PLANING HULL FOR ROUGH SEAS

TECHNICAL FIELD

[0001] The present invention relates to a watercraft, and particularly, to a watercraft hull having a very high deadrise central planing hull portion including longitudinal flat planing steps or panels.

BACKGROUND OF THE FNVENTION

[0002] Watercraft which are designed to operate in the planing mode are well known. Empirical evidence based on naval architecture and hydro-dynamic research, testing and experimentation has established beneficial performance attributes from three important features of such watercraft.

[0003] First, flat bottom planing hull surfaces with 0 degree deadrise angles are known to achieve the most efficient planing lift forces when operating at optimal trim angles. A watercraft utilizing flat planing surfaces will therefore generate more efficient planing lift than one with planing surfaces with higher deadrise. However, conventional wisdom is that a watercraft with exclusively flat planing surfaces cannot achieve high seakeeping and seakindliness in rough seas. [0004] Watercraft with a relatively flat or shallow V planing hull bottom, as measured relative to the horizontal, have efficient planing lift and are very stable, but have very poor seakeeping in rough seas, i.e., they also lack seakindliness and directional stability in rough seas.

[0005] Consequently, watercraft with a deep V hull bottom were developed to introduce better seakeeping and directional stability. The hulls of such boats, as taught in U.S. Patent No. 3,237,581 and U.S. Patent No. 3,085,535, are typically "V" shaped in cross section, with each leg of the V being generally flat and forming an angle to the horizontal, known as the deadrise angle, of approximately 20 to 30 degrees. The deadrise increases toward the forward end of the boat, and as a general rule, has a deadrise greater than 43 degrees at the bow to provide a fine entry. As such boats move forward in the water the narrow bow entry slices through the water, while the flatter surfaces aft provide some planing area, providing a balance between planing lift and seakeeping.

[0006] The planing lift for conventional deep-V hulls is typically augmented by the provision of running strakes on the hull surfaces as shown in Figure 1. These strakes are usually strips of triangularly shaped elements, in cross-section, appended to the outer hull surface that provide additional surface area for additional lift. They also cleanly separate water flow off the hull to reduce spray and drag. Indeed these strakes were originally called "spray strips."

[0007] Despite the improvements found with the deep V hull design, planing boats can provide uncomfortable rides. With too high a running trim, the bow pitches up over the crest of the wave, then plunges downward slamming back to the free surface. Another type of slamming occurs when the hull completely leaves the water, and is called re-entry slamming.

[0008] Conventional deep-V hulls will have excellent seakeeping if they can be controlled to run at speed with low trim while remaining upright (i.e., not heeled to either side). The stable mode of operation with the waterflow along the hull is shown in Figure 2a. Maintaining a conventional planing hull upright however is difficult to achieve since the deep-V hull is characteristically soft in roll and will heel in response to any asymmetric load such as weight shift, propeller torque, cross wind and waves. A dynamic system may be added to control the boat attitude; however, this adds complexity and cost.

[0009] When a deep-V boat heels to either side, its effective deadrise is decreased by the heel angle such that it loses the low slamming benefits of a deep-V hull. For example, a 24 degree deadrise hull heeled over by 10 degrees becomes a 14 degree deadrise hull normal to the water surface. In very high seas, it is not atypical for a small craft to experience up to 15 degrees of heeling so that the effective 9 degree deadrise surface is relatively flat to the water and pounds in waves, as illustrated in Figure 2b.

[0010] A particularly dangerous condition in which to have excessive roll is when turning in rough seas from a head to a quartering to a beam sea. Heeling over during this maneuver causes excessive pounding and uncomfortable to dangerous levels of roll.

[0011] A steeper deadrise than conventional deep V hulls would greatly improve the seakeeping and seakindliness of the hull. Even when heeled over, the surface of a deeper V hull will retain a significant deadrise relative to the water surface and thus cushion any impacts. Furthermore, the higher deadrise hull has less pitch excitation, thus allowing the hull forebody to penetrate the wave rather than kiting off of it. One such example is shown in U.S. Patent No. 3,415,213.

However, it appears that several problems must be resolved before a planing monohull with an extremely high deadrise can be successfully reduced to practice. For example, an extremely deep V hull has greater stability problems than a deep V being even more tender in roll. Further, although the orientation of its surfaces relative to the water improves its seakeeping and seakindliness, an extremely deep V hull also produces far less dynamic lift than a flatter hull. The inadequate planing lift of a deeper V makes getting over critical speed, also called hump speed, more difficult, reduces the payload capacity, and increases operating draft. In addition, the limited hull beam of an extremely deep V restricts arrangements and has low internal volume.

[0012] Also, narrow watercraft hulls with ultra high deadrise angles greater than 50 degrees and typically greater than 60 degrees in forward sections are known to transit through waves by penetrating and slicing into them with less heave and pitch vertical motion excitation than a hull with lesser deadrise, thereby improving a watercraft 's seakeeping and seakindliness. The hull can have sufficient vertically arranged and increasing buoyant volume to provide progressive lift to counter hull plunging motions when transiting through wave troughs; however, conventional wisdom on these vessels is that a watercraft with ultra high deadrise panels cannot achieve high lift and planing efficiencies.

[0013] Finally, monohulls, with higher fineness ratios, improve seakeeping of watercraft but can have static and dynamic stability issues as well as non-optimal running trims. However, conventional wisdom is that a narrow planing hull is not as efficient as a beamier hull and cannot carry as heavy loads. But, watercraft with entrapment tunnels and amas improve a narrow vessel's stability at rest or at speed and improve the vessel's ability to achieve critical planing speeds and carry high loads.

SUMMARY OF THE INVENTION

[0014] It is an object of this invention to provide a novel watercraft planing hull with improved seakeeping and seakindliness (in rough seas), seaworthiness, stability, planing efficiency, and payload capacity.

[0015] It is also an object of this invention to improve boat handling by providing a planing hull that produces fully banked turns and eliminates heeling and chine walking.

[0016] It is another object of the invention to provide a watercraft hull that will operate with substantially lower slamming than a conventional deep-V hull, especially when the hull hits the water surface heeled to a side when the hull is not symmetrically upright.

[0017] Such a craft could find use in military, commercial, and recreational boating markets, or in other words, applications that require a high seakeeping, high payload capacity craft that is able to maintain its speed and course in a seaway without excessive slamming or discomfort to the crew. BRIEF DESCRIPTION OF THE INVENTION

[0018] The subject of this invention is a watercraft hull formed with at least one pair of flat planing panels, also referred to herein as a "longitudinal step", which have substantially 0 degree deadrise angles and at least a pair of ultra high deadrise (UHD) panels associated therewith and connected to a pad keel, with a fine bow entry, and hard chine. The watercraft hull may also include a pair of outboard amas or sponsons that are symmetric about the hull centerline.

[0019] In accordance with one aspect of the present invention an entrapment tunnel monohull watercraft is provided that has a central hull portion formed of at least a pair of relatively flat panels having substantially 0 degree deadrise on opposite sides of the hull's centerline and a pair of ultra high deadrise panels associated therewith having a minimum average deadrise from transom to the bow of 50° or more, or in another embodiment, a deadrise of 50° or greater throughout the length of the hull. The ultra high deadrise panel arrangement improves seakeeping and seakindliness while maintaining the directional stability and performance for which entrapment tunnel hulls are well known.

[0020] In accordance with another aspect of the invention the described hull may include relatively flat panels (when viewed in transverse cross section), referred to herein as "fillets", bridging the flat 0 degree deadrise panels defining the longitudinal steps and adjacent ultra high deadrise panels and whose deadrise is between 20 degrees and 35 degrees at the transom. These fillets taper to blend into the UHD panels and the flat panels or longitudinal steps going forward to provide more beam for more favorable arrangements and better maneuvering capabilities, while staying consistent with the seakeeping and seakindliness features of the hull.

[0021] In accordance with another aspect of the invention the described hull features longitudinal steps that are relatively flat and substantially wide planing panels as integral parts of the hull having deadrise of about 0 degrees and variable widths in order to augment planing lift, improve seakindliness, and optimize efficiency.

[0022] A still further aspect of this invention is a planing watercraft with a hull form designed to be seaworthy, seakindly, stable and efficient when operating in rough seas that is comprised of generally flat panels to form planing surfaces with approximately 0 degree deadrise to which panels are attached having ultra high deadrise angles that are either greater than approximately 50 degrees along their length or have a minimum average deadrise angle of 50° along their length. The watercraft is symmetric about its hull centerline longitudinal axis with a fine entry bow, transom stern, hard chines with large planing flats, and a flat pad keel tapered towards the bow. The 0 degree deadrise surface defines at least one longitudinal hull step on each side of the hull configured between the pad keel and hard chines. Unlike existing planing craft, the planing stagnation lift line achieved by the hulls of the present invention is not a continuous line but rather a segmented one since the ultra high deadrise panels between stagnation planing lift surfaces provide relatively very little lift. It has been found that such a lift discontinuity can cause insufficient planing lift stability to the watercraft unless there are at least two stagnation lift planing surfaces between the pad keel and chine planing flats and the vertical offset between any two planing surfaces along the planing stagnation line is less than 6 inches. With the aforementioned longitudinal hull steps as the first stagnation lift planing surfaces, the second stagnation lift planing surface can be another longitudinal hull step with planing flats, triangular shaped running strakes or simple flat plate strips attached to the hull.

[0023] In accordance with another aspect of the invention, high deadrise fillet panels with deadrise angles between 20 and 35 degrees are attached between the ultra high deadrise panels that are attached to the sides of the pad keel and the lowest longitudinal hull step planing flats. The fillet panels are employed to reduce peak slamming pressures attributable to the longitudinal step planing surface and reduce hull wetted surface area frictional drag and are tapered into wedges at their forward end to blend into the adjacent hull panels. In addition ventilated aft swept flow interrupters (VASFI) may be installed in the hull fillet panels to improve seakeeping by maintaining an optimal running trim, to improve hull loading lift efficiency, to reduce hull wetted surface area frictional drag and to improve the watercraft 's turning capabilities. [0024] Still further, the watercraft may have one or more ventilated transverse hull steps. The steps improve seakeeping by maintaining an optimal running trim, improve hull loading lift efficiency and reduce hull wetted surface area frictional drag. Transverse steps that incorporate an aft sweep will also improve the watercraft's turning capabilities.

[0025] Transverse stability improving means may also be symmetrically attached to the watercraft outboard of the chine. The transverse stability improving means alternatives include entrapment tunnels, struts, amas, sponsons, demi-hulls, hydrofoils, lifting bodies, buoyancy collars including types that are inflatable, double chine hull panels and/or a combination thereof.

[0026] In another aspect of the invention, two or more hulls made according to the invention can be joined by a cross structure to form a multi-hulled watercraft.

[0027] In another aspect of the invention, the hull can be separated into two half hulls along the centerline longitudinal axis and each half made watertight. The two halves can be separated transversely from each other and joined by a cross structure to form an asymmetric catamaran.

[0028] The above and other objects, features and advantages of the present invention will be apparent in the following detailed description of illustrative embodiments thereof when read in connection with the accompanying drawings wherein:

BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 is a transverse cross-section at the transom of a conventional deep V planing hull;

[0030] Figure 2a is a front view of the hull of Figure 1 landing upright on the water surface and cushioning the landing;

[0031] Figure 2b is also a front view of the hull of Figure 1 shown impacting on its side and slamming the water when it is heeled over;

[0032] Figure 3 a is a side view of a watercraft hull designed in accordance with one embodiment of the invention;

[0033] Figure 3b is a front view of the watercraft hull shown in Figure 3a;

[0034] Figure 3 c is a bottom view of the hull shown in Figure 3 a; [0035] Figure 3d is a bottom perspective view of the hull shown in Figure 3a;

[0036] Figure 3e is an aft view of the hull shown in Figure 3a showing the deadrise and beam dimensions of interest;

[0037] Figure 4a is a side view of another embodiment of the present invention;

[0038] Figure 4b is a front view of the embodiment of Figure 4a;

[0039] Figure 4c is a bottom view of the hull of Figure 4a;

[0040] Figure 4d is a bottom perspective view of the embodiment of Figure 4a;

[0041] Figure 5 a is a side view of a third embodiment of the invention;

[0042] Figure 5b is a bottom view of the embodiment of Figure 5a;

[0043] Figure 5c is a bottom exploded perspective view of the embodiment of figure 5 a;

[0044] Figure 5d is a transverse cross-section of the bottom of the hull of the embodiment of Figure 5 a;

[0045] Figure 5e is a transverse cross-section of the forebody of the embodiment of Figure 5 a;

[0046] Figure 6a is a side view of a fourth embodiment of the invention;

[0047] Figure 6b is a bottom view of the embodiment of Figure 6a;

[0048] Figure 6c is a bottom exploded perspective view of the embodiment of Figure 6a;

[0049] Figure 6d is a transverse cross-section of the bottom of the hull of the embodiment of Figure 6a;

[0050] Figure 6e is a transverse cross-section of the forebody of the embodiment of Figure 6a;

[0051] Figure 7 is a bottom perspective view of yet another embodiment of the invention;

[0052] Figures 8a and 8b are schematic cross-sectional views at the transom of a watercraft according to the present invention, similar to Figure 3 a and

respectively including, in dashed lines, as an overlay, the transom cross-section of a conventional deep V planing hull landing upright, and heeled over;

[0053] Figures 8c and 8d are similar views taken midship of the embodiment of Figure 5 a; [0054] Figures 8e and 8f are similar views to Figures 9c and 9d but taken midship of the embodiment of Figure 6a;

[0055] Figures 9a and 9b are bottom plan views of hull pressure patterns for hulls designed in accordance with the embodiments of the invention, shown in Figures 3 a and 5 a respectively;

[0056] Figures 10a and 10b are bottom views of the hull wetting distribution on the hull bottoms of the embodiments of Figures 3a and 5a respectively operating a speed of about 35 knots;

[0057] Figures 11a and 1 lb are bottom views of the hull wetting patterns for the embodiments of Figures 5 a and 6a;

[0058] Figures 12a and 12b and 13a and 13b are respectively side and bottom views of the embodiments of Figures 5 a and 6a showing the location of the stagnation lift line for those hulls and the vertical offset of the stagnation points on the hulls;

[0059] Figures 14a and 14b are profile and bottom plan views, respectively, of a multi-hull watercraft designed in accordance with another embodiment of the invention, featuring a twin hull or catamaran using the hull structure of the embodiment of Figure 3 a; and

[0060] Figures 15a and 15b are profile and bottom plan views, respectively, of a multi-hull watercraft designed in accordance with one embodiment of the invention, featuring two half hull structures according to the embodiment of Figure 3a.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

[0061] Referring now to the drawings in detail, Figure 1 shows the transverse cross-section, at the transom, of a conventional deep-V hull. The hull has a V shaped bottom, including a conventional narrow keel 1, a plurality of (in this case three) pairs of flat panels 2, 4, and 6, separated by longitudinal strakes 3 and 5, and flat chines 7. The strakes are typically narrow wedge shaped elements with reverse deadrise primarily intended to separate water spray from the hull. The deadrise angle a for all the flat panels 2, 4 and 6 of the hull at the aft end or transom 8 is generally between 20 and 30 degrees. Typically, such hull panels increase in deadrise moving forward to a deadrise of about 43 degrees or slightly higher to provide a bow entry to slice through waves rather than slamming into them. The hull also includes a conventional curved bow 9 (see Figure 2a), a forebody section, and a forefoot.

[0062] As noted above, contemporary deep V hulls possess relatively good seakeeping characteristics; however, their abilities are limited and need much improvement. Seakeeping of such hulls remains acceptable when the

conventional hull is controlled to run at speed with low trim while remaining upright as shown in Figure 2a. However, maintaining conventional deep V planing hulls upright is difficult due to their softness in roll. When a deep V hull heels over, as seen in Figure 2b, its effective deadrise is decreased by the heel angle such that it loses the low slamming benefits of a deep V hull.

[0063] It has been found that at high speeds a deadrise between 50 and 65 degrees is required to mitigate slamming, particularly in the uppermost hull panels. In accordance with the present invention, the hull deadrise angle of the central planing hull portion is increased along its entire length such that it has enough deadrise to mitigate high speed slamming. In addition longitudinal planing steps are provided to provide planing lift surfaces.

[0064] Figures 3a, 3b, 3c, 3d, and 3e, provide various views of a first embodiment of a watercraft hull 10 according to the present invention. Multiple embodiments of the invention are described hereinafter and common reference numerals are used in the specification and drawings to indicate like parts.

[0065] Hull 10 has a bottom 12 including a substantially flat pad keel portion 30 and a pair of angularly related flat panels 31, immediately outboard and adjacent to the pad keel 30, which are symmetric about the hull centerline 14. The flat pad keel has a generally uniform width in the aft half of the hull having a beam of about 15 to 25% of the hull beam at the outer hull chines as measured at the transom. The pad keel tapers from about amidship forward to its apex 40 and curves upwardly. The panels 31 possess an Ultra High Deadrise (UHD) significantly greater than a conventional V hull and they extend the full length of the pad keel 30 from the transom 16 to the pad keel apex 40 (Figures 3c and 3d). That apex may be located adjacent to or at the forefoot 42 of the hull or between the forefoot and the intersection of the hull's design waterline 42' with the bow 11.

[0066] Hull 10 also includes one or more pairs of additional upper UHD panels which also are symmetrically located about the hull centerline. In the

embodiment seen in Figure 3a, the hull includes two pairs of upper UHD panels 34 and 36. The UHD panels 31, 34, and 36 have deadrise angles B, E, and G, as seen in Figure 3e respectively, that are approximately 50 degrees or more at the transom. The deadrise of the UHD panels can be identical or different. In one embodiment, the deadrise B, E, and G of the UHD panels 31, 34, and 36 are all 50 degrees at the transom and increase in deadrise angle in the bow area to provide a fine bow shape. In another embodiment, the deadrise at the transom may be less than 50° but the deadrise increase going forward from the transom is such that the average deadrise of the UHD panels along their length is a minimum of 50°.

[0067] Watercraft hull 10 of this invention also includes a pair of longitudinal hull steps 32 located immediately outboard and adjacent to the upper ends of UHD panels 31 symmetrically about the hull centerline. These longitudinal steps form flat planing surfaces and have a deadrise of approximately 0 degrees at the transom and along their entire length. The beam dimension of the longitudinal step will vary with the length and beam of the hull and their combined width may be 14% to 20% of the hull chine beam as measured at the transom 16. As seen in Figs. 3a and 3d, since the steps 32 from the transom forward to the bow have an angle of attack inclined upward relative to the pad keel the spacing between the pad keel and the lower longitudinal steps 32 increases forward of the transom. In accordance with the present invention the pad keel and steps 32 are vertically spaced a dimension D (Fig. 3e) that is no less than an average of four inches along the length of the steps or no less than four inches along their entire length. In the embodiment of Figure 3 the watercraft hull also includes a second pair of longitudinal hull steps 33 located between the top edge of UHD panels 34 and the lower edge of UHD panels 36. These steps also have approximately a 0 degree deadrise along their length, and are symmetrically arranged about the hull. [0068] As seen in Figures 3a and 3b the UHD panels 36 decrease in height as they move toward the bow of the hull and form an apex at the bow; the longitudinal steps follow the curvature of the hull and also curve upwardly in the bow. As a result the height of the UHD panels 31 and 34, while remaining relatively uniform in the aft and mid sections of the hull, increases in the bow area. It has been found that while the height of the UHD panels can be varied with the size of the vessel, the operation and seakindliness of the vessel is improved if the vertical offset between vertically spaced planing surfaces does not exceed 6 inches. The vertical spacing between successive steps or planing surfaces of the vessel need not be equidistant. In one embodiment the successive spacing upward from the pad keel may decrease. In addition, with a higher vertical spacing in rough water where the vessel is pounding on waves the delay between engagement of the successive planing surfaces can become too great and can cause uncomfortable slamming. To overcome this concern and maintain the benefits of the presence of the UHD panels in water reentry additional flat planing devices such as wedge or triangularly shaped strakes 33', having flat approximate 0 degrees of deadrise and a width of no more than 4% to 7% per side of the hull chine beam measured at the transom, may be placed in those areas of a UHD panel where the vertical spacing between the longitudinal steps exceeds 6 inches. In the embodiment of Figure 3, the demi-strakes 33' are mounted on the panels 31 in the bow area between the pad keel and the longitudinal steps 32 where the height of the panels exceed six inches and are extended from there to the bow. Outboard of the last UHD panel 36 the main hull portion includes hard chines 37 having a flat to slight reverse deadrise which extend along the top of UHD 36 to a point about amidships and then follow the curvature of the hull to the bow portion of the vessel. Alternatively, the chine may have a severe reverse deadrise or a concave curvature.

[0069] The innovative use of UHD panels and longitudinal steps as described above allows for the vessel to provide superior seakeeping while maintaining turning and maneuvering capabilities and providing more beam for favorable arrangements. [0070] This is shown, for example, with reference to Figures 8a and 8b which illustrate a schematic cross-section of the hull of Figure 3 including in dotted lines the outlines of a conventional V hull as shown in Figure 2. When an ultra deep V hull according to the present invention is heeled up to say 15 degrees as shown in Figure 8b, as compared to what is seen in Figure 2b the hull's UHD panels heel into the seaway and retain a deadrise as much as or greater than a conventional deep V hull which has a deadrise of 20 to 30 degrees. If the UHD panels have a deadrise of 50 degrees, and there is 15 degrees of heel, the effective deadrise is 35 degrees on the impacting hull panel, thereby greatly reducing slamming and pounding of the hull even when heeled over.

[0071] As also seen in Figure 3a, the hull of this invention may also feature amas or sponsons that form entrapment tunnels 39. Entrapment tunnel planing hulls are well known in the art. They provide longitudinal tunnels alongside a central planing hull portion, i.e., between the central hull portion and outboard sponsons or amas. These tunnels are designed to entrap dynamic air and hydraulic pressure from the central and amas hull portions at speed to create greater hull lift raising the hull further out of the water. This reduces wetted surface area on the hull, and increases speed and efficiency.

[0072] An improved form of an entrapment tunnel was proposed in U.S. Patent No. 7,418,915. The hull disclosed in that patent includes outboard amas which provide the benefits of mitigation of capsizing, efficient progressive lift, and improved directional stability for navigation course keeping.

[0073] An entrapment tunnel is formed in this embodiment between the hard chine 37 on the hull, the tunnel ceiling, and a depending ama. These surfaces may be shaped using a pair of splined curve shapes, or they may be constructed of relatively flat or curved panels 50, 51 (as shown in Figures 3e, 5e and 6e). The inner surfaces of the tunnel of this invention can also be formed as taught in U.S. Patent 7,418,915, the disclosure of which is incorporated herein by reference.

[0074] Both the amas and the longitudinal steps provide transverse stability to help keep the hull upright both at rest and underway in rough seas. As noted above, a hull that remains upright provides superior seakeeping and

seakindliness. [0075] It is also noted that in this embodiment the roof of the tunnel 39

terminates in a step several feet forward of the transom 16 to allow for the placement of trim tabs in the aft end of the tunnels.

[0076] Referring now to Figures 4a-4d another embodiment of the present invention is illustrated which represents a modification of the embodiment of Figure 3. In this embodiment the tunnel panels are continued to the rear transom 16 and fillet plates or surfaces 41 are added at the aft end of the hull. These fillet plates or surfaces have a lower deadrise than the UHD panels 31 and extend transversely from a position adjacent and/or slightly spaced above the outer edge of the pad keel to a point at or adjacent the outer edge of the longitudinal step 32 at the transom and going forward past the longitudinal center of gravity (LCG) of the hull. The high deadrise (HD) fillets 41, which typically would have a deadrise of 25 degrees to 35 degrees, (shown shaded in the drawings for clarity) are tapered symmetrically at their forward ends to blend into the adjacent UHD panels 31 and longitudinal step 32 forward of the LCG. The provision of these fillets reduces peak slamming pressures attributable to the longitudinal step planing surfaces at the aft end of the hull and reduces wetted surface area frictional drag.

[0077] A further variation is also shown in Figures 4a-d, in that the fillet structures 41 bridging the pad keel and longitudinal steps 32 may be provided with Ventilated Aft Swept Flow Interrupters (VASFI), as detailed in U.S. Patent 7,845,301, the disclosure of which is incorporated herein by reference. VASFI improve planing hull efficiency but also improve turning. In the illustrated embodiment two VASFI devices 45 are used on either side of the hull centerline in fillets 41 in a swept back arrangement. One pair are aft of the LCG and one pair forward of the LCG. As described in Patent No. 7,845,301 these VASFI constitute extendable plates which, when extended, act as transverse hull steps to interrupt flow and reduce wetted surface area as well as to assist in rapid turns.

[0078] Referring now to Figures 5a and 5b, another embodiment of the invention is shown which includes the same panel arrangement as the embodiment of Figures 4a-4e (wherein elements marked with the same reference number signify like parts). In this embodiment the pad keel includes a pair of transverse steps 50 formed therein. These transverse steps are swept rearwardly and ventilated from an internal hull ventilation system in any known or convenient manner.

Transversely stepping a planing hull is a well-known technique to improve its efficiency by increasing the planing lift and reducing the hull drag. In the embodiments of Figures 4 and 5 the fillets extend longitudinally from the transom and are tapered both longitudinally and transversely as they extend forward, gradually exposing an increasing amount of the adjacent UHD panels and longitudinal planing steps. This creates wedge shaped panels that terminate in an apex at the joint between the adjacent UHD panels and step 32 near or forward of midship and no more than 60% of the hull's waterline from the transom. In a preferred embodiment, the forward-most points of the tapered fillets coincide with the stagnation point on the adjacent longitudinal step 32 to augment the stagnation pressure on the step, while allowing for the

aforementioned benefits of the fillets on the aft end of the hull.

[0079] Figures 5a-5e illustrate a preferred embodiment of the present invention in which the hull's hard chine and the forward end of the amas are carried forward to the bow to a straight bow portion at the top of the bow as seen in Figure 5b.

[0080] Figures 5d and 5e illustrate how the deadrise of the UHD panels and the width of the longitudinal steps may vary moving forward in the hull.

[0081] Figures 6a-6e illustrate another smaller embodiment of the invention whose pad keel 30 terminates forward of transom 16 defining an aft step 32'. At the transom the hull has a single UHD panel 34 on each side of the hull. At the step 32' the pad keel 30 begins, as does the UHD panel 32 longitudinal step 33 and fillet 41. In this embodiment the forward portion of the hull includes the strakes 31' previously described. In addition, because the height of the UHD panel 34 is greater than 6 inches between the step 33 and the chine 37 (but preferably less than 12 inches) an additional longitudinal strake 35 is provided to mitigate slamming as described above. In this case the strake is illustrated as a flat plate member extending laterally from the hull with zero deadrise midway between chine 37 and step 33 from the bow to the transom. [0082] As also seen in Figures 6a-6c the ama tunnel structure extends to the bow but merges into bow surface.

[0083] Figure 7 is a schematic illustration of another embodiment of the invention in which the main hull has a pad keel, a lower pair of UHD panels 31 and a first longitudinal step 33 above it. In this case the step tapers in width moving forward to provide increased lift at the stern. A second set of UHD panels 34 are provided above the lower step. They terminate at the hard chine of the main hull above which the ama tunnels begin. In this embodiment the keels of the amas are provided as long narrow hulls constructed in accordance with this invention having narrow pad keels 30', UHD panels 31" above them terminating in longitudinal planing steps 33" and an additional pair of UHD panels above that step.

[0084] Figures 8c-8f are similar to previously described Figures 8a and 8b. They illustrate the effective deadrise on the heeled over hulls of Figures 3 and 5 amidships at a 15° heel. As seen therein the hull sides have significantly greater average deadrise to enter the water during rough seas and mitigate pounding as compared to a conventional V hull.

[0085] Figures 9a and 9b are bottom views of the hulls of Figures 3a and 5a shaded to show the pressure distributions on the hulls of the present invention. (The darker shaded areas are of higher pressure than the lighter ones.) As seen therein at a speed of 35 knots the hulls of this invention have a segmented planing stagnation lift line with at least two stagnation lift planing surfaces between the pad keel and chine planing flats for planing lift stability and seakindliness.

[0086] Figures 10a and 10b are similar bottom views showing the wetted surface areas on the hulls of Figures 3 a and 5 a at 35 knots speed. These illustrations indicate that the wetted surface areas for these hulls are generally triangular and narrow in shape, thereby minimizing drag.

[0087] As seen in Figure 10a the wetted surface is staggered moving aft as the longitudinal steps interrupt flow from the UHD panel directly above it. In addition, wetting ends at the steps formed at the aft end of the pad keel and the tunnels again reducing drag. Similar effects are achieved with the hull shown in Figure 10b where the VASFI interrupters act as steps and substantially reduce if not eliminate water contact with the lower fillets 41 aft of the first set of VASFI interrupters.

[0088] Figures 11a and 1 lb are similar to Figures 10a and 10b and illustrate the wetted surface areas of the hulls of Figures 5 and 6 at 35 knots speed. The pressure distribution patterns for those hulls will be substantially the same as the hulls of Figures 3 and 5.

[0089] Figures 12a and 12b and Figures 13a and 13b illustrate in dotted lines the stagnation lines for the hulls of Figures 5 and 6, the location of the stagnation points on the pad keels, demi-strakes, longitudinal steps, chines and ama tunnels and the vertical spacing between successive stagnation points on those hulls. The creation of a segmented stagnation line with vertically spaced stagnation points which result from the hull structures of the present invention produce a hull which will remain stable in rough seas, piercing the waves with reduced pounding while providing sufficient planing surface area to operate at high speeds.

[0090] A further variation of this invention includes multi-hull watercraft comprised of two or more hull structures designed according to this invention. For example, Figures 14a and 14b show one embodiment comprised of a catamaran hull structure 60 including twin-hulls 62 and a deck or upper hull structure 64 between them. In another embodiment, shown in Figures 15a and 15b the catamaran hull structure is formed of two half hull structures 66

connected by a deck or upper hull 68 and defining a central tunnel 70.

[0091] Although illustrative embodiments of the invention have been described herein, it is to be understood that the invention is not limited to these specifically disclosed embodiments, but that various changes and modifications may be effected therein by those skilled in the art without departing from the scope or spirit of the invention.