Technical Field The present invention relates generally to a guard member for the propeller of an outboard motor. More specifically, the present invention relates to a propeller guard which is designed for maximizing the performance of an outboard motor, and to a high performance bracket for attaching the guard to the motor.

Background Art The propeller of an outboard motor typically rests below the bottom surface of the boat when in use, and propels the boat through the water. Due to its position during operation, the propeller of an outboard motor tends to be very susceptible to damage from under water objects such rocks, sandbars, marine life and the like. If the propeller of the outboard motor becomes damaged due to its impingement on underwater objects, it may become unable to perform as designed. The need for repair and/or replacement of a propeller damaged thus, generally occurs at very inconvenient times, and is always very expensive.

Therefore, a need exists to develop a guard which can protect the propeller of an outboard motor to prevent its being damaged by underwater objects.

Also, the propeller of an outboard motor spins at an extremely high RPM during use. Should a passenger, skier, swimmer, or other person be accidentally hit by the propeller during operation of the motor, serious injury will inevitably result. Therefore, a guard which will inhibit accidental contact of a person with the propeller to prevent accidental bodily injury is also needed.

Many prior art attempts have been made to solve the above problems. Prior art devices which are representative of the many previous attempts to develop a prop guard

responding to the above identified problems are shown in U.S. Patent No. 2,551,371 to Grieg; U.S. Patent No. 2,963,000 to Fester; U.S. Patent No. 2,983,246 to Manley; and, U.S. Patent No. 4,078,516 to Balius. In each of these devices, an enclosure, generally including a hollow cylindrical member, is attached to the outboard motor so as to surround the propeller. The device is designed to allow water to have fluid flow access to the propeller in order to allow the propeller to function as designed. Although these prior art devices are somewhat successful in preventing damage to the propeller by preventing contact of the propeller with underwater objects, several drawbacks nevertheless remain. Most importantly, each of these devices tend to severely reduce the performance characteristics of the outboard motor.

As is well understood, an outboard motor pushes a boat forward in reaction to the propellers of the motor forcing water backwards. However, an outboard motor which also includes a propeller guard is inhibited in its performance due to the fact that water flowing past the propeller tends to be dispersed and/or disrupted by the guard. Also, water impinging on prior art guards during operation of the motor tends to increase the drag characteristic thereof, thus decreasing motor performance. Further, the presence of the guard, since not necessarily designed as an integral part of the motor, can cause instability, vibrations, control degradation, and unpredictability of motor response during use. Finally, prior art propeller guards are attached to the motor in such a manner as to be incapable of preventing damage or failure of the attachment members during high speed use.

Accordingly, it is needful that a propeller guard be developed and designed which affords protection against contact between the propeller and underwater objects, and which at the same time is designed so as to maintain or

improve motor performance characteristics, such as steering, top end speed, planing, acceleration, etc.

U.S. Patent No. 4,680,017 to Eller, attempts to address the problem of maintaining and/or improving performance characteristics of the motor through the design of a propeller guard. The propeller guard of the Eller invention functions to prevent radial dissipation of water passing through the propeller, to thereby cause all water to be directed in a linearly rearward direction as it passes through the propeller so as to be useful in generating forward motion of the boat. However, in operation, the drag characteristics of Eller's propeller guard tend to off-set advantages of its use. Further, motor control characteristics can be significantly degraded due to the design and positioning of Eller's propeller guard.

Disclosure of Invention It is a principle object of the present invention to provide a propeller guard for an outboard motor which can prevent inadvertent contact of underwater objects with the propeller thereof during use.

It is also a principle object of the present invention to provide a propeller guard which is designed to maintain or improve the performance characteristics of the motor.

It is another object of the present invention to design a propeller guard attachment bracket which is resistant to failure due to forces thereon such as vibration or cyclical loading.

It is another object of the present invention to design a propeller guard which improves motor control characteristics such as planing, top speed, acceleration, and steering.

It is further an object of the present invention to design a propeller guard which is simple to manufacture and

therefore relatively inexpensive, yet durable and reliable in design.

These and other objects of the present invention are realized in a specific embodiment of a propeller guard, described herein by way of example and not limitation, which includes a generally cylindrical ring having a diameter which is greater than the diameter of the propeller over which it is to be attached. The ring may include a small concave attachment plate at one position thereabout, and an attachment bracket diametrically opposed thereto. The attachment plate and bracket allow the ring to be securely attached to the outboard motor at the bottom of the motor's anti-ventilation fin, and at the motor's lower fin, respectively. The ring includes a series of ports (or openings) therethrough which are oriented at radially spaced apart locations there around. Water passing over the interior surface of the ring is accelerated due to the shape of the front edge thereof, and causes a vacuum like effect through the ports which pulls water through the ports (from the exterior of the ring to the interior thereof) as the guard passes through the water. The ports are positioned around the ring in a generally uniform manner and are oriented in a manner which causes the water passing therethrough to be directed slightly inwardly toward the propeller. This added flow gives increased thrust and control (specifically steering control) , to the motor. The size, number and general distribution of the openings about the ring are calculated to allow sufficient radial flow of water for precise control and steerability of the motor, while at the same time, avoid problems of flow blockage during a sharp turn when the ring is moved into blocking relationship with water moving past the propeller. The ring is formed with a tapper in the interior side of the inlet opening and a similar tapper on the exterior side of the outlet opening. The shape of the ring functions to diminish

the drag and vibration characteristics of the guard, while at the same time improve the controllability thereof by generating the above-mentioned vacuum through the ring openings which pulls water in toward the propeller. The attachment bracket of the invention secures the ring to the motor in a rigid and stable fashion and is designed to minimize vibrations and other cyclical loading thereon to inhibit premature metal fatigue, cracking, or failure.

Brief Description of Drawings FIG. 1 is a perspective view of a propeller guard formed in accordance with the principles of the present invention, the propeller guard being shown attached to an outboard motor (drawn in dashed lines) ;

FIG. 2 is a side view of a propeller guard formed in accordance with the principles of the present invention; FIG. 3 is a cross sectional view of the attachment bracket of the present invention taken along line III-III of Figure 1;

FIG. 4 is a cross sectional view taken along line IV-IV of FIG. 2; and

FIGS. 5 and 6 are cross sectional views identical to FIG. 4, however, with arrows showing change in water flow direction during operation.

Modes for Carrying Out the Invention The prop guard 10 of the present invention is adapted for use on motor boats having either an outboard motor 13 (as shown in dashed lines in FIG. 1) , or on an inboard/outboard motor (not shown) . The motor includes a propeller 14 having blades 15 which are operatively connected inside motor 13 to a conventional type drive. The prop guard 10 of the present invention is attached to the motor 13 at a location on the underside of the cavitation plate 16 thereof by an attachment plate 18, and is also

attached to a lower fin 17 of the motor 13 by an attachment bracket 12.

The prop guard 10 of the present invention is shown for purposes of the present disclosure as being attached to a typical outboard motor design, such as a well known motor of approximately 100 hp. It is well within the scope of the present invention however to attach the prop guard 10 to any sized or type of outboard or inboard-outboard motor. Dimension given hereinbelow therefor are given for purposes of describing the shown preferred embodiment only. It should be understood that the particular dimensions identified would likely be modified should the prop guard 10 be adapted for placement on other types or sizes of motors, and such modifications are considered to be within the scope of the present invention.

The propeller guard 10 is preferably formed from a flat elongated rectangular section of metal which has been rolled into the shape of a circular ring 11. It is preferred that the metal be aluminum however other metals may be used, or other materials such as wood or plastic may be used if desired. In the shown embodiment of the invention, an aluminum band having a length of four feet (121.92 cm), a width of four inches (10.16 cm} and a thickness of one quarter inch (0.64 cm) is used. When rolled into a circle, the diameter thereof is preferably seventeen and one quarter inches (43.82 cm).

The attachment plate 18 is preferably formed of a similar aluminum having a length of approximately seven inches (17.78 cm), a width of approximately four inches (10.16 cm) and a thickness of one quarter inch (0.64 cm).

The attachment plate is preferably formed with a slight, one quarter inch (0.64 cm) inward bow located centrally therein, which corresponds to the curvature of the bottom of the cavitation plate 16 of the motor 13 to which it is to be attached.

The attachment plate 18 may be drilled with four holes 19, each approximately five-sixteenths inches (0.79 cm) in diameter and each located at a corner of the attachment plate 18 approximately three quarters of an inch (1.91 cm) in from each side forming each corner. The attachment plate 18 is then placed into the ring 11 and welded to each end thereof to form a completely continuous circumference. The plate 18 is formed so as to cause the bowed shape thereof to be directed inwardly into the interior of the ring 11. It should be noted that the entire ring may be cast if desired, instead of cut and welded as described, without departing from the spirit and scope of the invention.

The attachment bracket 12 is preferably formed of stainless steel. The attachment bracket 12 includes a generally flat, rectangular metal plate 20 preferably approximately seven inches (17.78 cm) long by one inch (2.54 cm) wide by one-half inch (1.27 cm) thick, and a pair of side plates 22. The side plates 22 are cut to form front edges 21 which are at an angle (a) of approximately forty degrees with the top edges 23 thereof. In the preferred embodiment, the angle (a) is approximately thirty-eight degrees. The rear edge 24 of side plates 22 are cut to form an angle (b) of approximately sixty degrees with the bottom edge thereof, and in the preferred embodiment, the angle (b) is approximately sixty degrees.

The metal plate 20 is attached to the ring 11 at a position diametrically opposed to the center line 25 of the attachment plate 18. The plate 20 is formed with three holes 26 therein which are preferably one quarter inch (0.64 cm) in diameter and which are evenly spaced along the length thereof which contacts the ring 11. The plate 20 includes an extension 27 which is of a reduced thickness and which includes holes 28 preferably of quarter inch (0.64 cm) diameter which correspond with holes 29 of the side plates 22 when the side plates are properly attached to the metal

plate 20. Side plates 22 may be attached to the metal plate 20 by means of bolts 30, and the metal plate 20 may be attached to the ring 11 by bolts 31.

As best shown in FIG. 2, ring 11 includes an inlet opening 32, an outlet opening 33, and a central longitudinal axis 34. From center line 25 of attachment plate 18, proceeding in both directions around the interior surface 35 of the ring 11, ports 36 are positioned in the ring 11, preferably at about four inch (10.16 cm) intervals around the entire circumference thereof. The total preferred number of ports 36 around the ring 11 of the particular embodiment shown is ten, with each port 36 centered approximately one and one quarter inches (3.18 cm) back from the inlet opening 32. Each port 36 is drilled through the ring 11 at an angle (c) of approximately thirty-four degrees from the central axis of the ring 11. It is preferred that the two ports 36 closest to attachment plate 18 be of a diameter of approximately seven tenths of an inch (1.78 cm) and formed at an angle (c) of approximately thirty-four degrees, with the remaining ports 36 being of a diameter of approximately one-half inch (1.27 cm) and at an angle (c) of approximately twenty-two degrees.

Although each port 36 in the shown preferred embodiment is shown to be oriented such that the central longitudinal axis of each port 36 intersects with the central longitudinal axis 34 of the ring 11, the present invention is not intended to be so limited. If desired, the longitudinal axes of the ports 36 may be directed inwardly in the manner shown in Figures 1 and 2, yet fail to intersect with axis 34 of the ring 11. For example, if desired each port 36 may be formed such that each longitudinal axis thereof is parallel, and directed at and offset from the axis 34, thus generating a rotational (swirling) flow of water as it passes through the ports 36. In this manner, the increased load on the propeller 14 due

to incoming water through ports 36 would be minimized since the incoming water would already be imparted a rotational flow direction prior to impinging upon the propeller 14.

As shown in FIG. 4, the interior surface 35 of the ring 11 at the inlet opening 32 thereof is preferably formed with a somewhat rounded taper 37. Similarly, the exterior surface 44 of the ring 11 at the outlet opening 33 thereof may be shaped with a taper 38 therein.

As shown in Figs. 1 and 2, a series of grooves 46 may also be located on the exterior surface 44 of the ring 11 to extend from the inlet opening 32 into each of the ports 36, such that each groove 46 is oriented parallel to the central longitudinal axis 34. Similar grooves 47 may be located parallel to grooves 46 and spaced between each port 36 to extend either partially or entirely along the exterior surface 44 of the ring 11. These grooves 46 and 47 aid in increasing the stability of the guard 10 as it moves through the water, and also, in the case of grooves 46, which can be drawn in through ports 36. The prop guard 10 is attached to a motor 13 by locating attachment plate 18 against the bottom surface of cavitation plate 16, and bolting the attachment plate 18 thereto by bolts 39 passing through openings 19. The side plates 22 are then bolted by bolts 40 to the lower fin 17 of the motor 13.

As best shown in FIGS. 5 and 6, when in operation the prop guard 10 is generally oriented to allow water to pass along the longitudinal axis 34 thereof (as shown by lines 41) . Edge 37 of ring 11 is shaped so as to cause water flowing there against (such as represented by line 42) to be diverted to flow along interior surface 35. Because line 42 has been diverted, as is well known in fluid dynamics, the speed of fluid represented by line 42 is increased, thus causing a vacuum effect through port 36. The vacuum effect generated in port 36 causes water to be drawn from the

exterior surface 44 of ring 11, through port 36 and into the interior of the ring 11 as shown by flow line 43.

The net effect of surface 37 and ports 36 therefore is to draw additional water into the interior area of the ring 11 where it can impinge upon the propeller 14 to increase the thrust and control capabilities of the motor 13.

As shown in FIG. 6 when the motor 13 is moving at a velocity through the water, and the propeller is rotated relative to the flow of water (such as in order to effect a turn) it can be seen that water flow lines 41 will impinge upon exterior surface 44 of the ring 11 and be diverted over the end surface 38. In prior art prop guards, when the propeller is rotated in this manner to effect a turn, the water is deflected from its course into the propeller by the exterior surface of the guard. However, in the present invention, rotation of the propeller 14 to effect a turn instead causes ring 11 to orient a plurality of the ports 36 (those ports 36 lying directly in line with the water flow lines 45) such that water can flow directly through ports 36 and into the blades 15 of the propeller 14 without interference from the ring 11. Prior art prop guards completely inhibit flow of water directly into the propeller during a turn such as shown in FIG. 6, and therefore cause cavitation at the area of the propeller. The cavitation causes a loss of thrust of the motor, and also a loss of steering control. The design of the present invention, including the ports 36, insures that a flow of water is always directed into the propeller 14, even while effecting sharp turns at high speeds. Thus, the problem of prior art prop guards creating cavitation at the propeller thereof during turns has been solved in the design of the present invention.

The grooves 46 also aid in increasing the flow of water through ports 36 by guiding an added amount of water towards the ports 36. The additional water flow is especially

useful when the ring 11 is turned relative to the water flow as shown in Figure 6. Since a volume of water is diverted directly into port 36 by the grooves 46, less water is being diverted along exterior surface 44 (as shown by flow lines 41) . This not only aids in avoiding cavitation as described above, but also helps to increase the stability and controllability of the ring 11 during a turn.

As has been explained above, the prop guard 10 can generate additional thrust and control to the motor 13 when attached thereto. Further, the control and handling of the boat with the prop guard 10 is improved, since cavitation is greatly reduced or eliminated during hard turns.

In actual use, there have been other noted advantages of the present invention. In very choppy water, the prop guard design of the present invention significantly inhibits "keel waking" (i.e., lateral movement of the boat during turns), thereby aiding in keeping the boat under control. Also, it is possible to achieve similar top end speed characteristics from various types of propellers 14, such as for example, fifteen and nineteen pitch propellers, when the prop guard of the present invention is used in conjunction therewith. This allows the use of a lower pitch propeller (such as a fourteen pitch propeller known for its advantages of higher power when accelerating from a dead stop) , while at the same time maintaining a good top end speed (as is generally the purpose of a higher pitched propeller, such as a nineteen pitch propeller) . This advantage of the present invention allows a lower pitched propeller to take on the characteristic of the more elaborately designed two speed propellers.

It will be apparent from the foregoing that, while particular embodiments of the invention have been illustrated and described, various modifications can be made thereto without departing from the spirit and scope of the

present invention. Accordingly, it is not intended that the invention be limited, except as by the appended claims.