Field of the Invention

This invention relates to marine vessels particularly sea-going vessels for commercial or military use. The invention has been devised particularly, although not solely, as a multi-hulled vessel configured as a trimaran comprising a centrally located main hull and two side hulls.

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 for commercial or military use is generally designed such that resistance to forward motion in a calm sea is minimised with a view to optimising fuel efficiency. The shape of the hull is significant in relation to minimisation of drag, and the drivers of the ideal shape are generally well understood by those skilled in the art.

One of these drivers of optimum performance is the length of the waterline of the vessel, which should ideally be as long as practical. This is also desirable to minimise the vessel motions and to provide a comfortable ride. However a longer vessel involves a greater construction cost, and generally the extra length is not justified.

Another driver is the location of the centre of the immersed hull volume relative to the length of the vessel. The location is termed the Longitudinal Centre of Buoyancy (LCB), and experience has shown that for a low resistance it should be ideally located between 48% and 53% of the vessel length measured from the after end of the water line length of the vessel (for example Saunders H.E. "Hydrodynamics in Ship Design", Society of Naval Architects and Marine Engineers SNAME, New York, USA).

Another term used by those knowledgeable in the art, is the waterplane area, which describes the footprint of the vessel on the surface of the water. The centroid of this shape, the waterplane area, is called the Longitudinal Centre of Flotation (LCF).

On most conventional sea-going vessels, the LCF value is approximately similar to the LCB value, being within 5% at normal vessel draughts. Typically, the LCF value is between 43% and 53% of the vessel length measured from the after end of the water line length of the vessel.

Figures 1 and 2 of the drawings illustrate LCB and LCF positions of conventional hull configurations. Figure 3 is a view corresponding to Figure 1 for a three-hulled vessel.

In Figures 1 and 2, the vessel depicted comprises a hull 1 having a bow 2 and a stern 3. The design waterline is represented by the line denoted by reference numeral 4 and has length L. The LCB is denoted by reference numeral 5 and the LCF is denoted by reference numeral 6.

In Figure 3, the vessel is of three-hull configuration comprising a centrally located main hull 1 and two side hulls 7. The design waterline LCF have corresponding reference numerals to those used for the hull shown in Figures 1 and 2. The design waterline 4 is also shown for each side hull 7.

At high speed, typically above approximately 30 knots, the resistance and comfort factors dominate the design process. Additional vessel length becomes desirable in order to maximise speed for the available power, or to conversely reduce the power and hence fuel consumption for a given speed. A longer vessel will also generally have a lesser pitching, heave and yaw motions.

A three-hulled vessel, having a main central hull with two amahs or side hull is disclosed in US 6736080 (Armstrong). This type of vessel arrangement can usefully benefit from additional length when designed for high speed. When the three-hulled arrangement is designed for a high-speed ferry use, it is desirable to moor the vessel stern-on and to provide a wide stern such that the loading and unloading process can be rapidly achieved, as discussed in US5269245 to Bystedt and Toreskog. It is against this background that the present invention has been developed.

Disclosure of the Invention

According to a first aspect of the invention there is provided a vessel comprising a hull having an LCF at the design load waterline at rest with a value of less than about 35% of the vessel waterline length measured from the aftermost point of the vessel waterline.

Preferably, the LCF is between about 30% and 34% of the vessel waterline length measured from the aftermost point of the vessel waterline.

Preferably, the design vessel speed at design load waterline is at or above Froude Number of 0.45. Preferably, the main hull has a length-to-beam ratio on the design waterline of greater than about 8.0.

Preferably, the slenderness ratio of the vessel, described as the length on the design waterline divided by the cube root of the volume of displacement in consistent units, is greater than 7.0. Preferably, the vessel waterline length is between 24 metres and 250 metres.

Preferably, the LCB is between about 30% and 45% of the vessel waterline length measured from the aftermost point of the vessel waterline.

More preferably, the LCB is between 34% and 42% of the vessel waterline length measured from the aftermost point of the vessel waterline The vessel may comprise a single hull vessel. The vessel may comprise a multi-hulled vessel. The multi-hulled vessel may be configured as a trimaran comprising a centrally located main hull and two side hulls, wherein the main hull constitutes the hull in accordance with the invention.

The trimaran may be configured as a ferry. According to a second aspect of the invention there is provided a trimaran comprising a main hull and two side hulls, the main hull having a LCF at the design load waterline at rest with a value of less than about 34% of the vessel waterline length measured from the aftermost point of the vessel waterline.

Brief Description of the Drawings The invention will be better understood by reference to the following description of one specific embodiment thereof. The description will be made with reference to the accompanying drawings in which:

Figure 1 is a schematic plan view of the waterline of a conventional hull configuration, illustrating the LCF position; Figure 2 is a schematic side view of a conventional hull configuration, illustrating the LCF and LCB positions;

Figure 3 is a view similar to Figure 1 but for a conventional three-hull configuration;

Figure 4 is a schematic perspective underside view of the hull configuration of a three-hulled vessel according to the embodiment;

Figure 5 is a schematic plan view of the waterline of a conventional hull configuration, illustrating the LCF position; and

Figure 6 is a schematic side view of the main hull of the three-hulled vessel according to the embodiment, illustrating the LCF and LCB positions. Best ode(s) for Carrying Out the Invention

The embodiment shown in Figure 4 and 5 of the drawings is directed to a multi- hulled vessel 10 according to the embodiment. In the arrangement shown, the vessel 10 comprises a three-hulled vessel (being a trimaran) configured as high speed commercial or military vessel, such as a ferry, for passenger and cargo transport, including vehicle transport.

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

The triamaran 10 comprises an understructure 11 and a superstructure (not shown), both constructed primarily of aluminium. The waterline in relation to the understructure 11 is identified in Figure 3 by reference numeral 13.

The under structure 1 1 comprises a centrally located main hull 15 and two laterally spaced side hulls 16 commonly known as amahs.

The main 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 main hull 15 is represented by the line denoted by reference numeral 23 and has length L. The design waterline for each side hull 16 is represented by the line denoted by reference numeral 25. The LCB is denoted by reference numeral 27 and the LCF is denoted by reference numeral 29.

The superstructure (not shown) is configured such that the majority of the weight of the vessel lies in the after part of the vessel (aft of centre of the vessel measured along the waterline length), which for a level trim implies that the centre of buoyancy is also aft of amidships. Such an arrangement allows the vessel to be moored stern-on and provides a wide stern such that the loading and unloading process can be rapidly achieved. The main hull 15 extends forwardly beyond the useful cargo areas and especially the passenger cabin, in order to provide the longest practical hull within financial constraints.

By virtue of being constructed in accordance with the invention, the main hull 15 is designed for, and facilitates, implementation of this superstructure configuration. Specifically, the trimaran 10 has a Froude Number of greater than 0.45 and the main hull 15 has a length-to-beam ratio on the design waterline of greater than 8.0.

The main hull 15 has a LCB lying between 34% and 42% of the vessel waterline length measured from the aftermost point of the vessel waterline 23 which is represented by the value L. This position of the LCB is considerably further aft than the value used for the design of more convention vessels, as depicted in Figures 1, 2 and 3..

The main hull 15 also has a LCF at the design load waterline at rest with a value of less than about 35% of the vessel waterline length L measured from the aftermost point of the vessel waterline. More particularly, the LCF is preferably between about 30% and 34% of the vessel waterline length L.

This hull configuration offers relatively low resistance and also the possibility of improved comfort from the reduction of vertical acceleration. The LCB and LCF values described above are for the vessel floating at least at the design load waterline.

From the foregoing, it is evident that the present embodiment provides a vessel with a hull configuration which delivers improved performance while also accommodating a superstructure configured such that the majority of the weight of the vessel lies in the after part of the vessel. Such an arrangement allows the vessel to be moored stern-on and provides a wide stern such that the loading and unloading process can be rapidly achieved. Further, the centre hull extends forward beyond the useful cargo areas and especially the passenger cabin, in order to provide the longest practical hull within financial constraints. It should be appreciated that the scope of the invention is not limited to the scope of the embodiment described, and that various changes and modification may be made without departing from the scope of the invention.

While the embodiment has been described in relation to three-hull vessel, it should be understood that it may also be applicable to other hull configurations, including for example a single-hull configuration, a double-hull configuration (being a catamaran), and a pentamaran.

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. ^λ