Line cutter for propellers

A device shears foreign matter such as lines, wires, nets, and weeds that can entangle and befoul propellers, propeller shafts, bearings and the like of propeller-driven sea-going vessels that are sheared by cooperative shearing action of rotating blades that rotate in conjunction with the propeller and at least one non-rotating blade mounted on a non-rotating portion of the vessel. Positioning mechanism maintains the non-rotating blade in proximity to the rotating blades, for effective shearing operation. The position of the propeller will change relative to the hull, advancing axially when under way in forward drive due to the forward thrust of the propeller and retreating in reverse. Heating and cooling of the shaft will also change propeller position. The positioning mechanism senses the propeller location and moves the non-rotating blade to accomodate changes in propeller position to maintain a fixed, very close spacing between the two blades to enable them to shear foreign matter caught between them. A damping mechanism retards sudden movement. A secondary moving mechanism causes the two blades to come closer together at the moment of shearing to overcome forces that tend to push them apart.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to devices that cut underwater lines, weeds, nets 
and the like and more particularly to shearing cutters that include a 
blade rotating with the shaft and propeller of a vessel that cooperates 
with a blade mounted on a non-rotating portion of a vessel adjacent the 
shaft with means for controlling the distance between rotating and 
non-rotating blades. 
2. Description of the Prior Art 
U.S. Pat. Nos. 4,447,215; 4,507,091, 4,544,363 and 4,801,281 have been 
issued to the inventor for propeller protecting devices that carry both a 
rotary cutter blade assembly and a stationary blade assembly on the 
rotating shaft or propellers of a boat. The rotary cutter blade assembly 
is fixedly connected to the rotating part and the stationary blade 
assembly is rotatably held in a fixed axial position relative to the 
rotating blades by bearing means and a flexible connection to the 
non-rotating part of the boat such as the strut or propeller shaft 
housing. 
This bearing means is a source of wear, vibration and noise since it is 
continuously exposed to underwater debris, abrasive sand and fouling by 
marine organisms. Maintenance of the bearing is a minor problem for small 
boats that are frequently hauled out of the water. However, large 
commercial vessels that are in almost constant operation for prolonged 
periods are confronted with serious expense if the bearing must be 
serviced. 
When a propeller is pushing a vessel forward in the water, the propeller 
and shaft exert a great forward force on the hull on a line coincident 
with the long axis of the shaft. This tends to move the shaft forward into 
the shaft housing. When in reverse, the axial movement is in the opposite 
direction. Thrust bearings take up the force and limit this axial 
movement. Temperature changes in the shaft also cause axial movement. When 
both the rotating and stationary blade assemblies are mounted at a common 
point on the shaft, the axial movement of the shaft does not effect the 
spacing between the two assemblies. However, when the rotating blade 
assembly is mounted on the shaft and the stationary blade assembly is 
mounted on the hull, then some mechanism must be provided to maintain a 
spacing between the blades close enough for shearing despite these axial 
movements. That mechanism must respond slowly to the axial movement to 
avoid moving away abruptly at the moment the moving blade and the 
stationary blade engage a foreign object for shearing action. A secondary 
mechanism that tends to bring the blades together at the moment of 
engaging the foreign object would further enhance the shearing action. 
SUMMARY OF THE INVENTION 
It is, accordingly, an object of the invention to provide an assembly that 
includes a rotating blade means for affixing to the rotating shaft or 
propeller of a water-born vessel and a stationary blade means for 
connecting to a non-rotating portion of the vessel close to the shaft such 
as the propeller shaft housing or strut. It is another object to provide 
positioning means for maintaining the spacing between rotating and 
stationary blades so close as to provide a shearing action without forcing 
the blades together. It is yet another object to provide a time delay to 
the positioning action to prevent a foreign object held between the blades 
from causing the positioning action to separate the blades before shearing 
can be achieved. It is yet another object to provide a secondary 
positioning mechanism that tends to bring the blades together at the 
moment of engaging the foreign object to further enhance the shearing 
action. 
The rotary blade assembly includes a ring that encircles the shaft. This 
ring may be fixed to the shaft or to the propeller. Extending radially 
from the ring are one or more blades having a shearing plane perpendicular 
to the axis of the shaft. 
The stationary blade assembly includes: 
(1) a base for affixing the stationary blade assembly to the shaft housing 
or strut; 
(2) a stationary blade having a shearing plane parallel to the shearing 
plane of the rotating blade; and 
(3) positioning means for holding the stationary blade in shearing position 
closely approximated to the rotating blade despite axial movement of the 
shaft relative to the vessel. 
The positioning means includes: 
(A) sensing means for sensing the distance between moving and stationary 
blades; 
(B) primary moving means for moving the stationary blade toward or away 
from the rotating blade in response to the sensing means; 
(C) retarding means for preventing rapid movement of the moving means; and 
(D) secondary moving means for rapidly approximating the stationary blade 
to the rotating blade in response to engagement of a foreign object 
between the stationary and rotating blades. 
The sensing means may be any one of the well known sensors including a 
rotating contact wheel or a non-contacting proximity sensor such as a Hall 
effect magnetic detector or magnetic reed switches. The primary moving 
means may be any one of the well known moving means such as spring, 
pneumatic, hydraulic, electric drive mechanisms or combinations thereof 
with retarding means including restrictive fluid flow paths and electric 
time delays well known in the art. 
The secondary moving means includes a pivoting stationary blade with a 
wedge interacting with an inclined plane to force it toward the rotary 
blade when a foreign object between the blades applies a rotary force to 
the stationary blade causing it to pivot about its support. 
There may be situations in which it is useful to retract the blades. An 
alternative embodiment applicable to those situations may include means 
for retracting the blades centripetally when not in use and for extending 
the blades centrifugally when required for line shearing operation. 
These and other objects, advantages and features of the invention will 
become more fully apparent when the following detailed description of 
preferred embodiments of the invention are read in conjunction with the 
accompanying drawings.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
Referring now first to the embodiment shown in FIGS. 1 and 2, a vessel 1 
has a propeller shaft housing 12, and a propeller shaft 13 journalled 
therein with a propeller hub 3 carrying propeller 14 affixed to the shaft. 
A rope guard 2 surrounds the shaft and is secured to the housing 12 by 
bolts 15. A notch 16 in the rope guard receives the stationary blade 
assembly 1 which is bolted to the rope guard by bolts 17. A blade support 
ring 4 is bolted to the propeller hub 3. Rotary blades 5 are bolted to the 
ring 4 by bolts 18 so that they extend radially beyond the hub 3. This 
positions the blades so that they catch the foreign matter as they turn 
and tend to twist it inward where it will be caught and sheared against 
the non-rotating blade 8. Blade 8 is held radially extended with its flat 
shearing plane parallel to the flat shearing plane of the rotating blades 
by blade support assembly 1. Stationary blade support assembly 1 includes 
a metal base portion 6 bolted to the rope guard 2 and a blade holder 7 
that has a controlled fore-and-aft axial motion parallel to the axis of 
the shaft. Guide rods 19 move in recesses 20 in base 6 to maintain the 
shearing face 21 of non-rotating blade 8 parallel to the shearing face 22 
of rotating blade 5. As shown, a rubbery block 23 of polyurethane plastic 
separates the base 6 from the blade holder 7 and provides spring bias 
forcing the blade 8 against the blade 5. A roller 24 rotatably supported 
in blade holder 7 by axle 25 is forced against the rotating blade support 
ring 4. When contact is made, the two blades are kept apart at an optimal 
distance, found to be 0.005 inches in one case. The roller acts as a 
mechanical sensor that maintains this distance between blades despite 
axial movement of the propeller. When the propeller moves forward, the 
roller 24 forces blade holder 7 forward, compressing the block 23. When 
propeller is reversed, it moves backward increasing blade separation, but 
compressed block 23 expands until roller 24 again contacts ring 4. The 
roller is shown away from its contact with the ring for illustrative 
purposes. As an alternative to a rubbery block, other means of providing 
spring bias for blade moving may be provided such as a coil spring 26, 
shown in phantom in FIG. 2. To prevent the foreign matter trapped between 
the blades from pushing blade 8 forward before shearing can take place, a 
velocity reduction, damper, or retarding means is provided, shown in FIG. 
2 as a hydraulic piston 27 in a cylinder 28 containing a fluid 29 that 
resists sudden motion. This primary blade positioning means is 
supplemented by a secondary blade moving means that forces the two blades 
closer together at the moment foreign matter is caught between rotating 
and stationary blades. The torque from the rotating blade is transmitted 
through the foreign matter to the stationary blade. The stationary blade 8 
is supported on blade holder 7 by a pivot pin 9. Blade 8 pivots about pin 
9 under the influence of the torque transmitted through the foreign 
matter. Blade 8 has a wedge element on its forward face with the narrow 
edge of the wedge 29 facing forward and extending perpendicular to the 
axis of the pivot pin. In registry with the wedge is a rear opening, 
wedge-shape recess 30 in the blade holder 7, better seen in FIGS. 3, 4. As 
blade 8 pivots about pin 9, an inclined plane action of the wedge 29 
against the sloping side of recess 30 causes blade 8 to be forced toward 
blade 5. The axial movement will be very small but it occurs at just the 
moment when it is needed. The small amount of axial movement may be 
provided through flexing of blade 8 or other means such as a resilient 
washer 31 under the head of the pivot pin. (FIGS. 2, 7) 
Referring now to FIGS. 3 and 4 for details of the two shearing blades, each 
blade has a flat shearing face 21 and 22 and lateral edges 32 sharp at the 
shearing faces to provide a scissors like action on the rope 100 caught 
between. Each blade is narrow at the base and wider at the outer portion, 
terminating in ears 101. The tapering sides tend to pull the rope toward 
the shaft, to enhance engagement while shearing. Each ear 101 has an inner 
ramp portion 102 that forces blades apart before shearing edges meet in 
case of malposition of the blades. 
FIGS. 5 and 6 illustrate an embodiment of the invention with hydraulic 
moving means, a mechanical roller sensing means and a pneumatic pressure 
reservoir for maintenance of hydraulic pressure. 
The apparatus consists of a rotary cutter ring 4 having replaceable cutter 
blades 5 and attached to the face of the propeller hub 3, with stationary 
blade unit assembly 1 being fixably mounted to the rope guard 2 in a 
working proximity to the rotating cutter blades 5. 
The stationary blade unit 1 is made up of the following: A base portion 6 
that bolts onto rope guard 2; has slide bearings 42, held in place by 
screw 43. Mounted in bearings 42 is a slideably mounted stationary cutter 
block 7, attached to which is pivotable blade or blades 8, blade pivot and 
attachment screw 9, blade wedge block 10 which limits the lateral swing of 
the blade 8, and locater roller bearing 24. 
Control assembly 51 having a fluid motor such as a hydraulically 
pressurized cylinder 52, having a piston and rod assembly 53 which is 
mechanically attached to the cutter block 7. A conduit 54 having a flow 
control unit 55 at its entrance to the piston chamber 56, connects the 
fluid motor to an air over hydraulic accumulator chamber 57. A second 
conduit 50 attached to the air end of the accumulator 57, having a check 
valve 49 at its entrance to the accumulator 57, connects the accumulator 
57 to a pressure regulator 48. A third conduit 47 attaches the regulator 
48 to a high pressure air receiver tank 46 and a high pressure fill valve 
45 to charge the receiver or reservoir. 
The high pressure receiver 46 is the energy source for the operation of the 
positioning apparatus. Dependent on the size of this unit and the charged 
pressure level, it can provide many months of operation before requiring a 
recharge. The pressure regulating valve 48 will supply a low pressure to 
the accumulator 57 and only permit flow when the accumulator pressure is 
lower than its set-point as determined by the setting of control spring 
44. 
Approximately 50% of the accumulator volume, all of the first conduit and 
the cylinder piston chamber are to be charged with hydraulic fluid. The 
air receiver tank is to be charged with high pressure air or nitrogen. 
The roller bearing will ride against the rotating blade ring to maintain a 
fixed relationship between the rotating and stationary blade surfaces. 
When axial movement of the propeller occurs, the pressurized hydraulic 
cylinder (fluid motor) 52 will move the slideably mounted stationary blade 
block 7 along slide bearings 42 to maintain blade relationship. Should the 
propeller move axially toward the stationary blade block, fluid will flow 
out of the cylinder 52 through the flow control unit 55 and the first 
conduit 54 into the accumulator 57. As the second conduit 50 is fitted 
with a check valve 49, pressure in the accumulator 57 will rise slightly 
as the fluid volume entering through the first conduit will cause the air 
in the chamber to compress. The check valve 49 will protect the regulating 
valve 48 against the higher back pressure which could shorten its useful 
life. To maintain blade position during the high shock loading when a 
mooring line or other material is cut by the blades, the flow control 55 
orifice will retain the fluid in the cylinders 52 momentarily and will 
also protect the other components from the resultant high pressure shock 
wave. 
An alternative embodiment of the invention, illustrated in FIG. 7 employs 
hydraulic moving means with an electric motor driven pump and a mechanical 
sensor. 
The apparatus consists of a rotary cutter ring 4 having replaceable cutter 
blades 5 and attached to the face of the propeller hub 3, with stationary 
blade unit assembly 1 being fixably mounted to the rope guard 2 in a 
working proximity to the cutter blades 5. 
The stationary blade unit assembly 1 is made up of: stationary cutter block 
7, attached to which is pivotable cutter blade or a multiplicity of blades 
8, blade pivot and attachment screw 9, and blade wedge block 10 which 
limits the lateral swing of blade 8, and the roller assembly consisting of 
carrier 38, roller 24, axle 25, ratio lever 35, pivot pin 36 and pivot 
ball 37. The block assembly is slideably mounted into the base portion on 
bearings 42 and attached to piston 18 by means of washer 33 and nut 34. 
Piston assembly 18 includes valve 131, spool valve 130, valve spring 129, 
valve retainer 128, seals 123, 132 and 144, and conduits 126, 147, 148, 
adjustable orifice 27, grooves 45 and 46 for fluid passage. 
Housing 6 also includes fluid pressure pump 111, pressure conduits 115 and 
116, piston and rod seals 124 and 125, pressure unloading valve 119, 
pressure setting spring 120, retainer 121 with seal 122, fluid sump 113, 
pump supply conduit 114, face seal 149 and sump vent port 141. 
Detachable cover 150 includes electrical pump drive motor 112 with its 
appropriate seals for protection from the sea water. A vent tube should be 
attached at port 141 and be of sufficient length to be protected from 
water entry, and be fitted with a suitable breather filter. Electrical 
cable for pump drive to be suitably connected to an environmentally 
protected ON-OFF switch assembly. Sump chamber 113 is to be filled with 
hydraulic fluid. 
When switch is turned ON, pump 111 will operate to supply hydraulic fluid 
under pressure (as set by unloading valve 119 and spring 120) through 
conduits 115 and 116 into piston chamber 117. Fluid under pressure will 
enter piston 18 through conduit 147 and groove 145 to valve 130. If spool 
land is not covering groove 145, fluid will be permitted to enter conduit 
126 through orifice 127 into piston head chamber 151. Due to the 
difference of piston areas, the piston will stroke to extend the piston 
rod and cutter block towards the rotating blade ring. When both lands of 
spool 130 are aligned with the center edges of grooves 145 and 146, fluid 
flow will be cut off and further movement of piston and cutter block will 
be stopped. 
When the propeller is rotating in the Ahead direction, the resultant power 
thrust may cause the propeller and rotating blade assembly to move axially 
in the direction of the stationary blade assembly. Due to this movement, 
the position relationship between rotary and stationary blades will 
change. Roller 24 will move with the rotary blades and through the ratio 
of the pilot lever 35 will multiply the movement acting on valve plunger 
131 to move valve 130 quickly towards the piston head to open chamber 151 
through conduit 126 and variable control orifice 127 to the sump 113 
through conduit 148. Should a net, line or other material be ingested into 
the propeller area, the rotating blades will gather it and carry it to the 
stationary blade where it will be cut and carried away by the water flow 
created by the propeller. In the process of cutting the material, a shock 
loading is absorbed by the blades which will have a tendency to move them 
apart. To minimize this reaction, control orifice 127 will restrict the 
flow of fluid from the piston chamber 151 thereby maintaining the blades 
relationship to each other. When the propeller is rotating in the Astern 
direction, the power thrust may cause the propeller and rotating blade 
ring to move axially in the direction away from the stationary blade. Due 
to the valve spring 129, the roller and carrier will follow. Lever 35 will 
rotate on its pivot 36 to quickly open valve 130 to conduit 148 and groove 
145 to permit fluid under pressure to enter piston chamber 151 through 
conduit 128 and control orifice 126. This will cause piston 18 to exert a 
force on the stationary cutter block 7 which will move to maintain the 
blade position relationship required to provide the optimum efficiency of 
the antifouling gear. Consequently, any axial movement of the propeller 
and rotating blade ring will cause the same axial movement in the 
stationary blade assembly, thereby reacting to correct the blade 
relationship regardless of direction or power level acting on the 
propeller. 
An alternative embodiment of the invention, illustrated diagrammatically in 
FIG. 8, employs electronic sensing and control means and hydraulic moving 
means for correct positioning of the non-rotating blade. 
The power to move the non-rotating blade 8 is provided by hydraulically 
pressurized cylinder 61 having a piston and rod assembly 62 that is 
mechanically attached to blade 8. Hydraulic fluid under pressure is 
supplied by remotely located pump 63 through conduits 64 and 65 to 
electrically operated two way valves 66 and 67. The piston end, chamber 
68, of cylinder 61 is connected to both valves 66 and 72 through conduit 
69 and orifice 70. The rod end, chamber 71 of cylinder 61 is connected to 
both valves 67 and 73 through conduit 74. Valves 72 and 73 are connected 
to the hydraulic fluid tank by means of conduits 75 and 76. 
Blade position is monitored by electronic proximity sensors 78 and 79, each 
of which is reading its position in relation to its specific target. In 
this case, sensor 78 is reading its position in relation to the rotating 
blades 5 attached to propeller hub 3, while sensor 79 is reading its 
position in relation to the piston and rod assembly 62. Both sensors are 
immovably mounted relative to the hull. When the blades 5 and 8 are set in 
their correct shearing relationship to one another, both sensors will be 
equidistant from their respective targets and will generate signals of 
equal amplitude. 
Both sensors are connected to control cabinet 77 by cables 80 and 81. 
Electrical power is turned on to supply control cabinet 77 and run 
hydraulic pump 63. A power supply panel located in the control cabinet 
will regulate the voltage and control power surge to protect the 
electronic circuitry. The sensors 78 and 79 are reading their respective 
targets and developing a voltage or current output signal which is 
transmitted to the electronic circuit board through cables 80 and 81. The 
signal levels from sensors 78 and 79 will be compared electronically and 
if a mismatch occurs, a signal will be generated and directed to either 
cables 82 and 83 or cables 84 and 85 to open valves 66 and 73 or valves 72 
and 67 which will cause cylinder 61 to either extend or retract 
respectively. 
When the propulsion machinery is operating in the Ahead mode, the thrust of 
the propeller will cause the hub and rotating blades 5 to move towards 
sensor 78. As this occurs, the sensor output signal will change which will 
immediately be compared to the output signal of sensor 79 and due to this 
error in the compared signals, a new signal will be developed and directed 
through cables 85 and 86 to operate valves 67 and 69 to send hydraulic 
fluid under pressure to the chamber 71 of cylinder 61 through conduit 74, 
and permit hydraulic fluid from chamber 68 of cylinder 61 to go to tank 
through conduits 69 and 75. The non-rotating blade 8 will thus be moved 
axially to maintain its relative position with the rotating blades 5. Any 
increase in thrust that is intense enough to initiate further axial 
movement of the hub will result in further retraction of the piston-rod 
assembly 62 and non-rotating blade 8 to maintain the proper working 
clearance between the blade sets. When the propulsion machinery is 
operating in the Astern mode, the propeller thrust will cause the hub 3 
and blade ring 86 to move away from the hub sensor 78. This will result in 
a voltage or current change which when compared by the electronics will 
initiate a signal through cables 82 and 83 to turn on valves 66 and 73. 
Hydraulic fluid under pressure will be directed through valve 66 and 
orifice 70 to chamber 68 of cylinder 61 via conduits 64 and 69, and at the 
same time chamber 7 of cylinder 61 will be connected to the fluid tank via 
conduits 74 and 76 through valve 73. Piston-rod assembly 62 and 
non-rotating blade 8 will move axially to maintain its relative position 
with blade ring 86. When the hub and blade ring 86 stop their axial travel 
and the sensor signals again equalize, valves 66 and 73 will close thereby 
locking the non-rotating blade 8 in its new position. 
Orifice 70 provides two primary functions and is positioned at the piston 
end of cylinder 61 which sees the greatest fluid flow during operation. 
The first function of orifice 70 is to control the operating speed of the 
cylinder, and the second vital function when a line, net or weed contacts 
the blades 15 is localizing the resulting shock within the chamber 68 of 
the cylinder 61. 
In an alternative embodiment of the invention illustrated diagrammatically 
in FIG. 9, two electronic proximity sensors 78 and 79 sense positions of 
rotary ring 86 and piston assembly 62 respectively and feed signals to 
electrical control 77 to maintain equal spacing of their two targets as in 
the mechanism described above for FIG. 8 with a reversible gearmotor 90 
providing the moving force for moving piston assembly 62 back and forth 
through rack and pinion drive 91. Appropriate controlling power for the 
moving means are supplied through cables 92 and 93 to adjust piston 62 and 
blade 8 to correct position for shearing action between the blades. A 
third sensor 94 senses rotation of the ring 86 and sends a signal via wire 
95 to control 77. Control 77 sends power to gearmotor 90 causing clockwise 
rotation that moves blade 8 away from blade 5 when sensor 94 indicates 
that rotation has stopped. This mechanism ensures adequate spacing between 
the blades when starting Ahead. Piston 62, moving in hydraulic cylinder 96 
forces hydraulic fluid between forward chamber 97 and rear chamber 98 
through conduits 133 and 134. Check valves 136 and 135 cause fluid to flow 
through conduit 133 when piston 62 moves toward the propeller and through 
conduit 134 when piston 62 moves away from the propeller. Constriction 99 
reduces flow through conduit 134 so that blade 8 cannot move away rapidly 
from blade 5 when shearing takes place. 
The above disclosed invention has a number of particular features which 
should preferably be employed in combination although each is useful 
separately without departure from the scope of the invention. While I have 
shown and described the preferred embodiments of my invention, it will be 
understood that the invention may be embodied otherwise than as herein 
specifically illustrated or described, and that certain changes in the 
form and arrangement of parts and the specific manner of practicing the 
invention may be made within the underlying idea or principles of the 
invention within the scope of the appended claims.