WO2012174592A1

WO2012174592A1 - A multi-hulled vessel

Info

Publication number: WO2012174592A1
Application number: PCT/AU2012/000710
Authority: WO
Inventors: Neville Anthony Armstrong; David Raymond ELLERY
Original assignee: Austal Ships Pty Ltd
Priority date: 2011-06-24
Filing date: 2012-06-21
Publication date: 2012-12-27

Abstract

A marine vessel is disclosed that comprises at least 3 hulls. At least one of the hulls has a first hull part and a second hull part, the first hull part corresponding to about 60% of the maximum underwater length of the at least one hull, and the second hull part corresponding to about 40% of the maximum underwater length of the at least one hull. A first ratio between a maximum underwater plan area at the first hull part and a waterline plan area at the first hull part at any navigable waterline is greater than about 2.0. A second ratio between a maximum underwater plan area at the second hull part and a waterline plan area at the second hull part at any navigable waterline is less than the greater of about half the first ratio or about 1.15. The waterline plan area at the second hull part is greater than the waterline plan area at the first hull part.

Description

A MULTI-HULLED VESSEL

Field of the Invention This invention relates to a multi-hulled vessel of the type including at least 3 hulls.

Background of the Invention A catamaran type vessel that has a relatively large plan area below the waterline in order to maintain the vessel afloat and a relatively small plan area at the waterline in order to minimize excitation of the vessel due to wave motion is often referred to as a Small Waterplane Area Twin Hull or SWATH vessel.

A common problem with SWATH hull forms is that relatively large changes in draft can occur when the vessel is at rest and the load supported by the vessel changes, for example when loading and unloading cargo.

While SWATH type vessels typically include control devices for controlling resonance type motions, such control devices rely on water flow to be an effective force generator and are therefore ineffective at low and zero speeds .

Conventional type hulls, either monohull or multi-hull, also experience draft changes when loading and unloading but to a lesser extent than SWATHs because of the

relatively larger plan area at the waterline. A

relatively large plan area at the waterline, however, causes this type of conventional hull to also have large motions in waves. This is normally exacerbated at low and zero speeds and the largest motions normally occur at the bow. In some circumstances, for example servicing of off-shore installations, significant changes in draft at rest can be particularly problematic and dangerous, because servicing personnel and associated tools and parts are required to be moved between the vessel and the off-shore

installation. This is especially true of unmanned offshore installations such as wind farm turbine pylons that are not equipped with the cargo handling facilities that may be present on larger installations. Summary of the Invention

In accordance with a first aspect of the present

invention, there is provided a marine vessel comprising at least 3 hulls;

at least one of the hulls having a first hull part and a second hull part, the first hull part corresponding to about 60% of the maximum underwater length of the at least one hull, and the second hull part corresponding to the other about 40% of the maximum underwater length of the at least one hull;

wherein a first ratio between a maximum underwater plan area at the first hull part and a waterline plan area at the first hull part at any navigable waterline is greater than about 2.0;

wherein a second ratio between a maximum underwater plan area at the second hull part and a waterline plan area at the second hull part at any navigable waterline is less than the greater of about half the first ratio or about 1.15; and

wherein the waterline plan area at the second hull part is greater than the waterline plan area at the first hull part.

In one embodiment, the first hull part is disposed forwardly of the vessel and the second hull part is disposed rearwardly of the vessel.

In one embodiment, the at least one hull has a continuous form such that the waterline plan area transitions gradually to the maximum underwater plan area. In one embodiment, the at least one hull includes at least one appendage disposed so as to contribute to the maximum underwater plan area.

In one embodiment, the maximum width of the maximum underwater plan area at the first hull part is about the same as the maximum width of the waterline plan area at the second hull part.

In one embodiment, the vessel comprises 3 hulls. The at least one hull may be a central hull, and the vessel may include 2 side hulls, the total . underwater volume of the side hulls constituting less than about 20% of the total underwater volume of the vessel at any navigable

waterline .

In one embodiment, one or more of the hulls may be configured so as to generate lift in order to minimize resistance during use in transit. In accordance with a second aspect of the present

invention, there is provided a marine vessel comprising a substantially centrally disposed hull having a first hull part and a second hull part, and at least 2 other hulls; wherein a first ratio between a maximum underwater plan area at the first hull part and a waterline plan area at the first hull part at any navigable waterline is greater than about 2.0;

wherein the width of the waterline plan area at the second hull part is greater than the width of the

waterline plan area at the first hull part.

Brief Description of the Drawings

The present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic underside perspective view of a hull portion of a multi-hulled vessel in accordance with an embodiment of the present invention;

Figure 2 is a diagrammatic side view of the hull portion shown in Figure 1; and Figure 3 is a underside plan view of the hull portion shown in Figures 1 and 2 showing respective waterline plan areas of a central hull and side hulls of the vessel. Description of an Embodiment of the Invention

Referring to the drawings, there is shown a hull portion 10 of a marine vessel of the type including at least three hulls. In this example, the vessel is of trimaran type and accordingly includes three hulls.

The hull portion 10 in this example is configured so as to include a relatively large central hull 12 that supports^' most of the weight of the vessel, and two side hulls 14, often referred to as "amahs" or "amas", that support a relatively small proportion of the weight of the vessel and serve as floats to maintain the desired orientation of the vessel relative. to the waterline. However, it will be understood that other types of■ trimaran are envisaged. For example, a trimaran may be provided wherein the weight of the vessel is supported more evenly across the hulls, with the side hulls also serving to support a significant amount of the weight of the vessel as well as to maintain the desired orientation of the vessel relative to the waterline.

In the present embodiment, the side hulls 14 have a combined underwater volume that is at most about 20% of the total underwater volume of the hull portion 10. This type of vessel allows for favourable roll accelerations whilst still enabling a designer to retain suitable stability for safety regulations. Low vertical accelerations occur at the bow b virtue of the shape of the central hull 12 and low roll accelerations occur by virtue of the small side hull configuration.

The central hull 12 is configured such that a frontmost part of the central hull 12 is of SWATH-like form, that is, having a relatively large plan area below the

waterline and a relatively small plan area at the

waterline, and. a rearmost part of the central hull 12 is of non-SWATH like form, in this example of conventional form having a plan area that does not significantly change between a lowermost part of the hull and the waterline.

In the present example, the central hull 12 includes a first hull part, in this example a front hull portion 16, of SWATH-like form and a second hull part, in this example an aft hull portion 18, of non-SWATH like form, with the front and aft hull portions 16, 18 identified conceptually in the Figures by a virtual line 19 disposed at a location from the rear of the vessel corresponding to about 40% of the maximum underwater length (L) of the vessel. In addition, the width of the waterline plan area of the central hull 12 increases from the front hull portion 16 to the aft hull portion 18 such that the waterline plan area at the aft hull portion 18 is larger than the waterline plan area at the front hull portion 16.

It will therefore be understood that the front hull portion 16 has a relatively small waterline plan area, and the aft hull portion 18 has a relatively large waterline plan area. This contributes to providing a sea going vessel that is optimised for reduced vertical motions at low speeds especially near the forward end of the vessel, while still retaining features for transit speeds.

The transit speeds would be individually suited to each vessel and operator. However, it would be expected to be greater than 15 knots and normally greater than 20 knots. Vessel speeds are often expressed by a non-dimensional number called a Froude number. The Froude number Fr is given by:

V

Where V is the vessel speed, L' is the waterline length and g is the acceleration due to gravity. The transit speeds for vessels according to embodiments of the invention would typically have an associated Froude number between about 0.4 and about 1.1, which corresponds to the speed range that is sometimes referred to as characteristic of semi-planing vessels.

·

As vessels travel through waves, the average resistance to forward motion increases with increasing wave height. The average resistance to forward motion- is also proportional to vertical vessel motions. With the present vessels, such vertical motions are reduced at low speeds, and these reductions of motions may also be seen at transit speeds. With the present vessels, therefore, the increased resistance in waves as the wave height increases will be relatively small, thereby allowing for faster transit times in waves and generally more efficient operation.

It will be appreciated that the relatively small waterline plan area of the front hull portion 16 may result in a fine angle of entrance at the bow. The fine entrance angle may reduce the waves produced by the bow at transit speeds and, as a consequence, will for example have less environmental impact if the vessel is travelling near shorelines .

In order to achieve the desired characteristics at low and zero speeds without unduly compromising transit speed properties, the shape of the central hull 12 is configured according to hull plan area ratios as follows.

The hull plan area ratios are determined by considering the plan areas at any navigable waterline and the maximum underwater plan area. The maximum underwater plan area is determined by the outer envelope of all the plan areas beneath the navigable waterline. Plan areas used to determine the hull plan area ratios in the present invention are shown in the plan view in Figure 3. As shown, for the central hull 12, a waterline plan area 30 increases in width from a frontmost part 40 of the vessel to a rearmost part 42 of the vessel. The maximum

underwater plan area of the central hull 12 is marked by reference numeral 32, and the waterline plan areas for the side hulls 14 are marked by reference numeral 34. For the front hull portion 16, a first ratio between the maximum underwater plan area at the front hull portion 16 and the waterline plan area at the front hull portion 16 at any navigable waterline is greater than about 2.0. For the aft hull portion 18, a second ratio between the maximum underwater plan area at the aft hull portion 18 and the waterline plan area at the aft hull portion 18 at any navigable waterline is less than the greater of half the first ratio or about 1.15. In this example, the aft hull ratio is greater than 1.0 in order to allow for a faired hull shape. Where the front hull portion has a ratio significantly greater than 2.0 an increase in the aft area may be required to account for the fairing required for a smooth hull transition to this large forward ratio. As such, the aft ratio may increase to as much as about half the forward ratio to account for this additional fairing. It will be understood that a ratio of 1.0 has no SWATH like properties as the underwater area is no greater than the waterplane area.

While the above embodiment is described in relation to a trimaran having a relatively large central hull and relatively small side hulls, it will be understood that other implementations are possible. For example, an embodiment of the invention could comprise a multihull vessel wherein the hulls are of similar volume and shape to each other and the shape of each hull conforms to the plan view area ratios described above. This could include a trimaran vessel with 3 similar hulls where the side hulls have a combined underwater volume greater than 50% of the total underwater volume.

It will also be understood that variations that include multiple numbers of hulls greater than 3, in some

embodiments an odd number of hulls such as 5 or 7, are also envisaged.

Moreover, while the above embodiment is described in relation to a vessel having at least a central hull with a frontmost part of SWATH like form, and a rearmost part of non-SWATH like form, it will be understood that these parts may be reversed; that is, the frontmost part of may be of non-SWATH like form, and the rearmost part may be of SWATH like form. With this alternative arrangement, it will be understood that the aft hull portion may

correspond to a region extending from the rear of the vessel corresponding to about 60% of the maximum

underwater length (L) of the vessel.

It will also be appreciated that instead of or in addition to achieving motion damping by providing a continuous hull form that is relatively thin at the waterline and

increases in width below the waterline, similar damping could be achieved using suitable appendages under the waterline attached to the hull. With this arrangement, it will be understood that the appendages are considered part of the hull form and contribute to the underwater plan area of the SWATH like hull form. Such appendages that are configured to contribute to increasing the underwater plan area and thereby contribute to motion damping are distinct from other appendages that do not provide a significant contribution to vertical motion damping, such as vertical rudders and structural support for propeller shafts .

Preferably the side hulls are significantly shorter in waterline length than the central hull. Typically, the waterline length of the side hulls is between about 30% to 60% of the waterline length of the central hull. With this shorter length, the side hulls are often located towards the aft portion of the central hull so that the waterplane area of the side hulls is longitudinally aligned with the larger waterline area of the central hull. It is of lesser importance to align the side hulls with the main hull if the side hulls only support a small fraction of the vessel buoyancy, because typically the smaller buoyancy only has a small effect on vertical motions of the vessel. It will be understood that the side hulls may also extend outside the extents of the main hull. This can be useful if the vessel is propelled by waterjets or has some other appendage aft of the main hull, since for example the side hulls may serve to protect the appendages.

. .

The low roll accelerations inherent in good trimaran design can be further improved by utilizing motion control systems, for example of the type including roll fins or other motion control surfaces, anti-roll tanks, gyroscopic stabilizers or similar. These surfaces could also be configured to further reduce the vertical motions of the vessel as well as minimise roll motions.

In an example vessel according to an embodiment of the present invention, the maximum underwater length of the vessel is 32m. In a typical loading condition, the total volume displaced is about 105 cubic metres, with a combined side hull volume of 12 cubic metres split evenly between the two side hulls. The design transit speed is about 24 knots which for this vessel corresponds to a

Froude number of 0.7. The total waterline plan area may be about 49.6 square metres, split at 60% of the maximum underwater length from the forward end of the vessel such that the waterline plan area at the front hull portion is about 17.8 square metres and the waterline plan area at the aft hull portion is about 31.8 square metres. The maximum underwater plan area in. this example is about 75.6 square metres, split at 60% of the maximum underwater length from the forward end of the vessel with 41.2 square metres in the front hull portion and 34.4 square metres in the aft hull portion. This produces a first ratio at the front hull portion between the maximum underwater plan area and the waterline plan area of 2.31, and a second ratio at the aft hull portion between the maximum

underwater plan area and a waterline plan area of 1.08.

Modifications and variations as would be apparent to a skilled addressee are deemed to be within the scope of the present invention.

Claims

CLAIMS :

1 . A marine vessel comprising at least 3 hulls;

at least one of the hulls having a first hull part and a second hull part, the first hull part corresponding to about 60% of the maximum underwater length of the at least one hull, and the second hull part corresponding to about 40% of the maximum underwater length of the at least one hull;

wherein a first ratio between a maximum underwater plan area at the first hull part and a waterline plan area at the first hull part at any navigable waterline is greater than about 2 . 0 ;

wherein a second ratio between a maximum underwater plan area at the second hull part and a waterline plan area at the second hull part at any navigable waterline is less than the greater of about half the first ratio or about 1 . 15 ; and

2 . . A marine vessel as claimed in claim 1 , wherein the first hull part is disposed forwardly of the vessel and the second hull part is disposed rearwardly of the vessel.

3 . A marine vessel as claimed in claim 1 or claim 2 , wherein the at least one hull has a continuous form such that the waterline plan area transitions gradually to the maximum underwater plan area.

4 . A marine vessel as claimed in claim 1 or claim 2 , wherein the at least one hull includes at least one appendage disposed so as to contribute to the maximum underwater plan area.

5. A marine vessel as claimed in any one of the

preceding claims, wherein the maximum width of the maximum underwater plan area at the first hull part is about the same as the maximum width of the waterline plan area at the second hull part.

6. A marine vessel as claimed in any one of the

preceding claims, wherin the vessel comprises 3 hulls..

7. A marine vessel as claimed in claim 6, wherein the at least one hull is a central hull, and the vessel comprises 2 side hulls, the total underwater volume of the side hulls constituting less than about 20% of the total underwater volume of the vessel at any navigable

waterline.

8. A marine vessel as claimed in any one of the

preceding claims, wherein a plurality of the hulls of the vessel but not all of the hulls each have a first hull part and a second hull part, the first hull part

corresponding to about 60% of the maximum underwater length of the at least one hull, and the second hull part corresponding to about 40% of the maximum underwater length of the at least one hull;

wherein a first ratio between a maximum underwater plan area at the first hull part and a waterline plan area at the first hull part at any navigable waterline is.

greater. than about 2.0;

wherein the waterline plan area at the second hull 5 part is greater than the waterline plan area at the first hull part.

9. A marine vessel as claimed in any one of claims 1 to 7, wherein each hull of the vessel has a first hull part l^'o and a second hull part, the first hull part corresponding to about 60% of the maximum underwater length of the at least one hull_r and the second hull part corresponding to about 40% of the maximum underwater length of the at least one hull;

15 wherein a first ratio between a maximum underwater plan area at the first hull part and a waterline plan area at the first hull part at any navigable waterline is greater than about 2.0;

wherein a second ratio between , a maximum underwater

20 plan area at the second hull part and a waterline plan area at the second hull part at any navigable waterline is less than the greater of about half the first ratio or about 1.15; and

wherein the waterline plan area at the second hull

25 part is greater than the waterline plan area at the first hull part .

10. A marine vessel as claimed in any one of the

preceding claims, wherein one or more of the hulls is

30 configured so as to generate lift during use.

11. A marine vessel comprising a substantially centrally disposed hull having a first hull part and a second hull part, and at least 2 other hulls;

wherein a second ratio between a maximum underwater plan area at the second hull part and a waterline plan area at the second hull part at any navigable waterline is less than the greater of about 1.15 or about half the first ratio; and

wherein the waterline plan^' area at the second hull - part is greater than the waterline plan area at the first hull part.

.

12. A marine vessel as claimed in claim 11, wherein the first hull part is disposed forwardly of the vessel and the second hull part is disposed rearwardly of the vessel.

13. A marine vessel as claimed in claim 11 or claim 12, wherein the centrally disposed hull has a continuous form such that the waterline plan area transitions gradually to the maximum underwater plan area.

14. A marine vessel as claimed in claim 11 or claim 12, wherein the centrally disposed hull includes at least one appendage disposed so as to contribute to the maximum underwater plan area.

15. A marine vessel as claimed in any one of claims 11 to 14, wherein the maximum width of the maximum underwater plan area at the first hull, part is about the same as the maximum width of the waterline plan area at the second hull part.

16. A marine vessel as claimed in claim 6, wherein the vessel comprises 2 side hulls, the total underwater volume of the side hulls constituting less than about 20% of the total underwater volume of the vessel at any navigable waterline.

17. A marine vessel as claimed in any one of claims 11 to 16, wherein the first hull part corresponds to about 60% of the maximum underwater length of the at least one hull, and the second hull part corresponds to about 40% of the maximum underwater length of the at least one hull.

18. A marine vessel substantially as hereinbefore described with reference to the accompanying drawings.