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None
Research and development of this invention and Application have not been federally sponsored, and no rights are given under any Federal program.
Not Applicable
1. Field of the Invention
This invention relates to sterndriven marine vessels, in general, and to an improved propeller drive system for V-hull and catamaran racing and/or pleasure vessels, in particular.
2. Description of the Related Art
As will be appreciated by those skilled in the art, the Bravo Drive form of propulsion developed for high performance marine vessels would be more attractive for use in the Offshore Racing Circuit were it not for the fact that while it may increase a vessel's speed, it also tends to fail quickly. My analyses and testings have shown that this premature failure results from a high frequency harmonic caused by propeller slippage—which also makes it more difficult for the operator to stabilize a vessel's path of direction. At high speeds, such failure could very well lead to the possibility of crashes, injuries and deaths; at the very least, it could result in significant vessel and component damage.
As will also be appreciated, these problems can become all the worse as the propeller shaft is sought to be raised from below the water line in an attempt to enhance higher performance and obtain higher speed from the vessel. This follows because it is accompanied by even higher slippage and greater vibration.
As will become clear from the following description, the improved propeller drive system of this invention allows a racing vessel to run approximately 10 miles per hour faster, without failure or damage to the propeller. A reduction of slippage from the 14-16 percent common to the Bravo Drive down to approximately 4 percent also will be understood to result, significantly decreasing propeller vibration.
To understand the advance of the present invention, it must first be appreciated that the original development of the Bravo Drive by Mercury Marine utilized a propeller intended to run submerged below the water line. In trying to increase the vessel's speed toward 80, 90 and 100 miles per hour, the installation was changed to run the propeller on the surface, utilizing a different Mirage or Maximus propeller. However, with one blade of these propellers being out of the water at any instant of time, these propellers became unevenly loaded, with the impact in its striking the water then eventually damaging the shaft to breakage—with the resulting loss of the propeller. My analysis showed that with these propellers being of a 30 inch pitch, running them in the water produced a slippage of between 14 and 16 percent; and it was this harmonic vibration which threw the propeller out of balance and eventually over time destroyed the entire drive. Substituting, instead, a propeller intended to be run on the surface seemed to be an possible solution as its increased blade area would bring the slippage down, leading to less harmonic vibration. But this suffered disadvantages of its own: a) first of all, in increasing the cost from the Bravo Drive of approximately $8,000.00 to one of $35,000.00 if a Mercury Marine #6 Drive were used instead; and b) secondly, such a substitute drive would require a significant increase in horsepower to reach the same vessel speeds. The result would then be that a 36 foot boat with a #6 Drive would cost approximately $400,000.00, as compared to $250,000.00 for the Bravo Drive vessel. However, even so, #6 Drives are not user friendly to many vessels, at least due in part to their mass and weight.
As will be seen from the description that follows, the present invention sets out a new and improved propeller shaft and bearing carrier for a Bravo Drive. This will be appreciated to allow the vessel to use an offshore racing cleaver propeller of a type meant to run on the surface. Being of a design whose blades leave and enter the water more smoothly, the resultant slippage and vibration are reduced. Being more massive, a longer invention, to fit the shaft is used as well.
These and other features of the invention will be more clearly understood from a consideration of the following description, taken in connection with the accompanying drawings, in which:
FIG. 1 pictorially illustrates a stern driven, Bravo Drive motor with its propeller removed, typifying the prior art;
FIG. 2 is a top view of an offshore racing cleaver propeller utilized in accordance with the present invention;
FIGS. 3a and 3b respectively illustrate the propeller shaft of the Bravo Drive of FIG. 1, and the longer, thicker, propeller shaft of the invention;
FIGS. 4a and 4b illustrate the bearing carrier of the type employed in the prior art arrangement of FIG. 1, and as used according to the invention, respectively;
FIG. 5 is a schematic drawing helpful in an understanding of the increased size of the propeller shaft of the invention; and
FIGS. 6a, 6b and 6c are schematic diagrams of the front, side and rear views of the bearing carrier of the invention helpful in an understanding of its construction.
Referring to the Drawings, the propeller shaft 10 of FIG. 3b and of FIG. 5 will be understood to be longer and thicker than the prior art propeller shaft 11 of FIG. 3a so as to support the offshore racing cleaver propeller 12 of FIG. 2. Although such propeller is shown as having four blades 14, the improvement of the invention will be appreciated to extend still further where five and six blade cleaver propellers are employed. Such blades enter the water smoothly during its rotation in mellowing the motor down more slowly, and exhibit a slippage of some 4 percent. In one construction of the invention, a 16.5 diameter, 31 inch pitch four blade propeller was employed, while in a second construction, a 16.5 diameter, 35 inch pitch blade was utilized. With them installed, and with the propeller shaft 10 of FIGS. 3b and 5 being utilized with the bearing carrier of FIGS. 6a-6c, vessel speeds in excess of 160 mph have been reached without suffering any failure or damage. The use of such cleaver propellers allows the propeller shaft 10 to run above the water line—and, in accordance with the teachings of the invention, have been set to extend as far as 2½ inches above the bottom of the boat. This is to be contrasted with the typical Bravo Drive where the propeller shaft 11 runs below the water line—although in some high performance applications, they have been installed to run even with the water line. As will be appreciated, such installations lead to the high slippage, the harmonics, and the unsafe conditions which accompany the premature Bravo Drive failures that result as the boats are driven at increased speeds. With the cleaver propeller of the present invention, higher speeds are attained, with decreased slippage, and significantly reduced drive failure.
While Applicant does not wish to be restricted to any particular set of dimensions, the following dimensions for the propeller shaft 10 of FIG. 5 have proven quite useful:
FIGS. 6a-6c illustrate the bearing carrier 18 of the invention for fitting the longer, thicker propeller shaft 12 to the motor drive 20 of FIG. 1. Manufactured of aircraft 2024 aluminum billet, hard anodized steel, the bearing carrier (Shown as 22 in FIG. 4b), replaces that more commonly employed, shown as 24 in FIG. 4a. With the present invention, the following dimensions have proved useful in accepting the propeller shaft 10 of FIG. 5 with the Bravo Drive unit:
As will be appreciated by those skilled in the art, the teachings of the present invention allow a designer to run more horsepower than the Bravo Drive was designed for, although not as much as with the Mercury Racing Six Drive. The invention also will be seen to allow one to run the vessel at higher speeds than with the prior constructed Bravo Drive, yet without its slippage and possible drive failures. Although less able to reach the speeds of the Mercury Racing Six Drive, the teachings of the invention allow a significant savings as associated with the latter's increased cost—and thus effectively fills a gap between the Bravo Drive and the Racing Six Drive.
While there have been described what are considered to be preferred embodiments of the present invention, it will be readily understood by those skilled in the art that modifications can be made without departing from the scope of the teachings herein. For at least such reason, therefore, resort should be had to the claims appended hereto for a true understanding of the invention.