Means for improving the performance of planing-type boat hulls

An improved hydrofoil system is provided for boats with planing-type hulls Two hydrofoils, one mounted adjacent to each chine, are provided in a submerged position. The attack angle of each hydrofoil is controlled independently by a hydraulic cylinder or the equivalent thereof. Because both positive and negative attack angles of each hydrofoil may be presented, the hydrofoil system disclosed has the ability to raise and lower the bow, raise and lower the stern, provide lateral stability and also act as an auxiliary rudder by rotating the boat about its longitudinal axis. The submerged hydrofoil system is intended for use with boats with planing-type hulls.

This invention relates generally to devices for controlling the running 
attitude of planing-type boat hulls and specifically to hydroplanes or 
hydrofoils that can both raise and lower the bow (and stern) and also 
provide lateral stability and act as an auxiliary rudder. 
BACKGROUND OF THE INVENTION 
It is known to use trim planes or hydroplanes, mounted from the transom to 
lower the bow of boats with planing hulls to reduce the time it takes to 
achieve the planing condition. However, the ability to control the wetted 
area of planing hulls has been narrowly limited to the single function of 
forcing the bow down by the use of transom-mounted trim planes. However, 
this single function is insufficient for various hull designs and sea 
conditions. Namely, there is a need for a hydrofoil system that will not 
only lower the bow, but raise the bow, improve lateral stability and 
assist in steering the boat as may be required for various hull designs 
and sea conditions. 
An understanding of the contribution made by the present invention requires 
an understanding of planing boat hulls and previous hydrofoil designs or 
trim planes for planing hulls. Boats having planing hulls are designed to 
operate most efficiently at speeds where the hull "planes" on top of the 
surface of the water and a minimum area of the hull is in contact with the 
surface of the water. Typically, about one-half to two-thirds of the hull 
surface area is wetted at planing speeds. However, the extent of the 
wetted area may vary. With hulls having a transom deadrise, or an upward 
angle from the keel to the chine, of 10 degrees or more, less than 
one-half of the hull area may be wetted at planing speeds. Depending upon 
the hull design, as little as one-fourth of the hull area may be wetted 
during high speed operation. 
When a boat accelerates, the natural tendency of the boat is to push the 
stern down and raise the bow. This stern-down, bow-up position is an 
inefficient use of engine power and fuel. Because the planing condition of 
the hull increases both speed and fuel efficiency, the primary goal of 
most hydrofoil or trim planes designs is to force the bow down to a 
horizontal angle thereby promoting planing of the hull and reducing the 
time for the boat to achieve the planing condition. Unfortunately, the 
existing designs perform this function only and do not address other 
performance and handling problems that arise. 
For example, when the sea conditions are quite rough, it is desirable to 
raise the bow thereby causing the face of the waves to hit the boat hull 
rather than the tip of the bow causing the boat to take on water. Further, 
as stated above, many planing-type boat hulls employ a transom deadrise 
When the transom deadrise, or angle from the keel to the chines, is 10 
degrees or more, the boat is less stable because the hull is not flat, but 
is V-shaped. Therefore, extra stability it desirable, especially during 
rough sea or water conditions Previous hydrofoil designs do not address 
this lateral stability problem. 
Further, prior hydrofoil designs fail to acknowledge that dual hydrofoils 
can act as a quasi-rudder and assist in the steering and control of the 
boat. This additional function of the hydrofoils is desirable for rough 
handling boats and would be essential if the rudder system broke or 
because dysfunctional. 
Thus, there is a need for transom-mounted hydrofoils that not only act to 
lower the bow, but also act to raise the bow and provide lateral stability 
and directional control. Hence, the opportunity to add additional safety 
and handling features to a boat with a planing-type hull should not be 
foregone as it is when current hydrofoil or trim systems are employed. 
SUMMARY OF THE INVENTION 
An improved hydrofoil system for planing-type boat hulls is provided. The 
hydrofoil system includes two hydrofoils, each hydrofoil mounted on 
opposing sides of the transom, near each chine. Each hydrofoil includes a 
foot, a control leg and a means for adjusting the attack angle of the 
foot. Each hydrofoil is mounted on opposing sides of the transom of the 
boat near a chine. 
The foot is fixably attached to the control leg, normally by welding, and 
is disposed below the chine. The control leg is pivotally attached to the 
mounting brackets and also provides an anchor means for accommodating one 
end of the attack angle adjustment mechanism. The attack angle adjustment 
mechanism provides a mechanically non-complicated way to adjust the attack 
angle of the foot. 
In the preferred embodiment, the attack angle adjustment means is a 
longitudinally adjustable arm with two ends. One end is mounted to the 
transom; the other end is mounted to the anchor means on the control leg. 
The preferred embodiment features a manually controlled motorized 
mechanism for independently expanding and contracting the length of each 
longitudinally adjustable arm. Manual fingertip controls are provided for 
controlling the length of each control arm and therefore the attack angle 
of each foot. 
The submerged hydrofoils of the present invention perform more than the 
single function of lowering the bow for planing. As stated below, the 
objects of the hydrofoils of the present invention include the ability to 
lower the bow, but also include the ability to raise the bow, improve 
lateral stability and provide supplemental directional control. 
It is therefore an object of the present invention to provide a submerged 
hydrofoil system that reduces the time it takes for a boat to achieve the 
planing condition. 
It is also an object of the present invention to provide a submerged 
hydrofoil system that lowers planing speeds. 
It is also an object of the present invention to provide a submerged 
hydrofoil system that will compensate for excessive bow or stern weight. 
Other objects of the present invention include providing submerged 
hydrofoils that improve directional control, improving lateral stability, 
eliminating stern lift from surface drives or stern lift from conventional 
inboard drive systems, reduction of turning radius and improvement of top 
speed under most operating conditions.

DETAILED DESCRIPTION OF THE INVENTION 
Like reference numerals will be used to refer to like or similar parts from 
figure to figure in the following description of the drawings. For 
simplicity, in the drawings, elements appearing on the starboard side of 
the boat 10 shown in FIGS. 1-3 are designated with a number followed by 
the letter "A". Elements appearing on the port side of the boat 10 shown 
in FIG. 1-3 are designated with a number followed by the letter "B". When 
an element is discussed in functional terms without regard to its 
placement on the port or starboard sides, it will be designated with a 
number only. 
FIG. 1 is a starboard side view of an inboard motorboat 10 with a 
planing-type hull 11 that is also equipped with the hydrofoil system 
disclosed by the present invention. The boat 10 includes a planing hull 
11. The hull 11 includes a substantial transom deadrise, as best seen in 
FIG. 2. In the preferred embodiment depicted in FIGS. 1-3, when the hull 
11 includes a substantial transom deadrise, the foot 12 of the hydrofoil 
system 28 is vertically disposed above the keel 13 but below its 
respective chine 14. 
The relative location of the hydrofoils is best seen in FIG. 2. Two 
mounting angle plates 15, 16 are attached in parallel relationship to each 
other near the respective chine 14. The control leg 17 fits between the 
mounting angle plates 15, 16 and is pivotally attached to the mounting 
angle plates 15, 16 by a pivot bolt 18 (see FIG. 3). A friction adjustment 
bolt 19 controls the lateral clearance of the control leg 17. 
The means for adjusting the attack angle of the foot 12 is best understood 
upon examination of FIG. 3 As seen in FIG. 3, the foot 12 is in an 
approximate horizontal position or zero attack angle. In this position, 
the foot 12 is merely providing lateral stability to the boat 10 and is 
not providing an upward or downward force on the bow 23. An extensible and 
retractable arm for adjusting the angle of attack is indicated at 22, the 
arm 22 being an extension of the piston rod of the hydraulic cylinder 24. 
The hydraulic cylinder 24 is controlled manually by the pilot of the boat 
10. Preferably, an electric control is available to the pilot which 
activates a motor which thereby controls the extension of the adjustable 
arm 22 and hence the angle of attack of the foot 12. 
As shown in FIG. 2, the lower end of the arm 22 is attached to the anchor 
flange 25 of the control leg 17 and to the lower end of the hydraulic 
cylinder 24. The upper end of the control arm 22 is mounted directly to 
the transom 29 at the mounting bracket 26 and to the upper end of the 
hydraulic cylinder 24. The two hydraulic cylinders 24A, 24B may be 
uniformly controlled by the pilot or independently controlled by the pilot 
depending on the effects required 
FIGS. 4-6 illustrate the three primary positions of any one hydrofoil 
during operation. FIG. 4 illustrates the hydrofoil 28 in the zero attack 
position; the foot 12 is at an attack angle substantially parallel to the 
direction of the boat and the surface of the water. The water flows around 
the foot 12 and around the control leg 17 without substantial drag caused 
by either element. In various tests to determine the effect of underwater 
drag caused by the hydrofoils 28, no loss of boat speed nor loss of motor 
rpms could be detected in hulls 11 ranging from 20 to 27 feet long with 
speeds of up to 55 mph when the feet 12 were operating at zero degrees of 
attack or the neutral angle shown in FIG. 4. 
FIG. 5 shows the control leg 17 and foot 12 in the negative attack angle 
position which brings down the stern 27 and raises the bow 23 of the boat 
10. In contrast, FIG. 6 shows the control leg 17 and foot 12 in a positive 
attack angle position which raises the stern 27 and brings down the bow 23 
of the boat 10. If the pilot wishes to raise the bow 23 when encountering 
rough sea conditions, the pilot adjusts both hydrofoils 28A, 28B to a 
position similar to that shown in FIG. 5. If the pilot wishes to lower the 
bow 23 in order to reduce the time to achieve planing, the pilot adjusts 
both hydrofoils 28A, 28B to a position similar to that shown in FIG. 6. 
FIGS. 7 and 8 illustrate the auxiliary or emergency steering capability of 
this invention that may be employed in the event the rudder or primary 
steering mechanism fails. In FIG. 7, the boat 10 will turn in the port 
direction because foot 12B is in the negative attack angle position and 
foot 12A is in the positive attack angle position. The foot 12B acts as a 
brake along the port side and the foot 12A provides a lifting force along 
the starboard side thereby causing the boat 10 to pivot to the port 
direction. Similarly, in FIG. 8, the boat 10 will turn to the starboard 
side because foot 12A is in the negative attack angle position and foot 
12B is in the positive attack angle position. The boat 10 will pivot 
toward the starboard side due to the braking action the foot 12A and the 
lifting action of the foot 12B. 
FIG. 9 shows the two hydrofoils 28A, 28B in a position to counteract a roll 
or a running list to the starboard side. The starboard hydrofoil 28A is in 
a neutral position and the port hydrofoil 28B is in a negative attack 
angle position. The hydrofoil 28B is acting to bring down the port side of 
the boat 10 to counteract a downward force on the starboard side of the 
boat 10. 
Conversely, in FIG. 10, the hydrofoils 28A, 28B are in a position to 
counteract a roll or a running list to the port side. The port hydrofoil 
28B is in a neutral position and the starboard hydrofoil 28A is in a 
negative attack angle position thereby providing a downward force to the 
starboard side of the boat 10. The result of the positions shown in FIG. 
10 is to counteract a roll to the left or the port side of the boat 10. 
Thus, the present invention provides the pilot with the ability to (a) both 
raise and lower the bow 23 of the boat 10, (b) stabilize the boat 10 and 
(c) steer the boat 10. This ability may be provided at the pilot's 
fingertips because conventional electric motors may be used to activate 
and adjust the hydraulic cylinders 24A, 24B and the adjustable arms 22A, 
22B independently. The present invention can provide all these functions 
because both hydrofoils 28A, 28B are submerged thereby employing both the 
top 30 and bottom 31 surfaces of the hydrofoils. As shown in FIGS. 9 and 
10, the hydrofoils 28A, 28B provide additional safety and lateral 
stability when employed with hulls having a transom deadrise For safety 
reasons, the combined effective area of the bottoms 31A, 31B is not large 
enough to generate enough force to lift the stern 27 above the running 
surface of the water. 
Because the hydrofoils 28A, 28B of the present invention reduce the time to 
achieve planing, the hydrofoils 28A, 28B contribute to fuel efficiency of 
the boat 10. Further, because the hydrofoils present very little forward 
surface area when in the zero attack position (see FIG. 4), the hydrofoils 
28A, 28B do not significantly affect the underwater drag of the boat 10. 
The hydrofoils 28A, 28B may also compensate for excessive bow weight or 
stern weight When both hydrofoils 28A, 28B are in a positive attack angle 
position as shown in FIG. 6, the upward forces provided by water engaging 
the bottoms 31A, 31B of the feet 12A, 12B compensate for excessive stern 
weight When both hydrofoils 28A, 28B are in a negative attack angle 
position, see FIG. 5, the downward forces provided by water engaging the 
tops 30A, 30B of the feet 12A, 12B compensate for excessive bow weight. As 
shown in FIG. 1, the bottom 31A, 31B of both hydrofoils 12A, 12B are 
located above the keel line 13 thereby preventing damage from grounding or 
other submerged hazards 
Finally, the installation and removal of the hydrofoils 28A, 28B is 
relatively fast and simple. Installation takes less than three hours and 
removal less than one-half hour. 
Although the preferred embodiment of the present invention has been 
illustrated and described, it will once be apparent to those skilled in 
the art that variations may be made within the spirit and scope of the 
invention. Accordingly, it is intended that the scope of the invention be 
limited solely by the scope of the hereafter appended claims and not by 
the specific wording in the foregoing description.