WO2007041809A1

WO2007041809A1 - Planning boat hull with keel bounded by recesses

Info

Publication number: WO2007041809A1
Application number: PCT/AU2006/001525
Authority: WO
Inventors: Jens Gravlev
Original assignee: Farallon Capital Pty Ltd
Priority date: 2005-10-14
Filing date: 2006-10-13
Publication date: 2007-04-19

Abstract

A boat hull (10) extends between a stem (7) and a transom (8) and has chines (12) bounding chine planing surfaces (13) sloping outboard and down at (14). Convex major planing surfaces (15) each have a lower edge defined by a lateral planing surface (17), the inner edge forming the lower edge of a substantially vertical hull tunnel wall (20), the upper edge meeting a tunnel top (21). Between the respective port and starboard tunnel tops (21) is a vee keel (22) of substantially constant prismatic section and comprising a keel planing surface (23) bounded by upwardly and transversely sloping inner tunnel surfaces (24). The spaced recesses (18) formed thereby maintain a longitudinally prismatic form substantially for the length of the planing surface. The stem (7) above the chine forward (14) presents a conventional monohull appearance. The topsides, deck, interior space, and ratio of LOA to beam, all present as a conventional monohull.

Description

PLANING BOAT HULL WITH KEEL BOUNDED BY RECESSES

This invention relates to a boat hull.

This invention has particular but not exclusive application to a high speed

(planing) pleasure boat hull, and for illustrative purposes reference will be made to such application. However, it is to be understood that this invention could be used in other applications, such as planing hulls of patrol, race and work boats generally.

PRIOR ART

Planing boat design represents a series of compromises. In monohull planing boats a relatively high loading per unit area is attainable, but in order to get a good ride, a relatively steep deadrise of, for example, 23° for a 6m boat, means that stability is compromised and that draft is increased relative to displacement.

Lowering the deadrise improve planing and stability, but the ride is compromised.

At the other end of the compromise, a multihull design achieves stability, but at a much lower loading ratio, resulting in a large beam for a given load.

Compromises between these two extremes have resulted in any number of tunnel hull designs, Hydrofield^®, gull wings, split vees and the like. Each of these configurations is an attempt to provide some multihull characteristics including the multihull characteristic of trapping air between downwardly depending hull portions.

The present invention provides an alternative means of improving the stability of a monohull, while reducing draft relative to displacement, improving planing lift, maintaining large effective deadrise angles without increasing draft, and improved spray control. DESCRIPTION OF INVENTION

In one aspect the present invention resides broadly in a boat hull including a monohull planing section disposed between opposed chines, said monohull section including a keel extending substantially from transom to bow and bounded on each side by a recess extending substantially from transom to bow and formed between a transversely sloping inner surface adjacent the keel and a substantially vertical outer surface, each said outer surface being bounded by lower edges transitioning to a hull surface portion extending to a respective said chine.

The keel may present a lower V-section or may alternatively include a substantially flat keel planing surface.

The upper edges of each of the transversely sloping inner surface adjacent the keel and the substantially vertical outer surface may meet at a conjunction edge or may be separated by a tunnel upper surface. For example, the tunnel upper surface may be a flat surface. The tunnel flat surface tends to decrease wetted surface and improve effectiveness of planing lifting surfaces.

The lower edges of the outer surfaces may transition via the edge directly to the deadrising hull surface portion. Alternatively the transition may be via a lateral planing surface portion. For example, transition may be via a respective port or starboard, substantially flat or concave, lateral planing surfaces. The outer edge of the lateral planing surfaces may form the lower edge of the respective hull surface portions.

The deadrise angle is selected having regard to the maximum desirable deadrise angle for that boat length, in the knowledge that, for a given deadrise angle, the disadvantages of less stability and deep draft are ameliorated by use of the invention. It has been surprisingly determined that to use a deep vee deadrise angle whilst effectively truncating the draft by disposing a relatively shallow keel between two recesses bounded by lateral lower edge portions bounding the hull major surfaces provides the soft-riding advantages of the deep vee with the shallow draft of a flatter deadrise.

The overall width of the preferred keel and lateral flats may be selected to provide that there is considerable displacement required to submerge the section. The effect of the "double vee", that is, an outer vee defined by the hull surface portions embracing an inner vee defined by the keel and its bounding transversely sloping inner surfaces, in embodiments of the present invention, is that about 40% less draft is attainable for a given displacement.

The widths of the respective keel planing surface and lateral planing surfaces may be maximised to minimise the vessel draft for a given displacement, and may be moderated to reduce pounding while providing planing lift. The form created by said keel and its respective transversely sloping inner surfaces may present as a warped plane along the length of the vessel in the convention manner of fairing a theoretical sheet surface toward the bow. Alternatively, the form created by the keel and its respective transversely sloping inner surfaces may present a longitudinally prismatic form for substantially the length of the monohull planing section, thus avoiding any reduction in cross section from the bow.

The substantially vertical outer surfaces may be selected from warped planes, or surfaces bounding a longitudinally prismatic form for the length of the planing surface. Preferably, the substantially vertical outer surfaces and the transversely sloping inner surfaces bound longitudinally prismatic forms for substantially the length of the planing section. By this means the constant section prevents hydrodynamic choking of the effective tunnel. This principal is termed in the art "the retention of a consistent curve of sectional hull areas".

Hulls in accordance with the present invention may include such known devices as a transverse step, longitudinal inner chines or the like. The hulls may be powered by any suitable means including outboard engines, sterndrives, shaft drive inboard engines, water jets or surface drives.

The keel and/or lateral planing surfaces, when present, also make the boat sit better on a trailer, improve lift efficiency and allow the aforementioned increase in hull deadrise. The surfaces stop wallow at low speed. The surfaces stop chine and strake walk at high speed and improve turning, etc.

The lateral planing surfaces preferably extend to the bow of the vessel and are permitted to diminish in width from the turn-up of the bow.

The hull surface portions are preferably slightly convex to assist in reduction of drumming (that is, to provide some stiffening against flex) and to increase effective deadrise angle outboard where it is more necessary. The hull surface portions may be provided with conventional planing strakes.

It has been determined that the effective deadrise is not the intuitive angle between the centreline of the boat and the bottom shell at chine. Instead, effective deadrise is the angle of major planing surfaces.

The chines may be undercut with planing surfaces that come into play in the turns and also improve planing lift and spray reduction. At least a portion of each chine planing surface may be inclined outboard and down. For example, as the chines disappear into the bow, it is preferred that the chine planing surfaces forward are inclined outboard and down for increased spray control. BRIEF DESCRIPTION OF THE DRAWINGS

In order that this invention may be more readily understood and put into practical effect, reference will now be made to the accompanying drawings which illustrate a preferred embodiment of the invention and wherein: FIG. 1 is a bottom plan view of hull apparatus according to the present invention;

FIG. 2 is bow-on view of the hull of FIG. 1;

FIG. 3 is a front perspective view of the hull of FIG. 1 ;

FIG. 4 is a rear perspective view of the hull of FIG. 1; FIG. 5 is a side view of the hull of FIG. 1 ;

FIG. 6 is a diagram of water action on the hull of FIG. 1 in the transverse direction viewed from the bow;

FIG. 7 is a diagram of water action inside the tunnel of a hull according to FIG. 1, in use; FIG. 8 is a diagram of a transverse vertical sectional through a hull in accordance with the present invention;

FIG. 9 is a diagram of a transverse vertical sectional through a 19° deadrise hull in accordance with the prior art;

FIG. 10 is a diagram of a transverse vertical sectional through a 23° deadrise hull in accordance with the prior art; and

FIG. 11 is a diagram to show comparative righting moments of the hulls of FIGS. 8 to 10.

DESCRIPTION OF THE PREFERRED EMBODIMENT

In the figures, there is provided a boat hull, indicated generally as 10 and having a topsides portion extending downward from a gunwale 11 to port and starboard chines 12. The chines 12 bound chine planing surfaces 13. The chine planing surfaces 13 are turned down outwardly of the hull at 14 to deflect spray downward. The hull 10 extends fore and aft between a stem 7 and a transom 8

The major planing surfaces 15 of the hull extend from the region of the chines 12 toward the centreline of the vessel at a notional deadrise angle of approximately 23°. The major planing surfaces 15 are slightly convex to reduce drumming through form stiffness and to increase the effective deadrise angle toward the chine 12. Each of the major planing surfaces has a full planing strake 16 outward of a reduced-drag partial planing strake 9, both disappearing toward the bow of the hull 10.

The lower edges of the respective major planing surfaces 15 are defined by a pair of spaced, port and starboard planing flats 17, disposed in substantially parallel arrangement and extending from the region of the transom 8 and disappearing into the bow of the hull 10. These planing flats 17 improve planing lift and reduce planing drag.

The inner edges of the respective planing flats 17 form the lower edges of respective substantially vertical hull tunnel walls 20. The substantially vertical hull tunnel walls 20 run substantially straight, true and of constant height for a majority (about 2/3) of the overall length of the hull 10. The tunnel walls 20 diverge slightly to accord with the disappearing width of the planing flats 17 toward the bow, and curve upward to maintain substantially constant tunnel cross section and to delay the disappearance of the tunnel defined there between until substantially clear of the normal immersed proportion of the stem 7.

The upper edges of the tunnel walls 20 are bounded by substantially horizontal, port and starboard tunnel flats 21 that run substantially true, flat and straight from the transom 8 until forced to diminish at the bow to blend with the monohull bow form adjacent the stem 7.

Between the respective port and starboard tunnel flats 21 is a vee keel 22 of substantially constant prismatic section and extending substantially from transom 8 to stem 7. The vee keel 22 comprises a substantially horizontal keel planing flat 23 bounded by upwardly and transversely sloping inner tunnel surfaces 24, which meet the inner edges of the respective port and starboard tunnel flats 21.

The respective port and starboard tunnel flats 21 , port and starboard tunnel walls 20 and their respective transversely sloping inner tunnel surfaces 24 form a pair of spaced recesses 18 which maintain a longitudinally prismatic form substantially for the length of the planing surface. The recesses 18 and the structures that form them sweep smoothly up in diminishing fashion whereby the tunnel walls 20 disappear at and intersect the chine 14 at the point of its disappearance at the stem 7. This point is well above the datum waterline at the stem 7, at which point the section of each of the recesses 18 is an appreciable proportion of its prismatic cross section in the planing section. The recess above this point now increases substantially in width and acts as a spray knocker in waves. The tunnel recess gradually increases in depth downward from its highest point on the stem. The tunnel recesses trap air to decrease surface drag, cushion wave impact and improve turning of the vessel at speed.

The stem 7 above the chine forward 14 presents a conventional monohull appearance. The topsides, deck, interior space, and ratio of LOA to beam, all present as a conventional monohull. In FIGS. 6 and 7, an analysis of water action (with the port side only illustrated) indicates that water flow from the major planing surfaces 15 is deflected outward as in a conventional hull and the inner and outer strakes is deflected outward as expected. The water flow from the central vee keel flat 23 and transversely sloping inner tunnel surfaces 24 is directed aft in the recesses creating additional lift. At speed, water from the planing flats 17 deflects outward and inward. The inward deflection generates lift by striking the upwardly and transversely sloping inner tunnel surfaces 24. The water flow along the vee keel transversely sloping inner tunnel surfaces 24 is directed outward and aft as is the water flow along the vee keel flat. The water flow from the chine flat 13, 14 is deflected outward as per an ordinary vee hull.

In the present embodiment, a vessel built on the hull of 6.5m LOA and 2.5m has a design displacement of 1 ,850 kg in salt water at rest. The proportions that provide the optimized performance of the described embodiment may be determined empirically. In the present case, the overall truncation of the standard monohull form is a plane having a nominal width of about 79 cm. The width of the port and starboard planing flats 17 is about 10cm, the keel flat about 10cm and the port and starboard tunnel flats 21 about 5 cm, totalling 40cm, or just over 50% of the said nominal width and available progressively from high speed to low speed at minimal change of draft.

In FIGS 8 to 11 the unexpected results on stability of the present invention as embodied are explained with reference to comparison between the hull of the present invention in FIG 8 and two prior art hulls, of 19° (FIG. 9) and 23° (FIG. 10) deadrise respectively. In each case, the dashed lines 30, 31 and 32 represent the waterline at zero, 10 and 20° of heel. For comparison, the calculations are made for a 6.5m LOA x 2.5m beam for the hulls of FIGS and 8 and 8 and 6.0m LOA x 2.5m beam for the vessel of FIG 10 in view of the extra volume under the chines. All 3 hulls were immersed to displace approximately 1 ,850kg in salt water at rest. The test results are summarised in Table 1 :

FIG .8 FIG .9 Fig. 10

Heel C ') 0 10 20 0 10 20 0 10 20

W'line 300 270 210 370 340 270 425 400 330

(mm)

Disp. (kg) 1845 1820 1866 1845 1844 1835 1834 1870 1854 TCB^* (mm) 0 315 543 0 312 530 0 279 494

Transverse Centre of Buoyancy

TABLE 1

FIG. 11 plots the respective righting arms, where traces 33, 34 and 35 correspond to the righting arms of the hulls of FIGS 8, 9 and 10 respectively. It can be seen that the typical monohull of 23° deadrise of trace 35 has the most draft and the least righting arm. The trace 33 of the hull of the present invention has the greatest righting arm and least draft when compared to the hull of trace

35. The present hull has 10% more righting arm and 42% less draft that the 23° deadrise conventional monohull of trace 35. The 19° deadrise hull of trace 34 is in between.

Boat hulls in accordance with the foregoing embodiment are useful in applications where, were it not for the invention, the vessel would have a deeper draft and less stability with increasing (i.e. deepening-vee) deadrise angle. The lateral planing/lifting surfaces are separated, akin to a catamaran, moving the transverse centre of buoyancy outboard further than a regular vee hull when heeled statically and dynamically. This provides more stability than a regular single vee hull. Embodiments of the present invention are approximately

10% more stable than a conventional 23° deadrise monohull. The interaction of

the shapes of the central vee about the keel flat and the outer vee form separated by the recesses creates extra lift. Specifically, the horizontal or substantially horizontal keel flat creates lift effectively. The water deflected off the keel flat and the sloping surfaces bounding it create additional lift when striking the tunnel top. The tunnel top may include substantially horizontal surfaces that convert the force of this deflected water into additional lift. At speed the portion of water deflected by the lateral flats will impinge on the transversely sloping surfaces bounding the keel flat, thus further contributing to lift.

Air and aerated water is entrapped in the recesses at speed. This reduces skin friction and creates a partial air cushion. The recesses meeting at the bow creates an effective spray knocker close to the centreline of the boat, creating a drier-riding boat in a seaway. The longitudinal prismatic line of the center vee and tunnel formed by the recesses aids tracking of the boat and reduces the tendency to broach. Once a turn is initiated, the hull banks on the outer hull surface portions as does a regular vee hull. The tunnel minimizes the stern sliding in turns. The frontal area sections are similar to that of a regular vee monohull, and so the wave impact characteristics remain essentially unchanged.

It will of course be realised that while the above has been given by way of illustrative example of this invention, all such and other modifications and variations thereto as would be apparent to persons skilled in the art are deemed to fall within the broad scope and ambit of this invention as defined in the claims appended hereto.

Claims

1. A boat hull including a monohull planing section disposed between opposed chines, said monohull section including a keel extending substantially from transom to bow and bounded on each side by a recess extending substantially from transom to bow and formed between a transversely sloping inner surface adjacent the keel and a substantially vertical outer surface, each said outer surface being bounded by lower edges transitioning to a hull surface portion extending to a respective said chine.

2. A boat hull according to claim 1 , wherein said keel is selected from a V- section keel and a section having a keel planing surface.

3. A boat hull according to claim 2, wherein the keel planing surface is substantially flat.

4. A boat hull according to claim 1 , wherein the upper edges of each of said transversely sloping inner surface adjacent the keel and said substantially vertical outer surface are separated by a tunnel upper surface.

5. A boat hull according to any one of the preceding claims, wherein the lower edges of the substantially vertical outer surfaces transition via the edge directly to the deadrising hull surface portion.

6. A boat hull according to any one of claims 1 to 4, wherein the lower edges of the outer surfaces each transition to the respective deadrising hull surface portion via a lateral planing surface portion.

7. A boat hull according to claim 6, wherein the planing surface is selected from substantially flat and concave lateral planing surfaces.

8. A boat hull according to claim 7, wherein the outer edge of the lateral planing surface form the lower edge of the respective hull surface portion.

9. A boat hull according to any one of claims 2 to 8, wherein the widths of the respective keel planing surface and lateral planing surfaces are maximised to minimise the vessel draft for a given displacement, and moderated to reduce pounding while providing planing lift.

10. A boat hull according to any one of the preceding claims, wherein the form created by said keel and its respective transversely sloping inner surfaces is selected from warped plane-developed forms and a longitudinally prismatic form for substantially the length of the monohull planing section.

11. A boat hull according to any one of the preceding claims, wherein the substantially vertical outer surfaces are selected from warped planes, and surfaces bounding a longitudinally prismatic form for substantially the length of the monohull planing section.

12. A boat hull according to claim 11 , wherein the substantially vertical outer surfaces and the transversely sloping inner surfaces bound longitudinally prismatic forms for substantially the length of the planing section.

13. A boat hull according to any one of the preceding claims, wherein said lower edges transition to the hull surface portions by lateral planing surfaces extending to the bow of the vessel and diminishing in width from the turn-up of the bow.

14. A boat hull according to any one of the preceding claims, wherein said hull surface portions are convex.

15. A boat hull according to any one of the preceding claims, wherein said chines are undercut to form planing surfaces.

16. A boat hull according to claim 15, wherein at least a portion of each chine planing surface is inclined outboard and down.

17. A boat hull including a monohull planing section disposed between opposed chines, said monohull planing section including a keel having a keel planing surface extending substantially from transom to bow and bounded on each side by a recess extending substantially from transom to bow and formed between a transversely sloping inner surface adjacent the keel and a substantially vertical outer surface, each said outer surface being bounded by lower edges transitioning to a hull surface portion extending to a respective said chine.

18. A boat hull according to claim 17, wherein the lower edges of the outer surfaces transition to the deadrising hull surface portion via a lateral planing surface.

19. A boat hull according to claim 18, wherein the lateral planing surface substantially flat or concave.

20. A boat hull according to claim 19, wherein the widths of the respective keel planing surface and lateral planing surfaces are maximised to minimise the vessel draft for a given displacement, and moderated to reduce pounding while providing planing lift.

21. A boat hull according to any one of claims 17 to 20, wherein the substantially vertical outer surfaces and the transversely sloping inner surfaces bound longitudinally prismatic form spaces for substantially the length of the monohull planing section.

22. A boat hull including a monohull planing section disposed between opposed chines, said monohull section including a keel extending substantially from transom to bow and bounded on each side by a recess extending substantially from transom to bow and formed between a transversely sloping inner surface adjacent the keel and a substantially vertical outer surface, each said outer surface being bounded by lower edges transitioning, via a lateral planing surface, to a hull surface portion extending to a respective said chine.

23. A boat hull according to claim 22, wherein said keel is selected from a V- section keel and a section having a keel planing surface.

24. A boat hull according to claim 23, wherein the keel planing surface comprises a substantially flat keel planing surface.

25. A boat hull according to any one of claims 22 to 24, wherein the lateral planing surface is selected from substantially flat and concave lateral planing surfaces.

26. A boat hull according to claim 25, wherein the outer edge of the lateral planing surface forms the lower edge of the respective hull surface portion.

27. A boat hull according to claims 25, wherein the keel includes a substantially flat keel planing surface.

28. A boat hull according to claim 27, wherein the widths of the respective keel planing surface and lateral planing surfaces are maximised to minimise the vessel draft for a given displacement, and moderated to reduce pounding while providing planing lift.

29. A boat hull according to claim 22, wherein the form created by said keel and the respective transversely sloping inner surfaces is a longitudinally prismatic form for substantially the length of the monohull planing surface.

30. A boat hull according to claim 22, wherein the substantially vertical outer surfaces and the transversely sloping inner surfaces bound longitudinally prismatic form spaces for substantially the length of the monohull planing section.