US 3793980 A
A propulsion system for high speed planing hulls, employing a tunnel-mounted propeller of the supercavitating type in conjunction with means for causing the propeller to operate partly submerged at planing speeds and, aided by the tunnel, to operate fully-submerged with great effectiveness at low hull speed to enable the propeller to develop ample thrust to drive the craft up to and into planing speed.
Description (OCR text may contain errors)
United States Patent 1 Sherman 1 1 Feb. 26, 1974 [5 1 MARINE PROPULSION SYSTEM 3,515,087 6/1970 Stuart 115/39 x  Inventor: Peter M. n, Stuart Fla 3,604,384 9/1971 Coles 114/665 H  Assignee: Hydrodynamic Development Corp., Primary ExaminerDuane A. Reger Salem, Mass. Assistant ExaminerCharles E. Frankfort Filed: Dec- 30 1971 Attorney, Agent, or Ftrml(enway & .lenney  Appl. No.: 214,337  ABSTRACT A propulsion system for high speed planing hulls, em-  US. Cl. 115/39 ploying a tunnel-mounted propeller of the super-  Int. Cl B63h 5/16 cavitating type in conjunction with means for causing  Field of Search,.... 115/39, 34, 35; 114/665 H, the propeller to operate partly submerged at planing 114/665 P, 61, 62, 57 speeds and, aided by the tunnel, to operate fullysubmerged with great effectiveness at low hull speed  References Cited to enable the propeller to develop ample thrust to UNITED STATES PATENTS drive the craft up to and into planing speed.
1,121,006 12 1914 Fauber 115 39 x 30 Claims, 18 Drawing Figures PATENTED FEB? 6 SHEET 2 [IF 3 FIG. 10
a o a o o o o o 0 o 0 o o o o a o 0 n 0 n o u o o o o o o o u o o o a a u a o o o o o 0 o o 0o 00 a o o o o c o o a 0 Q o o o o 0 Q o o a o u w c Q 0 c o o o ce a o u a o 6 o 8 c 6 o o o o a co o a a o o Q 0 0 O a De n 0 o o 0 0 O o a o as O o 0 0 a 0 a 7 a u a c 0 O GOD D 0 G3 0 a oo o o 0 e0 0 o a o o o o a no 6 .v w u on o 00 V a c n 3 an o o o MARINE PROPULSION SYSTEM BACKGROUND OF THE INVENTION The theoretical advantages of so-called surface type propellers for high speed power boats have long been recognized, and many attempts have been made to utilize such propellers. The term surface propeller arises because the propeller, instead of operating fully submerged as does a conventional propeller, is so positioned that its center, or hub, is approximately at the level of the water in which it is operating. That is, the propeller has a portion of its effective disc area in the water and the remainder of its area in the air. Thus the blades succesively dip into the water as the boat advances, and the propeller develops its thrust only on the faces (pressure sides) of the blades.
These surface propellers, more recently termed semisubmerged supercavitating propellers because their action creates voids in the water on what would normally be termed the suction or back sides of the blades, are capable of driving a given hull at speeds substantially higher than can be obtained from either a fully submerged conventional (non-cavitating) or a fully submerged supercavitating propeller operating at the same shaft horsepowers. This increase in performance with the surface propeller results from the fact that there is no appendage drag associated with converting the rotative power of the prime mover into propulsive thrust to propel the hull. Also, there are no adverse effects due to cavitation on a surface propeller. Cavitation will decrease the efficiency (or lift/drag ratio) of a fully submerged conventional propeller. The design performance of the fully submerged supercavitating propeller will be altered due to the fact that the design condition, corresponding to a cavitation number equal to zero, can never be attained short of an infinite speed.
The problem, and one which has been a major obstacle to the adoption of surface propellers, is their inability to develop adequate thrust at low speeds, when the boat is required to make the transition from the displacement mode of operation to the planing state. This lack of thrust at low speeds is not the result of any lack of engine power, but rather the inability of the propeller to utilize the available power. At low speeds, technically known as low advance ratios, a phenomenon called cavity blockage occurs. When the advance of the boat is zero or very small, in relation to propeller rotation, the cavity left by one blade is in the path of the next blade, so that the following blade encounters this cavity rather than undisturbed water. As the forward speed of the boat increases, this cavity blockage takes another form in which the cavity formed by the leading blade does not actually impinge on the following blade; at this point the blades and their large attendant cavities cause an actual choking of the flow through the propeller disc. Either of these cavity blockage forms is usually sufficient to prevent the surface propeller from generating the required thrust to get the craft through the transition region, often termed the resistance hump, into planning condition.
Various means have been proposed and employed, such as using excessively large propellers, or using a supplementary propulsion system, to enable the boat to be driven through the resistance hump. Still another approach has involved mounting the surface-type propeller aft of the transom so that at speeds below planing the propeller may have some additional disc area immersed in the stern wave that builds up behind the transom at low speed. This last-mentioned expedient creates major problems in providing adequate propeller shaft strength to withstand the stresses resulting from the inability to provide bearing support close to the propeller, and also places the propeller and propeller shaft in a position where they are easily subject to accidental damage.
SUMMARY OF THE INVENTION In accordance with the present invention, it becomes possible for the first time to have a propulsion system which permits semi-submerged operation of a supercavitating propeller under optimum conditions for high hull speeds, yet enables the same propeller to operate effectively at low hull speeds so that it can readily develop the thrust necessary to get the craft through the resistance hump and up onto plane.
This is accomplished, in accordance with my invention, by providing a tunnel in the underbody of the boat and mounting the propeller in the tunnel so that the upper part of the propeller, above the hub, is within the tunnel, while the portion of the propeller below the hub is exposed below the hull. At low hull speeds, before planing, water flows into the tunnel ahead of and to the propeller and the propeller operates fully immersed, with its thrust enhanced by the shrouding effect of the tunnel partially surrounding the propeller.
At higher speeds, aided by special flow control means ahead of the propeller, the flow of water is caused to bypass the tunnel so that the propeller operationundergoes a transition to the semi-submerged mode, with its high propulsive efficiency. Under these conditions, with the flow of water streaming aft under the hull and below the tunnel, and with the tunnel vented to atmosphere through its opening at the transom, the tunnel and its flow control means cause no appreciable drag.
DESCRIPTION OF THE DRAWINGS In the drawings illustrating a preferred configuration of the tunnel of my invention and disposition and arrangement of the propulsive and flow control elements therein, as well as showing the utilization of the propulsion system in typical single and twin-screw embodimerits,
FIG. I is a top plan view, partly in section and taken on the line 1-1 of FIG. 2, showing the structural configuration and arrangement of the propulsion system.
FIG. 2 is a sectional elevation of the structure shown in FIG. 1, taken on the line 2-2 of said Figure.
FIG. 3 is a sectional detail of the tunnel and adjacent portion of the hull, taken on the line 3-3 of FIG. 2 looking forward.
FIG. 4 is a view in elevation of the aft end of the structure, looking forward as indicated at 4-4 in FIG. 2 and showing a portion of the stern transom of the hull.
FIG. 5 is a view, on a smaller scale than FIG. 4, showing the stern of a typical V-bottom vessel suitable for high-speed operation, illustrating the disposition of the propulsion system in a single-screw installation on the center line of the craft.
FIG. 6 is a sectional detail of one of the flow control elements located ahead of the propeller and shown in section in FIG. 2.
FIG. 7 is a sectional detail through a portion of one of the rudders, taken on the line 7-7 of FIG. 2.
FIG. 8 is a view of the stern of a typical V-bottom high speed hull, illustrating the embodiment of the propulsion system in a twin-screw installation.
FIG. 9 is a sectional detail of the left hand tunnel and structure of FIG. 8, taken at a location corresponding to the line 3-3 of FIG. 2, showing the relationship of the flow-control elements to the underbody of the hull.
FIG. 10 is a view of the aft end of the left hand propulsion unit shown in FIG. 8, showing the disposition of the rudder in relation to the deadrise angle of the hull.
FIGS. 1 1, .12 and 13 are diagrammatic views illustrating the flow patterns and resulting different modes of operation of the propulsion system at various speeds. In particular, FIG. 11 represents the flow pattern at low hull speeds, with the propeller operating fully submerged.
FIG. 12 is representative of transition operation, with formation of cavities commencing as a result of increasing hull speed.
FIG. 13 shows typical high speed operation, with only the blade region of the propeller below the hub effectively engaging the-water and operating in the semisubmerged super-cavitating mode of propulsion.
FIG. 14 is a side view of the aft portion of a high speed power boat, showing a typical mode of singlescrew installation of the propulsion system and power driving means therefor.
FIG. 15 is a bottom view of the hull with propulsion system on the centerline.
FIG. 16 is a side view of the aft portion of a hull having a twin screw installation, also with V-drive power plant. I
FIG. 17 is a bottom view of the hull and tunnels of FIG. 16, illustrating the disposition of the axes of the propeller shafts at slightly oblique angles to the centerline of th hull.
FIG. 18 is a graph showing curves representing relative values of propeller thrust provided by the propulsion system of the invention, compared with that of a conventional surface propeller, in relation to hull resistance for a typical hull, over a wide range of hull speeds.
DESCRIPTION OF THE INVENTION The propulsion system of the invention is adapted to be incorporated in high speed planing hulls having relatively flat sections or moderate deadrise aft, as well as in hulls having the so-called deep-V configuration maintained to the transom that is advantageous for rough water use. The system is also adaptable to both single screw and multiple screw installations.
First will be described a single screw installation in a V-type hull of relatively constant deadrise, represented by the angle between the bottom surfaces 22 and 24 where they terminate at the transom 26, illustrated in FIG. 5. As best'shown in FIGS. 1 and 2, (and also on a somewhat smaller scale in FIGS. 14 and 15) a tunnel 32 is provided in the bottom of the boat, disposed along the center of the underbody in the aft portion of the hull and extending to the transom 26. This tunnel has a generally semi-circular configuration throughout its length and may be formed by molding as an integral part of the hull during the construction of the boat, or may be separately fabricated and installed within a suitable slot-like opening prepared in an existing hull. At its forward end above transverse lip 40, the interior surface 42 of the tunnel curves forwardly, upwardly and then aft as shown in FIG. 2 to merge with the semicylindrical region 44. At the juncture of the forward end of the tunnel with the bottom of the hull, the transverse lip 40 provides an abrupt discontinuity to enable the flow of water to stream straight aft at high hull speeds.
The propeller shaft 46, on which propeller 50 is mounted in a position between the forward end of the tunnel and the stern of the hull and preferably somewhat aft of the midpoint, as illustrated, extends through a combined bearing and stuffing box 52 mounted on the central flat and thickened region 54 within the hull at the forward end of the tunnel. Another bearing 56 supports the shaft just ahead of the propeller. Both bearings preferably include bearing sleeves of a rubber or rubber-like material dependent on water for lubrication. In order that they may operate properly in the propulsion system of the invention, they are provided with a positive supply of water connected to passages 58 and 60 via conduits indicated schematically at 62 from a source derived either from the main power plant or by means of a separate pump, not shown. The passage 60 to the bearing 56 adjacent the propeller runs inside bearing support strut 64 extending upwardly to the roof of the tunnel, suitably reinforced above.
The propeller shaft is preferably mounted as nearly parallel to the axis of the tunnel as is practical. In particular, the stern bearing 56 is mounted so that the lowermost portion of the propeller hub 66 is close to, or
coincides with the dash line 68 representing a straightline extension aft toward the transom of the central region of the underbody 70 of the hull ahead of the tunnel. Thus, as will be more fully explained hereafter, the propeller hub 66 is just above the level of the fastmoving water, represented by line 68, when the boat is operating at planing speeds. The fact that both shaft bearings 52 and 56 are normally above the level of the water when the craft is planing explains the need for the provision of a positive supply of water to the bearing sleeves.
The propeller 50, having a plurality of blades, is of a design especially suitable for operating in semisubmerged manner at high hull speeds, for example, in excess of 40 knots, where conventional fully submerged propellers not only lose effectiveness but are likely to suffer severe damage due to erosion caused by partial cavitation.
The preferred type of propeller for my propulsion system is known as a supercavitating propeller, having a blade configuration that has been found most effective for operation under conditions where the thrust is developed solely on the pressure faces of the blades, with a complete cavity associated with the back of each blade. Only by having complete cavities extend past the trailing edge of the blade section during high speed operation can the destructive erosion caused by partial cavitation at the backs (or suction sides) of the blades be avoided.
It is not necessary for an understanding of the present invention to set forth the procedure for the design of super-cavitating propellers, as full information on this subject is found in published technical papers, for example, reports of the David Taylor Model Basin. The invention instead is concerned with the provision of means by which a supercavitating propeller may be utilized at maximum efficiency at high design hull speeds when operated in a semi-submerged manner with the blades naturally ventilated, while making it possible for the same propeller at low hull speeds to operate fully submerged in a manner that is effective to accelerate the hull from rest out of its displacement-mode speed range, through the resistance hump, to a speed where the propeller can go into its semi-submerged mode of operation and provide the thrust for further acceleration to the design hull speed. This design hull speed will generally be substantially above the transition speed, and represents the speed attainable in accordance with the design of hull and propeller and available horsepower.
To achieve the desired modes of operation of the propeller for adequate thrust at low hull speed and high propulsive efficiency at high hull speeds, means are provided across the bottom of the tunnel to bring about the proper control and separation of the flow of water. Such means, comprising small spaced hydrofoil elements, not only serve to determine the flow pattern as a function of hull speed, but may also be configured to develop hydrodynamic force as means of controlling the trim of the boat. For this purpose the bottom surface of each of the hydrofoil members preferably has a configuration corresponding closely to the contour the underbody of the hull would have if there were no tunnel, that is, if the tunnel were closed in at the location of the hydrofoil by continuation of the bottom of the hull across the tunnel opening. Thus, in a singlescrew, on-centerline installation in a deep-V hull, the hydrofoils will have a V-configuration as viewed along the axis of the tunnel, while in flat-bottom bulls and in twin screw V-hull installations, the hydrofoils will bridge the bottom of the tunnel in substantially a straight line configuration, as hereinafter described and shown.
One of the hydrofoil members is advantageously located just ahead of the propeller, where it can be associated with the stern bearing 56 to provide rigid lateral support therefor. As best shown in the sectional view FIG. 3, the hydrofoil comprises elements 72 and 74 whose bottom surfaces lie in the planes of and represent inward extensions of the bottom surfaces 22 and 24 of the V-shaped hull. The elements-72 and 74 join at 76 with the intersection of the V-angle close to line Another hydrofoil member is preferably located aft of the propeller, in the region of the rudder. As shown in FIG. 4, this aft hydrofoil has its elements 82 and 84 intersecting at 86 in the same V-configuration as that of the hull underbody so as to merge with the side surfaces 22 and 24 of the hull alongside the tunnel.
By reason of the disposition of the aft hydrofoil in the region of the rudder, the rudder is divided into two parts, one above and the other below the aft hydrofoil. The upper blade 90 is mounted on the rudder post 92 which extends upwardly through the usual bearing and stuffing box 94. Because of the curvature of the tunnel and the V-configuration of the aft hydrofoil, the upper and lower edges of the upper rudder blade 90 are curved to provide clearance when the blade is turned at angles to the tunnel centerline over the range of normal steering requirements. It will also be noted, referring to FIG. 1, that the blade is shown as wedge-shaped ing control.
Below the aft hydrofoil is mounted a lower blade 96, having a short stock 98 extending upwardly through a central passage in the hydrofoil into a socket in the main rudder post, where it is pinned or keyed in place. The lower rudder blade may have somewhat less area than the upper blade 90. The lower blade preferably has its top edge substantially on the same level as the bottom of the propeller hub, and therefore on the extended centerline 68. The bottom edge of the lower rudder 96 preferably is at approximately the depth of the propeller blades in their lowest position. FIGS. 3 and 4 illustrate, by means of the dot and dash line 100, the swept circle or disc area of the propeller. The lower rudder blade 96 provides the entire steering action at high speeds. Preferably the forward portion 102 of this rudder, shown in section in FIG. 7, has an asymmetric configuration in order to develop a side force which produces a resulting torque about the center of gravity of the boat that is approximately equal and opposite to the torque unbalance created by the partially submerged propeller when used in a single screw application, or in a twin screw application without opposite propeller rotation. I
The hydrofoil elements 72-74 just ahead of the propeller and 82-84 at the rudder region have as their primary function the maintenance of flow separation. To establish the initial flow separation requisite to conversion of the propulsion mode from fully submerged to semi-submerged, other hydrofoil elements are disposed in spaced relation across the tunnel bottom in the region ahead of the propeller. These members 106, in a single-screw installation on the centerline of a hull, will have approximately the same configuration, when viewed along the axis of the tunnel, as the hydrofoil elements illustrated in FIGS. 4 and S, and similarly represent extensions or continuations of the hull underbody across the bottom of the tunnel. The number, spacing, chordal dimensions and sectional shape of these hydrofoil elements 106 across the open region of the tunnel ahead of the propeller are determined by design considerations and performance evaluation in order to correlate the occurrence of flow pattern transition with propeller thrust and hull speed which will most effectively accelerate the craft out of the displacement mode-through the resistance hump and into the planing mode. Thus the leading edges 112 and trailing edges 114 are subject to modifications in shape, and the hydrofoils may be tilted slightly out of the neutral plane, in order to achieve optimum control of flow.
The manner of operation of the propulsion system will now be described, with particular reference to the diagrammatic views, FIGS. 11, 12 and 13. At low hull speeds, when the craft is just getting underway or ma neuvering under crowded conditions, the craft will be operating as a displacement vessel, at speeds not appreciably in excess of that defined by the relationship in which speed in knots is approximately equal to the square root of the waterline length of the hull. At such speeds, say 7 to 10 knots for craft in the 25 to 50 foot sizes, the hull will be relatively low in the water, close to its level when at rest. As a consequence of both its low speed and its close to maximum immersion, the suction force acting on the tunnel causes the tunnel to be full of water. Even though the boat is moving ahead, the water will readily flow upwardly between the relatively narrow flow control elements 106 and along the top of the tunnel, as indicated by the flow lines in FIG. 11. Thus the propeller will be fully immersed so that even though the blade form and pitch of the propeller may be more suited for maximum thrust at much higher advance ratios, a substantial thrust will nevertheless be developed through utilizing the total blade area. Furthermore, the shrouding effect of the semi-cylindrical tunnel close to the tips of the blades, as illustrated in FIGS. 2 and 3, contributes substantially to the development of effective thrust. Additional thrust is derived as the result of the reduction in cross-sectional area of the tunnel region 108 aft of the propeller which provides a nozzle region having the effect of increasing the velocity of the water driven aft by the propeller.
With an increase in speed of rotation of the propeller, and hence increased thrust, the hull speed becomes greater than that for a displacement hull. Cavities begin to form'just above, that is, on the back faces of the hydrofoils. Also, there may be partial cavitation on the backs of the propeller blades. As there is not likely to be sustained operation in this transition mode, any erosion due to this partial cavitation will be minimal.
What is significant, during this transition mode of operation, is that (l) the propeller is generating effective and substantial thrust and (2) the local pressures are approaching the critical vapor pressure of water which results in the commencement of ventilation for the propeller blades above the hub, and thus the start of operation in the partially submerged mode. FIG. 12 illustrates the generation of cavities above the lip 40 at the beginning of the tunnel, also above and downstream of the hydrofoils,'so that the cavities flow into the propeller above the hub level, enabling the propeller to begin to operate in at least a partially ventilated manner. The hull is now advancing considerably faster than the limit set by its critical speed-length ratio for the displacement mode and is thus commencing to operate in the planing state. Its speed therefore increases until full planing speed is attained, dependent on the maximum thrust available from the propulsion system.
Under full plane, the mode of operation is that typified by the flow lines diagrammed in FIG. 13. The hull speed is such that, in effect, the water is streaming straight aft from lip 40 and substantially tangent to the bottom of the hydrofoil elements ahead of the propeller and also beneath the wider hydrofoils adjacent the propeller and rudder, the hydrofoil elements thus functioning as lift elements and as flow dividers. Under these conditions, the only appendage immersed in the slip stream is the relatively small lower rudder blade, relied on for steering control during high speed operation. The propeller shaft, the stern bearing, the vertical strut, the propeller hub and the upper rudder blade are each out of the streaming water and create no drag. Most importantly, the tunnel itself is open all the way aft to the transom for the admission of air to enable the propeller to operate with full natural ventilation (i.e., at the vapor pressure of air) in the semi-submerged mode so as to avoid damaging erosion occasioned by incomplete cavitation. The arrows on the upper flow lines in FIG. 13 indicate the general circulation of air within the tunnel, with the hydrofoil aft of the propeller being effective to maintain flow division between water and air to insure ample access of air to the propeller at planing speed. A further advantage of the tunnel, during high speed operation. is its effective suppressionof the propeller spray, so as to confine and discharge aft the great quantities of spray generated by the operation of the semi-submerged propeller, which is so troublesome when a surface-type propeller is mounted aft of the transom.
The propulsion system of the invention is equally well adapted to twin screw installations. This is illustrated in FIGS. 8, 9 and 10, also in FIGS. 16 and 17. Two tunnels are employed, disposed on each side of the centerline of the hull. The general arrangement of each propulsion unit is similar to that of FIGS. 1 and 2, except the several hydrofoil elements extend straight across the tunnel openings at their bottom, as shown in FIGS. 9 and 10. That is, the undersurfaces of the hydrofoils are disposed at the deadrise angle of the hull so as to form continuations across the tunnel from the hull underbody on each side of the tunnels. FIG. 9 shows the hydrofoil 122 at the stern bearing 124, with the upwardly extending strut 126 inclined to the vertical in a position perpendicular to the hydrofoil.
At the aft hydrofoil 132, as seen in FIG. 10, the rudders 134 and 136 are likewise mounted on an axis likewise perpendicular to the hydrofoil, so that they may swing without interference with the hydrofoil above and below which they are mounted. FIGS. 9 and 10 show the left hand unit in which the hydrofoils, strut and rudder assembly are tilted to the right; the right hand propulsion unit will of course have its hydrofoils and rudder tilted a corresponding angle to the left, as appears in FIG. 8, to provide the proper relation to the adjacent underbody of the hull. In accordance with conventional twin screw practice, the propellers will be driven in opposite rotations.
As best shown in FIG. 17, the axes of the propeller shafts 140 are preferably not quite parallel to the hull centerline, but instead diverge outward slightly toward the transom. This enables the tunnels to be more nearly aligned to the flow directions of the water, especially at speeds where the water flows into and along the tunnels. Due to the V-configuration of the underbody of the hull, progress of the boat through the water produces a small outward component of velocity of the water away from'the centerline. This slightly oblique orientation of the tunnels therefore tends to align the tunnels parallel to the local flow.
An indication of the improved performance of my propulsion system, particularly in the critical low speed region just prior to planing, is provided by the curves shown in FIG. 18 which are representative of relative values. The lower solid line is illustrative of the variation in resistance of a typical planing type hull in calm water, as a function of speed. The very steep rise in resistance, (the resistance hump), indicated at 162, occurs at the transition point between displacement mode and planing mode. Under rough water conditions, the resistance, plotted in the lower dash line 164, is markedly higher.
The upper solid line 166 typifies the thrust available with a surface type propeller, operated entirely in the surface mode, for various hull speeds. While such a propeller develops very high thrust at planing speeds, the thrust drops sharply to very low values at lower speeds. In calm water, there is barely enough thrust to overcome the hull resistance, at about the 10 knot.
point. In rough water, the hull resistance exceeds the thrust that can be generated by the propeller, so the vessel will never attain planing except with smooth water.
In the top dashed line 168 is shown the thrust which can be developed by the same surface type propeller represented by the upper solid line 166, when operated at below-planing speeds in accordance with my invention. The very large values of thrust developed at low speed by the partially shrouded and fully submerged propeller, even though it may be of optimum design for attaining very high hull speeds, are clearly evident as being substantially in excess of the hull resistance even under rough water conditions.
Because my invention permits the optimum propeller to be used for high speed operation, my propulsion system enables substantially higher maximum speeds to be obtained for a given engine horsepower, or as an alternative, the same speed to be obtained with lower horsepower and consequently greater economy of operation, in comparison with vessels where less efficient propellers have to be employed if the vessel is to be able to pass through the resistance hump and ever attain the planing state.
1. In a high speed power boat of the planing type, a tunnel in the aft underwater portion of the hull, said tunnel having a generally semi-circular configuration extending to the stern of the hull, a propeller shaft within the tunnel, a propeller on the shaft, means for rotatably supporting the shaft with the hub of the propeller in generally coaxial relation to the axis of the tunnel, there being a substantial portion of the tunnel ahead of the propeller, and flow control means associated with said tunnel portion ahead of the propeller, said means having passages to admit water to the tunnel ahead of the propeller at low hull speeds to fully immerse the propeller, said flow control means having flow separating surfaces to divert water from the tunnel when the hull is planing and thereby cause the propeller to operate partly submerged.
2. A high speed planing power boat according to claim 1 wherein only the blade portions of the propeller below the hub are submerged when the hull is planing.
3. A high speed planing power boat according to claim 1 wherein the propeller is of a supercavitating type.
4. A high speed planing power boat according to claim 1 wherein the flow means ahead of the propeller are spaced hydrofoil elements extending across the bottom of the tunnel.
5. A high speed planing power boat according to claim 4 wherein the hydrofoils have a configuration to induce aeration within the tunnel at a hull speed corresponding to the onset of planing.
6. A high speed planing power boat according to claim 1 wherein the propeller shaft adjacent the propeller is supported within a bearing and said bearing is mounted on a hydrofoil extending across the bottom of the tunnel.
7. A high speed planing boat according to claim 6 wherein said hearing has a strut extending upwardly to the roof of the tunnel.
8. A high speed planing power boat according to claim 1 wherein a hydrofoil extends across the bottom of the tunnel aft of the propeller.
9. A high speed planing boat according to claim 8 wherein a steering rudder is associated with said hydrofoil aft of the propeller, said rudder having a blade portion above said hydrofoil and another blade portion below said hydrofoil.
10. A high speed planing boat according to claim 9 wherein the lower rudder blade is connected to the upper rudder blade by a shaft passing through said hydrofoil.
11. A high speed planing boat according to claim 9 wherein the lower rudder blade is smaller in area than the upper blade.
12. A high speed planing boat according to claim 9 wherein the lower rudder blade has an asymmetric sectional configuration to counteract oblique thrust on the lower rudder blade from the water stream below the level of the propeller hub.
13. A high speed planing boat according to claim 9 wherein the blade portion of the rudder above the hy drofoil has a curved top edge to clear the top of the tunnel over the turning range of the rudder.
14. A high speed planing boat according to claim 1 wherein the tunnel portion aft of the propeller has a smaller semi-circular configuration than the portion in the region of the propeller.
15. A high speed planing power boat according to claim 1 wherein the underbody of the hull has a V- configuration in section extending to the stern and the tunnel is located on the centerline of the hull.
16. A high speed planing power boat according to claim 15 wherein the flow control means are hydrofoil elements extending across the bottom of the tunnel and are disposed in a V-configuration.
17. A high speed planing power boat according to claim 15 wherein each of the hydrofoil elements extending across the tunnel has a V-configuration corresponding to the V-configuration of the hull.
18. A high speed planing power boat according to claim 15 wherein the hydrofoil elements are coextensive with the underbody of the hull and merge in the vicinity of the centerline of said underbody.
19. A high speed planing power boat according to claim 15 having a plurality of hydrofoil elements disposed across the tunnel in spaced relation along the tunnel, said hydrofoil elements havng a V- configuration corresponding to the V-configuration of the hull, there being a hydrofoil element aft of the propeller, a steering rudder associated with the hydrofoil element aft of the rudder, the rudder having a rudder blade above the hydrofoil and within the tunnel and another rudder blade below the hydrofoil, means extending through said hydrofoil and connecting the lower rudder blade to the upper rudder blade, the top and bottom of the upper rudder blade being shaped to clear the top of the tunnel and hydrofoil below over the range of angular movement of the rudder.
20. In a high speed power boat of the planing type in which the underbody of the hull has a V-configuration extending to the stern, a pair of tunnels in the aft underwater portion of the hull, there being a tunnel on each side of the centerline, each tunnel having a generally semi-circular configuration extending to the stern of the hull, a propeller shaft within each tunnel, a propeller on each shaft, means for rotatably supporting the shafts with the hubs of the propellers in generally coaxial relation to the axes of the tunnels, there being a substantial portion of each tunnel ahead of the propeller, and flow control means associated with each tunnel portion ahead of the propeller, said means having passages to admit water to the tunnels ahead of the propellers at low hull speeds to fully immerse the propellers, said flow control means having flow separating surfaces to divert water from the tunnels when the hull is planing and thereby cause the propellers to operate partly submerged.
21. A high speed planing power boat according to claim wherein the flow control means comprises hydrofoil elements extending across the tunnels ahead of the propellers, said elements being disposed adjacent the bottoms of the tunnels substantially at the angle of deadrise of the underbody of the hull adjacent said hydrofoil elements.
22. A high speed planing power boat according to claim 21 wherein other hydrofoil elements are located just ahead of the propeller and aft of the propeller, said elements also being disposed at the angle of deadrise of the underside of the hull adjacent said hydrofoil elements.
23. A high speed planing power boat according to claim 22 wherein a steering rudder is located in each tunnel aft of the propeller, the axes of each rudder being substantially perpendicular to the hydrofoils of the tunnel within which the rudder is mounted.
24. A high speed planing power boat according to claim 20 wherein the propeller shafts and the tunnels are inclined at small angles to the centerline of the hull so as to diverge outwardly from the centerline toward the stem.
25. A propulsion system for high speed planing boats having a tunnel in the aft underwater portion of the hull extending to the stern, comprising a supercavitating propeller beneath the hull partially within the tunnel and partially projecting below the hull portions alongside the propeller, there being a substantial portion of the tunnel ahead of the propeller, and flow control means across the tunnel ahead of the propeller for causing the propeller to operate fully immersed at hull speeds corresponding to the displacement mode of operation and to operate semi-submerged at planing speeds.
26. A propulsion system according to claim 25 wherein the flow control means comprises hydrofoil elements ahead of the propeller at approximately the level of the underside of the propeller hub.
27. A propulsion system according to claim 26 including other hydrofoil elements, at least one of which is mounted closely ahead of the propeller and another aft of the propeller.
28. A propulsion system according to claim 27 wherein the hydrofoil elements closely ahead of the propeller and aft of the propeller have surface areas greater than the surface areas of the hydrofoil elements of the other flow control means ahead of the propeller.
29. A propulsion system according to claim 25 wherein the tunnel has a generally semi-circular configuration in the region of the propeller, and a plurality of flow control elements extending across the bottom of the tunnel, said elements being disposed at spaced intervals along said tunnel, the propeller being located in one of the spaces between said flow control elements.
30. A propulsion system according to claim 29 wherein there are a plurality of flow control hydrofoil elements ahead of the propeller and at least one hydro-.
foil element aft of the propeller.