BACKGROUND AND SUMMARY OF THE INVENTION

This invention relates to marine drives, and more particularly to a drive incorporating the concept of maintaining the drive propeller in a position so that it pierces the surface of the water during normal operating conditions. Such so-called surfacing drives are often used in high speed competition, and it is important that they provide maximum output with minimum drag.

Generally, a marine surfacing drive can be defined as a drive wherein at least one blade of a propeller is disposed above the water surface at design conditions, i.e., high speed. Such a drive can also be defined as a drive in which the propeller centerline is generally adjacent or above the water surface, again at design conditions.

Examples of known marine surfacing drives are disclosed in U.S. Patents 3,933,11.6, 4,544,362 and 4,565,532. The constructions disclosed in these pat¬ ents incorporate a single propeller carried by a single propeller drive shaf . Patent 4,544,362 additionally discloses an embodiment in FIG. 11 thereof of a pair of separate engines driving a pair of laterally spaced separate surface piercing propellers mounted on sepa¬ rate drive shaf s. Other U.S. patents of general interest in this regard are 3,057,320 and 3,430,603, although the units described therein are apparently not intended for normal continuous driving in surfacing mode .

Most marine stern αrives, to which the pre¬ sent invention is basically directed, include a propel¬ ler carrier i'roπ: which downwardly depends a stabilizing fir; or skeg juεt ± ^' orvardiy ^■ -. f ^* .Le propeller itself. Tiit

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skeg is designed to be parallel to the boat centerline during straight forward travel. See, for example, the member 90 in the aforementioned U.S. Patent 4,544,362. Problems have been observed with the known single propeller surfacing drives. Because the upper portion of the propeller is out of the water, the propeller creates a strong lateral force on the propel¬ ler carrier. To keep the boat on a straight forward course, this lateral force must be countered by steer- ing the propeller carrier so that the skeg is turned so that it assumes an angular, rather than parallel, position with respect to the boat centerline. The result is the creation of undesirable high drag forces as the angular skeg is pushed through the water and propeller thrust is directed at an angle to the boat path.

Further, if the surface piercing propeller bounces in and out of the water due to wave conditions or trim attitude, radical and destabilizing steering forces can result. A large skeg may help to alleviate this problem, but again at the cost of high drag.

In addition, the imbalance in steering caused by the angularly adjusted skeg results in making the boat easy to turn in one direction, but very difficult to turn in the opposite direction.

Due to the aforesaid difficulties, many applications of high speed surfacing drives have re¬ quired dual engines, dual propeller drive shafts, and laterally disposed dual oppositely rotating propellers, in an attempt to overcome the problems. However, the high cost and weight of dual systems has made them less than practical.

It is an object of the present invention to essentially eliminate the unbalanced lateral forces en the propeller carrier, even when the drive is used in a

continuously surfacing mode,and without utilizing expensive and heavy dual drives, thus allowing propeller thrust to be aligned with the boat,

The present invention provides a marine surfacing drive for attachment to a boat having a longitudinal centerline, said drive comprising a longitudinal propeller drive assembly including a propeller carrier defining a drive axis, means for pivotally mounting said carrier on the boat, steering means for selectively pivoting said carrier laterally relative to the boat centerline, means for vertically pivoting said carrier relative to the water surface, and control means for said last-named means to position said carrier so that at least a portion of said drive assembly is normally disposed in water surface piercing position, characterized by balancing means on said drive assembly to maintain the lateral forces on both sides of said carrier in balance when said drive axis is disposed parallel to the boat centerline and when a portion of said assembly is in surface piercing position during driving the boat in a straight course through the water.

In a preferred embodiment, the propeller assembly includes a pair of concentric drive shafts to which are mounted a pair of closely adjacent fore and aft coaxial surface piercing propellers mounted on a common axis. The carrier also includes a downwardly extending skeg. The shafts are connected to a source of power and drive the propellers in contra-rotating relationship at essentially equal rotational velocities. As a result lateral forces created on the propeller carrier by one rotating surface piercing propeller are counterbalanced by the other propeller when the skeg and propeller line of thrust are parallel to the boat centerline.

In the preferred embodiment the leading (or fore) edges of both propellers are relatively sharp for surface piercing, while the trailing (or aft) edges of both

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propellers are relatively blunt. The sharp leading edge of one propeller faces the blunt trailing edge of the other. While coaxial reverse-rotating propellers are known in marine drives, such as in U.S. Patents 4,529,387 and 4,619,584, they have previously been fully submerged in normal operation and did not create undesirable lateral forces on the propeller carrier, as has been the case with propellers which are designed to normally pierce the water surface. In the drawings:

Figure 1 is a generally schematic side elevation of a marine stern drive incorporating various aspects of the present invention, and showing a control therefor;

Figure 2 is a top plan view of the drive, taken on line 2-2 of Figure 1;

Figure 3 is an enlarged longitudinal generally sectional view of the drive; and

Figure 4 is an enlarged section of the propellers taken on line 4-4 of Figure 1. As shown in the drawings, the various aspects of the invention are incorporated in a marine stern drive 1 which is mounted to the transom 2 of a boat 3 having a longitudinal centerline 4, with drive 1 adapted to be powered by a single suitable engine 5. Engine 5 is provided with an output shaft 6 which extends rearwardly through spaced bearings 7 in a tubular boss 8 which in turn extends through a suitable opening in transom 2. Boss 8 merges outwardly into a tubular support casing 9 which is secured to transom 2,

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as by bolts 10. A universal joint 11 of any suitable well-known type is disposed within casing 9 and con¬ nects engine output shaft 6 to a central axial longi¬ tudinal main propeller drive shaft 12. A tubular propeller shaft housing or carrier

13 is adapted to be mounted adjacent its forward end to support casing 9. For this purpose, casing 9 is provi¬ ded with a ball socket 14 which is adapted to receive a hollow ball 15 which is mounted for universal pivoting movement within the socket. Ball 15 forms the forward portion of an open ended housing 16 which is threaded, as at 17, into the forward end of carrier 13. See the aforementioned U.S. Patent 4,544,362, for a generally similar construction. Universal joint 11 is connected to a sleeve

18 which is keyed or otherwise fixedly secured to the forward end portion of main propeller drive shaft 12. A secondary propeller drive shaft 19 is of tubular construction and telescopes over main shaft 12 rear- wardly of sleeve 18, and is mounted for separate rota¬ tion relative thereto. A coil spring 20 between shafts 12 and 19 assists in generating oil circulation there¬ between. A first propeller 21 is suitably fixed to the outer end portion of main shaft 12 for rotation there- with, while a second propeller 22 is suitably fixed to the outer end portion of secondary shaft 19.

Propellers 21 and 22 are of the surface piercing type and are basically mirror images of each other, and are adapted to be driven at esεentially equal rotational velocities and in a contra-rotating manner. For this purpose, and in the embodiment shown, sleeve 18 is journalled in annular bearings 23 within carrier 13 and is provided with an input side bevel gear 24 fixed thereon. Likewise, secondary shaft 19 is also .iournajlec ii. bearings 25 within carrier IL and if.

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provided with an output side bevel gear 26 fixed there¬ on and spaced from gear 24.

Means are provided to drivingly join bevel gears 24 and 26 to provide the ultimate contra-rotating propeller drive. For this purpose, and in the present embodiment, a pinion gear 27 is suitably affixed to the inner end of a pinion or jack shaft 28 which extends radially outwardly through the wall of carrier 13, with gear 27 meshingly joining bevel gears 24 and 26. Jack shaft 28 is disposed within a housing 29 and is supported for rotation on bearings 30. Other forms of drive-splitting may be utilized without departing from the spirit of the invention.

As shown in FIGS. 1 and 2, a stabilizing fin or skeg 31 extends downwardly from the body of propel¬ ler shaft carrier 13, is generally planar.. During normal operation of drive 1, when boat 3 is traveling straight ahead, skeg 31 is disposed in parallelism with boat centerline 4. See FIG. 2. As best shown in FIG. 4, the contra-rotating propellers 21 and 22 each have a body which may be gene¬ rally wedge-shaped, with the forward or leading edge of each propeller being relatively sharp, as at 32,33 respectively. Likewise, the aft or trailing edges of each propeller are relatively blunt, as at 34,35 respec¬ tively. Thus, forward sharp edge 32 of aft propeller 21 is disposed closely adjacent and facing the blunt - trailing edge 35 of forward propeller 22.

Some of the elements described above form a propeller assembly 36. These elements include prop shaft carrier 13, drive shafts 12 and 19, propellers 21,22, and skeg 31.

Means are provided for selectively shifting carrier 13 laterally for steering boat 3, and for providing for vertical movement of the carrier to tr m

the boat. For this purpose, mounting brackets 37 are provided on the stern of the boat, while opposed ears 38 extend laterally outwardly from the side of carrier 13 aft of beam 37. A pair of opposed steering cylin- ders 39 and 40 are mounted between mounting brackets 37 and respective ears 38, and are connected to any suit¬ able steering control, such as a steering wheel, not shown. The control may be hydraulic or of any other suitable nature. In addition, a trim cylinder 41 is connected between ears 42 mounted on the outer end of jack shaft housing 29 and a suitable bracket 43 mounted on transom 2. In this instance, a control system is schematically illustrated in FIG. 1 for selectively raising, lowering or setting the position of trim cylinder 41, and thus the angular position of propeller assembly 36, relative to the surface 44 of the water. The control system 45 shown is connected through a hydraulic or other system, via lines 46,47 to trim cylinder 41. Propeller assembly 36 will be hydraulically fixed in any position selected by the operator.

By providing coaxial contra-rotating surface piercing propellers, the undesirable lateral forces on the common axis 4S of propellers 21,22, and thus on carrier 13 and boat 3, will be balanced on this same single axis during surfacing drive mode and when skeg 31 and the propeller line of thrust are parallel to boat centerline 4, thus essentially eliminating the aforementioned steering imbalances and loss of efi'i- eiency.