Patent Application
20140096710
The present invention generally relates to hull designs for watercraft capable of planing such as power boats (including speed boats and yachts), surfboards, sailboards, stand up paddle (SUP) boards, and kite and wake boards.
Many watercraft are designed to operate in a planing mode as well as in a displacement mode. In the planing mode of operation, lift is derived from a downward deflection of water by the shape of the hull. In the displacement mode of operation, which generally occurs at lower speeds as compared with planing mode, lift is derived from the weight of water displaced by the hull.
In transition between these modes there is often considerable wave and turbulence drag. This is often due to the conflict in the preferred watercraft design features for displacement mode operation, e.g. a slender/narrow hull, versus preferred features for planing mode operation, e.g. a flat planing bottom or a flat planing bottom with a dead rise angle. A planing bottom may be split in the transverse direction (as in a tunnel boat) or split in the longitudinal direction with displacement in the vertical direction at the split. For most hulls intended to be operable in a planing mode of operation, the bottom shape is generally flat in the longitudinal direction near the back or stern and has rocker toward the bow.
For a wing/deep hydrofoil, as given in the “HYDROFOIL HANDBOOK Vol. II, Hydrodynamics Characteristics of Components”, OTS-US Dept of Commerce, Eq. 1.6, the two-dimensional lift coefficient, CL, is given by:
C
L=2π(αo+2f/c), (1)
where αo is the attack angle, f is the maximum deviation of the mean camber line from the chord line which goes from the nose to the tail of the wing section, and c is the chord (e.g. front to back dimension; the length of the cord line) of the wing.
Similarly, from this handbook and other sources, for a planing surface, the two-dimensional lift coefficient, CL, at small αo is given by:
C
L=0.9π(αo+2f/c), (2)
For three dimensional lift coefficient, CL, and a surface which is flat in the width dimension, CL is approximately:
C
L=0.9π(αo+2f/c)A/(2+A), (3)
where αo is the attack angle, f is the maximum camber of the wetted planing surface, c is the chord of the wetted length of the planing surface at a given speed and load, and “A” is the aspect ratio. Aspect ratio, A, is given by the equation A=b2/area, where b is the width of the planing surface and “area” is the wetted planing area. More accurate values of CL for a flat surface are given by Daniel Savitsky, in “Hydrodynamic Design of Planing Hulls”. Note that hereafter, f is used to mean the maximum camber of the wetted planing surface.
If the wetted planing length includes the above mentioned front rocker, which is a common feature for watercraft expected to transition from displacement mode to planing mode, then “f” is negative and CL is considerably less than that for a flat planing surface having the same wetted length and area. In sailboards and most planing watercraft, this leads to a peak, or larger peak, in the drag when attempting to go from a displacement mode to a planing mode. In power boats it leads to αo increasing to a value much bigger than is optimum and sometimes even produces cavitation of the propeller (i.e. “prop”).
While rocker (negative values of “f”) decreases the planing force (i.e. the lift force on the planing surface), camber (positive values of “f”) can have even worse effects on the performance of a planing surface of a planing hull. Camber at the stern of the hull of a planing power boat, also known as hook and camber, can cause severe porpoising. Even though a cambered surface with αo=0 has no dynamic drag while still having lift, porpoising and the force of the water on the front can cause a watercraft to submerge at the bow.
In general, drag is undesirably increased for a planing hull with a camber at the stern due to the increased wetted area that results from a reduced planing angle. Three examples of this type of camber are given in European patent no. 0059345, and U.S. Pat. Nos. 3,274,966 and 5,582,123.
The effects of net concavity/camber in the longitudinal direction include: 1) at transition speed it will increase the transom depth thus increasing the hump drag and/or 2) will push the bow into the water at high speed. If it does, the drag will be larger. Hump drag is a peak in drag often occurring in the transition mode of a watercraft.
Various hull designs have been developed in an attempt to overcome drawbacks of a mono-hull with a front rocker. Tunnel boats, for example, are efficient in displacement mode and at high planing speed, but due to a reduced planing surface, they require achieving much higher speeds as compared to mono-hulls in order to transition from displacement mode to planing mode.
U.S. Pat. Nos. 3,149,351 and 4,843,988 teach the use of a slot alongside of a planing surface to reduce drag. U.S. Pat. No. 6,138,601 teaches the use of slots above a winglet which are trim tabs at the rear corners.
U.S. Pat. No. 5,456,202 teaches the use of a planing surface in front of a total center of gravity. It is not inclined at a larger attack angle than the other planing surface and is rockered in the front like a normal mono hull power boat. These hulls have the problem that when transitioning to planing mode the step causes turbulence and additional wave drag.
U.S. Pat. No. 3,802,370 teaches a planing surface with a portion having an incline relative to the rest of the planing surface; however, it consists of two longitudinal surfaces which are small and narrow in width compared to the other planing surfaces.
U.S. Pat. No. 6,138,602 describes a hull with a cambered front and a rear planing surface which is rockered in the middle where it would normally be in the water when planing. Thus it would have a downward suction force that will reduce its efficiency at slower planing speeds.
U.S. Pat. No. 4,924,742 teaches using three point planing, a concept which is generally well known in the art. The general concept is to have two sponsons in front of a hull's center of gravity, both sponsons extending below the remaining surfaces of the hull's underside. Various shapes for the sponsons are known. Such three point hydroplanes are designed for planing at over 40 mph. The width of a sponson planing surface is small compared to the width of the hull. This together with the drag behind the sponsons causes the lift/drag to be small when transitioning to the planing mode. Such hulls have the problem that when transitioning to planing the sponsons cause turbulence and additional wave drag, and since the size and lift of the sponsons is small, increased speed is needed for transitioning to planing mode.
Keller in U.S. Pat. No. 7,793,604 and W. Sottorf in NACA TN No. 739, 1934 show that angling or curving the outer edges of a planing surface can increase lift/drag efficiency. Keller shows that a 14° angled/curved outer edge is more efficient than a flat edge. Sottorf shows that surface with a 10 degree dead-rise which curves down at 23° is more efficient than a flat surface for planing angles >6° and has a higher maximum lift/drag vs. planing angle. Sottorf also shows that for a 48° dead rise, a 28.7° edge angle is better than both 0.0° and 48° outer edge angles.
Blount, D. L. and Codega, L. T. in “Dynamic Stability of Planing Boats” Marine Tech. Vol. 29, No. 1, January 1992, pp. 4-12, have shown that hydrodynamic forces on a rocker surface can cause suction, similar to that on the top surface of a wing, and that this can lead to bow down and unstable conditions both in the longitudinal and transverse directions. They and others like Brian Hinde have suggested using steps near this front rockered surface to correct this downward suction force.
Clement, E. P., “A Configuration for a stepped Planing Boat Having Minimum drag (Dynaplane Boat)” and Johnson, V. E. Jr., “Theoretical and Experimental Investigation of Supercavitating Hydrofoils Operating Near the free water Surface” NASA tech. Report R-93 1961. Second edition describe a motorboat design optimized for speeds of 40 to 80 mph and more. The planing surface is small, with a design aspect ratio of 2. At the hump speed, the resistance is shown to be larger than that for a normal motorboat with the same dead rise angle. “Hump speed” is used to refer to the transition speed at which a peak in drag/lift is observed over the range of transition speeds.
Harper, J. A., U.S. Pat. No. 8,122,840 uses a Johnson 3 term camber on the back part of a displacement hull.
For power yachts, size and speed affect the ideal shape. The high speed power boats might be a tunnel boat, a so called cigarette boat, or a three point hydroplane type. For a somewhat lower speed, they may preferably be a type of deep Vee hull. However, particularly in bigger yachts where their size requires a lot of power and a lot of fuel, there is a need for improved efficiency in speeds of 20 mph up to about 35 mph.
In an embodiment, a watercraft hull is provided having large planing lift and efficiency (i.e. lift to drag ratio) at low speeds of, for example, about 6-15 mph for a sailboard and 12-30 mph for a yacht.
Generally, a watercraft hull according to an embodiment is dynamically stable even in choppy water. It has a large range of planing speeds (8-25 mph or more for sailboards, 12-80 mph or more for power boats, and 12-35 or more for large yachts).
Exemplary embodiments furthermore have a smooth flow of water around the hull with minimal wave and turbulent drag, particularly at transition speeds.
To achieve the foregoing and other advantages, a watercraft hull has a main planing surface wherein at least the back 20% has a planing angle which is greater than an average planing angle for the hull. The main planing surface, which may also be referred to as a high lift surface, is cambered with the possible exception of roughly the front ⅔rds. That is to say, at least the back one third of the main planing surface is cambered. This bears some similarity to the bottom surface of some cambered wings, foils, and supercavitating foils. The maximum width of the hull and a front edge of the at least a back one third of the high lift surface are preferably at the same longitudinal position plus or minus 15% the length of said hull. The front part of the high lift planing surface can have negative camber (i.e. rocker), which decreases the average planing angle of the cambered part and thus decreases the dynamic drag. The beam of this surface is greater than ⅔rds of the hull width.
Even at the highest intended speed of a watercraft hull, the center of lift of the high lift surface should be in front of or near the center of gravity of both the hull and the load, i.e. the total center of gravity, CG. The center of lift of the high lift surface is closer to the longitudinal midpoint of the mean wetted surface length (about 65% of the mean wetted length) of this surface from the end of the mean wetted surface length at a given speed, especially as compared with a flat or rockered surface. In the case of a flat or rockered surface, the center of lift is much closer to the start of the wetted surface.
Part of a high lift surface may be the bottom of a wing/winglet. In embodiments having this feature, a main purpose of the wing or winglet is to allow water which flows over top the wing/winglet to smoothly combine with water flowing under the wing/winglet, thereby reducing the turbulence and wave drag of the hull. The top surface of the wing/winglet can also provide some lift.
In an embodiment having one or more wings or winglets, a wing/winglet can also reduce the bow wave by providing an area in which the length is about 5-20 times larger than its width. To increase reduction of drag, the hull can have slots above the back and/or front of the wing, such that the water during displacement, transition, and slow planing modes of operation can flow smoothly around the center of the hull. Slots which may be used in accordance with the invention include those taught in PCT/US2010/029785 and U.S. patent application Ser. No. 13/946,798 by the same inventor, the complete contents of both references being hereby incorporated herein by reference. One or more back slots can allow for a smaller transom width and/or further reduce the transom's depth below the water level, particularly at displacement and transition speeds. These effects serve to further reduce the hull's drag in transition mode.
A watercraft hull according to an embodiment has a cambered planing lift surface (hereafter referred to as a front lift surface) in the front 40% of the length of the watercraft. This front lift surface preferably supports <50% of the total planing lift of the hull and more preferably <30% of the total planing lift of the hull. This surface can provide a larger minimum value of the planing attack angle αo, particularly at high planing speeds. For very high planing speeds, the cambered front lift surface can have limited width or be separated into two parts. In this way the main planing surface will normally have a part which is wetted, and as a result three planing areas are formed from the main planing surface (i.e. the high lift surface) together with the front lift surface.
The hull preferably has a back planing surface in back of the high lift surface. This back planing surface together with the high lift surface and the front lift surface controls the attack angle (αo) when in planing mode. As a result, at higher planing speeds the hull is stable and porpoising is minimized or prevented. A back planing surface in back of a high lift surface should be narrower, preferably about ½ the width of the end of high lift surface. The back planing surface preferably forms over about 15% of the end/rear of the hull. The back planing surface can taper to zero at the transom. An advantage of the narrower back planing surface is reduction of the drag due to the width and depth of the transom. It is preferred that both the back of the high lift surface and some part of the back planing surface be cambered with increasing camber toward the end of said surfaces for some smaller watercraft like sailboards (the end being a rearward portion as determined longitudinally with respect to the hull).
In some embodiments it is preferred that there is another planing area/surface at the back/rear of the hull which is at a higher height such that at slow planing speeds it balances the lift from the cambered front lift surface and/or the front of the high lift surface. For higher planing speeds this additional planing area/surface can have a height which keeps most of it out of the water.
In some embodiments, a back planing surface is over a part of the watercraft which should not be ventilated, such as a fin or propeller. For such cases, a back planing surface should be a smooth continuation of a center rockered keel area. This back planing surface can be cambered, and for embodiments having a propeller configured to operate with a portion above the water, the back planing surface can be stepped from that of a high lift surface and the center keel area. A suitable step includes that which is disclosed in PCT/2009/057138, the complete contents of which are hereby incorporated herein by reference. This step offers the advantage of limiting additional drag at slower speeds.
For sailboards, a back planing surface can be an extension of the keel area of the high lift surface, and for yachts and power boats it can be recessed into the hull behind a camber/slope step or a combination of the two.
To further increase lift, a high lift surface may be concave downward in the transverse direction toward the edge for confining or reducing water outflow. Particularly for sailboards, the curve downward may change to a curve upward at the edge of the hull to provide a soft rail. Keller in U.S. Pat. No. 7,793,604 teaches an optimum downward curved angle is ≧14° for purposes of lift, while W. Sottorf in NACA TN No. 739, 1934 shows that for a 48° dead rise 28° is better than both 0 and 48°. These teachings can be used with the practice of the invention. For a flat or small dead rise near the keel area and for slower speeds, the downward curve in the transverse direction may be roughly 20°. Those of skill in the art will recognize this angle may vary depending on the length of the downward curve, and angles for specific embodiments may be determined by routine experimentation and/or basic geometrical calculations. While angling or curving the outer edges of the planing surfaces can increase the lift/drag efficiency, it can also increase the rolling instability. For sailboards, roll is controlled by a sailboarder, and thus this possible drawback is minimized. However, for yachts and power boats it is preferable to flatten and/or slightly round the rail similar to the rail in a slalom water ski. This reduces the lever arm of the elevated side versus the deeper side, because the water on the elevated side will clear at the end of the curve, similar to the effect of a step.
Another purpose of this front lift surface is to control αo if the center of pressure on the high lift surface is behind the CG, and thus to maintain a high efficiency, i.e. lift/drag. For this purpose the bottom part of the front lift surface should be cambered.
For many watercraft, a front lift surface should be divided into two surfaces. The first is a lower cambered surface for controlling αo. This may have a triangular shape in plan view to slice into smaller waves for a smoother ride as in Peter Payne's Seaknife watercraft. The second surface is an upper surface which raises the bow over large waves.
To add longitudinal stability in choppy water and waves, the front of the hull can have a second front lift surface at a planing angle on the order of 15°, which serves to lift the nose of the hull when the wave or chop would attempt to override and submerge the nose of the hull (and thereby add considerable drag). In embodiments having a front lift surface and/or a second front lift surface, the front lift surfaces take the place of the normal bow of a rockered hull. Since it has been shown by Blount et al. (referenced above) that rockered surfaces generally produce a downward suction force, it is preferred that a front lift surface and a second front lift together have one or more steps to reduce or eliminate this downward force. These steps should not be above another surface. This is preferable so that the hydrostatic pressure in the water, and not a surface which is part of the hull, turns the water. The purpose of one or more front lift surfaces and the steps in it are to give the hull dynamic stability for normal waves and chop and for movements which shift the center of gravity. Things which can shift the CG slightly in a yacht are the amount of fuel, where some load is stored, or movement of people.
In some embodiments, a hull according to the present invention reduces resistance at transition/hump speed and also gives lower than normal resistance in the 20-30 mph range, even to the point where a “hump” in the drag characterization is lower than the drag at the start of planing mode for some embodiments. Hump speed drag is a peak in drag in the transition mode of a watercraft.
This invention can greatly improve that efficiency of a planing mono-hull or even a tunnel/catamaran, or trimaran. It may also be used for a bass type boat up to about 60 mph or more.
The foregoing and other objects, aspects, and advantages will be better understood from the following detailed description, in which:
FIGS. 5A1-5A3 show multiple features in
For the purposes of this disclosure, “planing mode” is defined as the lift being mainly hydrodynamic lift (≧90%) and when the hydrostatic lift is ≦10% of the total lift. “Displacement mode” is where the lift is mainly hydrostatic and the drag vs. speed is increasing nonlinearly with increasing speed. As used herein, “displacement mode” is used to indicate that ≧70% of the lift is hydrostatic lift and the remaining lift (≈30% or less) is hydrodynamic lift. Thus the board or watercraft hull is in “transition mode” when the hydrostatic lift is between 70% and 10% of the total lift and the hydrodynamic lift is most of the remaining lift, that is, 30% to 90%. In “transition mode”, the drag vs. speed normally goes through a hump or peak, but this is not always the case if the weight is small or the wave drag is sufficiently reduced.
The main drag forces for a hull in planing mode are the dynamic drag, which is the dynamic force in the backward direction, and the skin friction. The main drag force in displacement mode is wave drag, which is the difference of pressure on forward facing surfaces and backward facing surfaces. In transition mode, all three—dynamic drag, skin friction, and wave drag—are important, with wave drag and dynamic drag being the most important.
It should be noted that that although some features of the invention are described in the context of particular exemplary embodiments disclosed herein, these features are not limited to the embodiment providing such context. Features which correspond across various embodiments described are identified by the same numeric identifier.
Unless otherwise noted, the watercraft hulls discussed herein and shown in the figures are generally symmetrical across a longitudinal plane of symmetry. For clarity, some structures are numerically labeled only on a starboard side or only on a port side of the boat although the structures are present on both sides. Furthermore, features (e.g. a planing surface) which are bisected by the longitudinal center line of the hull may be discussed in the singular and have a reference number pointing only to the left half or right half. It should be understood that the center line of the hull does not define a limit to a feature, region, surface, or structure to which a reference number points unless such intent is clear by the context of the reference numeral as discussed herein.
One way in which the performance of a watercraft hull may be characterized is by a dimensionless Froude number. Froude numbers are dimensionless and allow for comparison of watercraft hulls of different size. Using a Froude hull length number (Fl),
F
l
=v/(gl)1/2, (4)
where V is hull velocity, g is acceleration due to gravity, and l is the watercraft hull length.
Note that v, g, and l must be in the same unit system so that Fl is dimensionless. For this invention, approximate Froude hull length numbers for the different modes/speeds are as follows:
The values above for transition and planing speeds are below typical transition and planing speeds in the art due, for example, to the high lift surface and the resulting high efficiency thereof according to the present invention.
Referring now to the drawings and more particularly to
The amount of curvature of the rocker over the front portion of high lift surface 2 should be small enough that any negative pressure caused by it does not ventilate this surface until such speed that a step in front of it ventilates part or all of the rocker (i.e. the rocker of high lift surface 2 does not ventilate until step 8 causes it to ventilate). Thus, this rocker is much smaller than that which is the common rocker of a typical monohull in the art or the camber after it produces more lift than the down force of this rocker. As a result of the greater camber, the end planing angle of the camber/rocker surface is greater than the planing angle of the start of this surface. This is exactly opposite of what is typical for prior art, although similar to what is taught in Clement.
In general, significant features of the invention include:
It is preferred that an average camber of the front lift surface, back planing surface, and high lift surface together is less than or equal to zero. Said differently, a line from the front of the front lift surface to the middle of the high lift surface to the back of the back planing surface generally has zero or negative camber.
In some embodiments, the mean wetted length of high lift surface 2 may be as little as about ⅕th of its width. It is then the general case that greater camber over a back portion of high lift surface 2 gives greater f/c (see Equations 1-3) for higher speed, thus increasing the efficiency, defined as the ratio of lift to drag (i.e. lift/drag). The beam or width of high lift surface 2 is preferably greater than ⅔rd of the hull width. A high lift surface preferably forms at least ⅔ of a portion of an underside of the hull, this portion starting 30% of the hull length from a front of the hull and ending 20% of the hull length from a back of the hull.
Configurations for a camber of the high lift surface 2 may be similar to the three term (3 term) Johnson camber as described in Clement, “A Configuration for a stepped Planing Boat Having Minimum drag (Dynaplane Boat)” page 47, the entirety of the Clement reference being incorporated herein by reference, or a five term (5 term) Johnson camber such as is described in NASA Technical Report R-93, “Theoretical and Experimental Investigation of Supercavitating Hydrofoils Operating Near the Free Water Surface” by Johnson (the entirety of which is incorporated herein by reference). A camber of high lift surface 2 may also be similar to a combination of a three term camber and a five term camber. In short, the general configuration for the curvature of high lift surface 2 is a camber in the back and a slight rocker in the front. The cambers of embodiments having a five term camber are notably more exaggerated than the cambers of embodiments having a three term camber, with more/greater camber at the back of high lift surface 2 in the former case.
“y”, the three term Johnson camber from Clement above, is given by:
y=C
L,d
×c×{(−20χ3/2)+(80χ2)+(−64χ5/2)}/(7.5π), (5)
where “y” is measured from a reference line, CL, d is the two dimensional lift coefficient for a cambered surface when the planing angle is zero, “χ” is x/c, where “x” is longitudinal distance from the front of the Johnson's camber and “c” is the chord length of said camber. Note that “y” is negative for χ=1, i.e. the end of the camber. This is so that when the reference line is at zero attack angle, all of the surface has a positive lift pressure.
The five term Johnson camber is treated herein as:
y=C
L,d
×c×{72χ−2240χ3/2+12600χ2+−30912χ5/2+35840χ3−15360 χ7/2}/(819), (6)
where y=0 for χ=1. Note that this equation differs from that disclosed in the Johnson reference; specifically, the first cofactor is “72” instead of “210” as in Johnson. This variation aligns the reference line to the chord line, which roughly aligns a 3 term Johnson camber with a 5 term Johnson camber.
The back of a 5 term Johnson camber is very similar to a 3 term Johnson camber. As a result, some embodiments advantageously provide approximations of both camber types such that the speed and hydrodynamic mode (e.g. displacement, planing, or transition) determine which camber is actively affecting the hydrodynamics of the watercraft. Specifically, a 5 term camber is provided over the area of the hull including the wetted length at speeds in which the boat is in transition mode or slower speeds of planing mode. The wetted planing length is reduced as the watercraft increases to high speeds in planing mode. The so called high speed wetted planing length is roughly the back/rear portion of the 5 term camber region, in particular the region representative of a Johnson 3 term camber. Thus at low planing speeds and transition speeds, the hull interfaces with the water surface via a 5 term camber, and at higher planing speeds the hull interfaces with the water surface via a 3 term camber. However, the camber in the back and the rocker in the front can be variations of this, i.e. not restricted to 3-term and 5-term.
In some embodiments, the center of lift/pressure on high lift surface 2 for high speeds is about ¾ of the wetted length from the end/rear of high lift surface 2. If this condition occurs at the maximum design speed, then the center of lift is preferably in front of and/or near of the total center of gravity, CG. The CG position for some power boats, particularly for outboards and stern drives, is located roughly in the back ¼ of the hull. For other power boats and yachts, it may be closer to the center of the hull depending on where the motor is located. Ideally, the center of lift is furthest to the back of the hull when the hull is operating at the maximum design speed. At any operation speed less than the maximum design speed, the center of lift is further forward on the hull. By “in front of and/or near”, it is generally meant that in an exemplary embodiment, a center of dynamic lift of a high lift surface 2 is at or in front of a point which is a fraction of the hull length behind a total center of gravity of the hull under loading, the fraction being preferably 15% of the hull length. At least high lift surface 2 should be configured in size and longitudinal position to achieve this effect.
High lift surface 2 would result in a reduction in the attack angle of a conventional rockered bow. Instead of a traditional bow, embodiments are provided with a front lift surface 7. Front lift surface 7 is a second cambered surface in the front 40% of the hull and supports <50% of the hull's planing lift and preferably <30% of the hull's planing lift. A purpose of this front lift surface is to control αo if the center of pressure on the high lift surface is behind the total center of gravity (CG), and thus to maintain a high efficiency, i.e. lift/drag. For this purpose the bottom part of the front lift surface should be cambered with a mean angle in a range of 2-10°, preferably about 4°, and end in a small step with an end angle of 7-14°. Thus this front surface camber, together with the main lifting surface, controls αo when αo is small. It is preferred that the center of dynamic lift/center of pressure of the high lift surface is at or in front of a point which is 15% of the hull length behind a total center of gravity of the hull under loading (i.e. the total center of gravity of the hull together with a sailor, cargo, etc. as the case may be).
At least part of this front lift surface 7 ends/terminates in at least one step, the step being configured to dewet at least a longitudinal center portion or a longitudinal outer portion of the high lift surface in planing mode. Multiple configurations for step 8 which are usable in the practice of the invention will occur to those of skill in the art. One such configuration is that taught in PCT/US2009/057138, which is incorporated herein by reference. The radius of curvature of the step is on the order of 1 cm (i.e. range of 0.3 cm to 3 cm) with a depth (i.e. difference in surface location in a vertical direction) behind and near the step of less than 1 cm (for watercraft of 230 cm×70 cm size, i.e. a typical sailboard). Both the radius of curvature and depth should be scaled, however, according to the size of the watercraft for a given embodiment. Both the radius of curvature of the step and the depth behind and near the step for a given hull which is not 230 cm×70 cm may be scaled by at least one of the following factors: i) the length of the given hull divided by 230 cm, or ii) the length of the planing surface behind the step divided by 40 cm. (In the case of the sailboard measuring 230 cm×70 cm, 40 cm is the length of the planing surface behind the step.) In this way less drag is produced by a step 8, particularly in transition mode. In short, at least one of one or more steps can have a radius of curvature on both sides of 0.3-3 cm times a factor substantially equaling the length of the hull in centimeters divided by 230 cm. The attack angle of the end of front lift surface 7 can be roughly 10° (i.e. range of 5-20 degrees), preferably in the range of 8-14 degrees, relative to the back of keel area 10.
In some embodiments, more than one step 8 may be provided on one or more of front lift surfaces 7 and 71. The radii of curvature for additional steps 8 (e.g. steps 8′ and 8″ in
The planing angle at the end of front lift surface 7 (such as at step 8) can be adjusted by changing CL,d and the average attack angle (αo) of front lift surface 7. These parameters are preferably configured such that, at the highest desired planing speed, the water off of step 8 reconnects on S2.
The embodiment shown in
As discussed in the preceding paragraph, the end of S7 may include a central step 8 with a step 81 to either side. In planing mode, a hull according to this configuration can plane on three surfaces where one of the three surfaces is to the front of the hull and the remaining two surfaces are to the rear.
Step 81 may be smaller than step 8 or entirely absent in some embodiments. At very high planing speeds, three planing surfaces are generally achieved, similar to a 3 point hydroplane. Water which flows over/passes off of step 8 passes under high lift surface 2 (also identified herein as “S2”) without making contact to at least a front portion of S2. Water passing beneath the hull to either side of step 8, such as over step 81, does make contact with S2 and thereby produces lift thereon. In short, lift can be generated on a left side of S2, on a right side of S2, and on front lift surface 7 (also identified herein as “S7”). Generally, this lift is produced on portions 27 of S2 which are to either side of the hull but not in the center (i.e. behind step 8) and are preferably toward the rear of the watercraft, as shown in
An advantage of this invention embodiment is increased lift/drag efficiency at very high speeds, pushing the planing speed range higher than otherwise possible. At such high speeds, hull features contributing to this advantage include portions 27 of S2 and portion 26 of S7.
Generally, one or more steps 81 have a smaller planing attack angle than step 8 such that in waves or chop the entire length of S2 behind step 8 is not wetted, but water passing off of a step 81 reattaches to the hull before the end of S2 (that is, at a rearward portion of S2) even at the highest desired speed of the watercraft.
One or more grooves 82 may be provided behind steps 8 and/or 81, in addition to one or more grooves which may be provided on either side of the hull and which extend above the water line when the watercraft is planing. The grooves increase ventilation of the steps. Grooves 82 are shown in the watercraft depicted in
Back planing surface 15 (i.e. S15), can be an extension of the middle of S2, an extension of S10, or a distinct planing surface behind (that is, aft of) S2. S15 generally has a transverse width which tapers from front to rear and may have zero width at the transom. An advantage of S15 is to control porpoising and if needed prevent ventilation, for example, of a fin or propeller. One or more surfaces 115 may be provided, for example, to either side of S15 as shown in the embodiments in
Advantages of embodiments which can have three or more separate planing surfaces as described above include i) increased lift/drag efficiency and ii) a larger range of planing speeds which include lower speeds which may not conventionally correspond with planing mode. At such speeds, these advantages are largely provided by S2, S7, S15, and S115.
Particularly for watercraft where the total CG may vary depending on sailor/operator positioning relative the watercraft, the center of lift of high lift surface 2 is preferably in front of the CG for watercraft where back planing surface 15 has a camber which runs to the very end of back planing surface 15. An example is an embodiment for a sailboard wherein the planing angle αo is controlled mainly by S2 and S15. Alternatively, the center of lift of high lift surface 2 is preferably in back of (i.e. aft of) the CG for watercraft where S15 has a camber only for a front portion of S15, the camber not extending to the aftmost portion of S15. In such an embodiment, αo is controlled mainly by S2, S7, and/or S115 at low speeds. The largest transverse width of planing surface 15 is preferably about ⅓ of the width of S2 at an end/aftmost portion of surface 2. However, the largest width of S15 may be any value in the range of 10% to 80% of the width of an end portion of S2. Furthermore, the length of S15 can be 5% to 30% of the hull's total length.
Back planing surface 15 can prevent ventilation of a fin or propeller. Depending on the desired reduction or prevention of ventilation to the fin and/or propeller, a width and length to S15 can be selected by simple calculation and/or routine experimentation. S15, as shown in
As shown in both embodiments for yachts in
One or more surfaces 71 (also identified herein as S71) provide lift to the bow in conditions of large waves. Both S7 and S71 of
A high lift surface 2, as well as the top of a wing 9, may have some downward curve 16 in the transverse direction and then an upward curve back to flat about 60-70% of the distance from the hull's midline to the hull edge. A flat or soft rail can thus be provided at the hull edge. This feature is usable to help reduce the outflow of water while maintaining some rolling stability. While angling or curving the outer edges of the planing surfaces can increase the lift/drag efficiency, it can also increase the rolling instability. For sailboards, roll is controlled by a sailboarder, and thus this possible drawback is minimized. However, for yachts and power boats it is preferable to flatten and/or slightly round the rail similar to the rail in a slalom water ski. This reduces the lever arm of the elevated side verses the deeper side when the hull heels.
For the embodiments shown in
Any one or more of the high lift surface 2, back planing surface 15, and keel area 10 may have a camber 33, such as a three term Johnson camber or similar. A camber 11 for high lift surface 2 generally has a larger CL, d and smaller chord length “c” (as given in the equations above). In some embodiments, high lift surface 2 can have strakes on it.
An important distinction exists between embodiments for a sailboard and embodiments for a powerboat/yacht. In the case of a sailboard, the sailor can adjust the CG of the sailor-hull combination by adjusting his position on the board at a given speed. This allows the sailor some control over the planing angle (α0) of the sailboard. In the general case of a yacht, however, the sailor cannot adjust the location of the CG at different speeds. That is to say, the location of the CG of a yacht is generally fixed and constant as a result of the larger mass of the yacht. The mass of the sailor is generally insignificant such that the sailor's position on the yacht has negligible impact on the total CG of the sailor/yacht combination. Provided this consideration, it is especially important for a yacht that proper structural means be used to control the planing angle (α0) at transition and planing speeds. It should be noted, however, that varying amounts of fuel in a yacht's fuel tank(s) or a large concentrated number of passengers can impact the total CG of a yacht.
For high speed planing, the beginning of the wetted surface shifts back along a longitudinal direction of a hull. The shift in the starting location of the wetted surface can shift the center of pressure from the water near to or even slightly behind the CG of the watercraft. This shift is generally undesirable. To counteract this shift the invention includes cambered front lift surface 7 for controlling the planing angle (αo) at high planing speeds. Hence the combination of back planing surface 15, front lift surface 7, and high lift surface 2 will dynamically control the planing angle over the planing speed range. Front lift surface 7 preferably slopes/angles back similar to the front edge of a jet wing as in the Clement's Dynaplane reference cited above. This has the desired effect that the ends of step 8 are roughly at the same depth as the center of the step (e.g. when the hull is at rest). As a result, the ends of step 8 do not pass over water near the outside edges of front lift surface 7, causing the water to miss the step and undesirably make contact near the front of S2. This would result in an increased wetted surface and thus increased drag. Said differently: providing step 8 at a constant depth in the transverse direction—at least at each of the ends and center of step 8—allows water to uniformly pass from S7 and over step 8 such that the front portion of S2 which is behind step 8 is dewetted at high planing speeds.
In some embodiments, a swept back hydrofoil may be used near front lift surface 7 to aid in the control of the high speed planing angle (i.e. the planing angle of the hull at high speeds when the hull is in planing mode). A swept back hydrofoil generally runs near the water surface at such high planing speeds.
One or more hydraulic trim tabs 34 can be used behind high lift surface 2 and/or back planing surface 15 or surface 115 to increase the effective CL,d of surfaces S2, S15 and/or S115 and for adjusting the trim angle at transition and slower planing speeds. They can be out of the water and spray streams for speeds near or at the maximum design speed of the hull (i.e. the fastest speed at which the boat is designed to operate). These trim tabs can also be cambered in the longitudinal direction to match a camber of S2 and/or S15. While for simplicity these trim tabs are not shown in
In addition, the planing surface 115 and the top of slot 12 (shown behind a winglet 9 in
An embodiment for a sailboard hull 1 is shown in
Sailboard hull 1 has a high lift surface 2, at least the back 20% of which has a larger attack angle than an adjacent rockered keel area surface 10 (i.e. “S10”). The greater attack angle of S2—shown in the figures as 0.025 radians—can be 0.005 to 0.2 radians and is preferably on average 0.02 to 0.14 radians greater than of the attack angle of S10. High lift surface 2 is cambered with, for example, a constant curvature as shown in
Camber 11 of high lift surface 2 is similar to a 3 term Johnson camber, and camber 33 of keel area 10 and an extension thereof is similar to a 5 term Johnson camber. These are preferable because 1) they have more lift/drag and 2) these two cambers 11 and 33 produce a better match in elevation between keel area 10 and S2, as seen in the cross sections in
A sailboard has a yaw angle to provide side lift on the sailboard fin to counter the side lift on the sail. The sailboard fin is normally near the back of the sailboard, generally in the back 20% of the sailboard. In some sailboard hulls like “stand up paddle”, SUP, the fine or centerboard (a movable fin) will be closer to the center of the sailboard. This yaw angle puts a side force on the leeward side of the sailboard. Thus surface 15, which for sailboards desirably protects the fin from ventilation, extends to the end of the board and generally must be in the water by the fin. For the sailboard embodiment, S15 is an extension of the keel area surface 10 (i.e. there is no step on S15 or between S15 and S2). In this embodiment, S15 is wider at the end for controlling ventilation. For embodiments having this characteristic, significant features for controlling planing angle include S15 and S2. However, S7 and step 8 also control the planing angle when the planing angles are small, for example 1 to 4 degrees.
For embodiments for a sailboard, S15 and keel area 10 preferably form a 3 or 5 term Johnson camber over the high planing speed wetted surface. The center of lift/pressure on surface 2 at high speeds may be only about ¾ of 20 cm (i.e. approximately 15 cm) from the back end of surface 2. If this corresponds to the maximum design speed, than this center of lift, shown as point 5, should be in front of the total center of gravity, CG. This CG position is roughly between ¼ and ½ of the distance from the front foot straps 21 to back foot straps 22, when the sailboarder is in the foot straps and sailing fast.
As previously stated, in this embodiment and similar embodiments S7 and step 8 control the lower limit of the planing angle (α0) of the board/hull and the amount of wetted surface area on S2.
Preferably the high lift surface 2, as well as the top of the wing 9, have a downward curve 16 in the transverse direction. This reduces the out flow of water. These angles and depth should be greater in the front part of S2, which is a wetted surface at slower planing speeds and smaller in the back to reduce wetted surface at high planing speeds. Likewise, the front side edges of S2 should also have an upward curve 17, such as is shown in
The vertical dotted lines in
The slots 12 above the wing 9 are seen at the cross sections taken at 90 cm and 150 cm. The front and back of these slots 12 are the space under front lift surface 7 and the space alongside back planing surface 15.
As previously noted, S15 together with S2 give the watercraft hull dynamic stability in flat water. The center of lift/pressure is in front of the total center of gravity, CG, while most or all of S15 is in back of the CG. The total center of gravity is the hull when loaded; that is, the hull and sailor's combined center of gravity. The size of the sailboard hull 99 shown in
The camber 11 shown in
As a short summary thus far, an embodiment of this invention is a watercraft hull with a high lift surface 2, keel area 10, and back planing surface 15. S10 and S15 extend beyond the back of the high lift surface 2 for dynamic stability. These surfaces may have 3 and/or 5 term Johnson cambers or similar cambers (negative camber in the front and positive camber in the back). That is these two surfaces/area start with rockered lengths (negative camber) in the front then have more and more camber toward the rear of the given surface/area. The end of surface 2 can protrude deeper than the adjacent keel area 10, and back planing surface 15 may have edge rails, or transverse downward curvatures, of roughly the same depth as the end of high lift surface 2. Back planing surface 15 may also transition to other shapes such as a “V” shape and be double concave at its end. One exemplary camber is with the back roughly 30% designed for high speed planing (shorter length/higher aspect ratio) with the back roughly 60% of a 3 term Johnson camber with the reference line at about −2 to −3° blended in to the front roughly 70% of a 5 term Johnson camber design for slow planing speed (longer length/lower aspect ratio) with the reference line at zero degrees.
Surface 116 is a surface behind a step 117, similar to what is shown in PCT/2009/057138. Like surfaces S115, one or more surfaces 116 can provide lift at transition speeds and slow planing speeds. At higher planing speeds, however, surfaces 116 are generally mostly above the water flow beneath the sailboard 99. Surfaces 116 can also reduce wave drag at transition speeds by reducing the depth of the transom at the end of surfaces 116. From data collected on models of the embodiments for a sailboard hull as described herein, it appears that the cambered shape of a surface 115 gives more lift/drag than the shape of a surface 116. The hull in
Referring again to sailboard hull 99 as shown in
Again in reference to the sailboard shown in
1) allow water flowing over winglet 9 to smoothly join water flowing under the sailboard at the back of winglet 9, thus reducing drag,
2) add some lift, and
3) allow water to flow more smoothly around the center of the hull 1.
The flow is thereby streamlined, which further minimizes drag. The thickness of a winglet 9 shown for sailboard hull 1 is on the order of 3.5% the chord length of the winglet. The slots 12 above wings 9 for a yacht hull 41 (shown in
A high lift surface 2, as well as the top of a wing 9, may have some downward curve 16 in the transverse direction and then curve back to flat about 80-90% of the distance from the hull's midline to the edge. This feature is usable to help reduce the outflow of water while maintaining some rolling stability. While angling or curving the outer edges of the planing surfaces can increase the lift/drag efficiency, it can also increase the rolling instability. For sailboards, roll is controlled by a sailboarder, and thus this possible drawback is minimized. However, for yachts and power boats it is preferable to flatten and/or slightly round the rail similar to the rail in a slalom water ski. This reduces the lever arm of the elevated side verses the deeper side.
Surfaces S15 and S2 give the hull 41 dynamic longitudinal stability in flat water. The center of lift/pressure is near of the total center of mass, CG, while most or all of back planing surface 15 is in back of the CG.
Referring again to the sailboard hull embodiments of
It was unexpected that the drag for models made according to the present invention, including the model for the yacht or power boat which will be discussed below, would be so small considering how long people have been designing hulls for sailboards and planing powerboats. The Series 2 data from the model according to the invention show substantially superior hull performance as compared to the Series 1 data. To verify these results, the inventor retested two prior art models to obtain Series 3 and Series 4 data, respectively. As shown in
As shown in
Estimates from the Series 2 model according to the invention together with equations 2 and 3 above show that about 50% of the increased efficiency, and thus the lower minimum planing speed, may be due to the camber of high lift surface 2. Of the remaining improvement in efficiency, about 25% may be due to the negative camber (rocker) at the beginning of the high lift surface 2 which contributes to a larger vertical component to the lift vector over the cambered region, thereby reducing the dynamic drag. (Note that “vertical” refers to the directional axis corresponding to gravity.) The additional improvement in efficiency of the Series 2 model with respect to the Series 1, 3, and 4 models at high speed and possibly at all planing speeds may also be due to the keel area 10 extending past the high lift surface 2 in the Series 2 model. This extension in the tested model (Series 2) was 18% of the total length of the model's hull and accounted for approximately 20% of the high speed lift. Furthermore, no porpoising was seen in testing the Series 2 model, this effect being at least in part due to the extension of the keel region past the end of high lift surface 2.
During operation of a sailboard, a boarder moves backward on the board as speed increases, resulting in a shift of the CG toward the stern of the board. This effect on the CG of the hull-sailboarder combination was therefore accounted for in the experiment and reflected in the data shown in
Froude number, F∇, is a dimensionless number. There are different formulas for calculating Froude numbers depending on the length, width, depth, and volume of displaced water of the one or more watercraft hulls being tested. For the present disclosure and experimental testing provided herein, the formula used is
F
∇
=v/(g∇1/3)1/2, (7)
where v is the velocity of the model or watercraft, ∇ is the volume of water displaced by the model or watercraft at rest, and ‘g’ is acceleration due to gravity. This formula is also what Clement uses (reference provided above). For the watercraft model of Series 1 in
The same invention model was tested without the wing 9 and slots 12, from 3.9 mph to 13.5 mph. It appears that the drag was approximately 20% more at the transition or hump speed, but above 7 mph the drag was the same. Thus it is believed that for speeds above 3.9 mph (that is, above 4.4 mph for a full scale sailboard and above about 7 mph for a yacht), slots which are only at the back of the hull perform as well as slots extending at least the full length of the winglets. To represent this distinction,
The low drag at 10.5 mph shown in
The speed of 33 mph for the Series 1 model of
Although other boat configurations like Clement's Dynaplane, three point hydrofoils, and tunnel boats may have efficiencies similar to those of the present invention at very fast planing speeds, e.g. 60 to 100 mph, no non-foil based configurations are known to the inventor which have:
1) such comparatively small drag at transition speed,
2) such comparatively small drag at low planing speed, or
3) such a comparatively large planing range with a low minimum planing speed threshold,
as compared to the present invention.
From the bottom view in
From the knowledge of building and testing these embodiments, it is preferred that the position of the widest part of the hull be at the start of the camber of the high lift surface 2 (that is, the intersection or line between the rockered part and the cambered part) + or −15% of the hull length. This is behind the widest part shown in
In summary, one or more of the following advantages may be attainable according to the invention:
Although the experimental data shown in
Although the invention has been described predominantly in reference to sailboards and yachts/power boats, those skilled in the art will understand and recognize that this invention can be applied to other watercraft including, for example, stand up paddle (SUP) boards, sailboards designed for speed, surfboards, catamarans, and trimarans. It may also be used in combination with other inventions and technologies such as wave piercing planing hulls like P. R. Payne, U.S. Pat. No. 3,763,810, and E. P. April, U.S. Pat. No. 4,649,851, in accordance with the teachings herein.
Thus the scope of the invention should be determined by the appended claims and their legal equivalents rather than by the examples given. The abstract is given with the understanding that it will not be used to interpret or limit the scope or meaning of the claims.
This application claims priority to U.S. provisional patent application No. 61/710,960 filed Oct. 8, 2012, which is hereby fully incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61710960 | Oct 2012 | US |
