Dual propeller drive for ski boat

Abstract

A dual prop drive for a ski boat has a gear box having an input gear that is connected to an engine output shaft. The gear box has two laterally spaced output gears on opposite sides of the input gear, with the output gears being drivingly connected to the input gear. The dual prop dive unit has two propeller shafts, each of which is drivingly connected to one of the output gears. The output gears and propeller shafts desirably rotate in counter-rotating directions. The gear box desirably reduces the rate of rotation of the propeller shafts relative to the engine output shaft. The gear box is lubricated without a pump by a gravity feed splash oil system.

Description

CROSS-REFERENCES TO RELATED APPLICATIONS [0001] This is a non-provisional application based on and claiming the filing priority of co-pending provisional patent application Ser. No. 60 / 489,746, filed Jul. 23, 2003.BACKGROUND OF THE INVENTION [0002] The present invention relates to an improved drive mechanism for a recreational motor boat having a planing hull, such as the type used for water skiing and the like, and a method for retrofitting an existing motor boat to incorporate the improved drive mechanism. [0003] As used herein, reference to a “recreational motor boat” is intended to include the class of boats having planing hulls, which are larger than row boats and small boats with outboard motors. Generally such boats are smaller, than larger, non-planing cabin cruisers, yachts, and large ships. These boats are typically in the range of 16-28 feet in length and frequently are powered by a single inboard engine that turns a propeller by means of a rotating propeller shaft that e...

AI Technical Summary

Benefits of technology

[0040] Another important advantage of the present invention is that the drive mechanism provides increased pulling power with little decrease in speed under load. Thus where one or a large number of skiers are pulled, the maximum speed of the boat is not reduced nearly as much as when a single prop engine is used. This increased pulling power also makes it easier to maintain a constant speed through a slalom course, even though this load varies substantially.

[0041] Likewise, when a skier is pulled from a sitting position on a dock, the tow boat does not lose momentum due to prop slip when the rope gets tight. A strong steady increase in speed is achieved, and this minimizes falls.

[0042] Another outstanding advantage of the two propeller drive is when a bare footed skier steps off his ski at 40 mph, the boat speed is not dramatically reduced like it is with a single prop.

[0043] The present invention also is advantageous for wake boarding. A wake board is different from a water skiing operation, because a larger wake is desired. In order to achieve a larger wake with a conventional ski boat is customary to add ballast to the boat, which causes the boat to ride lower in the water and thus increases the wake. More power is necessary to drive a boat when it is riding lower in the water, and the drive mechanism of the present invention provides the additional power.

[0044] While the present invention is particularly desirable with a water ski boat, the advantages of the present invention can also be achieved with larger family boats as long as about 28 feet or so in length which are generally used only recreationally for water skiing. Boats of this nature sometimes are driven by a single prop and a single motor, but these boats can be underpowered. An option for a larger boat is the use of two engines, but this is considerably more expensive and adds weight to the boat. Good performance characteristics, including good power and good top speed, can be achieved with a single engine in a boat as large as 28 feet or larger by employing the dual-prop drive mechanism of the present invention.

[0045] In the foregoing exemplary embodiment the transmission is mounted to the rear of the engine and in front of the props. The present invention also can be used in installations where the engine is mounted to the rear of the transmission, in which case the engine output shaft faces forwardly and is connected to the rear side of the transmission. The props also are connected to the rear side of the transmission.

Problems solved by technology

Larger boats, such as 28-foot boats, are heavy and require greater power than smaller boats.

This increases dramatically the cost of the ski boat.

This in turn was thought to produce unacceptably reduced top speeds, at least without the added expense of the two-speed transmission.

Two prop drives also have required a redesign of the boat interior and have not been adaptable as a retrofit in an existing one prop boat.

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