US 3547064 A
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United States Patent FOREIGN PATENTS 517,633 2/1940 Great Britain Primary Examiner-Andrew H. Farrell Attorney-John F. A. Earley The boat hull includes a small step on the bottom of the hull which is in the form of a V with the apex of the V facing forward. The V runs for a considerable portion of the length of the boat.
Ports are formed in the bottom of the hull aft of the step so as to vent to atmosphere the portion of the hull behind the step and provide an air cushion aft of the step on which the boat rides when planing.
The boat hull also includes planing fins which extend rearwardly and outwardly from the hull to increase its effective beam and thereby provide a wider planing surface.
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. mvem'on JOHN F: GLASS ATTORNEY PAIENTEU m1 SIBYB 547L064 I SHEET u 0F 4 v INVENTOR JQHN P GLASS ATTORNEY PLANING STEP BACKGROUND OF THE INVENTION water than through thewater and therefore much attentionhas been given to the design of a boat hull which planes over the water at high speeds.
In small high speed boats (lengths to 60 feet and speeds above 1.4 knots times w/length in feet the skin friction is a very substantial contribution to drag, being of the order of one-halfor more of the total. This is in contrast to large boats and ships, where the skin friction is a small factor, and to slow displacement sailboats (both'of these run at'speeds less than l.4** The wave-making drag of small high speed boats depends on the weight to be lifted, the beam of the boat and the speed. With proper design, the wave-making drag and even the power expended on wave-making can be reduced with increased speed. However,- the drag dueto friction of the wetted surface goes up very rapidly and becomes a limiting factor.
Boats have been designed having a step across the bottom of the hull. These steps have been'quite high but still have not provided the desired. cushion of air beneath'the boat. hull. Also, such boats have a tendency to squat 'deeplyand heavily and require a large'power source to move the boat hull from the nonplaning positionto the planing position.
SUMMARY OF THE- INVENTION It is an object of this invention to provide a planing boat having greater stability than-conventional planing boats.
It is another object to reduce the power necessary to overcome the induced drag of the boat, and therebycut down on It is another object todecrease the wetted area of the boat hull at planing speeds.
It is another object to provide a planing boat hull which behaves like a conventional boatat slow speeds when the boat is not planing. It is another object to lift the boat to planing position without making large changes in the trim angle of the boat.
It is another object to distribute lift foreand aft and carry the boat on "a lesser area of wettedsurface of the bull to thereby give a soft ride.
The present invention includes a small step running diagonally along the bottom of the boat hull on each side of the keel, and the step is vented. This vented step may be adapted to boats-of conventional design by making very minor changes'in the shape of the conventional boathull. My boat tom type such as the U.S.--Navy's 40-foot personnel boat MK- 5. Other'preferred bulls are any of the'older twisted bottom V BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an isometric view, looking from underneath and to the side. of a boat hull constructed in accordance with this invention, and shows the boat planing at high speed through the water;
FIG. 2 is a schematic view in longitudinal section along buttock line 21 of the boat hull of FIG. I and of a similar buttock line of a conventional boat hull;
FIG. 3 is a view in side elevation of the boat hull of FIG. 1;
FIGS. 4 and 5 are views in section taken as indicated by the lines and arrows 4-4 and 5-5 which appear in FIG. 1;
FIG. 6 is a partial view in longitudinal section of the boat hull of FIG. 1; and
FIG. 7 is an isometric view, looking from underneath and to the side, of a conventional boat hull.
DESCRIPTION OF THE PREFERRED EMBODIMENT Turning now to the specific embodiment of the invention selected forillustration in the drawings, there is shown a boat hull having a bow l3 and a stem 15. For the sake of clarity, the keel, rudder, and propellers are not shown.
The hull 11 includes a keel line 17, andtwo buttocks lines 19 and 21 are shown. A chine 23 is formed on both sides of the boat hull, and a step 25extends diagonally along the bottom of the hull from each side of keel line 17 to form a V-shape with the apex 27 of the V pointed forwardly. A pair of planing fins 29 extend rearwardly and outwardly from the bottom of the hull and serve to broaden the effective beam of the hull and thereby broadenthe effective planing surface.
A series of ports 3] are formed in'the bottom of the hull just aft of the step 25 and these ports vent the bottom of the hull to the atmosphere'to form a cushion of air beneath the hull aft of the step 25' when the hull is planing.
A line 33 marks the perimeter of a front wetted surface 35 which is the front wetted surface of the hull when the boat hull is planing. The rear of wetted surface 35 is defined by step 25. A line 37 defines the-front perimeter of a rear wetted surface 39 which is also wetted when the boat hull is planing. Flaps 41 extend from the stem 15 of the boat hull at the bottom to provide additional planing surface and further reduce squat of the boat hull when planing.
hulls behaVe in about the same manner as do conventional type planing hulls. With the preferred hulls; the shallow, long V-step of the present invention maybe worked into their bottoms with a minimum change of the'shape of the original hull.
In FIG. 2, buttocks line 21 is shown at the bottom and buttocks line 43 of a conventional boat hull 45 shown in FIG. 7 is shown just above buttocks line 21. As may be seen, the buttocks lines are very similar except that buttocks line 21 has a small sharp'step 25 and a slightly different shape of bottom. The bows are shaped differently, but that difference in shape is for ornamental reasons.
The height of step25 may be in the range of about A inch to 2 inches in a 40-foot boat hull, and the angle'of the step riser to the fore part of the hull bottom may be in the range of about 45 to The fore part of the boat bottom may slope downwardly from the at rest water line at about 1 to 4, and the hull bottom to the rear of the step may slope upwardly at about 2 to 4 to the at rest water line.
Rear portion 47 of the boat hull again slopes downwardly at the same angle as front portion 49 approaches step 25 so that wetted surfaces 35 and 39 have the same attack angle to the water.
A preferred angle from the at rest water line of front portion 49 and rear portion 47 is 1W, and a preferred angle of middle portion 51 of the bottom of the boat hull leading away from step 25 is.3.
FIG. 3 is a view in side elevation of the boat hull of FIG. I and shows another buttocks line 53. FIG. 6 is a partial view in longitudinal section of the boat hull of FIG. 1, and illustrates the venting means of my invention. An air inlet 55 admits air to a duct 57 which passes air to the ports'3l to vent the area beneath the boat hull aft of step 25. Duct 57 decreases in size as-the-distance from air inlet 55 increases. This is shown in FIG. 4 and 5 which are taken along the lines and arrows 4-4 and 55 which appear in FIG. 1.
FIG. 7 is an isometric view, looking from underneath and to the side, of a conventional boat hull 45 and is shown for comparative purposes. Boat hull 45 includes a bow 59, a stern 61, keel line 63, chine 65, at rest water line 67, and below-water buttocks line 69.
The fore-and-aft position of the long V-step 25 is such that the center of effective lift is ahead of the center of gravity of the boat hull if the stern of the boat is to remain in contact with the water in order to increase stability and to keep the propeller immersed and protect it from cavitation.
Step 25 is not deep but is abrupt or sharp, and is adequately vented to avoid unnecessary suction forces beneath the boat hull.
Referring to FIG. 6, a blower 71 may be positioned in duct 57 if it is desired to decrease the cross-sectional area of the duct or to increase the volume of air passing therethrough.
Planing speed boats of conventional design may include a transverse step, but step 25 of my invention is smaller than is customary. In the conventional stepped hull, the step is made large in order to allow air toreach the area beneath the hull aft of the step from the sides of the boat. This is a disadvantageous arrangement because the side entrances for the air are small compared to the area to be supplied with that air. The problem is overcome in my invention by providing duct 57 which passes air from air inlet 55 to vent the rear of step 25 through ports 31. Also, the smaller step 25 of my invention decreases drag when the boat is moving but not planing, as compared to the drag caused by the conventional stepped hulls.
In conventional planing boats, as the boat nears lift speed, water is pushed out from beneath the boat hull and it loses buoyancy. Since the planing areas are forward of the center of gravity of the conventional boat hull, the hull changes its angle of pitch and squats with its stern deeper in the water before it starts to plane. This increases the drag of the boat hull, and it requires a considerable amount of power to bring the boat from its slow-speed position supported by its buoyancy, to its high-speed planing position.
Step 25 sweeps rearwardly from keel line 17 at a wide sweep-back angle, such as the approximately 30 angle shown in the drawings, and the outer portions of the planing fins 29 extend well behind the center of gravity of the boat. The planing fins 29 extend outwardly from the sides of the boat and make the boat run more level. Besides increasing stability, the planing fins greatly reduce the power required to overcome the induced drag in the boat hull because the planing breadth is increased.
By extending planing fins 29 well to the rear, and by providing flaps 41, the squat of the stern of the boat is decreased.
Planing fins 29 rise upwardly at an angle to the at rest water line and this angle of rise is preferably about 3 to 8. Also, the after portions of the V-step 25 should be higher than the forward portions so that when the boat is running at moderate speeds, the V-step 25 and the planing fins 29 are approximately level because of the moderate squat assumed by the boat.
The boat hull of my invention is provided with a small step, and a pair of planing fins 29 having a wide span. These changes amount to modest differences from the conventional boat hull 45 shown in FIG. 7, but they result in major changes in performance. Because of the greater reactive area provided by planing fins 29, the planing action of the boat hull may start at more modest speeds than would a conventional planing boat hull.
The boat hull of my invention planes with less squatting than conventional planing boats which change their pitch so that the bow rises and the stern lowers in the water before the boat hull lifts upwardly and starts to plane.
It is preferred that the V-step 25 has a length in the range between Ato %the length of the boat hull itself.
A number of spray rails may be provided beneath the boat hull and may extend in the fore-and-aft direction. Such rails provide against unwanted spray of the water and help to maintain the water in position beneath the boat hull.
In operation, as the boat hull reaches planing speeds, it lifts partly out of the water and planes on front wetted surface 35 and rear wetted surface 39, riding on an air cushion beneath the hull aft of step 25, with air passing from the bow 13 of the boat hull through air inlet 55 and duct 57 to ports 31.
In addition to providing a broad planing surface, planing fins 29 help to stabilize the boat against pitching because of their length, and against rolling because of their extension from the sides of the boat.
At slow speeds, planing fins 29 ride below the water, and the boat hull behaves in about the same manner as the conventional boat hull supported by its buoyancy, except for some damping of pitch and roll by planing fins 29 and except for the lesser drag of the smaller step 25.
It may be necessary to taper the height of the step 25 in order to maintain the preferred angle between the bottom of the step and the at rest water line.
The small step of the boat hull in my invention reduces shock from waves as compared to conventional planing hulls, increases stability, and yet represents a very small change structurally from nonplaning hulls so that my hull has the fine and easy running qualities of a smooth bottom boat.
It is to be understood that the form of the invention herewith shown and described is to be taken as a presently preferred embodiment. Various changes may be made in the shape, size and arrangement of parts. For example, equivalent elements may be substituted for those illustrated and described herein, parts may be reversed, and certain features of the invention may be utilized independently of the use of other features, all without departing from the spirit or scope of the invention as defined in the subjoined claims.
1. In a boat, a boat hull having bow, stern, beam, and a keel line running along the bottom, and a long shallow planing V- step running diagonally under the bottom on each side of the keel line, said planing step extending aft diagonally in a long V for substantially one-third to two-thirds the length of the boat.
2. In a boat, a boat hull havlng bow, stern, beam, and a keel line running along the bottom, a long shallow planing V-step running diagonally under the bottom on each side of the keel line, venting means venting air to the area beneath the hull to the rear of the planing step, said venting means including a series of ports formed in the bottom of the hull aft of said step, an air inlet, and a duct connecting the air inlet to the ports.
3. The boat of claim 2, wherein the cross-sectional area of the duct decreases as the distance from the air inlet increases, said cross-sectional area decreasing as air is tapped by successive ports.
4. In a boat, a planing hull having bow, stern, beam, and bottom, a shallow V-step with legs running aft diagonally from a forwardly positioned apex, and means for venting to atmosphere the hull bottom aft of the step and for air-cushioning the hull bottom aft of the step.
5. The planing hull of claim 4, wherein said step defines the rear edge of a wetted surface planing area, and said step breaks away sharply from the hull bottom which lies forward of the step.
6. The boat of claim 4, wherein the planing step runs from about one-third boat length from the bow and extends to the beams of the normal water line.
7. The boat of claim 4, wherein means are provided for extending the lifting surface of the hull beyond the beam of the hull to increase the effective beam.
8. The boat of claim 4, wherein the height of the step in a 40-foot boat hull is in the range of %inch to 2 inches.
9. The boat of claim 4, wherein the hull bottom slopes downwardly from the bow at about 1 to 4 to the at rest water line.
10. The boat of claim 4, wherein the hull bottom slopes upwardly aft of the planing step at about 2 to 4 to the at rest waterline.
11. The boat of claim 4, including a planing fin on each side of the hull which continues the step and extends rearwardly and outwardly.