Watersports involving powered watercraft have enjoyed a long history. Waterskiing's decades-long popularity spawned the creation of specialized watercraft designed specifically for the sport. Such “skiboats” were optimized to minimize the wake in the water behind the watercraft's hull, thereby providing the quietest possible water to the trailing water skier.
More recently, watersports have arisen at the other extreme by actually taking advantage of, and benefitting from, the wake produced by a watercraft. Sports such as wakesurfing, wakeboarding, wakeskating, kneeboarding, and others use the watercraft's wake to allow the participants to perform various maneuvers or “tricks” including becoming airborne.
To address this changing market, skiboats dedicated to a single watersport have yielded to a new type of watercraft known as a “wakeboat”. Wakeboats seek to more completely manage the spectrum of wakes that are produced behind the hull—diminishing it for some activities, while enhancing it for others.
The wake that forms behind the hull of a wakeboat as it moves through water is affected by many factors, including but not limited to the hull's aspect ratio (relationship of length to width), the width of its transom (the rearmost portion of the hull), the velocity of the hull through the water, and the hull's draft (depth in the water).
As mentioned above, modern watersports take advantage of, and benefit from, the wake produced by a wakeboat. For watersports such as wakesurfing, the wake is intentionally made asymmetric: An actual wave is formed behind one side of the hull, thus approximating the unidirectional behavior of a naturally formed ocean wave. A wakesurfing participant can employ a surfboard on the wave behind a wakeboat much as surfboards have historically been used in the ocean, with the wave “breaking left” or “breaking right” depending upon which side of the hull is forming the wave.
An asymmetric wake is formed by the hull having an asymmetrical relationship to the water. One method of introducing asymmetry is to rotate the hull around its longitudinal axis, the axis running lengthwise from the front (bow) to the rear (stern). The result is commonly referred to as “tilt”, “roll”, or the nautical term “list”. A hull that is not level with the water's surface creates an asymmetrical wake as it moves through the water.
One common technique for changing the roll angle of a hull is the use of trim tabs. These comprise plates at or near the transom of the hull, often installed in groups of two or more distributed across the width of the transom, that by angling down into the water below the normal hull profile, cause the moving water to impart a lifting force to the hull. When multiple such trim tabs are deployed in synchronization (e.g. at roughly the same angle), the lifting force is roughly even across the width of the hull and the lifting effect is primarily around the lateral axis—a rotation often referred to as “pitch”.
More usefully for asymmetric wake formation, when multiple such trim tabs are deployed in an unsynchronized fashion some amount of the lifting force contributes to rotation around the longitudinal axis—and thus the hull experiences tilt/roll/list as described above.
For example, a trim tab mounted on the left (port) side of the transom, and deployed into the water, will experience a lifting force from the moving water that will lift the left (port) side of the hull and lower the right (starboard) side of the hull—thus rotating the hull around its longitudinal axis. A trim tab mounted on the opposite side, and deployed into the water, will reverse these directions and lift the right (starboard) side of the hull while lowering the left (port) side.
These asymmetrical lifting forces cause the hull to have an asymmetrical relationship to the water, which in turn causes an asymmetrical wake to form behind the hull.
Trim tabs are a very old and well known technology. For example, U.S. Pat. No. 2,576,744 to Anderson (incorporated herein by reference) describes a pair of independently adjustable trim tabs.
U.S. Pat. No. 2,816,521 No. to Alexander (incorporated herein by reference) goes into even greater detail: “blades 6 may be set to various or different angular positions with respect to each other, to insure the boat operating on an even keel regardless of the location of the load or cargo within the hull” (see Col. 2, Lines 31-34).
U.S. Pat. No. 3,159,131 to Frederick (incorporated herein by reference) reiterates the asymmetric effect of trim tabs: “the upward thrust effected by the flaps may be increased or decreased either simultaneously or individually. By increasing and decreasing the downward inclination of the trim flaps the inclination of the hull may be adjusted about both transverse and longitudinal generally horizontally disposed axes” (see Col. 1, Lines 15-21). Thus the use of trim tabs to impart rotation about the transverse (pitch) and longitudinal (roll) axes has a long history in the art.
While trim tabs have a long history of use for hull control, and are in common use today for asymmetrical wakesports, they suffer from certain restrictions. One such restriction is their limited dynamic range. The effects that trim tabs can impart to a hull are limited in scope; plainly stated, there is only so far that a hull can be safely tilted, and that degree of tilt may not, by itself, achieve the desired asymmetry of wake.
Trim tabs alone being insufficient, the achievement of the desired asymmetry of wake may require one or more supplementary techniques.
A second technique for asymmetric wake formation is based on convergence of the disturbed water coming off the two sides of the rear of the hull. As described in U.S. Pat. No. 3,200,782 to Walden (incorporated herein by reference), in the absence of any convergence controlling element “the slip-streams 76 at the two sides pass close to the sides of the boat at 77 and then converge behind the boat at 78” (see Col. 6, Lines 41-43 and FIGS. 10 through 12).
Walden then describes using vertically oriented trim tab elements to delay the convergence: “As shown in FIG. 12, however, when the vanes are used extending upwardly and curving outwardly from the outboard sides of the elevator plates, the slip-stream 77′ flares outward at 80 in the wake” (see Col. 6, Lines 45-48 and FIG. 12). Walden both describes, and illustrates, delaying the convergence of the wake formed behind a hull using vertically oriented trim tab elements.
While Walden may have originated the concept of delayed convergence, it is not without its disadvantages. One such disadvantage is the fixed nature of its delayed convergence. Walden offers no way to adjust the traditional effect of its trim tabs independently from the convergence delaying effect of its vertically oriented trim tab elements.
The concept of delayed convergence via vertically oriented trim tab elements from U.S. Pat. No. 3,200,782 to Walden is later disclosed by Gasper in a series of US Patents including U.S. Pat. No. 9,260,161 which states: “The neutral position of surf wake system 32 is shown in FIG. 13(a) in which flaps 33 are in their neutral, retracted position. In this position, the flow of water past the transom is unimpeded by the flaps and the water is allowed to converge at it is natural intersection relatively close to the transom. When a surfable starboard side wake is desired, the operator may deploy the port side flap 33p as shown in FIG. 13(b). In this position, the flow of water along the port side past the transom is disrupted such that the flow of water is redirected outwardly and/or rearwardly thereby delaying convergence of the port side flow with starboard side flow to a point further from the transom.” (see Col. 12, Lines 23-38 and FIGS. 13a and 13b.)
As with FIGS. 10 through 12 of U.S. Pat. No. 3,200,782 to Walden, FIGS. 13a and 13b of U.S. Pat. No. 9,260,161 to Gasper show the use of vertically oriented trim tab elements to delay the convergence of wakes behind the hull of a boat.
Gasper describes its vertically oriented trim tabs as a “pair of upright water diverters including a port diverter and a starboard diverter” (see Col. 2, Lines 1-2). Gasper requires that “the pivot angle may be substantially vertical, substantially parallel to the side edge, some other angle therebetween, or some angle slightly inclined with respect to the side edge” (see Col. 6, Lines 16-19). The hinge of Gasper is disclosed as being at or near vertical: “the angle between the pivot axis and the side edge is less than approximately 15 degrees, more preferably less than 10 degrees, and even more preferably less than 5 degrees” (see Col. 6, Lines 19-22).
This at- or near-vertical orientation in the Gasper specification is shown in the figures in which all hinges and flaps are at or near vertical. See flaps 33p and 33s of FIG. 1, hinge 37 and flap 33 of FIG. 2, hinge 37p and flap 33p of FIG. 4A, hinge 37p and flap 33p of FIG. 4B, hinges 37p and 37s and flaps 33p and 33s of FIG. 5A, hinges 37p and 37s and flaps 33p and 33s of FIG. 5B, hinges 37p and 37s and flaps 33p and 33s of FIG. 5C, flap 33 of FIG. 10, flap 33 of FIG. 11, flaps 33 of FIG. 12A, hinges 37 and flaps 33 of FIG. 12B, flaps 33p and 33s of FIG. 13A, flaps 33p and 33s of FIG. 13B, flaps 33p and 33s of FIG. 13C, hinges 37 and flap 33 of FIG. 14A, flap 33 of FIG. 14B, hinges 37 and flap 33 of FIG. 15A, flap 33 of FIG. 15B, flap 33 of FIG. 15C, flaps 33 (also labeled “Surf Gate”) of FIG. 16A, flaps 33 of FIG. 16B, hinges 37p and 37s and flaps 33p and 33s of FIG. 17, and flaps 33p and 33s of FIG. 18.
The disadvantages of the vertically oriented trim tab elements of Walden have already been addressed above. Chief among these is their fixed nature relative to the horizontally oriented trim tabs to which they are attached.
Likewise, the Gasper requirement that the hinges and flaps of its “upright water diverters” be oriented vertically bears its own disadvantages. For example, the sides of the hull often require recesses to permit the hinges and flaps of Gasper to fully retract out of the “flow of water past the transom”. Such recesses complicate hull design and fabrication, and may weaken the structural integrity. They may also compromise aspects of hull design by limiting the freedom of the hull engineer(s) to optimize for hull performance.
More seriously, the Gasper requirement that the hinges and flaps of its “upright water diverters” be oriented vertically may potentially also threaten the safety of nearby persons. When the “upright water diverters” of Gasper are in their deployed positions they extend outboard of the natural curve of the hull and may potentially present an impact and snagging hazard to nearby swimmers or anyone entering the water. Furthermore, the “upright water diverters” of Gasper are articulated by actuators with sufficient power to overcome the extreme water pressure flowing against them—an amount of force sufficient to potentially injure a person or marine animal snagged or entrapped by them. This potential problem of Gasper is compounded by the partial or complete submersion of its “upright water diverters”, potentially rendering them almost invisible to the very people to whom they pose a dangerous threat. For at least these reasons, any benefit from the “upright water diverters” of Gasper is potentially outweighed by downside risks.
A third technique, which is a variation on the “delayed convergence” of Walden and Gasper, is described in U.S. Pat. No. 9,315,235 to Wood. Wood discloses a traditional, full width hinged trim tab with “a second pivot axis forward the first pivot axis. The second pivot axis allows for the device to be installed on boats having different shapes, such as differently sloped transoms” (see Col. 2, Lines 19-22). The second pivot axis of Wood is an installation device, does not play a role in wake creation, and is required to span the entire width of the trim tab.
The first pivot axis of Wood is angled such that “when the water deflectors 216 rotate downwardly, they deflect water in the outboard direction as the boat moves forward, which affects the wake” (see Col. 4, Lines 35-37) and “water deflector 216 deflects the water that released from the stern trailing edge 114 downwardly and in the outboard direction, effectively digging a hole in the water behind the boat 100” (Col. 4, Lines 51-53). In other words, Wood is yet another delayed convergence system.
A fourth technique for asymmetric wake formation is proposed in US Patent Application Publication 2013/0228114 by Gasper. Therein is described the addition of secondary, tertiary, or even more rudders along the keel of a boat hull which are linked by a complex linkage system to operate synchronously. The disadvantages of such a system are numerous, including but not limited to additional complexity of hull manufacture, the displacement of other components otherwise preferentially located within the hull in that volume near the keel, the additional piercings of the hull to accommodate the numerous additional rudder shafts, the necessary additional waterproof fittings on the numerous additional rudder shafts to prevent intrusion of the surrounding water into the hull despite the through-hull rotating mechanisms required below the waterline, and the manufacture and cost and ongoing maintenance of the linkage system to coordinate the numerous additional rudders as described and illustrated in the Publication.
It is clear from the above discussion that individually operated trim tabs and delayed convergence of wakes have been areas of research for decades. However, existing proposals for achieving these ends are fraught with limitations, compromises, and in some cases outright hazards.
There is an ongoing need in the wakeboat industry for a surf wake forming system that delivers desirable asymmetric wakes without adding complexity and cost and, in some cases, without adding a potentially dangerous safety risk.
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