GB2481581A

GB2481581A - Boat monohull with central hull portion and two lateral hull portions

Info

Publication number: GB2481581A
Application number: GB201010756A
Authority: GB
Inventors: Christopher Peter Kirk
Original assignee: Pet Mate Ltd
Current assignee: Pet Mate Ltd
Priority date: 2010-06-28
Filing date: 2010-06-28
Publication date: 2012-01-04
Anticipated expiration: 2030-06-28
Also published as: GB201010756D0; GB2481581B

Abstract

A boat hull is disclosed which comprises a thin central hull portion 14 of the displacement type, a pair of thin lateral hull portions 16 disposed to either side of the central hull portion and with a relatively small spacing between the central hull portion and each lateral hull portion, and an upper hull portion (12, Fig 4) connecting the central hull portion to the lateral hull portions so that the central, lateral and upper hull portions form a substantially continuous monohull shell. A respective tunnel (52, Fig 3) may be formed between the central hull portion and each lateral hull portion and between the upper hull portion and the waterline 18, 20.

Description

TITLE

Boat hulls

DESCRIPTION

This invention relates to boat hulls.

The invention was originally conceived as a hull for a 40-foot (12-metre) leisure boat, but is also applicable to hulls for other types and sizes of water vessel.

Most leisure boats have monohulls either of the displacement' type or the planing' type. A displacement hull is designed to travel through the water, rather than planing over it, whereas a planing hull is designed to be used so that it skims over the water. For a displacement hull, the top speed is effectively limited by the length at the waterline of the hull, and is typically about 8 knots (4 m/s) for a 40-foot (12-metre) boat. Displacement hulls are usually relatively fuel efficient, typically having a fuel economy of 5 nautical miles per Imperial gallon (0.5 litres/km) but have limited speed. On the other hand, a planing hull requires a very powerful engine to ride up on its bow wave and achieve planing, but can typically attain a speed of 30 knots (15 m/s) or more. However, fuel economy is poor, typically about 1.5 nautical miles per Imperial gallon (1.6 litres/km) for a 40-foot (12-metre) hull. At lower speeds, when a planing hull is not planing, its fuel economy is typically far worse than a displacement hull. A planing hull also produces a poor, bouncy ride, which demands a strong heavy and expensive hull construction. Some hulls are of the semi-displacement' type and are designed to ride up on their bow wave, but not to plane. They typically combine poor fuel economy with moderate speeds, for example 15 knots (7.7 m/s) and 1.5 nautical miles per Imperial gallon (1.6 litres/km) for a 40-foot (12-metre) hull. Multi-hull boats such as catamarans and trimarans are not typically employed as leisure boats due to their wide beam and the difficulty in providing accommodation on the boat. The hulls of multi-hull boats are usually of the displacement type.

An aim of the present invention, or at least of specific embodiments of it, is to provide a boat hull which has a maximum design speed which is greater than a comparable conventional displacement type monohull, which provides better fuel economy, which does not have an excessive beam to length ratio, which has good stability and which provides a good ride.

In accordance with the present invention, there is provided a boat hull having a central hull portion of the displacement type, a pair of lateral hull portions disposed to either side of and spaced from the central hull portion, and an upper hull portion connecting the central hull portion to the lateral hull portions so that the central, lateral and upper hull portions form a substantially continuous monohull shell. The boat hull of the invention therefore resembles a trimaran to some extent, but formed as a monohull with the upper hull portion which can conveniently provide good accommodation.

The central hull portion preferably has a length at the waterline which is at least seven times its beam at the waterline. The central hull portion is therefore substantially thinner than a typical conventional monohull and consequently experiences less wave-making resistance.

Stability is provided by the lateral hull portions.

In the specification, references to the "waterline" refer, unless the context otherwise requires, to the waterline of the hull when static and lightly loaded.

Over at least the majority of its length below the waterline, in section the central hull portion gently curves from the waterline on one side of the central hull portion to the waterline on the opposite side of the central hull portion. For example, the central hull portion may gently curve as aforesaid substantially as a semi-circle or half-ellipse. This provides a low ratio of water contact area to hull displacement and therefore reduces water drag for a given displacement. The beam at the waterline of the central hull portion is preferably at least 1.4 times the draft, and preferably no more than 2.3 times the draft, of the central hull portion.

A respective tunnel is preferably formed between the central hull portion and each lateral hull portion and between the upper hull portion and the waterline. Over at least the majority of its length above the waterline, in section each tunnel substantially smoothly arches, for example substantially as a semi-circle or half-ellipse, from the central hull portion to the respective lateral hull portion. The minimum height of each tunnel above the waterline is preferably at least 0.35 times the minimum width, and preferably no more than 0.65 times the minimum width, of each tunnel at the waterline. This shaping of the tunnels in combination with the shaping and relative proportions of the central and lateral hull portions enables the hull to have a high rigidity to weight ratio without the tunnels blocking with water at speed.

The central hull portion preferably has negligible rocker. More specifically, the maximum offset of the keel line of the central hull portion from a straight line extending between the base of the stem and the base of the transom of the central hull portion is preferably no more than 0.05 times the length of that straight line.

The central hull portion is preferably substantially longer than the lateral hull portions.

More particularly, the central hull portion has a length at the waterline which is preferably at least 1.3 times the length, and preferably no more than 2.2 times the length, of each lateral hull portion at the waterline.

The central hull portion and the lateral hull portions preferably have transom portions lying substantially in a common plane.

Each lateral hull portion preferably has a length at the waterline which is at least seven times its beam at the waterline. The lateral hull portions are therefore also relatively thin and consequently experience little wave-making resistance.

The central hull portion is preferably wider than the lateral hull portions. More particularly, the beam at the waterline of the central hull portion is preferably at least 1.4 times the beam, and preferably no more than 2.3 times the beam, at the waterline of each lateral hull portion.

Similarly to the central hull portion, over at least the majority of the length of each lateral hull portion below the waterline, in section the lateral hull portion gently curves from the waterline on one side of the lateral hull portion to the waterline on the opposite side of the lateral hull portion. For example, each lateral hull portion may gently curve as aforesaid substantially as a semi-circle or half-ellipse. Again, this provides a low ratio of water contact area to hull displacement and therefore reduces water drag for a given displacement. The beam at the waterline of each lateral hull portion is preferably at least 2.1 times the draft, and preferably no more than 3.4 times the draft, of the lateral hull portion.

Each lateral hull portion has a keel line which is preferably inclined at the waterline at the front of the lateral hull portion at an angle of no more than 30 degrees to the waterline. Each lateral hull portion can therefore generate a degree of dynamic lift.

The minimum spacing at the waterline between each lateral hull portion and the central hull portion is preferably at least 0.6 times the beam, and preferably no more than 1.2 times the beam, at the waterline of the central hull portion. The spacing of the hull portions is therefore substantially less than a typical conventional configuration of trimaran.

A respective tunnel is preferably formed between the central hull portion and each lateral hull portion and between the upper hull portion and the waterline. In this case, for each tunnel, the upper hull portion is preferably formed with a respective rib projecting into the tunnels and extending longitudinally of the hull. The ribs serve to deflect spray and reduce water attachment to the hull, which in turn reduces drag.

Because of their size and shape, the lateral hull portions are not particularly useful for providing accommodation. However, each lateral hull portion is preferably substantially filled with one or more buoyancy tanks or a buoyancy medium. Also, due to the size and shape of the central hull portion, the portion of the central hull portion towards the bow of the hull is also not particularly useful for providing accommodation and this portion of the central hull portion therefore preferably also contains one or more buoyancy tanks or a buoyancy medium.

However, the central hull portion is preferably arranged so that it can flood, which improves the stability of the hull upon flooding.

The invention also extends to a boat having a hull as described above. The centre of gravity of the boat is preferably disposed, when viewed from the side, between the fore and aft ends of the lateral hull portions. More particularly, the boat is preferably arranged so that the dynamic lift provided by the lateral hull portions is approximately vertically aligned, when viewed from the side, with the centre of gravity of the boat.

A specific embodiment of the present invention will now be described, purely by way of example, with reference to the accompanying drawings, in which: Figure 1 is a side view of a hull of a boat; Figure 2 is an underplan view of the hull; Figure 3 is a bow view of the hull; Figure 4 is a stern view of the hull; Figure 5 is an isometric view of the underside of the hull; Figure 6A-H are sectioned views of the hull taken on the section lines and planes marked 6A to 6H, respectively, in Figures 2 and 5; Figure 7 is a side view of the hull shown transparently to reveal buoyancy regions; and Figure 8 is a plan view of the hull.

Referring to the drawings, a hull 10 is formed as a single shell, i.e. it is of monohull configuration, and is constructed using any conventional materials and techniques. The complete hull 10 comprises an upper hull portion 12 which is statically above the waterline and which joins a main central hull portion 14 and a pair of smaller lateral hull portions 16 which are statically submerged below the waterline. In the remainder of this detailed description, the upper hull portion 12, the main central hull portion 14 and the smaller lateral hull portions 16 will simply be referred to as the upper hull, central hull and lateral hulls, respectively. The intended waterline for a boat incorporating the hull 10 when lightly-loaded and filly-loaded is indicated by the dash-dot lines 18 and 20, respectively, in Figures 1 and 3 to 7. The submerged central and lateral hulls 14,16 when lightly loaded are shown by the hatched areas 22 and 24, respectively, in Figure 2.

As shown particularly in Figures 2, 5 and 8, the upper hull 12 has a gunwale of conventional shape, having: a generally straight stern portion 26; a pair of generally parallel straight side 28 portions extending from the stern portion over about half the overall length of the hull 10, and a pair of curved side portions 30 which blend with the generally straight side portions 28 and meet at the bow 32 at an angle of about 75 degrees. The ratio LOA:B of the overall length LOA to the beam B of the hull 10 is about 21: 1 to 3:1, and the overall length LOA might typically be about 40 feet (12 metres).

Each side of the upper hull 12 has an upper portion 34 which depends vertically from the side gunwale 28,30 by an amount that increases towards the stern 36, and an inclined lower portion 38 which depends from the upper portion 34 at angle to the vertical which increases from about 2 degrees at the stern 36 to about 20 degrees at the bow 32. As shown particularly in Figures 1, 5 and 6, the height of the inclined lower side portion 38 of the upper hull 12 varies over the length of the hull 10 so that its lower edge reaches the fully-loaded waterline 20 over the rear third of the length of the hull 10, but rises to the bow 32 over the front two-thirds of the length of the hull 10.

As shown particularly in Figure 1, the transom 40 of the upper hull 12 has an upper portion 42 which depends vertically from the stern gunwale 26, and a lower portion 44 which depends from the lower edge of the upper portion 42 at an angle of about 15 degrees to the vertical.

The upper hull 12 also includes a pair of connecting portions 44 which join the central hull 12 to the lateral hulls 14. As shown in Figures 6E to 611, the connecting portions 44 generally have the shape of a semicircular inverted "U" over the rear half of the length of the hull 10. Towards the bow 32, this inverted "U" shape is progressively flattened-out and inclined (see Figures 6C & 6D), so that adjacent the bow 32, the hull 10 has a large dead-rise angle (see Figure 6B).

Referring in particular to Figures 6B to 6E, the central hull 14 is disposed between the two connecting portions 44. Nearer the bow 32 (see Figures 6B and 6C), the central hull 14 has a high dead-rise angle with a rounded keel portion 45. However, over the majority of the length of the central hull 14 (see Figures 6D to 611), the central hull 14 has a rounded section in the form of a "U" shape which is generally semicircular or half-elliptical. Therefore, as shown in Figure 3, the beam at the waterline BWL' of the central hull 14 is approximately twice the draft D' of the central hull 14. For example, the ratio BWL' :D' preferably lies in the range of 1.4:1 to 2.3:1. Referring in particular to Figure 1, the hull 10 has a stem 46 inclined at a steep angle, for example at 10 degrees to the vertical. Therefore, the length at the waterline LWL' of the central hull 14 is only slightly less than the overall length LOA of the complete hull 10. For example LWL' is 95% of LOA. It can also be seen from Figures 1 and 7 that the central hull 14 is only slightly rockered, or in other words the curvature of the keel line 48 between the base of the stem 46 and the transom 40 is only slight. As shown in Figure 7, the maximum deviation KO of the keel line 48 from a straight line 49 connecting the base of the stem 46 and transom 40 is about 0.02 times the length of the keel KL. Preferably the ratio KO/KL is no more than 0.05.

Referring in particular to Figure 2, it will be noted that the central hull 14 is peculiarly long compared to its beam and is sharply pointed. In the example shown, the ratio of the length at the waterline LWL' to the beam at the waterline BWL' is about 10.5:1. Preferably, the ratio LWL' :BWL' is at least 7: 1 and more preferably at least 9: 1.

Referring in particular to Figures 6E to 611, the lateral hulls 16 are disposed between the connecting portions 44 and the inclined lower portions 38 of the sides of the upper hull 12.

Over the majority of the length of each lateral hull 16 (see Figures 6E to 611), the lateral hull 16 has a rounded section in the form of a "U" shape which is generally semicircular or half-elliptical. As shown in Figure 4, the beam at the waterline BWL" of each lateral hull 16 is approximately 21 times its draft D". For example, the ratio BWL":D" preferably lies in the range of 2: 1 to 3.4:1. Referring in particular to Figure 1, the forward part 50 of the keel line of each lateral hull 16 is inclined forwardly out of the water at a shallow angle of for example 12 degrees, and the cross-sectional shape of the lateral hull 16 merges smoothly into the upper hull 12. Referring in particular to Figure 2, it will be noted that each lateral hull 16 is also peculiarly long compared to its beam and is relatively sharply pointed. In the example shown, the ratio of the length at the waterline LWL" to the beam at the waterline BWL" is about 11:1. Preferably, the ratio LWL" :BWL" is at least 7: 1 and more preferably at least 9: 1.

Comparing the central and lateral hulls 14,16, in the example shown, the ratio of the length at the waterline LWL' of the central hull 14 to the length at the waterline LWL" of each lateral hull 16 is about 1.7:1. Preferably this ratio LWL' : LWL" lies in the range from 1.3:1 to 2.2:1. Also, in the example shown, the ratio of the beam at the waterline BWL' of the central hull 14 to the beam at the waterline BWL" of each lateral hull 16 is about 1.8:1. Preferably this ratio BWL':BWL" lies in the range from 1.4:1 to 2.3:1.

It will be noted from Figures 3 to 6 that the connecting portions 44 form two tunnels 52 between the hull 10 and the water, and from Figure 2 that the tunnels 52 are generally straight and parallel. Referring to Figure 3, the minimum width at the waterline TWL of each tunnel 52 is approximately equal to the beam at the waterline BWL' of the central hull 14. The ratio TWL:BWL' preferably lies in the range 0.6:1 to 1.2:1.

In order to reduce water attachment to the connecting portions 44 of the hull 10 and consequent drag, a rib 54 projecting from each connecting portion 44 extends from the stern 36 to adjacent the bow 32.

Referring to Figure 4, the tunnels 52 are smoothly arched (apart from the ribs 54), and the ratio of the minimum height TH of each tunnel 52 above the waterline 18 to the minimum width at the waterline TWL of the tunnel 52 is about 0.5:1. Preferably, this ratio TH:TWL lies in the range 0.35:1 to 0.65:1.

The design centre of gravity 56 and design centre of buoyancy 58 of a boat incorporating the hull 10 are shown in Figure 1. It will be appreciated that the hull 10 described above is substantially of the displacement' type, i.e. it is designed to travel through the water, rather than to plane over it. The central hull 14 exhibits very little dynamic light. Each lateral hull 16 will exhibit a degree of dynamic lift due to the inclination of the forward part 50 of its keel line. This lift is centred about one-third of the way along the lateral hull 16 from the front, and will therefore coincide approximately with the centre of gravity 56 of the boat, as viewed from the side, so as not to have any significant effect on the pitch of the boat. If the boat heels at speed, the dynamic lift of the lateral hull 16 that becomes more or less submerged will increase or decrease, as the case may be, so as to improve the righting effect of the hull 10 at speed.

It will be appreciated that the central and lateral hulls 14,16 do not provide good accommodation space. However, portions of the central and lateral hulls 14,16 may be filled with buoyancy tanks or buoyant material to render the boat buoyant when flooded. Figures 6 to 8 illustrate by hatched areas an example layout of buoyancy tanks in which the lateral hulls and an area above them are completely filled with buoyancy tanks 60, and in which a forward portion of the central hull 14 contains buoyancy tanks 62. Together the buoyancy tanks 60,62 provide a buoyancy about 10% greater than the displacement of the boat. The central and rear regions of the central hull 14 are not filled with buoyancy tanks so as to improve the stability of the flooded boat.

It should be noted that the embodiment of the invention has been described above purely by way of example and that many modifications and developments may be made thereto within the scope of the present invention.

Claims

CLAIMS(The reference numerals and letters in the claims are not intended to limit the scope of the claims) 1. A boat hull comprising: a central hull portion (14) of the displacement type; a pair of lateral hull portions (16) disposed to either side of and spaced from the central hull portion; and an upper hull portion (12) connecting the central hull portion to the lateral hull portions so that the central, lateral and upper hull portions form a substantially continuous monohull shell (10).
2. A boat hull as claimed in claim 1, wherein: the central hull portion has a length at the waterline (LWL') which is at least seven times its beam (BWL') at the waterline.
3. A boat hull as claimed in claim 1 or 2, wherein: over at least the majority of its length below the waterline, in section the central hull portion gently curves from the waterline on one side of the central hull portion to the waterline on the opposite side of the central hull portion.
4. A boat hull as claimed in claim 3, wherein: the central hull portion gently curves as aforesaid substantially as a semi-circle or half-ellipse.
5. A boat hull as claimed in any preceding claim, wherein: the beam at the waterline (BWL') of the central hull portion is at least 1.4 times the draft (D') of the central hull portion.

-10 -
6. A boat hull as claimed in any preceding claim, wherein: the beam at the waterline (BWL') of the central hull portion is no more than 2.3 times the draft (D') of the central hull portion.
7. A boat hull as claimed in any preceding claim, wherein: a respective tunnel (52) is formed between the central hull portion and each lateral hull portion and between the upper hull portion and the waterline.
8. A boat hull as claimed in claim 7, wherein: over at least the majority of its length above the waterline, in section each tunnel substantially smoothly arches from the central hull portion to the respective lateral hull portion.
9. A boat hull as claimed in claim 8, wherein: each tunnel is smoothly arched substantially as a semi-circle or half-ellipse.
10. A boat hull as claimed in any of claims 7 to 9, wherein: the minimum height (Til) of each tunnel above the waterline is at least 0.35 times the minimum width (TWL) of each tunnel at the waterline.
11. A boat hull as claimed in any of claims 7 to 10, wherein: the minimum height (Til) of each tunnel above the waterline is no more than 0.65 times the minimum width (TWL) of each tunnel at the waterline.
12. A boat hull as claimed in any preceding claim, wherein: the central hull portion has a stem (46), a transom (40) and a keel line (48) extending between the base of the stem and the base of the transom; and the maximum offset (KO) of the keel line from a straight line (49) extending between the base of the stem and the base of the transom is no more than 0.05 times the length (KL) of that straight line.

-11 -
13. A boat hull as claimed in any preceding claim, wherein: the central hull portion has a length at the waterline (LWL') which is at least 1.3 times the length at the waterline (LWL") of each lateral hull portion.
14. A boat hull as claimed in any preceding claim, wherein: the central hull portion has a length at the waterline (LWL') which is no more than 2.2 times the length at the waterline (LWL") of each lateral hull portion.
15. A boat hull as claimed in any preceding claim, wherein: the central hull portion and the lateral hull portions have transom portions lying substantially in a common plane.
16. A boat hull as claimed in any preceding claim, wherein: each lateral hull portion has a length at the waterline (LWL") which is at least seven times its beam at the waterline (BWL").
17. A boat hull as claimed in any preceding claim, wherein: the beam at the waterline (BWL') of the central hull portion is at least 1.4 times the beam at the waterline (BWL") of each lateral hull portion.
18. A boat hull as claimed in any preceding claim, wherein: the beam at the waterline (BWL') of the central hull portion is no more than 2.3 times the beam at the waterline (BWL") of each lateral hull portion.
19. A boat hull as claimed in any preceding claim, wherein: over at least the majority of its length below the waterline, in section each lateral hull portion gently curves from the waterline on one side of the lateral hull portion to the waterline on the opposite side of the lateral hull portion.
20. A boat hull as claimed in claim 19, wherein: -12 - each lateral hull portion gently curves as aforesaid substantially as a semi-circle or half-ellipse.
21. A boat hull as claimed in any preceding claim, wherein: the beam at the waterline (BWL") of each lateral hull portion is at least 2.1 times the draft (D") of the lateral hull portion.
22. A boat hull as claimed in any preceding claim, wherein: the beam at the waterline (BWL") of each lateral hull portion is no more than 3.4 times the draft (D") of the lateral hull portion.
23. A boat hull as claimed in any preceding claim, wherein: each lateral hull portion has a keel line (50) which is inclined at the waterline at the front of the lateral hull portion at an angle of no more than 30 degrees to the waterline.
24. A boat hull as claimed in any preceding claim, wherein: the minimum spacing at the waterline (TWL) between each lateral hull portion and the central hull portion is at least 0.6 times the beam at the waterline (BWL') of the central hull portion.
25. A boat hull as claimed in any preceding claim, wherein: the minimum spacing at the waterline (TWL) between each lateral hull portion and the central hull portion is no more than 1.2 times the beam at the waterline of the central hull portion.
26. A boat hull as claimed in any preceding claim, wherein: each lateral hull portion is substantially filled with one or more buoyancy tanks (60) or a buoyancy medium.
27. A boat hull as claimed in any preceding claim, wherein: -13 -a portion of the central hull portion towards the bow of the hull contains one or more buoyancy tanks (62) or a buoyancy medium.
28. A boat hull substantially as described with reference to the drawings.
29. A boat having a hull as claimed in any preceding claim.
30. A boat as claimed in claim 29, wherein: the centre of gravity (56) of the boat is disposed, when viewed from the side, between the fore and aft ends of the lateral hull portions.
31. A boat substantially as described with reference to the drawings.*::r: INTELLECTUAL . ... PROPERTY OFFICE Application No: GB1010756.3 Examiner: Richard Collins Claims searched: ito 31 Date of search: 24 August 2010 Patents Act 1977: Search Report under Section 17 Documents considered to be relevant: Category Relevant Identity of document and passage or figure of particular relevance to claims X 1,3-W000/17041 Al 17,22,23, (ROBINSON) see the central hull portion 16, lateral hull portions 18 and 25-upper hull portion connecting them in figures 1 and 3.X 1-7,10-US2007/215029A1 19,23,26, (CAMPBELL) see the central hull portion 2, lateral hull portions 3 and 27,29,30 upper hull portion connecting them in figures 1, 3 and 4.X 1,2,5,7-US5265554 A 10,13-(MEREDITH) see figures 4 and 5 especially.16,18,22-24.26.27.X 1,2,7-FR954423 A 10,13,17, (AZEMAR) see the central hull portion 1, lateral hull portions 2 and 22,23,26, upper hull portion connecting them in figures 3 and 4.X 1,2,6,7,10 US2009/308300 Al 12-(BAKER) see the central hull portion 24, lateral hull portions 22 and 16,18,22, upper hull portion connecting them in figures 1, 3 and 4.Categories: X Document indicating lack of novelty or inventive A Document indicating technological background and/or state step of the art.Y Document indicating lack of inventive step if P Document published on or after the declared priority date but combined with one or more other documents of before the filing date of this invention.same category.& Member of the same patent family E Patent document published on or after, but with priority date earlier than, the filing date of this application.Field of Search:Search of GB, EP, WO & US patent documents classified in the following areas of the UKCX: B7A Worldwide search of patent documents classified in the following areas of the IPC B63B The following online and other databases have been used in the preparation of this search report Intellectual Property Office is an operating name of the Patent Office www.ipo.gov.uk *.:r: INTELLECTUAL . ... PROPERTY OFFICE EPODOC, WPI International Classification: Subclass Subgroup Valid From B63B 0001/04 01/01/2006 Intellectual Property Office is an operating name of the Patent Office www.ipo.gov.uk