Dock compensator

A constant force dock compensator that provides an mooring system for floating docks. The dock compensator is comprised of constant force power springs, a reel around which sufficient lengths of cable are wound, and a case containing the springs, cables and reel. The dock compensator is attached underneath a floating dock. The cables are withdrawn from the dock compensator and attached to weights placed on the floor of the body of water. The springs maintain a constant pull-force on the cables to hold the dock in place, and the cables automatically dispense or retract to compensate for changes in water level. Thereby, the dock has some leeway in terms of movement in response thereto, but is eventually stabilized by the dock compensator.

FIELD OF THE INVENTION 
The present invention relates to the field of recreational and commercial 
boating. Specifically, the present invention relates to the field of a 
mooring mechanism for floating docks. 
BACKGROUND OF THE INVENTION 
A floating dock is a very common method to secure a boat and gain access to 
it. People can readily embark and disembark the boat or ship tied 
alongside the dock. In the prior art, a floating dock is typically 
connected to either pilings, cables with manual adjusting winch or cables 
with counter weights to secure it in place. Otherwise, the dock would 
drift away. 
A piling is a pole similar to a telephone pole, or it may be made of steel 
or concrete. Pilings are driven vertically into the floor of a body of 
water. The pilings are of sufficient length to extend above the surface of 
the water. The dock floats on the water, and is connected to the pilings 
by retaining rings that reside in the floating dock or is fixed to lengths 
of cables or chains that are of sufficient length to permit the dock to 
rise and fall with changes in water level due to, for example, high and 
low tides. The fixed cable or chain type can be adjusted by either a 
manually adjusted winch or with the use of counter weights. 
If cables or chains are used instead of pilings, the sea anchors are placed 
on the floor of the body of water. The dock floats on the water, and in 
the prior art is connected to the sea anchors by fixed lengths of cables 
or chains as described above. 
The prior art method of mooring a floating dock in place engenders several 
disadvantages. The connecting cables or chains are of a fixed length, and 
must be long enough to accommodate the maximum anticipated change in water 
level and/or require regular manual adjustment to remove the cable slack. 
When the water is not at its maximum level, there is a significant amount 
of slack in the cables or chains. This allows even relatively minor 
perturbations, such as the wake of a passing boat, to cause the dock to 
move significantly up and down and also side to side, making the dock 
unstable. There is also no dampening of the dock's motion beyond the 
natural dampening of the water itself, so the dock will move for a long 
period of time, and will continue to move until the water stops moving. It 
is difficult to stand or move about on a dock that is simultaneously 
moving in various directions, and objects and supplies placed on the dock 
are also caused to move around unexpectedly. 
Furthermore, the slack in the cables or chains allows the dock to drift 
horizontally from its original position, due to forces acting on the dock 
from wind, waves, and changing tide. A drifting dock poses a concern to 
adjacent docks and boats. Also, the dock will drift to the point where at 
least one of the cables or chains is taut, placing a significant stress 
load on the fittings to which the cable or chain is attached, or on the 
fittings and hinges connecting the dock to the dock ramp. This could lead 
to failure of a fitting, creating a need for immediate repair. 
In addition, depending on the placement of the pilings or weights, the 
cables or chains connected to them from the dock may extend into areas 
where they create a hazard for individuals and/or boats. For example, a 
cable running underneath the water beyond the edge of the dock could be 
hit by someone diving or swimming, or could be hooked by the outboard 
drive gear of a passing boat. 
The use of pilings introduces additional disadvantages that are not present 
if weights are used. The pilings disturb the floor of the body of water 
when they are driven through and into it. If telephone poles are used, the 
creosote, oil or tar present in the pole will leach into the water. 
Concrete will also leach into the water. The leaching contributes to water 
pollution, and also may cause deterioration of the pilings to the point 
where eventually they require replacement. Pilings are expensive, and 
therefore the initial cost of a dock that utilizes them is high. Should 
replacement of the pilings be required, the lifetime cost of the dock is 
even more substantial. Finally, the pilings protruding from the water may 
be unsightly, especially if they are not periodically cleaned. 
Furthermore, pilings greatly loose their effectiveness in water depths 
beyond 25' because of excessive bending or flexing. 
Thus, there is a need for an apparatus that avoids the problems described 
above while addressing the concerns associated with prior art methods for 
mooring a floating dock. It would be highly preferable if such an 
apparatus allows vertical movement of the dock corresponding to changes in 
water level. Such an apparatus should also prevent the dock from drifting 
from its original position, and would compensate for lateral forces on the 
dock due to wind, waves, and currents. It would also be highly preferable 
if the apparatus actively dampens dock motion so as to maintain a stable 
surface and quickly return the dock to its initial ("neutral") position. 
In addition, it would be highly preferable because the apparatus 
eliminates the need for pilings. 
Accordingly, it is the object of the present invention to allow sufficient 
vertical movement of a floating dock to account for changes in water 
level, either shorter term changes such as waves or longer term changes 
such as tide. In addition, it is the object of the present invention to 
maintain the dock in its original horizontal position, by applying 
sufficient pulling force on the connecting cables so that there is no 
slack in the cables, and by compensating for lateral forces on the dock. 
It is also the object of the present invention to quickly dampen dock 
motion to maintain a stable surface and return the dock to its neutral 
position. 
Furthermore, it is the object of the present invention to provide a 
cost-effective and environmentally sound design that eliminates the need 
for pilings. Finally, it is the object of the present invention to be 
safe, compact and durable, and compatible with current floating docks. 
SUMMARY OF THE INVENTION 
The present invention pertains to a Dock Compensator which is designed to 
provide a mooring system for floating docks, using cables connected to sea 
anchors in the water. The present invention allows a floating dock to move 
vertically with changes in water level, but dampens the movement to 
maintain a stable surface and return the dock to its original position. 
The present invention also prevents the dock from drifting from its 
original position, by compensating for lateral forces on the dock and by 
dispensing only the required length of cable so that there is no slack in 
the cable that would allow the dock to drift. In addition, the present 
invention does not require the use of pilings. 
In its preferred embodiment, the present invention is comprised of constant 
force power springs, an arbor (shaft), a reel assembly, two stainless 
steel cables, and an outer case. The number of springs utilized by the 
present invention can be varied depending on the amount of pull-force 
desired; therefore, the concept of the present invention allows sufficient 
design flexibility such that the present invention can be utilized for 
large marina and/or small private dock installations. In the currently 
preferred embodiment of the present invention FIGS. 4A and 4B, three and 
ten springs are used respectively. 
The springs are mounted parallel to each other with their center points in 
alignment, with spacers in between the springs to reduce friction and to 
prevent them from interfering with each other. The end at the center of 
each spring is attached to the same single arbor, which is secured at each 
end to the outer case. The other end of each spring is attached to the 
same single reel assembly, which rotates with the arbor as its center 
axis. Two steel cables of sufficient length are wound around the same 
single reel. 
The springs are either stainless steel or treated carbon steel and are 
designed to exert a constant torque, or pulling force, on the reel. The 
constant torque capability of the springs is necessary for the present 
invention to accomplish its design objectives over the entire range of the 
springs and, concurrently, over the entire length of the cables. The 
amount of torque provided by the springs is by design small enough to 
allow the cables to extend as needed in response to waves or the changing 
tide, so that the dock is permitted to continue to float on the surface of 
the water. However, the amount of torque provided by the springs is by 
design large enough to dampen the motion of the dock caused by waves, so 
that the dock is quickly returned to its initial stable position. The 
amount of torque is also large enough to limit the amount of cable that is 
dispensed from the present invention, so that there is no slack in the 
cable. 
The two cables are wound side-by-side but are separated by a ring, or 
guide, that prevents the cables from tangling with each other. The reel is 
designed to hold the sufficient length of the cables, and to dispense and 
rewind the cables within the number of revolutions permitted by the range 
of application of the springs. Each cable passes through its own opening 
in the outer case. The openings are flared and equipped with rollers to 
reduce friction, so that the cables can be more easily dispensed and 
retracted. The outer case contains the springs, the arbor, the reel, and 
the cables. 
Additional features of the currently preferred embodiment of the present 
invention are implemented to make it durable and resistant to corrosion, 
easy to install and use, and compatible with current floating docks. The 
present invention is used as follows. The present invention is mounted 
either on the underside or on top of the dock, at the dock's center point. 
Two cement blocks or similar weights are placed on the floor of the body 
of water, one at each end of the dock. The steel cables are unwound from 
the reel, and one cable is attached to one weight, and the other cable is 
attached to the second weight. Because the cables are both around the same 
reel, the length of each cable that is dispensed will be equal. Unwinding 
the cables from the present invention compresses the springs. 
After the cables are attached to the weights, the constant pull force of 
the springs retracts the cables and removes any slack. As above, because 
the cables are wound around the same reel, each cable is also retracted by 
the same amount. With each cable at an equal length, the dock will remain 
in position until it is disturbed by a change in water level. When the 
water level changes, an equal length of each cable is dispensed or 
retracted depending on whether the water level increases or decreases. The 
present invention is designed to achieve equilibrium on the cables. If the 
dock is pushed laterally, 100% of the force of the power springs will 
transfer to the cable which is under load. For example, when the tide is 
rising, the cables extend (each by the same amount), and there is no slack 
in the cables because the power springs maintain a constant pull-force on 
them. For a shorter perturbation, such as a wake from a passing boat, the 
dock rises with the wave and the cables extend. The constant pull-force of 
the power springs serves to dampen the dock motion and quickly return the 
dock to its neutral and stable position. In a similar manner, the present 
invention compensates for lateral motion of the dock due to wind, waves 
and current.

DETAILED DESCRIPTION OF THE INVENTION 
In the following detailed description of the present invention, numerous 
specific details are set forth in order to provide a thorough 
understanding of the present invention. However, it will be obvious to one 
skilled in the art that the present invention may be practiced without 
these specific details. In other instances, well known methods, 
procedures, components, and materials have not been described in detail so 
as not to unnecessarily obscure aspects of the present invention. 
With reference to FIGS. 1A, 1B, 1C and 1D, the present invention reel 
assembly 100, power springs 110, outer case 120, frame 160, cable(s) 130, 
brake lever 161, brake actuator 162, brake band 163 and arbor 140 are 
illustrated. FIGS. 1A and 1D are a cut-away side view, and FIGS. 1B and 1C 
are a cut-away front view. The present invention is a device consisting of 
constant force stainless or carbon steel power springs 110 mounted within 
a reel assembly 100, which in turn is within an outer case 120 or frame 
160. With reference to FIGS. 1B and 1D, in the currently preferred 
embodiment three and ten springs are used respectively; however, the 
number of springs is variable in alternative embodiments depending on the 
size of the application. 
Separation between the springs is maintained by spacers 111. One end of 
each spring is attached to the single common arbor 140, and the other end 
of each spring is attached to the single common reel assembly 100. The 
springs 110 are attached to a single arbor and reel assembly to increase 
the total pull-force of the springs by taking advantage of the synergistic 
effect associated with such a mounting. In addition, such a mounting 
eliminates any undesirable effects associated with variability in spring 
performance; therefore, it is not necessary to ensure that each spring 
performs identically or to compensate for differences in performance. 
With reference still to FIGS. 1A, 1B, 1C and 1D, the reel assembly 100 
holds two separate 3/16"-1" steel cables 130. The cables 130 are located 
within one single reel assembly, so that when the reel assembly rotates by 
a particular amount, an equal length of each cable is dispensed or 
retracted. This is an important feature of the present invention, because 
it ensures that the dock will stay in one position, and return to that 
position if the dock is moved. Separation between the two cables is 
maintained by a guide 101. The cables 130 are of sufficient length to 
compensate for water level changes of up to thirty feet. 
At the end of each cable 130 is a wire thimble 131 used to attach the 
cables to concrete weights placed on the floor of the water body. The 
present invention transfers the torque from the springs 110 through the 
reel assembly 100 and cables 130. The present invention is attached to the 
underside or on top of the floating dock, and the cables 130 are extended 
and attached to concrete weights located at each end of the dock (refer to 
FIG. 5). The pull-force of the springs 110 will maintain the dock in a 
stable position and will compensate for long term changes in water level 
(e.g., due to tide), and return the dock to its initial and stable 
position after a short term change in water level (e.g., a wave or the 
wake of a passing boat). 
With reference to FIGS. 2A and 2B, a side-view of a single power spring 110 
is illustrated. Each power spring 110 is attached to an arbor 140. The 
other end of each spring 110 is attached to feature 143 on the reel 
assembly hub 142. Each spring 110 is made of stainless or carbon steel and 
is designed for a satisfactory fatigue life. Each spring 110 is designed 
to exert a constant torque; that is, as the springs 110 are compressed or 
released, the relationship of the pulling force to the amount of 
compression is linear. Whether the springs 110 are either fully compressed 
or fully expanded, the amount of pulling force exerted by the springs 110 
is constant. Therefore, if the cables 130 are extended by any amount up to 
their limit, the springs 110 will exert sufficient torque to rewind the 
present invention cables back onto the reel assembly 100 (FIG. 1A or 1D), 
returning the dock to its initial position. 
With reference still to FIGS. 2A and 2B, the springs 110 are designed to 
exert a specified amount of torque. The amount of torque provided by the 
present invention springs 110 is by design sufficient to maintain a 
floating dock in its initial and stable position. However, the amount of 
torque provided by the springs 110 is by design small enough to still 
permit the present invention cables 130 to extend as needed in response to 
waves, passing boats, the rising tide, and gusts of wind. Nevertheless, 
the amount of torque provided by the springs 110 is by design sufficient 
to return the dock to its initial and stable position after the 
disturbance has ended. In the currently preferred embodiment, between 
approximately ten and one-hundred thirty pounds of pull-force is 
implemented per spring 110; however, by design the present invention takes 
advantage of the synergistic effect associated with having springs mounted 
side by side on a single arbor, so that the total pull-force of the 
currently preferred embodiment of the present invention is between forty 
and one-thousand three hundred pounds. 
With reference to FIGS. 3A, 3B, 3C and 3D the arbor 140 is illustrated. A 
notch 501 is cut through the length of the arbor 140. One end of the 
spring 110 (FIGS. 2A and 2B) is fixedly attached to arbor 140 via notch 
501. The other end of the spring 110 (FIGS. 2A and 2B) is fixedly attached 
to a feature 143 (FIGS. 2A and 2B) on the reel case hub 142 of the reel 
assembly 100 (FIGS. 2A and 2B). Referring back to FIGS. 1A, 1B, 1C, 1D, 2A 
and 2B, the springs 110 are attached between the arbor 140 and feature 143 
on the reel case hub 142 of the reel assembly 100. The reel assembly 100 
and the springs 110 therefore work in conjunction with each other. 
Rotation of the reel assembly 100 in one direction or the other will cause 
the spring 110 to compress or expand accordingly, which transfers the 
corresponding torque from the springs 110 to the reel assembly 100. 
Referring back to FIGS. 1A, 1D, 2A and 2B, the reel assembly 100 is 
centered on the shaft 140 inside the case 120 or frame 160. The size of 
the reel assembly 100 is governed by the number of rotations of the reel 
permitted by the springs 110. In other words, the reel assembly 100 is of 
the proper size needed to permit the entire length of cables 130 to be 
dispensed and retracted, without exceeding the design capabilities of the 
springs 110 to correspondingly compress and expand. 
Referring to FIGS. 4A and 4B and also back to FIGS. 1A, 1B, 1C and 1D the 
reel assembly 100 and springs 110, including the shaft 140, are enclosed 
within an outer case 120 or frame 160. In the currently preferred 
embodiment, the outer case 120 and frame 160 is composed of high quality 
marine materials to provide resistance to corrosion. In the currently 
preferred embodiment FIG. 4A, the outer case is solid except for opening 
121 to allow access to the cables 130 if needed. In the currently 
preferred embodiment FIG. 4B, the frame 160 is open allowing access to the 
cables 130 if needed. For structural rigidity in FIG. 4A, the opening 121 
is bridged by center bar 122. The outer case 120 also incorporates two 
additional smaller openings 125. The cables 130 come off the reel at 
different points, and each passes through its own opening 125. For 
structural rigidity in FIG. 4B, the frame 160 is designed with a truss 
configuration. The cables 130 come off the reel at the same point, and 
each passes through the opening at the bottom of the frame 160. 
In FIG. 4A the smaller openings 125 are flared with a roller assembly 126 
to reduce friction on the cables as they pass through. The smaller 
openings are mounted on bars 127. The preferred orientation of the smaller 
openings 125 is 90 degrees relative to each other. This design feature 
permits the present invention to be mounted on smaller floating docks, 
with the cables 130 extending below the dock at a more vertical angle so 
that they don't extend beyond the edge of the dock. 
With reference still to FIG. 4, the arbor 140, about which the reel 
assembly 100 (FIG. 1A) and springs 110 (FIG. 2) are mounted, is passed 
through each side of the outer case 120 so that it is permitted to rotate 
freely. In the currently preferred embodiment, the arbor 140 is held in 
place using cotter pins. With reference to FIG. 5, the application of the 
present invention to anchor a floating dock is illustrated. The present 
invention is attached at the center point of the floating dock and 
attached to weights on the floor of the body of water. 
The preferred embodiment of the present invention, a floating dock mooring 
system, is thus described. While the present invention has been described 
in particular embodiments, it should be appreciated that the present 
invention should not be construed as limited by such embodiments, but 
rather construed according to the following claims.