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Title:
ROUND-BILGE HULL FORM WITH BULBOUS BOW, SPRAY RAILS AND DYNAMIC TRIM CONTROL FOR HIGH SPEED
Document Type and Number:
WIPO Patent Application WO/2011/126358
Kind Code:
A1
Abstract:
The invention pertains to a vessel for operating on water comprising, a round-bilge hull (1) hull having a design waterline (9), a length at the design waterline LwI, a maximum beam at said design waterline Bwi situated aft of the mid- length of that waterline, and a centre-line buttock (7) which forms the deepest part of the hull from the bow to a position short of the mid- length of the design waterline, and then runs aft in a smooth curve, at a shallow angle relative to the horizontal, a bulb (15) at the bow to further reduce hydrodynamic resistance and to widen the hull at the bow below the design waterline without increasing the entry angle of the relative waterlines there, with a length and width, and with the widest part located relatively close to the design water line, a spray rail (18) on, or integrated into, the fore-body of the hull and a trim device (21) fitted at or near the transom stern for controlling the running trim of the vessel.

Inventors:
VAN OOSSANEN, Pieter Gerrit (Sparrenbos 33, BB Wageningen, NL-6705, NL)
VAN OOSSANEN, Pieter (Sparrenbos 33, BB Wageningen, NL-6705, NL)
Application Number:
NL2010/050180
Publication Date:
October 13, 2011
Filing Date:
April 06, 2010
Export Citation:
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Assignee:
Van Oossanen & Associates B.V. (Sparrenbos 33, BB Wageningen, NL-6705, NL)
VAN OOSSANEN, Pieter Gerrit (Sparrenbos 33, BB Wageningen, NL-6705, NL)
VAN OOSSANEN, Pieter (Sparrenbos 33, BB Wageningen, NL-6705, NL)
International Classes:
B63B1/04; B63B1/06; B63B1/08; B63B39/06
Domestic Patent References:
WO1997043169A11997-11-20
WO1995016603A21995-06-22
Foreign References:
FR2600614A11987-12-31
GB1056033A1967-01-25
GB1361936A1974-07-30
US5263432A1993-11-23
DE3031239A11982-04-01
DE1506185A11969-06-19
GB2262718A1993-06-30
US4261278A1981-04-14
US2288490A1942-06-30
Other References:
TAYLOR DAVID W: "Influence of the Bulbous Bow on Resistance", MARINE ENGINEERING AND SHIPPING AGE, ALDRICH PUBL. COMP. & SIMMONS-BOARDMAN PUBL. COMP, vol. XXVIII, no. 9, 1 September 1923 (1923-09-01), pages 540, XP008117307, ISSN: 0272-2895
Attorney, Agent or Firm:
Ketelaars, Maarten (J.W. Frisolaan 13, JS The Hague, NL-2517, NL)
Download PDF:
Claims:
CLAIMS

A vessel for operating on water comprising:

a round-bilge hull having minimal hydrodynamic resistance, said hull having a design waterline, a length at the design waterline Lwi, a maximum beam at said design waterline Bwi situated aft of the mid-length of that waterline, and a centre-line buttock which forms the deepest part of the hull from the bow to a position short of the mid-length of the design waterline, and then runs aft in a smooth curve, at a shallow angle relative to the horizontal, selected to provide a draught of the hull at the transom which is small in relation to the maximum draught of the hull;

a bulb at the bow to further reduce hydrodynamic resistance and to widen the hull at the bow below the design waterline without increasing the entry angle of the relative waterlines there, with a length and width, and with the widest part located relatively close to the design water line;

a spray rail on, or integrated into, the fore-body of the hull and adapted to deflect the spray caused by the bow wave sideways, away from the deck and superstructure, and

a trim device fitted at or near the transom stern for controlling the running trim of the vessel.

The vessel of claim 1 , wherein the design waterline has an angle of entrance at the bow of between 35Bwi/Lwi degrees and 90Bwi/Lwi degrees.

The vessel of claim 1 or 2, wherein the design waterline gradually widens from the bow to where it attains the maximum beam Bwi at between 55% and 80% of the length of the design waterline Lwl from the forward extremity thereof.

The vessel of any one of the preceding claims, wherein the design waterline narrows aft of the location where it attains the maximum beam Bwl, reaching a beam at the transom of between 80% and 95% of the maximum beam of the design waterline Bwi.

5. The vessel of any one of the preceding claims, wherein the centre-line buttock forms the deepest part of the hull from the bulb to where this buttock starts to sweep aft and upwards towards the transom, in an embodiment at a location of between 25% and 50% of the length of the design waterline Lwl aft of the forward extremity thereof.

6. The vessel of claim 5, wherein the centre-line buttock runs upwards and aft towards the transom from in front of the mid-length of the design waterline, in a smooth curve such that the tangent to this buttock at the location of the transom makes an angle with the horizontal of between 2° and 8°.

7. The vessel of claims 6 or 7, wherein the centre-line buttock intersects the transom such that the draught at the bottom of the transom is no more than between 0% and 35% of the maximum draught of the hull, when the vessel floats on the design waterline, without bow-down or stern-down trim.

8. The vessel of any one of the preceding claims, wherein the location of the

transverse section at which the underwater transverse-sectional area is greatest, is located close to the mid-length location of the design waterline.

9. The vessel of claim 8, wherein the location at which the underwater transverse- sectional area is greatest is between 42.5% and 60%> of the length of the design waterline Lwl from the forward extremity thereof. 10. The vessel of any one of the preceding claims, wherein the bulb at the bow allows for the local widening of the waterlines of the underwater part of the hull without causing the angle of entrance of those waterlines to become anything but sharp.

11. The vessel of claim 10, wherein the length of the bulb forward of the forward

extremity of the design waterline is between 4% and 12% of the length of the design waterline Lwl.

12. The vessel of claims 10 or 11, wherein the maximum width of the bulb forward of the forward extremity of the design waterline is between 12% and 24% of the maximum beam of the design waterline Bwi.

13. The vessel of any one of claims 10-12, wherein the location of the maximum width of the bulb is located at a draught of between 30% and 60% of the maximum draught of the hull.

14. The vessel of anyone of claims 10- 13, wherein the cross-sectional area of the bulb at the forward extremity of the design waterline is between 10% and 20% of the maximum underwater cross-sectional area of the hull.

15. The vessel of any one of claims 10-14, wherein the angle of the tangent to the

bottom of the bulb, in the transverse section at the forward extremity of the design waterline, relative to the horizontal, is between 25 and 50 degrees.

16. The vessel of any one of the preceding claims, wherein the spray rail on the fore- body of the hull runs from the stem of the vessel to a location at or forward of the mid-length of the design waterline.

17. The vessel of claim 16, wherein the spray rail is situated higher at the forward end than at the aft end.

18. The vessel of claim 16 or 17, wherein the height of the forward end of the spray rail above the design waterline is at least 20% of the freeboard of the hull at the stem.

19. The vessel of any one of claims 16-18, wherein the aft end of the spray rail is

located just above or below the design waterline, with the distance between the spray rail from the design waterline at that position being between 0% and 10% of the height of the stem.

20. The vessel of any one of claims 16-19, wherein the length of the spray rail varies from between 30%> and 50%> of the length of the design waterline Lwl.

21. The vessel of any one of claims 16-20, wherein the width of the spray rail varies along its length.

22. The vessel of any one of claims 16-21 , wherein the width of the spray rail tapers to zero at the forward and aft extremities.

23. The vessel of any one of claims 16-22, wherein the location of the maximum width of the spray rail is between 0% and 15% of the length of the design waterline Lwl, aft of the forward extremity thereof.

24. The vessel of any one of claims 16-23, wherein the maximum width of the spray rail is between 175 mm and 400 mm, in an embodiment has an angle pspray between 0 and 15 degrees relative to the horizontal, and in an embodiment has a fillet below the spray rail at the location where the spray rail intersects the hull, in an embodiment with a radius of between 25 mm and 100 mm.

25. The vessel of any one of the preceding claims, wherein a trim-control device is added to the aft-body or the transom, in an embodiment said trim-control device comprising an interceptor or a flap.

26. The vessel of claim 25, wherein the trim-control device is an interceptor which is mounted on the transom and protrudes into the flow below the transom by an amount varying between 0 mm and 100 mm, depending on the speed.

27. The vessel of claim 25, wherein the trim-control device is a flap which is mounted on the transom and controlled by actuators, in an embodiment hydraulic cylinders, to vary the angle of the flap, depending on the speed. 28. The vessel of claims 27, wherein the flap has a longitudinal length of between 0.5% and 2.5% of the length of the design waterline Lwl.

29. The vessel of any one of claims 27 or 28, wherein the flap has a setting

corresponding with an angle of between 0 and 10 degrees relative to the horizontal.

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Description:
ROUND-BILGE HULL FORM WITH BULBOUS BOW, SPRAY RAILS AND DYNAMIC TRIM CONTROL FOR HIGH SPEED

BACKGROUND OF THE INVENTION

1. Field of the invention

The present invention relates to a vessel comprising a round-bilge hull with a bulb at the bow, a spray rail on the fore-body and means to control the running trim of the hull.

2. Description of the prior art

Usually a vessel has a hard-chine hull form when higher speeds are required. A hard- chine hull utilizes a phenomenon known as planing whereby the hull is partially lifted from the water due to the lift force developed on the bottom. Such hull forms, however, have a high hydrodynamic resistance at lower speeds, requiring a relatively high engine power at those speeds.

An example of a hard-chine hull form is found in US patent 2,288,490 which shows the typical box-shaped transverse-sections along the hull, with a knuckle at the bottom on the centre-line of the hull and at the bottom of each of the sides. This is the type of shape of most vessels that have speeds in excess of what is termed the "hull speed", corresponding with a Froude number value of around 0.4. The Froude number is defined by:

Fn = v/V(g.L wl ) in which v = speed in m/sec, g = the acceleration due to gravity (9.81 m/sec 2 ), and L wl = length of the design water line in m. The start of the fully planing speed regime corresponds with a Froude number value of around 1.0. When this type of vessel operates at less than fully planing speeds, in the Froude number interval of between 0.4 and 1.0, the hull hard-chine hull form is usually referred to as a semi-planing hull or a semi-displacement hull. The running trim of a hard-chine hull form varies over the speed range from 0 degrees at very low speeds to running trim angles as high as 6 degrees or more, depending on the length-beam ratio of the hull. Although high trim angles enhance the development of lift forces on the bottom of a hard-chine hull, such trim angles are experienced as hindering the comfort on board, the line of sight from the bridge on larger vessels and, above-all, usually results in an increase in hydro dynamic resistance.

The hard-chine hull form at higher speeds operates on the surface of the water, making it susceptible to the roughness of the water suface.

The round-bilge hull form is the most common type of hull form used for vessels with speeds up to a Froude number value of around 0.4. This hull form does not allow for the development of meaningful dynamic lift on the bottom, and this type of hull is fully supported by the hydrostatic pressure force associated with the immersed volume of the hull, according to Archimedes' Law. This hull form is usually referred to as a displacement hull. The round-bilge hull form is not lifted out of the water, it pierces the water. This renders the hull less susceptible to the roughness of the water surface.

Vessels with round-bilge hull forms usually experience a significant increase in hydrodynamic resistance when driven to speeds greater than the hull speed, in the Froude number range beyond 0.4. This requires a significant increase in engine power. Round-bilge hulls are therefore not often used when speeds are in the range between Froude numbers of 0.4 and 1.0.

In order to obtain a grasp of the relationship between Froude number, waterline length and forward speed, a table is inserted showing the relationship for a Froude number of 0.4 and of 1.0.

Waterline length (m) Speed (knots) for Fn = 0.4 Speed (knots) for Fn

10 7.7 19.3

20 10.9 27.2

30 13.3 33.3

40 15.4 38.5

50 17.2 43.1 60 18.9 47.2

70 20.4 50.9

80 21.8 54.5

90 23.1 57.8

100 24.4 60.9

150 29.8 74.6

200 34.4 86.1

An overview of the prior art is further described in a paper entitled: "Motor Yacht Hull Form Design for the Displacement to Semi-Displacement Speed Range", presented on 7 th October 2009, and afterwards published in the Proceedings of the 10 th International Conference on Fast Sea Transportation, "FAST 2009", Athens, Greece. The principal author of this paper is one of the inventors. The paper does not provide any details of the geometry of the vessel of the current invention.

SUMMARY OF THE INVENTION

1. Aim of the invention

The invention is aimed at reducing the hydrodynamic resistance of a vessel and hence at reducing the required engine power for a particular speed in comparison to other types of vessels. In particular, the invention seeks to reduce the hydrodynamic resistance in the speed range between a Froude number value of 0.4, that is the hull- speed, up to fully planing speeds, that is up to speeds corresponding with a Froude number value of 1.0.

Another or alternative object of the invention is to reduce the so-called running trim of the vessel over this speed range to no more than 1.0 or 1.5 degrees.

Another or alternative object of the invention in extending the applicability of the round-bilge hull form to higher speeds, is to secure more comfortable motion characteristics in waves in comparison to those experienced with hard-chine hull forms.

2. Description of the invention In order to achieve at least one of the objectives of the invention, the invention provides a vessel for operating on water comprising:

a round-bilge hull having minimal hydrodynamic resistance, said hull having a design waterline, a length at the design waterline L w i, a maximum beam at said design waterline B w i situated aft of the mid-length of that waterline, and a centre-line buttock which forms the deepest part of the hull from the bow to a position short of the mid-length of the design waterline, and then runs aft in a smooth curve, at a shallow angle relative to the horizontal, selected to provide a draught of the hull at the transom which is small in relation to the maximum draught of the hull;

a bulb at the bow to further reduce hydrodynamic resistance and to widen the hull at the bow below the design waterline without increasing the entry angle of the relative waterlines there, with a length and width, and with the widest part located relatively close to the design water line, and

- a spray rail on, or integrated into, the fore-body of the hull and adapted to deflect the spray caused by the bow wave sideways, away from the deck and superstructure, and

a trim device fitted at or near the transom stern for controlling the running trim of the vessel.

The invention in particular relates to the shape of the hull of a vessel, like a boat, yacht or ship, intended for high speeds. This hull has a round-bottomed shape, also referred to as a round-bilge shape, with a specific form. Furthermore, it has a specific form of bulb at the bow, spray rails on the fore-body, and means to control the longitudinal running attitude of the hull, hereafter called "running trim". The combined effect of these measures in particular leads to low hydrodynamic resistance, little or no running trim, and comfortable motions in waves, over a specific range of speeds

In particular when operating the vessel at Froude number values between 0.4 and 1.0, the hull of the vessel of the invention has superior performance over other types of hull forms. The invention in particular relates to the underwater shape of a round-bottomed hull with a specific shape and distribution of the volume over the length, fitted with a specific type of bulbous bow, and fitted with so-called spray rails on the fore body. Means to control the running trim are also fitted at, or near, the transom.

The shape of the hull according to the invention will not perform worse than existing hull shapes at speeds below Fn = 0.4. At speeds with Fn between 0.4 and 1.0, in particular, advantages will be significant. For instance, the advantages will occur for smaller vessels such as boats and small yachts if such vessels operate at speeds below about 19.3 knots when having a waterline length of 10 m, below about 27.2 knots when having a waterline length of 20 m, etc. The applicability of the invention for larger yachts is greater in terms of the range in speed, with the applicable speed range extending up to 33.3 knots for a waterline length of 30 m, and up to 43.1 knots for a waterline length of 50 m, etc.

In describing the invention use is made of standard naval architecture definitions and parameters. Particularly important in this regard are the so-called waterlines and buttocks. Waterlines are the curved lines obtained when a horizontal plane intersects the hull at various heights, and buttock curves are obtained when a vertical plane parallel to the symmetry plane of the hull intersects the hull. In this respect, the vertical plane of symmetry is defined as the vertical longitudinal plane at the centre-line of the hull. Also important are the transverse-sectional shapes of the hull at specific length positions. Reference is also made to the fore body of the hull which is the forward half of the hull, and the aft body, which is the aft half of the hull. The hull form here considered usually has a stem contour and a transom-type stern. The profile of the hull in elevation view is also the shape of the centre-line buttock. The top of the hull is bounded by the sheer line. Furthermore, a design waterline is defined as the waterline on which the hull floats when in the design condition, that is the condition in which the vessel has the so-called design load (cargo, passengers, and/or fuel and fresh water, etc) on board.

To reduce the formation of waves, and thus to reduce the hydrodynamic resistance at higher speeds, the fore body of the invention is unusually slender. In particular, the design waterline gradually widens from the bow to where the hull has its maximum beam. The location of this maximum beam position is well aft of the mid-length position of the design waterline. Aft of this maximum beam position the design waterline becomes narrower again, but still retains nearly the maximum width at the transom. The angle of entrance of the design waterline is small and reflects the slenderness of the fore body.

Contrary to the shape of the design waterline, the centre-line buttock achieves its maximum depth at the bow, directly aft of the location of the bulb. It further retains this depth for less than half the length of the hull. It then runs aft from there in a smooth curve, at a shallow angle relative to the horizontal, such that the depth of the hull at the transom is less than is usually the case, when floating on the design waterline.

The location of the transverse section at which the underwater transverse-sectional area is greatest, is close to the mid-length location of the design waterline, even though the waterline beam reaches its greatest beam well aft of this location. This is due to the fact that the depth of the hull steadily decreases from in front of the mid-ship location, towards the transom. To further reduce the hydrodynamic resistance of the hull and to widen the waterlines situated below the design waterline at the bow, so as to be able to add volume to the hull in that region without increasing the entry angle of the waterlines, a bulb is fitted which has a large length, and a significant width. The bottom of the bulb in an embodiment has a pronounced V-shape in cross-section to reduce the extreme wave loads on the hull in that area, when operating in high waves. The cross-sectional area of the bulb, at the transverse section at the forward extremity of the design waterline is relatively large.

To deflect the spray caused by the bow wave at high speed away from the deck of the vessel, a so-called spray rail is added. In a particular embodiment, it is integrated into the fore body. The length and position of the spray rail is chosen so as to be most effective in deflecting the spray. The preferred length of the spray rail is less than 50% of the length of the design waterline. The preferred width of the spray rail varies but at the location where the bow wave is highest the spray rail is up to 400 mm wide and, in a particular embodiment, reduces in width forward and aft of this location.

It is necessary to control the running trim of the hull at higher speeds and this is done by adding a trim-control device to the aft body of the hull, in a particular embodiment, at the transom. There is more than one way of achieving this. Use can be made of a so- called interceptor, or a flap, or some other means by which the stern is lifted to counteract the natural tendency of the hull to lift at the bow and to sink at the stern at higher speeds. It is advantageous to adopt means whereby the running trim of the hull can be fine-tuned by adjusting the depth of the interceptor or the angle of the flap.

An interceptor is a flat plate fitted to the transom such that this protrudes into the flow below the hull. The flow is deflected downwards at that location because of the protruding plate into the flow, which deflection causes a lift force at that location, lifting the stern of the vessel.

A flap can also be used for this purpose. Here too, the flap can be attached to the transom. In an embodiment, the orientation of the flap can be adjusted by means of actuators, for instance by means of hydraulic cylinders. The angle of the flap relative to the horizontal can thus be adjusted by adjusting the length of the cylinders. This also causes the flow to deflect downwards, thereby causing a lift force on the hull at the stern.

The invention, as thus described, pertains to the hull of a vessel comprising four features. The first of these is the slender hull as depicted by the shape of the design waterline and the centre-line buttock, the second is the long and voluminous bulb at the bow, the third is the spray rail on the fore body, and the fourth is a device fitted near the stern for controlling the running trim. All these features are part of the invention but each feature has more than a single embodiment.

The invention further pertains to a vessel comprising one or more of the characterising features described above and/or shown in the attached drawings. The invention further pertains to a method comprising one or more of the characterising features described in the description and/or shown in the attached drawings.

The various aspects discussed in this patent can be combined in order to provide additional advantages. Furthermore, some of the features can form the basis for one or more divisional applications

DESCRIPTION OF THE DRAWINGS The invention will be further elucidated by referring to the attached drawings, showing in:

Figure 1 an elevation view of the hull of a vessel;

Figure 2 a plan view of the hull of the vessel of figure 1 ;

Figure 3 the transverse-sectional shapes of the hull of figure 1;

Figure 4 the particular shape of the design waterline of the invention;

Figure 5 the shape of the centre-line buttock of the hull of figure 4;

Figure 6a the forward part of figure 5;

Figure 6b the shape of the transverse section at the forward extremity of the design waterline;

Figure 7a the position of the spray rail on the fore body;

Figure 7b the preferred shape of the transverse-section in way of the spray rail;

Figure 8 an interceptor fitted to the transom of the hull of figure 5, and

Figure 9 the alternative of a flap fitted to the transom of the hull of figure 5. In Fig. 1 an elevation view is shown of the hull of a vessel (1), with a fore body (2), an aft body (3), showing the sheer line forming the upper bound of the hull (4). The stem (5) is shown and also the transom stern (6). The profile of the vessel is given by the centre-line buttock (7), forming the bow, bottom and stern of the vessel. Other buttocks (8) are shown, as well as the design waterline (9) and other waterlines (10).

Figure 2 shows a plan view of the hull of a vessel, indicating the design waterline (9), other waterlines (10), the sheer line (4), the centre-line buttock (7) and other buttocks (8), and the transom stern (6). The ordinate (length) positions of the sections, displayed in the so-called body plan, are also shown (11).

Figure 3 shows the transverse-sectional shapes of the hull of a vessel. This view is commonly referred to as the body plan. The main feature shown here are the section shapes (12). Shown are also the sheer line (4), the centre-line buttock (7), other buttocks (8), the design waterline (9), and other waterlines (10).

Figure 4 shows the particular shape of the design waterline of the invention. The design waterline widens from the bow to where the hull has its maximum beam (13), at a length of L from the forward extremity of the design waterline. Aft of this maximum beam position the design waterline becomes narrower until, at the transom, this waterline has a width B t , which is less than the maximum width of the design waterline B w i. The angle of entrance of the design waterline (14), denoted as , is small and depends on the value of the beam- length ratio B wl /L wl .

Figure 5 shows the shape of the centre-line buttock (7) which attains its maximum depth at the location of the bulb (15) and before reaching the mid-length location of the design waterline (16) starts to lift to gradually run aft from there in a smooth curve, at a shallow angle to the horizontal (ο¾), such that the draught of the hull at the transom (T t ) is small in relation to the maximum draught of the hull (T), when floating on the design waterline.

Figure 6a shows the bulb (15), with a length (L bu i b ). Shown also is the location of the transverse-section at the forward extremity of the design waterline (17), the sheer line (4), the stem profile (5), the design waterline (9) and the bottom of the hull (7).

Figure 6b shows the shape of the transverse section at the forward extremity of the design waterline (17). The bulb there has a maximum width (B bu i b ). The location of the maximum width of the bulb relative to the water surface, at a depth (T B buib), is also shown. The angle of the tangent to the shape of the bottom of the bulb at the centreline, relative to the horizontal, is indicated by Pbuib- Figure 7a shows the position of the spray rail (18) on the fore body (2), the sheer line (4), the stem (5), the transom (6), the design waterline (9), the profile of the hull (7), and the bulb (15). The height of the spray rail where this intersects the stem is indicated (Fspray). The spray rail has a length indicated by L spray .

Figure 7b shows the preferred shape of the transverse section in way of the spray rail. The width of the spray rail (B spray ) varies along the length. It is small or zero at the stem, widening to where the bow wave is highest, to reduce in width aft thereof. At the aft extremity of the spray rail the width is small or zero. The angle of the spray rail relative to the horizontal is indicated by p sp ray- The fillet at the intersection of the spray rail with the hull below the spray rail is also shown (22).

Figure 8 shows the interceptor (19) fitted to the transom (6). The sheer line (4) is also shown, as is the design waterline (9), the centre-line buttock (7). The interceptor is a flat plate attached to the transom such that this protrudes into the flow below the hull. The depth or draught of the interceptor (that part of the interceptor protruding into the flow) is indicated by Ti nte rceptor.

Figure 9 shows the alternative of a flap (20) fitted to the transom, or alternatively below the hull near the stern. This is commonly attached to the transom by means of hydraulic cylinders (21). The angle of the flap (βίΐαρ), relative to the horizontal, can be fine-tuned by adjusting the length of the cylinders (15).

DETAILED DESCRIPTION OF EMBODIMENTS

The invention relates to the underwater shape of a round-bottomed hull with a specific shape and distribution of the volume over the length, fitted with a bulbous bow, fitted with so-called spray rails on the fore body, and means to control the running trim fitted at, or near, the transom.

To reduce the formation of waves, and thus to reduce the hydrodynamic resistance at higher speeds, the fore body of the invention, as portrayed by the waterlines, according to a particular embodiment, is slender. As indicated in Fig. 4, the design waterline and other waterlines below thereof, have a small angle of entrance (I E ). The preferred value of this angle is related to the beam-length ratio of the hull. In a preferred embodiment, this angle can be expressed as being between 35B w i/L w i and 90B w i/L w i (in degrees). Again referring to Fig. 4, the design waterline gradually widens from the bow, to where the hull has its maximum beam (17). Rather than positioning the maximum beam near amidships (defined to be the mid-length of the design waterline), the maximum beam of the design waterline, in a preferred embodiment, is positioned between 55% and 80% of the length of the design waterline from the forward extremity thereof (L BW I).

Aft of the maximum beam position (see Fig. 4), the design waterline becomes narrower until, at the transom stern, this waterline has a width (B T ) which, in a preferred embodiment, is between 80 to 95%> of the maximum width B WL . According to a particular embodiment, the centre-line buttock forms the deepest part of the hull from the bulb to where this buttock starts to sweep aft and upwards. In a particular embodiment, this occurs at between 25 and 50% of the length of the design waterline aft of the forward extremity thereof. This length is indicated by L T in Fig. 5. From this deepest location, the centre-line buttock runs aft in a smooth curve, at a shallow angle relative to the horizontal, such that the draught of the hull at the transom (T t ) is, in a preferred embodiment, between 0%> to 35% of the maximum draught (T) of the hull, when the vessel floats without bow-down, or stern-down, trim on the design waterline. In a preferred embodiment, the angle c¾, formed by drawing a tangent to the centre-line buttock at the transom, is between 2 and 8 degrees (see Fig. 5).

According to a preferred embodiment, the location of the transverse section at which the underwater transverse-sectional area is greatest, is close to the mid-length location of the design waterline, even though the waterline beam at that location is not maximum. In a preferred embodiment, the location at which the underwater transverse- sectional area is greatest is between 42.5% and 60% of the length of the design waterline from the forward extremity thereof. To further reduce the hydrodynamic resistance of the hull and to be able to widen the waterlines below the design waterline at the bow, adding volume there, without increasing the entry angle of the waterlines (IE), a bulb (see Fig. 6a) is fitted with a length (L bu i b ) which, according to a preferred embodiment, is between 4% and 12% of the length of the design waterline.

Reference is now made to Fig. 6b in which the main characteristics of the transverse- sectional shape of the bulb are shown at the forward extremity of the design waterline. The bulb has a maximum width (B bu i b ) which, in a preferred embodiment, is between 12% and 24% of the maximum width of the design waterline B wl . In a preferred embodiment, the location of the maximum width of the bulb below the water surface (Ts bu i b ), in the same transverse section, is between 30%> and 60%> of the maximum depth (T). In a further embodiment, the angle of the tangent to the bottom of the bulb at the centre-line, also in the same transverse section, relative to the horizontal, is between 25 and 50 degrees (f ib).

The cross-sectional area of the bulb, at the transverse section at the forward extremity of the design waterline, in a preferred embodiment, is between 10% and 20% of the maximum underwater cross-sectional area of the hull.

To deflect the spray caused by the bow wave away from the deck of the vessel a spray rail is added to the fore body (see Fig. 7a). The location of the spray rail is fixed by stipulating the height thereof at the forward end near or at the stem, and at the aft end of the spray rail, relative to the design waterline. In a preferred embodiment the height of the spray rail near the stem (Fspray) is at least 20% of the height of the stem (Fstem). At the aft end of the spray rail the location thereof is just above or below the design waterline and, in a preferred embodiment, is between 0% and 10% of the height of the stem (Fstem) from this waterline. The spray rail has a length (L spray ) which, in an embodiment, is between 30%> and 50%> of the length of the design waterline (see Fig. 7a). The width of the spray rail (B spray ), in a preferred embodiment, varies along the length and at its widest part is between 175 and 400 mm wide, increasing with the size of the vessel. The preferred transverse- sectional shape is as given in Fig. 7b, in which the angle p spray , in a preferred embodiment, is between 0 and 15 degrees, with a fillet on the inside (22) with a radius of between 25 and 100 mm, again increasing with the size of the vessel. In a preferred embodiment, the width of the spray rail towards the forward and aft extremities is reduced to zero from the widest part, which widest part is located where the bow wave is highest at the speed of greatest interest (usually the maximum speed). In a preferred embodiment, this location is between 0% and 15% of the length of the design waterline, aft of the forward extremity of that waterline. To control the running trim of the hull at higher speeds it is necessary to add a trim- control device to the aft body of the hull, near the transom. This can be a so-called interceptor (see Fig. 8) or a flap (see Fig. 9), or some other means by which the stern is lifted to counteract the natural tendency of the hull to lift at the bow and to sink at the stern, at higher speeds. In a preferred embodiment, the interceptor or the flap adopted is attached to the transom and designed so as to be able to change the setting while underway, to fine-tune the running trim of the hull. Usually, different optimum settings of the interceptor or the flap are required to maintain the optimum trim of the hull over the complete speed range. In an embodiment, an interceptor in the form of a flat plate (see Fig. 8) is fitted to the transom such that this protrudes into the flow below the hull. The exact amount by which this plate extends below the hull varies with speed. In an embodiment this ranges between 0 and 100 mm, depending on the trim of the vessel without interceptor. In another embodiment, a flap is fitted to the transom as shown in Fig. 9, and actuators like for instance hydraulic cylinders are used to deflect the flap to the required angle. The exact amount by which this flap is deflected from the horizontal varies with speed and the length of the flap. In a preferred embodiment, the length of the flap is between 0.5% and 2.5% of the length of the design waterline. In an embodiment the angle of the flap is between 0° and 10° relative to the horizontal.

It will be clear from the foregoing examples that many variations are possible within the scope of the invention. The above description serves to illustrate some embodiments of the invention, and not to limit the scope of protection. Starting from this disclosure, many more embodiments will be evident to a skilled person which are within the scope of protection and the essence of this invention and which are obvious combinations of prior art techniques and the disclosure of this patent.