1. Field of the Invention
This invention relates, generally, to boat lifts. More particularly, it relates to a four-cable boatlift having a master/slave cable system.
2. Description of the Prior Art
Lifting a boat from the water with a piling-mounted boatlift is problematic. Typically, a winch is used to wrap cables around drums when a boat is lifted and to unwrap the cables from the drums when a boat is lowered. Many boatlifts provide one winch for each cable, there being a winch on each piling. In addition to the expense of four winches, systems of this type also have the drawback caused by different winches operating at differing speeds. Thus, if one of the four winches operates slower or faster than the others, the boat will be unevenly lifted.
Some systems therefore use two winches, one for the inboard (dockside) end of the boatlift and one for the outboard end thereof. Still, if the two winches do not operate at the same speed, an uneven lift occurs. Uneven lifts are undesirable because a boat supported unevenly may slide from the boatlift.
Three piling systems are introduced by the present inventor in a co-pending U.S. patent application entitled xe2x80x9cThree Piling Boat Liftxe2x80x9d filed Jan. 3, 2001, bearing Ser. No. 09/681,095. However, that system also relies upon two independent winches.
What is needed, then, is a cable transmission system that synchronizes the winding and unwinding of cables around their respective drums so that boats are lifted evenly.
However, in view of the prior art considered as a whole at the time the present invention was made, it was not obvious to those of ordinary skill in the pertinent art how such need could be fulfilled.
The long-standing but heretofore unfulfilled need for a synchronous cable transmission system for lifting boats is now met by a new, useful, and nonobvious invention.
A three piling boatlift embodiment of the invention includes an upstanding inboard piling and a pair of upstanding outboard pilings disposed in transversely spaced apart relation to the inboard piling and in longitudinally spaced apart relation to one another. A truncate rigid plate is positioned in closely spaced relation to the inboard piling and in substantially parallel relation to the pair of outboard pilings. A first beam has an inboard end secured to a first end of the truncate rigid plate and an outboard end disposed in closely spaced relation to a first outboard piling of the pair of outboard pilings. A second beam has an inboard end secured to a second end of the truncate rigid plate and an outboard end disposed in closely spaced relation to a second outboard piling of the pair of outboard pilings.
A cable drum assembly is mounted to the inboard piling near an upper end thereof in vertically spaced relation to the truncate rigid plate and includes a longitudinally disposed master cable drum and a slave cable drum disposed in transversely spaced apart, parallel relation to the master cable drum. The master cable drum and the slave cable drum are disposed in a common horizontal plane. A motor means rotates the master cable drum. An interconnecting means translates rotation of the master cable drum into simultaneous and corresponding rotation of the slave drum.
A first master cable extends from a first end of the master cable drum to the first piling of the pair of outboard pilings and is adapted to lift the outboard end of the first beam when the master cable drum is rotated in a first direction and to lower the outboard end of the first beam when the master cable drum is rotated in a second direction. A second master cable extends from a second end of the master cable drum to the second piling of the pair of outboard pilings and is adapted to lift the outboard end of the second beam when the master cable drum is rotated in a first direction and to lower the outboard end of the second beam when the master cable drum is rotated in a second direction.
A first slave cable extends from a first end of the slave cable drum to a first end of the truncate rigid plate and is adapted to lift the inboard end of the first beam when the slave cable drum is rotated in a first direction and to lower the inboard end of the first beam when the slave cable drum is rotated in a second direction. A second slave cable extends from a second end of the slave cable drum to a second end of the truncate rigid plate and is adapted to lift the inboard end of the second beam when the slave cable drum is rotated in a first direction and to lower the second beam when the slave cable is rotated in a second direction.
The weight of a boat lifted and lowered by the boatlift is therefore distributed substantially equally between the first and second master cables and the first and second slave cables. Moreover, all of the cables are in synchronization with one another so that the boatlift is lifted and lowered in a substantially level plane.
The primary object of this invention is to provide a synchronous cable transmission system where all of the cables in the system are synchronized with respect to one another to avoid uneven boat lifting.
A more particular object is to provide a boatlift where a single winch drives a single master cable drum and all parts connected thereto.
These and other important objects, advantages, and features of the invention will become clear as this description proceeds.
The invention accordingly comprises the features of construction, combination of elements, and arrangement of parts that will be exemplified in the description set forth hereinafter and the scope of the invention will be indicated in the claims.