Marine outdrive with surface piercing propeller and stabilizing shroud

An improved fin structure for attachment to the propeller shaft mount of a surface piercing marine outdrive apparatus. The fin structure has one fin member at one side of the mount for the propeller drive shaft of the marine outdrive. The fin member is so situated that it is in a position to destroy any side thrust exerted by the propeller on the water so as to avoid "walking" of the mount on the water and the propeller laterally.

This invention relates to improvements in drives for boats, water pumps and 
the like and, more particularly, to a marine outdrive apparatus of the 
type using surface piercing propellers. 
BACKGROUND OF THE INVENTION 
Marine outdrives using surface piercing propellers have been known and used 
in the past. Representative disclosures relating to marine outdrives of 
this type include the following U.S. Pat. Nos. 4,645,463 and 4,909,175. 
A marine outdrive with a surface piercing propeller, as set forth in the 
above disclosures, has a tubular propeller shaft carrier or mount coupled 
to the transom of a boat by a universal joint in the form of a spherical 
ball. This construction allows the rotatable propeller at the rear end of 
the shaft rotatably carried by the mount to be shifted by fluid piston and 
cylinder assemblies into any one of a number of different attitudes with 
respect to the boat transom. Thus, the thrust of the marine outdrive 
itself can be generated and varied as to direction and magnitude, thereby 
providing great versatility to the outdrive and adapting it for a wide 
range of speed and other requirements for boats of different sizes. 
It has been found through extensive use of a marine outdrive of this type 
that the propeller itself tends to "walk" across the water from right to 
left for clockwise rotation (when viewing forwardly) of the propeller and 
from left to right for counterclockwise rotation of the propeller. This 
tendency of the propeller shaft mount to "walk" on the water gives rise to 
unstable forward movements of the boat on which the outdrive is mounted. 
It also causes the boat to be difficult to handle, especially at high 
speeds. The constant need to try to keep the steering gear of the boat 
steady under the adverse conditions caused by the "walking" of the 
propeller across the water causes fatigue of the operator of the boat over 
long periods of time. This is especially true with high speed boats which 
must continuously be steadied to maintain control of the boats. Also, the 
thrust line of the boat tends to vary relative to the transom which 
further complicates the operation of the boat and limits its top speed. 
Attempts have been made to eliminate this walking of the propeller across 
the water but such attempts have been generally unsuccessful for one or 
more reasons. The problem continues to plague suppliers and users of 
marine outdrives with surface piercing propellers. Accordingly, a need 
continues to exist for improvements in this area and the present invention 
satisfies this need by providing several solutions to the problem. 
SUMMARY OF THE INVENTION 
The present invention is directed to an improved shroud for attachment to 
the propeller shaft carrier or mount of a surface piercing marine outdrive 
apparatus. The shroud at least partially encircles the propeller and is 
located on at least one side of the carrier or mount for the propeller 
drive shaft. 
The rotation of the propeller blades creates an envelope which is caused by 
the rotation of the outer end faces of the blades. This envelope comes 
progressively closer to the inner surface of the shroud as the blades 
rotate and approach a downstream end edge of the shroud. Then, the 
envelope disengages from the shroud after the blades have passed the 
downstream end edge of the shroud. At an upstream end edge of the shroud, 
there is a relatively wide channel which progressively decreases in width 
as the central part of the shroud is approached and as the envelope 
approaches the narrowest parts of the channel. 
The inner surface of the shroud and the envelope define the channel which 
has the upstream and downstream end edges. This channel has a relatively 
wide, convergent entrance end and a relatively narrow divergent exit end. 
As the propeller blades rotate through the water, they effectively cause a 
volute or spiral movement of the water into which the propeller is 
partially submerged. The spiral movement of water creates a vortex which 
provides an increase in speed of the water in a direction rearwardly of 
the boat and propeller with a minimum of drag. This causes an increase in 
thrust because of the continuous generation of the volute. The net result 
is that the volute is in a position to destroy any side thrust exerted by 
the propeller on the water so as to avoid "walking" of the mount on the 
water. Any uncontrollable movement of the propeller laterally is avoided. 
This eliminates the instability associated with the "walking" of the 
propeller which, until now, has continued to be a problem. 
For a pair of marine outdrives coupled to and extending rearwardly from the 
transom of a boat, each outdrive will have its own shroud. Moreover, it is 
possible that, for a boat having dual marine outdrives, it need have only 
one shroud for one of the marine outdrives, the other outdrive being free 
of any shroud. In such a case, the stability problem is substantially 
eliminated because of the presence of the volute on the working shroud. 
The primary object of the present invention is to provide an improved 
shroud for the rear of the marine outdrive of a boat having a surface 
piercing propeller wherein the shroud extends partially about from the 
rear end of the tubular shaft mount for the propeller and is in a position 
to generate a volute which enhances the performance of the boat. 
Another object of the present invention is to provide an apparatus and 
method of controlling a boat using a marine outdrive with an improved 
surface piercing propeller smaller in diameter than a conventional 
propeller and designed to present outer blade extremities which mate with 
the inner surface portion of the shroud so that the certain instabilities 
associated with movements of such a boat over water can be eliminated by 
the use of the propeller with the shroud when the shroud is adjacent to 
the propeller shaft mount. 
Other objects of the present invention will become apparent as the 
following specification progresses, reference being had to the 
accompanying drawings for an illustration of several embodiments of the 
invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
The shroud of the present invention, in a preferred embodiment, is broadly 
denoted by the numeral 10 and is adapted to be used with a marine outdrive 
apparatus unit 12 which is attachable to the transom 14 of a boat 16. Boat 
16 can be of any suitable size and shape and typically it may have a pair 
of marine outdrive apparatus units 12a secured to and extending rearwardly 
from the transom 14 of the boat. Thus, the marine outdrive units may work 
alone or in unison with each other to produce forward thrust for the boat. 
A marine outdrive unit with which structure 10 is to be used includes a 
propeller shaft carrier or mount 18 (FIG. 3) having a pivot structure 20, 
such as a universal ball joint, secured to a support tube 22 attached by 
spider fasteners 24 to the shroud at the inner, front surface thereby and 
to mount 18 at several locations. Mount 18, therefore, is pivotal relative 
to support tube 22. 
Mount 18 and tube 22 house a rotatable shaft 30 which is connected through 
pivot structure 20 to a drive motor 32 mounted in the boat 16 at some 
suitable location thereon. The shaft extends to the rear end of mount 18 
and is secured by fasteners 34 to a surface piercing propeller 36 which is 
rotatable when motor 32 is actuated. The propeller is shown connected to 
shaft 34 in FIG. 6. At least a portion of the propeller is above water 
level 36 during normal operation of the marine outdrive unit. 
The mount 18 is raised and lowered so as to raise and lower the propeller 
36 by the actuation of a first fluid piston cylinder assembly 38 pivotally 
mounted at its forward end 40 on the transom 14 and secured by a pivot 42 
on mount 18 forwardly of the rear end of the mount 18. To effect lateral 
movements of mount 18, a second fluid piston cylinder assembly 44 is 
pivotally mounted by a pivot structure 46 on transom 14 and by a pivot 
structure 48 on mount 18. Changes in the attitude of mount 18 can be made 
by operating assemblies 38 and 44. 
The foregoing description, except for shroud 10 and the design of the 
propeller 36, relates to a conventional marine outdrive unit. Such a 
marine outdrive unit is of the type disclosed in the following U.S. Pat. 
Nos. 4,645,463, and 4,909,175. 
It has been found that the propeller 36, without shroud 10, tends to "walk" 
across the water from right to left for clockwise rotation of the 
propeller 36 (when looking toward the bow of the boat, i.e., in the 
direction of FIG. 4). This tendency of the propeller to "walk" causes 
unstable forward movements of the boat and causes the boat to be difficult 
to handle, especially at high speeds. The operator of the boat constantly 
has to keep the steering gear steady under adverse conditions caused by 
the "walking" of the propeller across the water. This causes fatigue of 
the operator and requires frequent stops or change of operators as a 
result. 
Shroud 10 of the present invention eliminates these problems. The shroud 
has a hollow interior and works in cooperation with the propeller to 
increase the load on the propeller blades and generates a volute which is 
a vortex or scroll-like phenomenon which causes the water to flow 
rearwardly at a higher velocity than would be the case in the absence of 
the volute. The volute is characterized in accelerating the scroll-like or 
spiral paths of water rearwardly by the blades rotating about the central 
axis of the propeller 36. 
The envelope traversed by the outer or rear ends of the blades of the 
propeller is denoted by the numeral 40 and typically rotates in a circle 
having a diameter in the range of 10" to 32" more particularly 13.5". 
An important feature of the propeller is the fact that the outer ends of 
the propeller blades are substantially complemental to the adjacent inner 
surface portion of the shroud. In this respect, the faces of the blades 
could be considered flat as to the inner surface of the shroud as they 
sweep out a somewhat cylindrical space concentric to the cylindrical inner 
wall surface of the shroud as shown in FIGS. 5 and 6. It is this 
substantial flatness and concentricity of the end faces of the blades 
which provides for maximum loading of the blades with water and thereby 
the greater acceleration rearwardly of the water as an increase in 
rotational speed of the blades. The outer ends of the blades are forwardly 
of the rear edge of the shroud by a distance in the range of 0.25" to 
2.5". 
This rotational speed is achieved by causing the blades to enter the 
circular channel 42 (FIG. 4) formed by the inner surface of the shroud 10 
and the envelope 40. The upstream end 43 of the channel 42 has an entrance 
opening. 44. A portion 46 of the shroud from the 7 o'clock position in 
FIG. 4 to the 9 o'clock position 46 is substantially straight and 
vertical. Past the 9 o'clock position the channel 42 has a curved part 47 
which continues on and merges with the wall portion 47 or at the location 
past the 12 o'clock position 48. The channel extends further outwardly and 
downwardly and terminates at about the 2 o'clock position spaced outwardly 
from the envelope 40 of the blades of the propeller. 
The shroud makes a divergent exit opening 50 at the downstream end of the 
channel. Also noteworthy is the fact that the shroud top part 48 is 
relatively close to but spaced from the envelope 40 of the blades to form 
a pinched-off channel segment 51 as spacing or gap which aids in causing 
the maximum loading of the blades as they enter the channel 48 and as they 
move toward the minimum spacing 51. Since the water is not compressible, 
the water is carried on the rear faces of the blades until the water can 
be accelerated rearwardly, at which time the rearwardly accelerated water 
generates a relatively high forward thrust force. 
Shroud 10 has a pair of vertically spaced side edges 54 and 56. The side 
edges are generally parallel with each other as shown in FIG. 5. 
Shroud 10 is made from an imperforate plate or panel from suitable 
material, such as stainless steel, brass, aluminum or carbon fiber. The 
shroud has an inner surface which is relatively smooth and hollow and is 
buffed and polished so as to minimize drag on the flow of water past the 
inner surface of the shroud. 
Shroud 10 has a front edge 62 and a rear edge 64. Thus, edges 44, 40, 56, 
64, and 62 define the boundaries of the shroud. Typically, the 9 o'clock 
positions of channel 42 have a width in the range of 0.5" to 1.5" more 
nearly 1.25". At the 12 o'clock position, the gap is normally about 0.25" 
for a propeller diameter of 13.5". The outer end of the shroud in the 
vicinity of the 1 o'clock to the 2 o'clock positions is at an angle 
typically in the range of 15.degree. to 30.degree. more nearly 25.degree., 
as shown in FIG. 4. Shroud 10 and propeller shaft 30 typically define a 
down running angle of about 7.degree. to about 10.degree.. In addition, 
bottom edges of shroud 10 are usually disposed at an angle of about 
3.degree. to about 7.degree. when viewing from the rear end of the shroud. 
In a preferred embodiment, the lower half of shroud 10 is rolled parallel 
to the horizontal running line so that shroud 10 passes through the water 
in a substantially straight line. In addition, the upper outer surface of 
shroud 10 typically has a running angle substantially parallel to the 
propeller shaft 30 angle. 
In operation, the shroud 10 is mounted on a marine outdrive unit 12, such 
as the right hand propeller and carrier unit looking forwardly, as shown 
in FIG. 4. By accelerating the boat forwardly upon rotation of the 
propeller, thrust is produced which accelerates the boat forwardly and the 
boat can readily go up on plane. The system can go at high speeds in all 
directions because of the fact that there is very little drag and the 
loading of the blades occurs which causes the water to stay with the rear 
face of the blades. As the blades rotate, they carry the water with them 
and the water is accelerated in the pinched off area denoted by the 
numeral 48. The accelerating water will have an equal and opposite 
reaction on the boat which will cause thrust to be applied to the boat 
even up to speeds of 160 to 180 mph. 
The plane of rotation of the blades of propeller 36 is shown in FIGS. 5 and 
6. It is clear that a rear part of the shroud is above and overlies the 
propeller 36. 
In the event that a double marine outdrive arrangement of the type shown in 
FIG. 2 is used, the propeller drive shaft of unit 12b will typically 
rotate in a counterclockwise sense when viewing FIG. 4 and the shroud will 
be facing the opposite direction from that shown in FIG. 4. For the 
outdrive on the right side of the transom, the shaft and propeller will 
rotate in a counterclockwise sense when viewing FIG. 4. 
The motor 32 will be operated to rotate drive shaft 30. Rotation of the 
drive shaft 30 will spin the blades 33 of propeller 36 of FIG. 4, in a 
clockwise sense when viewing FIG. 4. 
The plane of rotation of the rear ends of blades 33 of the propeller 36 is 
substantially at the rear edge of the envelope 40. At this position, the 
propeller efficiency is at a maximum, and the efficiency drops off as the 
blade assembly is at a location forwardly or rearwardly of the envelope. 
The water churned up by the rotation of the propeller is resisted by the 
movement of the shroud and the propeller blades passing through the water. 
The blades and shroud thus tend to reduce the turbulence, and the 
instabilities of the boat arising from forward and lateral movements of 
the boat are substantially eliminated. Moreover, the operator finds it 
much easier to operate the controls of the boat since the shroud 10 acts 
as a barrier for lateral movements of the water which tend to cause the 
propeller to "walk" on the water. This tendency to control the mass of 
water slung laterally by the propeller provides that the propeller has 
better control over the onslaught and rush of water against the inner 
surfaces of the shroud. The elimination of the instabilities associated 
with the shroud 10 thereon clearly utilizes the positions of the inner 
surfaces of the shroud. Shroud 10 is typically far enough away from the 
plane of rotation of propeller 36, as shown in FIG. 4, so as to prevent 
interference by the shroud to the rotation of the propeller itself. The 
inner surfaces of the shroud members also contribute to keeping the center 
shaft thrust direction stable so that there is no tendency for the 
propeller to lift out of the water and cause the operator of the boat to 
fight the steering and trim gears of the boat. 
Among the many advantages of the system of the present invention is that 
more thrust is obtained with a smaller diameter propeller. More bow lift 
is achieved because of less propeller lift and less propeller torque (side 
walking of propeller). The system of the present invention has the ability 
to adjust for offset side loading on a single engine installation if 
necessary. 
The propeller configuration is different from standard propeller units. The 
present invention has a propeller which is smaller in diameter with wide 
thick blade tips that make it very strong and efficient. This allows the 
boat to get on plane quicker and easier and maintains plane when the rpms 
of the system are decreased. Some conventional boats tend to fall off 
plane when this occurs; however, with the present system, it is much 
easier to maintain planing at a lower engine speed. 
Directional stability is very good and the propeller turns smoothly in the 
water. The system can be used in many types of installations, such as the 
following: 
Arneson drives; 
fixed shaft surface drives; 
surface inboard/outboard drives (surfacing); 
conventional inboard drives; 
conventional inboard/outboard drives; and 
conventional outboard drives. 
The present invention acts much like a water pump, drawing water into a 
volute shaped shroud that forces it downwardly into the propeller blade 
face where it is then converted into thrust. The shroud offers protection 
from propeller exposure and propeller protection such as when backing down 
near pilings, floats, docks and the like. The shroud eliminates the need 
to built expensive platforms over propellers for protection and peace of 
mind. By using smaller diameter propellers, this costs is greatly reduced. 
In almost three years of testing, a propeller has never been broken when 
used with the system of the present invention. The smaller diameter of the 
propeller reduces propeller structural failing. As a result, better 
steering control is achieved at all speeds and the cost to produce this is 
insignificant. Removal of the fin in front of the propeller eliminates the 
problem of disturbed and aerated water from entering the propeller. The 
elimination of present fin structures of conventional boats comes close to 
offsetting the cost of the system of the present invention. 
Acceleration of the boat is greatly improved. There is no need for 
sacrificing top speed experienced with this system. In many cases, top 
speed will be much higher than obtainable with conventional boats. 
Heavy fuel and passenger loading has no effect on planing ability as well 
as other performance figures. Such figures are much better than those 
achieved with a conventional system. With twin engine installations, it 
will make getting on plane with only one engine much easier. Larger 
diameter propellers used on present systems have a tendency to manhandle 
the boat, causing poor handling. This is eliminated by the system of the 
present invention. Present propellers can be machined to perform with this 
new system. 
The other aspect of this invention is the newly designed propeller 
configuration that will enhance the concept. The propeller is more like an 
impeller than a propeller. This impeller concept will be stronger and more 
efficient. It is also less costly to manufacture. Cavitation burns on the 
propeller face are practically nonexistent. The propeller shaft side 
loading is decreased. 
In a surface mode, the propeller is now carrying a load of water through 
almost 360.degree. thereby reducing cyclical impulses as the propeller 
blades enter and leave the water. It is now not necessary to use costly 
five or six blade propellers to enjoy smooth operation. Test boats have 
been found to cruise at the same speed as before but using less horsepower 
and less fuel. At least 225 documented tests have been conducted with the 
system of the present invention. An additional documented test has also 
been made consuming approximately 30,000 gallons of fuel. Ongoing testing 
is continuing and will probably continue for some time. 
Propeller costs can be reduced by use of the propeller of the present 
invention. For instance, for a 32" conventional propeller, the normal cost 
is about $6,200. A 24" propeller will do the same work as a 32" 
conventional propeller. The cost of a 24" propeller is $2,700. The 
difference between the $6,200 and $2,700 equals a savings of $3,500 that 
can be realized with a 24" propeller of the present invention versus a 32" 
conventional propeller. 
A second embodiment of the shroud of the present invention is broadly 
denoted by the numeral 10a and is shown in FIGS. 7A and 7B. The shroud 10a 
does not encircle the mount 18 or the propeller 36. Instead, shroud 10a 
has a pair of generally parallel side walls 13a and 15a which are 
relatively straight and extend downwardly from the 9 o'clock and 3 o'clock 
positions. The shroud 10 has a tangential portion 41a substantially 
parallel to a tangent of the propeller envelope 40 near the 9 o'clock 
position. The walls 13a and 15a terminate at lower edges which are below 
the envelope of the blades, the envelope being denoted by the numeral 40a. 
The shroud 10a is mounted by webs 24a or other suitable structure. The web 
has a curved upper part 43a which is integral with side walls 13a and 15a. 
The curved part has a gap 45a which is approximately 1/4" wide; whereas, 
the side gap at the upstream end of the channel 47a and the channel 
downstream portion 49a are in the range of 1/2" to 11/2". The entrance end 
tapers to 1/4" which is a minimum across the major portion of the central 
curved wall 45a or to the 3 o'clock position at which the space 49a 
commences to diverge. The blades of the propeller 36 in FIGS. 7A and 7B 
are substantially flat at the outer extremities thereof as shown in FIG. 
7B. The side walls 13a and 15a are substantially of equal height and 
terminate at substantially the same edge location where edges 17a and 19a 
are below the envelope 40a. 
A third embodiment of the shroud of the present invention is broadly 
denoted by the numeral 10b and is shown in FIGS. 8A and 8B. The shroud of 
FIGS. 8A and 8B is substantially the same in construction as shroud 10a of 
FIGS. 7A and 7B except that shroud 10b has a shorter downstream sidewall 
15b than that of shroud 10a (FIGS. 7A and 7B). Moreover, shroud 10b has an 
outer, relatively straight vertical leg 15bb which is at an angle in the 
range of 60.degree. to 75.degree. to the horizontal with respect to 
vertical sidewall 15b such that leg 15bb extends partially across the 
bottom of the shroud as shown in FIG. 8A. The upstream portion of shroud 
10 has a tangential portion 41b substantially parallel to a tangent of the 
propeller envelope 40 near the 9 o'clock position. All of the dimensions 
of the shroud 10b are substantially the same as those of shroud 10a. 
Shroud 10b has the blades 33 of the propeller 36 substantially flat at the 
outer extremities thereof. Wall 13b is substantially parallel with wall 
15b. The entrance and exit channels 47b and 49b are of the same dimensions 
as the corresponding regions of shroud 10a. The pinched-off portion 45b is 
of a minimum value, such as 1/4". 
A fourth embodiment of the shroud of the present invention is broadly 
denoted by the numeral 10c and is shown in FIGS. 9A and 9B. The sidewalls 
13c and 15c of shroud 10c are curved as shown in FIG. 9A. The side edges 
17c and 19c of the shroud are at the same level below and with respect to 
the central axis of the propeller 36, the central axis being denoted by 
the numeral 21c. Again, the 9:00 o'clock positions and the 3:00 o'clock 
positions have a gap in the range of 1/2" to 11/2", more nearly 11/4". 
There is also a pinched-off gap 51c which is optimally a 1/4" gap. The 
outer envelope of the blades 33 of the propeller 36 are essentially at the 
rear edge 53c of shroud 10c. Webs 24c mounts the shroud on mount 18. The 
rear margins of the blades of shroud 10c are in substantially the plane of 
rotation of the rear edges of the blades (FIG. 9A). 
Another embodiment of the shroud of the present invention is broadly 
denoted by the numeral 10d and is shown in FIGS. 10A and 10B. The shroud 
10 has a tangential portion 41d substantially parallel to a tangent of the 
propeller envelope 40 near the 9 o'clock position. Shroud 10d has an input 
channel 40d which tapers to 1/4" gap 51d as the channel extends around the 
curved part 48d of the upper extremity of the shroud. This gap is for the 
same purpose as the gaps of the embodiments mentioned above and for all of 
the embodiments of the shroud. Moreover, webs 24d are provided to mount 
the shroud 10d in place on mount 18 for rotation about the central axis of 
rod 30. 
What differentiates the embodiment for FIG. 10A from the other embodiments 
is that embodiment FIG. 10A has a 1/4" gap from the 10 o'clock position to 
approximately the 4 o'clock position. At the 3:30 position, the shroud 
terminates at an edge 44d, upstream edge 43d being substantially straight 
while edge 42d is substantially circular. The blades thus instigate the 
movement of the water around the central axis of the mount 18 and the 
water is accelerated rearwardly to give forward thrust to the mount of 
extremely high speed. 
FIG. 11A and 11B show another embodiment of the shroud of named embodiment 
10e which is the same in construction as that of embodiment 10d except 
that the sidewalls 12e and 14e are spaced outwardly and downwardly from 
the rotating blades 33 of propeller 36 such that the channel formed by the 
rotation of the blades is sufficient to load the blades near tangential 
portion 41e of the shroud end to cause the water to be thrust rearwardly 
so as to provide a forward thrust over the marine outdrive coupled to the 
shroud. It is clear that the 1/4" gap at the top of the shroud, and all 
other dimensions are the same as above, is still in place and is common 
for all of the embodiments of the invention.