waterline, when the underwater hull shape is bare and without any hydrodynamic force generators such as foils or fins, and without the assistance of any external force generators such as gyroscopic stabilisers. In this embodiment, the apparent centre of pitch 23 located at a position corresponding to about 20% of the length L. Aft of this location, the acceleration values rise, and forward of this location the acceleration values also rise at a reasonably consistent rate. The region of lowest vertical accelerations extends to each side of the centre of pitch 23 over a length identified schematically in FIG. 5 by line 24.

The vertical acceleration distribution for such a hull configuration is illustrated in

FIG. 6. In particular, FIG. 6 a graph of vertical acceleration (RMS) versus distance from the after end 19 of the hull 15 as a percentage of the length L of the vessel measured on the design waterline 20.

In order to obtain the desired location of the centre of pitch 23, it is necessary that the buoyancy distribution of the hull shape (and therefore the associated weight distribution of the vessel) be considerably further aft than is generally desirable for a commercially viable layout of a conventional sea-going vessel. Accordingly, the superstructure (not shown) is configured such that the majority of the weight of the vessel 10 lies in the after part of the vessel.

Such an arrangement is conducive to the desired layout of the vessel 10. In particular, it allows the passenger area of the vessel 10 to be located further aft where there are lower vertical accelerations (as depicted in FIG. 6), thus potentially affording a higher degree of comfort to passengers.

With the vertical acceleration distribution as illustrated in FIG. 6, it is evident that the acceleration values in the forward part of the vessel 10 are noticeably greater than those of the conventional ship illustrated in FIG. 4. This is addressed in this embodiment by a superstructure layout in which personnel are not accommodated in the forward part of the vessel 10, and consequently the acceleration values would not be relevant to personnel comfort or safety.

Referring now to FIG. 7, there is shown a vessel 30 according to a second embodiment. The vessel 30 is similar to the vessel 10 according to the first embodiment and so corresponding reference numerals are used to identify corresponding parts. In this second embodiment, the vessel 30 is fitted with a damping system 31 located forwardly to provide damping forces to reduce the vertical motion at the bow 17 and hence the vertical accelerations. The damping system 31 comprises a hydrodynamic damping device 33 mounted at, or close to, the bow 17. In the arrangement shown, the hydrodynamic damping device 33 is configured as a hydrofoil 35 or similar hydrodynamic appendage.

FIG. 8 a graph of vertical acceleration (RMS) versus distance from the after end of the hull 15 as a percentage of the length L of the vessel measured on the design waterline 20. FIG. 8 also includes data from FIG. 6 for comparative purposes.

The effect of such a damping system 31 would be as illustrated in FIG. 8. The apparent centre of pitch 23 would remain substantially in the same location, although there may be some forward movement by up to about 10% L.

More particularly, the apparent centre of pitch 23 would be located at a position between 10% and 35% of the length L of the vessel measured from the aftermost point of the vessel on the design waterline.

Referring now to FIG. 9, there is shown a vessel 40 according to a third embodiment. The vessel 40 comprises a multi-hulled vessel. In the arrangement shown, the multi-hulled vessel 40 comprise a trimaran having a centrally located main hull 41 and two laterally spaced side hulls 43 commonly known as amahs. In another arrangement, the multi-hulled vessel 40 may comprise a pentamaran having a centrally located main hull and four laterally spaced side hulls (two to each side of the main hull).

The main hull 41 has a design waterline 44.

The pitching motion of the vessel 40 from the neutral position is depicted by broken lines 40a and 40b, with solid lines 40c depicting the neutral position.

The hull 41 has a forward end terminating at a bow 45 and an aft end terminating at a stern 46. The bow 45 may incorporate a forwardly extending bulbous portion 47 below the design waterline 44. Additionally, the vessel 40 may be fitted with a damping system 48 located forwardly to provide damping forces to reduce the vertical motion at the bow 45 and hence the vertical accelerations. The damping system 48 comprises a hydrodynamic damping device 49 mounted at, or close to, the bow 45. In the arrangement shown, the hydrodynamic damping device 48 is configured as a hydrofoil, as was the case with an earlier embodiment.

The hull 41 has an apparent centre of pitch which is identified by reference numeral 42.

The hull 41 is configured to move the apparent centre of pitch 42 considerably further aft in comparison a conventional multi-hull vessel design as discussed above and depicted in FIG. 3. As mentioned in relation to earlier embodiments, this is generally not considered to be beneficial by those skilled in the art because such a configuration is likely to increase the resistance of the vessel to forward motion and hence to reduce the speed of the vessel.

In particular, the apparent centre of pitch 42 is located at a position between 10% and 35% of the length L of the vessel 40 measured from the aftermost point of the vessel on the design waterline.

From the foregoing, it is evident that the present embodiments each provide a vessel with a hull configuration which delivers improved comfort and safety to personnel onboard the vessel through a reduction in vertical accelerations in the area where personnel are likely to be accommodated.

It should be appreciated that the scope of the invention is not limited to the scope of the embodiments described, and that various changes and modification may be made without departing from the scope of the invention.

Throughout the specification and claims, unless the context requires otherwise, the word “comprise” or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

Claims

1. A vessel comprising a hull with an apparent centre of pitch located at a position between about 10% and 35% of the length of the vessel measured from the aftermost point of the vessel on the design waterline.

2. A vessel comprising a hull with an apparent centre of pitch located at a position between about 10% and 30% of the length of the vessel measured from the aftermost point of the vessel on the design waterline when the underwater hull shape is bare and devoid of any hydrodynamic force generators such as foils or fins, and without the assistance of any external force generators such as gyroscopic stabilisers.

3. A vessel comprising a hull with an apparent centre of pitch located at a position between about 10% and 35% of the length of the vessel measured from the aftermost point of the vessel on the design waterline, the hull being fitted with a damping system located forwardly to provide damping forces to reduce the vertical motion at the bow and hence the vertical accelerations.

4. The vessel according to claim 3 wherein the damping system comprises a hydrodynamic damping device such as a wing or foil mounted at or close to the bow.

5. The vessel according to claim 1 designed for speeds of between 20 and 70 knots

6. The vessel according to claim 1 having a length on the waterline of between 24 metres and 250 metres.

7. The vessel according to claim 1 comprise a single hull vessel

8. The vessel according to claim 1 comprising a multi-hulled vessel.

9. The vessel according to claim 8 comprising a trimaran having a centrally located main hull and two laterally spaced side hulls, wherein the hull constitutes the main hull.

10. The vessel according to claim 8 comprising a pentamaran having a centrally located main hull and four laterally spaced side hulls (two to each side of the main hull), wherein the hull would constitutes the main hull.

11. (canceled)