US3456611A

US3456611A - Hydrofoil craft

Info

Publication number: US3456611A
Application number: US747026A
Authority: US
Inventors: Lew W Johnson
Original assignee: LEW W JOHNSON
Current assignee: LEW W JOHNSON
Priority date: 1968-07-12
Filing date: 1968-07-12
Publication date: 1969-07-22
Anticipated expiration: 1986-07-22

Description

July 22, 1969 L. w.JoHNsoN 3,456,611

HYDROFOIL CRAFT Filed July 12. 1968 5 Sheets-Sheet 1 Tlcl.-

02d@ 15 WAM@ ATT RNEY5 July 22, 1969 n.. w. JoHNsoN HYDROFOIL CRAFT 5 Shets-Sheet 3 Filed July 12, 196e @f1/aga WM5 ATT RNEYS L. W. JOHNSON HYDROFOIL CRAFT July 22, 1969 Filefl July l2. 1968 5 Sheeis-Sheet 4 L. W. JOHNSON HYDROFOIL CRAFT 5 Sheets-Sheet 5 July 22, 1969 Filed July l2, 1968 /57/5 Y lNVENTOR United States Patent O 3,456,611 HYDRFGIL CRAFT Lew W. Johnson, Rnmson, NJ. (1927 Brightwater Blvd. NE., St. Petersburg, Fla. 33704) Continuation-impart of application Ser. No. 625,513, Mar. 23, 1967, which is a continuation-in-part of application Ser. No. 521,039, `Ian. 17, 1966. This application `Iuly 12, 1968, Ser. No. 747,026

Int. Cl. B631) 1/18 U.S. Cl. 114-665 17 Claims ABSTRACT GF 'THE DISCLOSURE A plural hull watercraft is provided with hydrofoils which are reversibly adjustable between inoperative positions and operative positions; the hydrofoils when in an operative position providing a hydroplaning function.

This application is a continuation-impart of my copending application Ser. No. 625,513, led Mar. 23, 1967, now abandoned, which is in turn a continuation-impart of my now abandoned application Ser. No. 521,039, filed Ian. 17, 1966.

This invention relates to plural hull watercraft, particularly catamarans, provided with hydrofoils.

The introduction of hydrofoils for use in watercraft, particularly seagoing craft, has enabled increased speeds. The typical hydrofoil craft utilizes at least one hydrofoil which is submerged in the water. The hydrofoil raises the hull of the craft to a higher position in respect to the water through which the craft is travelling. The hydrofoil provides an upward component of force or lift when the craft has forward velocity with respect to the water. When the forward velocity of the craft is sufficiently high, the lift created on the hydrofoil by the water raises the entire hull above the surface of the water and the craft may then be referred to as hydroplaning or being in flight.

There are a number of disadvantages associated with the typical hydrofoil craft. One problem is rolling and pitching of the craft. Another problem is a sometimes rough transition from a non-hydroplaning state to a hydroplaning state. Still another problem, not unique to hydrofoil craft, is the expense of drydocking for storage and repairs. Yet another problem is the formation of encrustations on the hydrofoils and related structure due to continual immersion in the water. The present invention isdirected to providing hydrofoil craft particularly adapted to overcoming various of these problems and other problems which will become apparent from the following description.

In its broadest aspect, the present invention provides a plural hull hydrofoil craft in which at least some hydrofoils are adjustable from inoperative positions for nonhydroplaning to operative positions for hydroplaning. The plural hulls may be referred to individually as hull sections in order to distinguish them from the hull collectively, i.e., the craft as a whole exclusive of the superstructure.

More specifically, according to one aspect of the present invention, particularly effective operation is obtained by employing to propel the craft a propulsion system comprising a water inlet duct having an inlet port for communication with the body of water on which the craft is to be propelled, water ejection means in communication with the inlet port to receive water therefrom, an engine drivingly coupled to the water ejection means and a water outlet duct having an outlet port in communication with the water ejection means to discharge water therefrom and with which is provided means to move the inlet port in accordance with movement of the hydrofoil. Typically, such a water propulsion system may be an engine driven turbojet, the water ejection means being a turbine.

According to another aspect of the invention, a ski-like member is provided b-etween the hydrofoil and the hull t0 render the transition, from non-hydroplaning to hydroplaning, and vice versa, particularly smooth.

In further aspects of the invention, the tunnel defined by spaced parallel hull sections is utilized for retraction of hydrofoils and associated structure above the waterline while the craft is cruising, i.e., not hydroplaning.

According to yet another aspect of the invention, to provide greater lateral stability of the craft, the craft iS equipped with adjustable dihedral hydrofoils.

The aforementioned features may be employed individually or in various combinations.

The retractability of the hydrofoils permits the craft to cruise in a non-hydroplaning state in shallow waters. In those embodiments in which hydrofoils are retracted above the waterline, there is the further advantage that the hydrofoils are not continually immersed in the water whereby the formation of encrustations on the hydrofoils proceeds less rapidly. Moreover, the adjustability of the position of the hydrofoils relative to the hull makes possible compensation of the positions of the hydrofoils for turbulence and waves. Also, as the hydrofoils are raised and lowered, they remain in an orientation effective for hydroplaning whereby transitions are smooth. These hydrofoils, furthermore, provide a self-drydocking feature in that the craft may be raised when beached by using the hydrofoils as jacks.

The feature of the ski member between the hydrofoil and the hull makes for a smoother transition from the non-hydroplaning state to the hydroplaning state and vice versa. The ski members also serve to deect any debris which may be floating in the water.

The adjustable dihedral hydrofoils provide greater lateral stability.

The invention is further described with reference to the accompanying drawings, in which:

FIG. 1 is a schematic, side elevational view of one embodiment of a hydrofoil craft laccording to the present invention showing the sloping ski-like surfaces and hydrofoil surfaces extending from the bottom of the hull;

FIG. 2 is an enlarged, fragmentary side elevational View of the aft end or stern of the craft shown in FIG. 1;

FIG. 3 is a schematic side elevation of another embodiment of a hydrofoil craft according to the present invention showing the sloping ski-like surfaces and hydrofoil surfaces extending from the bottom of the hull;

FIG. 4 is a front View of the craft shown in FIG. 3, with the fore or bow hydrofoils broken away to show the inlet ducts in the ski-like surfaces;

FIG. 5 is an elevation View, partly in section, taken along lines 5-5 of FIG. 4, showing features of the present invention in greater detail;

FIG. 6 is a detailed view of the hydrofoil surface and ski-like surface showing the inlet ports;

FIG. 7 is a detailed elevation View, in section, taken along line 7--7 of FIG. 6, showing the hydrofoil and skilike surface retracted within the hull;

FIG. 8 is a schematic side elevation view of a hydrofoil craft showing, in the dotted portions, the turbojet engine and propulsion system in which the outlet is in a different configuration than that shown in the embodiment of FIG. 3;

FIGS. 9 and 9a are fragmentary front elevations of another embodiment in which is illustrated a bow hydrofoil assembly with the hull of the craft appearing in cross section; FIG. 9 illustrates the lassembly in extended position and FIG. 9a in retracted position;

FIG. 10 is a fragmentary side elevation from the left side of FIG. 9 but with more of the hull illustrated;

FIG. 11 is a fragmentary side elevation with the hull partly in cross section taken on section line 11-11 in FIG. 9, with a dot-and-dash representation being employed to illustrate this portion of the bow assembly also in the retracted position;

FIG. l2 is a fragmentary side elevation, partly in section, taken on section line 12-12 in FIG. 13, illustrating in extended position a stern hydrofoil and duct assembly employed with the bow hydrofoil assembly of FIGS. 9 t 11, with a dot-and-dash representation being employed to illustrate the stern assembly also in the retracted position;

FIG. 13 is a fragmentary front elevation, partly in section, taken on section line 13-13 of FIG. 12; and

FIG. 13a is analogous to FIG. 13 but illustrating the stern assembly in retracted rather than extended position.

Referring now to FIGS. 3 and 4, a hydrofoil craft is shown comprising a hull 12 which is adapted to float in the water, when the craft is at rest, or travelling at relatively low speeds.

Forward and

aft hydrofoils

14 and 16 are provided for dynamic support of the craft after it gets under way and hull 12 is raised entirely out of the water. The

hydrofoils

14 and 16 are disposed sufficiently away from the hull to avoid substantial wave impact against any portion of the hull when the craft is riding on the hydrofoils. Fore and aft sloping ski-

like surfaces

18 and 20, are disposed between the

hydrofoils

114 and 16, respectively, land the hull 12, and slope upwardly from the end of the hydrofoils to a position within the hull 12. The ski-

like surfaces

18, 20 also serve to protect the hydrofoil surfaces 14, 16 by deflecting floating objects which would otherwise strike the hydrofoil surfaces.

The hydrofoil surfaces 14 and 16 are positioned relative to the hull by the vertical movement of rods which are connected to the top surface of the hydrofoil by connecting means 23. As more fully described below, the position of rod 25 is controlled by a hydraulic control system.

As shown in FIG. 4, the craft, by way of example, is essentially in the form of a catamaran having port and starboard sections, each of which has essentially similar ski-like surfaces and hydrofoil surfaces extending from the bottom surface thereof.

A turbojet water propulsion system is provided to supply forward velocity to the craft. The system takes up `water from the sea through an inlet port 22 which extends through sloping ski-like surface 20 from where it is sucked through a flexible duct 27, into a turbine 26. Turbine 26 is driven by an engine 24 or turbine. The turbojet 26 exhausts the liquid through a duct 29 and out from an exhaust port 21. A screen 28 is positioned over the inlet port 22 to prevent any debris from clogging the port and to insure trouble-free operation.

FIG. 3 shows one feature of the invention, in which the outlet port 21 is positioned with respect to the aft hydrofoil surface 16, to increase the eiliciency of the water jet propulsion system. The exhaust or outlet port 21 is positioned to exhaust at that location in the stern of each hull or from each rear hydrofoil surface 16 to insure the optimum efficiency of operation of the turbojet.

FIG. 5 provides `a more detailed structural view of the hydraulic control system for the hydrofoil and skilike surfaces. The rod 25 is fixedly connected to the lower end of a piston 30 which moves within a cylinder 32.

The movement of piston 30 is controlled by the introduction of hydraulic fluid into cylinder 32. The hydraulic fluid input to the cylinder is responsive to operations from a control system 43. Height sensors 42 are mounted to the craft at any convenient location on either side of the craft, land to the fore and aft sections of the craft. A velocity sensor y45 is also mounted to sense the forward velocity of the craft. Both sensors are coupled to a control apparatus 43, which processes the data received to send a mechanical signal to the hydrofoil contro-l cylinders 32 to raise or lower the pistons 30. The sensors and control apparatus may be similar to that shown in U.S. Patent No. 3,149,601.

Due to disturbances in the water surface such as waves, the relative height of the several hydrofoil surfaces may be unbalanced. The height sensors 42 sense the heights of each of the hydrofoil surfaces. This data is processed by the control computer 43 which may be hydraulic, mechanical, or electronic in nature. The resulting signals are compared to a reference signal, which is a function of the craft velocity as determined by velocity sensor 45. The control computer 43 then transmits mechanical signals through the mechanical linkage means 44 to equalize the pressure within the hydraulic cylinders 32 thereby stabilizing the craft by equalizing the relative positions of the several hydrofoil surfaces.

For this purpose pressure sensing means (not shown) may be used instead of the height sensing means to transmit data to the control computer. The hydraulic system is operated automatically in response to the forward velocity of the boat Within the water as sensed by velocity sensor 45. As the velocity increases, control computer 43 transmits .a mechanical signal to cylinders 32 through linkage means 44 to cause the rod 25 to descend in a substantially vertical direction, to lower the hydrofoils and ski-like surfaces into the water.

However, it should be noted that the hydraulic system not only operates the hydrofoils, but is also capable of lifting the hydrofoil craft when tbeached. Thus the hydraulic system acts as a jack and facilitates all drydocking operations, like hull painting, or any other repairs. By this dual functioning of the hydraulic system, namely to operate the hydrofoils and serving as a jack to lift the craft for drydocking operations, the necessity of cradling or blocking of the craft is completely eliminated.

As shown in FIG. 5, in which the hydrofoil 14 and skilike surface 18 are already positioned below the hull, the ski-

like surfaces

18 and 20 extend at a sloping angle to a pivot position 31 located within the hull. The ski-

like surfaces

18 and 20 are pivotally connected at the other end thereof to the

hydrofoil surface

16 and 14 by means of a pin 35.

As best seen in FIG. 6, each ski-like surface is a substantially flat surface which is narrow at the end which is fixed to the hydrofoil surface. The ski-like surface widens towards the end at which it joins with the hull.

In operation, as the velocity of the craft increases, the hull rises from the water. The craft then proceeds to travel along the ski-like and hull surfaces until the speed is further increased, so that the hull then rises further and the boat rides along the hydrofoil surfaces. During this increase in craft velocity, the hydrofoil surfaces are gradually lowered into position by the hydraulic control system.

A further feature of the present invention is the provision of an air dome, or air cushion 37, within each hydraulic cylinder 32 to provide shock absorption for the craft from any water turbulence, or impact caused by a hydrofoil Istriking a floating object. A sudden jarring of the hydrofoil 4will be transferred to piston 30 within the cylinder 32. The air cushion 37, positioned at the upper portion of the cylinder 32, will receive the sudden motion of the piston, and `will thereby cushion the shock by allowing the particular hydrofoil to deflect and quickly return to its former position through the resilient `action of the air cushion. This may be employed in each cylinder of each embodiment disclosed herein.

This feature will greatly smooth the operation of the hydrofoil craft even in the most turbulent of waters.

As shown in FIG. 7, when the craft comes to rest, or rides on the hull surface at low velocities, the hydrofoil surface 14 and ski-like surface 18 are retracted into a recess 41, located yat the bottom of the hull. This retraction Iis effected by moving piston 30 along with linking rod 25 upwards. The hydrofoil and ski-like surface pivot into the retracted position about pivot pins 31 and 35. The same action may also be provided for members 16 and 20f-at the aft end of the craft.

The embodiment yin FIG. 8 is quite similar to that shown in FIG. 3, except that the outlet port 40 exhausts the jet stream at a level within the hull.

The embodiment shown in FIGS. 1 and 2 illustrates the -alternative construction of a turbojet water propulsion system which can be used in the water going craft of the present invention. In this embodiment the ski-like sloping surfaces such as indicated by the

reference characters

18 and 20 in FIGS. 3, 5, 6 and 8 are eliminated at the fore and aft ends of the craft. Hydrofoil 16 is supported, in part, by strut means 50 pivotally connected to the bottom of the hull at 52 and to the hydrofoil surface at 23'. The hydrofoil surface 16' is also supported by rod 25' that is coupled to piston 30 of cylinder 32'. Hydrofoil surface 14' is supported, in part, by strut means 51 pivotally connected to the bottom of the hull at 53 and to the hydrofoil surface at 23. The movement of the

hydrofoil

14 and 16 are controlled #by an hydraulic system identical to that described in connection with the previous embodiment and which is synchronized with the speed of the craft. Accordingly the description of the control system need not be repeated at this time.

Means to take up water from the sea for propulsion purposes is provided by an inlet port 22 which extends from hull 12 from where it is sucked through a duct 27 into a turbine 26. Turbine 26 is driven by an engine 24'. The turbojet exhausts the liquid through a duct 29 and out from exhaust port 21. The portion of the free end of inlet port 22 that lis in communication with the water is adjustable by means ofA a rod 54 coupled to piston 56 of cylinder 58. The aforementioned hydraulic control system couples the movement of the inlet port to that of hydrofoil surface 16.

In FIGS. 9 to 13a is illustrated an embodiment in which the turbojet inlet ducts and most of the hydrofoil surfaces `are retractable into the tunnel between the hulls with the thus retracted hydrofoil surfaces and la portion of the thus retracted inlet ducts above the Waterline whereby harmful encrustation of the hydrofoil surfaces by prolonged immersion in the water is avoided and a bow hydrofoil assembly is provided with rotatable dihedral foils adjustably to provide greater lateral stability of the craft while in flight.

In this embodiment the bow hydrofoil assembly 100 (FIGS. 9, 9a, 10 and l1) lis comprised of a center hydrofoil 101 which is horizontal laterally and identical di- =hedral hydrofoils 102 and 103 which are very closely adjacent to or abut against the center hydrofoil 101. Hydrofoils 102 and 103 are rotatable between a position in which they `are laterally horizontal and therefore in lateral alignment with the hydrofoil 101 to la position rotated 30 upward from the horizontal and intermediate positions, hydrofoils 102 and 103 defining a dihedron when in a so rotated position.

Hydrofoil 101 is supported by identical rods 1014 and 106 and

identical struts

107 and 108. The rod 104 and the strut 107 are pivotally connected to the hydrofoil 101 by means of a bracket 109 rigidly mounted on the hydrofoil 101 and the rod 106 and the strut 108 are similarly connected to the hydrofoil 101 by means of a -bracket 110. The other end of

struts

107 and 108, respectively, are pivotally connected to the top of the tunnel between the hulls by means of brackets 111 and 112. The other end of

rods

104 and 106, resepectively, are rigidly connected to

pistons

113 and 114. The

pistons

113 and 114, respectively, are slidably mounted in

hydraulic cylinders

115 and 116.

Retraction of the hydrofoil 101 is effected by activation of the

hydraulic cylinders

115 and 116 to retract the

pistons

113 and 114 and therewith the

rods

104 and 106.

The rods and 121 are pivotally connected to the hydrofoil 102 by means of

brackets

122 and 123, respectively, each provided ywith a slot for sliding therein of the pivot pin. Similarly, the hydrofoil 103 is supported by

rods

124 and 125 pivotally connected to the hydrofoil 1013 by means of

like brackets

126 and 127, respectively. The

identical rods

120, 121, 124 and 125 are rigidly connected to

identical pistons

128, 129, 130 and 131, respectively, the

pistons

128, 129, 130 and 131 being slidably mounted in identical

hydraulic cylinders

132, 133, 134 and 135,

respectively.Cylinders

133 and 135 are controlled together as are

cylinders

132 and 134 in order that the dihedral angle may be varied.

Cylinders

132 and 134 may be activated independently of or in coordination with the

cylinders

133 and 135 in order to permit, alternatively, adjustment of the average elevation of the hydrofoils 102 and 103 without adjustment of the dihedral angle, adjustment of the dihedral angle without adjustment of the elevation of the inner edges of the hydrofoils 102 and 103 and simultaneous adjustment of the averge elevation and the dihedral angle of the hydrofoils 102 and 103.

The hull bottoms and 141 are laterally inclined from the horizontal by 30. In the retracted position, the upper surfaces of the hydrofoils 102 and 103 abut the

respective hull bottoms

140 and 141, the dihedral angle adjusted to 30. This is the preferred arrangement though, the hull bottoms may be provided with no inclination or one which is less than 30, in which event the dihedral angle of the hydrofoils 102 and 103 would be adjusted during retraction to the corresponding value. The hydro foil 101 is operated independently of the hydrofoils 102 and 103 because the vertical distance the hydrofoil 101 must travel to become operative is greater than the vertical distance to be traversed by the hydrofoils 102 and 103. Preferably, vertical movement of the hydrofoil 101 on the one hand and the hydrofoils 102 and 103 on the other hand is coordinated so that the hydrofoil 101 is lowered to the level of the inner edges of the hydrofoils 102 and 103 before lowering of the hydrofoils 102 and 103 begins, optionally the provision being made for locking of the hydrofoils into a unitary assembly at this level, and subsequently through further lowering the

hydrofoils

101, 102 and 103 move in unison. Retraction proceeds exactly in the reverse.

The stern assembly (FIGS. 12, 13 and 13a) is comprised of a hydrofoil 151 and for the turbojet propulsion system identical rigid

water inlet ducts

152 and 153 provided with screens 152a and 153a at their inlet ports. The stern assembly is supported by identical rods 154 and 155 pivotally mounted to the hydrofoil 151 by means of

respective brackets

156 and 157, which brackets also pivotally mount

ducts

152 and 153 respectively. Toward their other end the

ducts

152 and 153 are pivotally mounted on the inner walls of the respective hulls near the top of the tunnel by means of

respective joints

158 and 159. The rods 154 and 155 are rigidly connected to respective identical pistons 160 and 161, the pistons 160 and 161 in turn being slidably mounted in respective identical

hydraulic cylinders

162 and 163. Identical brackets 164 and iixed to the roof of the tunnel pivotally mount the

cylinders

162 and 163, respectively. The

cylinders

162 and 163 are controlled together.

Retraction of the stern assembly into the tunnel with the entire assembly but for a lower portion of the

ducts

152 and 153 above the waterline is effected simply by activation of the

cylinders

162 and 163 to retract the pistons 160 and 161. The suspended end of the assembly thus swings forwardly and upwardly into the tunnel to a rest position abutting the ceiling of the tunnel. Extension of the assembly to the operative position is by exactly the same operation in reverse.

-By means of height sensors 42, a velocity sensor 45 and linkage means 43, as in the other embodiments (see FIGS. l, 3 and 8), the craft 4may be stabilized by equalizing the relative positions of the

hydrofoils

101 and 151. Moreover, a rolling sensor may be linked to the cylinders controlling the dihedral angle of the hydrofoils 102 and 103 automatically to provide optimum lateral stablility by increasing of the dihedral angle in response to an increase in rolling thereby to decrease the rolling.

While I have described certain embodiments of my invention, I desire that the scope of my invention be limited only by the scope of the appended claims.

What is claimed is:

1. A craft comprising a hull constituted of a plurality of hull sections, hydrofoil surface means operatively connected to said hull for adjustment of the height of the hydrofoil surface means relative to said hull, means to lower said hydrofoil surface means from an inoperative position to an operative position while maintaining said hydrofoil surface means in an orientation to continuously provide a hydroplaning function, to support said hull when said craft reaches a predetermined speed, a propulsion system secured to said craft and arranged to propel said craft through a body of water, said propulsion system comprising a water inlet duct having an inlet port for communication with the body of water, water ejection means in communication with said inlet port to receive water therefrom, an engine drivingly coupled to said water ejection means and a water outlet duct having an outlet port in communication with said water ejection means to discharge water therefrom, and means to move said inlet port in accordance with the movement of said hydrofoil surface means.

2. A craft in accordance with claim 1, wherein said water ejection means is a turbine.

3. A craft in accordance with claim 1 including a ski-like member extending between said hydrofoil surface means and said hull section associated therewith.

4. A craft in accordance with claim 1 including a skilike member extending between said hydrofoil surface means and said hull section associated therewith and movable together with said hydrofoil surface means, said inlet port being disposed in at least one of said ski-like members.

5. A craft in accordance with claim 1 wherein said water inlet duct extends downwardly from at least one of said hull sections whereby said inlet port is in communication with the water.

6. A craft in accordance with claim 1 wherein said outlet port terminates above said hydrofoil surface means.

7. A craft in accordance with claim 1, in which said means to lower sai-d hydrofoil surface means comprises an hydraulic system including a cylinder, a piston movable within said cylinder and means connecting said piston to said hydrofoil surface means.

8. A craft in accordance with claim 7 including air cushion means coupled to said cylinder and arranged to absorb at least part of the movement of said piston.

9. A craft in accordance with claim 1 including means to sense the height of said hydrofoil surface means, means to provide a signal corresponding in magnitude to the height sensed and hydrofoil actuation means responsive to said signal means.

10. A craft in accordance with claim 9 including an hydraulic system arranged to move said hydrofoil surface means, said actuation means being coupled to said hydraulic system for actuation thereof.

11. A craft comprising a hull, hydrofoil surface means operatively connected to said hull to support said hull when said craft reaches a predetermined speed, a ski-like member extending between said hydrofoil surface means and said hull and propulsion means secured to said craft and arranged to propel said craft through water.

12. A craft according to claim 11, in which said hydrofoil surface means is movable.

13. A craft according to claim 12, in which said skilike member is movable with said hydrofoil surface means,

14. A craft adapted to travel on a body of water and comprising a hull constituted of a plurality of hull sections defining atleast one tunnel therebetween, said tunnel being open at the bottom and extending upwardly beyond the waterline of the craft, hydrofoil surface means operatively connected to said hull for adjustment of the position of said hydrofoil surface means relative to the hull and means reversibly to adjust the position of said hydrofoil means relative to the hull from a fully retracted position in which the hydrofoil means is retracted into said tunnel above said waterline to extended positions in which the hydrofoil means is positioned below the waterline to provide a. hydroplaning function.

15. A craft according to claim 14, further comprising propulsion system secured to said craft and arranged to propel the craft through water, said propulsion system comprising at least one water inlet duct having an inlet port arranged for communication with the body of water and said duct being arranged to move to change the position of the inlet port relative to the hull in accordance with the movement of the hydrofoil surface means.

16. A craft according to claim 15, in which `the duct is so arranged that it is positioned partly above the waterline when the hydrofoil surface means is in its fully retracted position.

17. A craft according to claim 15, in which said hydrofoil surface means and said `duct are positioned toward the stern of the craft.

References Cited UNITED STATES PATENTS 3,236,202 2/1966 Quady et al 114-665 FOREIGN PATENTS 553,450 5/1943 Great Britain.

ANDREW H. FARRELL, Primary Examiner