Boat propeller sled

A boat propeller sled comprising a spine, straps attached to the spine, and rails attached to the spine. The straps are sized to fit around an outboard motor lower unit, and to securely attach the spine to the lower unit. Each rail comprises a base attached to the spine, a forward ramp attached to the base, a runner attached to the forward ramp, and a rear ramp attached to the runner. In the preferred embodiment, the bases are attached to the spine at an angle of approximately ninety degrees, the forward ramps slope forward at an angle of approximately sixty degrees relative to the horizon, the runners are substantially horizontal, and the rear ramps slope upwards towards the rear at an angle of approximately thirty degrees relative to the horizon.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to boat propeller guards, and in particular to a 
boat propeller sled. 
2. Background of the Invention 
For some lime now, small boats have been powered by outboard motors. These 
small boats may include fishing boats, water ski boats, tour boats, and 
pleasure craft of all types. These outboard motor-powered boats generally 
range in size up to approximately twenty-five feet in length. 
Outboard motor-equipped boats may be operated in fairly shallow water. One 
ever-present danger associated with operating boats in shallow water is 
the possibility of running the boat aground. This may occur where an 
un-anticipated sandbar is encountered, or perhaps an oyster bed. This can 
be hazardous to the boat occupants, or cause other problems, in a number 
of ways. 
One danger is the boat occupants may be thrown overboard due to the sudden 
stop resulting from a boat abruptly running into a sand bar or oyster bed. 
Another problem may be damage to the outboard motor propeller: if the 
propeller strikes an oyster bed its rotation may be forced to stop against 
the urgings of the outboard motor, resulting in a damaged shear pin. If a 
shear pin is damaged, and no spare is available, then it may be impossible 
to change the propeller immediately. 
If the boat has to be temporarily abandoned while a new shear pin is 
procured, a real danger exists that the boat could be stolen. 
Another problem associated with current outboard motor design is that the 
propeller is sharp, and may rotate extremely quickly. Needless to say, 
this rapidly-spinning sharp propeller can present quite a hazard to 
swimmers and sea creatures in the vicinity of the propeller. Every year 
there are incidents of swimmers cut by outboard motor propellers, 
sometimes severely. And every year hundreds of underwater animals are 
injured, sometimes fatally, by outboard motor propellers. This problem is 
especially important where the injured animals are members of an 
endangered species such as manatees. 
Still another problem which exists where a boat powered by an outboard 
motor runs aground, is that the boat may become seriously stuck on the 
underwater obstruction upon which it ran aground. Under these conditions, 
it may be impossible to free the boat short of procuring a tow from 
another power boat, or waiting for the tide to rise (if the boat has run 
aground near water under oceanic tidal influence). While modem outboard 
motor designs incorporate lower units which are generally curved at their 
lower forward edge, these lower units generally terminate in a sharp point 
at their lower rear corner. When an attempt to back a boat in too-shallow 
water is made, this sharp point tends to dig into the bottom, thus 
immobilizing the boat 
Existing Design 
One solution to these outboard motor problems has been to enclose the 
propeller (and in some cases the entire lower unit) in a wire cage. For 
example, U.S. Pat. Nos. 4,078,516, 4,957,459 and Des. 322,256 were granted 
to Balius, Snyder, and Reeves respectively. While these designs protected 
the propeller from foreign object damage, the extensive caging disrupted 
the water flow to the propeller, and thus reduced its efficiency. 
Other designs making less extensive use of caging wire were taught in U.S. 
Pat. Nos. 5,176,550 and 4,565,533, granted to Hooper and Springer, 
respectively. While these designs appeared to impose less efficiency loss 
on the propeller, they terminated in a rear downwards slope. Such a rear 
downwards slope at the bottom of these propeller protectors caused the 
same digging-in problem while attempting to back a boat in too-shallow 
water described above. The result would be the same: to immobilize the 
boat. 
SUMMARY OF THE INVENTION 
Accordingly, it is an object of the present invention to provide a boat 
propeller sled which provides a wanting to a boat operator when shallow 
water is approaching. Design features allowing this object to be 
accomplished include forward-facing rail bases, and forward ramps. 
Advantages associated with the accomplishment of this object include the 
ability to reduce speed when approaching shallow water, and consequently 
the possibility of avoiding propeller damage and/or getting stuck. 
It is another object of the present invention to provide a boat propeller 
sled which is capable of protecting a propeller around which it is 
mounted. Design features allowing this object to be accomplished include 
forward ramps, runners, and rear ramps. A benefit associated with the 
accomplishment of this object is reduced propeller damage. 
It is another object of this invention to provide a boat propeller sled 
which allows a boat upon which it is mounted to back off an underwater 
obstruction without digging in the rear of the propeller sled. Design 
features enabling the accomplishment of this object include rear ramps is 
attached to framers at a rear ramp angle of approximately one hundred 
fifty degrees. An advantage associated with the realization of this object 
is speedier and easier egress off an underwater obstruction. 
It is still another object of this invention to provide a boat propeller 
sled which protects underwater creatures and swimmers from contact with a 
propeller. Design features allowing this object to be achieved include 
rail bases, forward ramps, runners, and rear ramps attached to an outboard 
motor lower unit. Benefits associated with reaching this objective include 
reduced human and animal casualties. 
It is a further object of this invention to provide a boat propeller sled 
which cushions the shock imparted a boat which runs aground at speed. 
Features permitting this object to be accomplished include forward ramps 
attached to bases and runners, which are attached to an outboard motor 
lower unit; the bases, runners and forward ramps being fabricated of 
semi-springy material. Benefits associated with the achievement of this 
object include reduced possibility of boat and motor damage, and increased 
boat passenger comfort. 
It is another object of this invention to provide a boat propeller sled 
which imposes minimum water resistance and minimal propeller efficiency 
reduction. Features permitting this object to be accomplished include the 
use of a minimum number of rails (two, in the preferred embodiment). 
Benefits associated with the achievement of this object include maximized 
boat performance and fuel efficiency. 
It is a further object of this invention to provide a boat propeller sled 
which has the capability of sliding up and over underwater obstructions, 
thus providing an inverse "cow-catcher" effect. Features permitting this 
object to be accomplished include forward ramps attached to runners at a 
forward ramp angle of approximately one hundred twenty degrees. Benefits 
associated with the achievement of this object include gentler and more 
gradual contact between a boat and underwater obstructions.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIG. 1 is a front isometric view of boat propeller sled 2 mounted on lower 
unit 8. Boat propeller sled 2 is comprised of straps 14 and rails 6 
attached to spine 4. Straps 14 are sized to frictionally admit lower unit 
8, and are tightened on lower unit 8 via fasteners 12. In the preferred 
embodiment, fasteners 12 were corrosion-resistant nuts and bolts. Rails 6 
protect propeller 10 from sand bars and other underwater obstructions, and 
also serve to protect swimmers and underwater animals from propeller 10. 
Rails 6 are attached to a lower extreme of spine 4. Referring now to FIG. 
2, which is a side isometric view of boat propeller sled 2, each rail 6 
may be observed to comprise base 16, forward ramp 18, runner 20, and rear 
ramp 22. 
As may be observed from FIG. 3, a side view of boat propeller sled 2, base 
16 is attached to spine 4 at an angle of approximately ninety degrees, so 
that base 16 is disposed approximately parallel to the water surface. The 
optimum angles of attachment of the various rail 6 components were 
established experimentally. Forward ramp 18 is attached to an extreme of 
base 16 opposite spine 4, at an angle of approximately sixty degrees. 
Runner 20 is attached to an extreme of forward ramp 18 opposite base 16, 
at a forward ramp angle 24 of approximately one hundred twenty degrees, so 
that runner 20 is disposed approximately parallel to the water surface. 
Rear ramp 22 is attached to an extreme of runner 20 opposite forward ramp 
18, at a rear ramp angle 26 of approximately one hundred fifty degrees. 
FIG. 4 is a side isometric view of boat propeller sled 2 attached to lower 
unit 8 in the process of running aground on sand bar 28, as indicated by 
forward arrow 30. As may be observed in FIG. 4, boat propeller sled 2 
provides advance warning of the imminent grounding of lower unit 8. At the 
same time, forward ramps 18 allow boat propeller sled 2 to slide up and 
over sand bar 28, acting as a species of inverse "cow-catcher". All the 
while, boat propeller sled 2 prevents lower unit 8 from coming into 
contact with sand bar 28, thus protecting propeller 10 from damage. 
FIG. 5 is a side isometric view of boat propeller sled 2 attached to lower 
unit 8 in the process of backing off of sand bar 28. The upward slope of 
rear ramps 22 relative to sand bar 28 prevent the rear ends of rear ramps 
22 from digging into sand bar 28. In this fashion, rear ramps 22 permit 
propeller 10 to pull rear unit 8 (and the boat to which it is attached) 
off sand bar 28, as indicated by rearward arrow 32. 
In the preferred embodiment, spine 4, straps 14, and rails 6 were 
constructed of steel, metal, synthetic, or other appropriate material. 
Rails 6 were fabricated of a semi-springy metal, which afforded rails 6 
some flexibility when coming into contact with underwater obstructions. In 
this fashion, the shock of such impacts is decreased, resulting in reduced 
possibility of boat and motor damage, and increased boat passenger 
comfort. 
While a preferred embodiment of the invention has been illustrated herein, 
it is to be understood that changes and variations may be made by those 
skilled in the art without departing from the spirit of the appending 
claims. 
DRAWING ITEM INDEX 
2 boat propeller sled 
4 spine 
6 rail 
8 lower unit 
10 propeller 
12 fastener 
14 strap 
16 base 
18 forward ramp 
20 runner 
22 rear ramp 
24 forward ramp angle 
26 rear ramp angle 
28 sand bar 
30 forward arrow 
32 rearward arrow