There are many lift mechanisms in use today. Elevators are one form, lifting and lowering people and other loads, usually within buildings. Another form of lift is a hydraulic lifts that is used to raise vehicles in service stations, allowing mechanics to work from beneath the vehicles. Jacks are also lifts that raise vehicles allowing for changing of tires. The list continues, but in general, the lift mechanisms in use today make space/speed tradeoffs that limit usability in certain applications such as watercraft.
For example the hydraulic lifts used to hoist vehicles in your neighborhood garage performs well for its intended purpose, but will not perform well as a lift on a watercraft for several reasons. The first reason is speed. Such lifts are very slow. In many at-sea situations, there are often reasons for quick operation. It is often important to deploy a life raft or return a dingy to the deck and due to emergencies or high surf, the operation must be performed relatively quickly without precluding the use of a service station type of lift that often requires several minutes to lift an object eight feet.
The next reason why a garage-type lift will not function in a watercraft is vertical displacement. For example, to lift a vehicle eight feet, the hydraulic cylinder must be set at least eight feet into the floor, and likely at least ten feet. This is easily accomplished beneath the floor of a service station, but in many of watercraft, there is insufficient clearance between the deck of the watercraft and the hull of the watercraft. Many a watercraft do not have sufficient vertical displacement for a garage-type lift, especially in areas of the watercraft towards the bow where the hull slopes upward, closer to the deck, for cutting through waves.
The next reason why a garage-type lift will not function in a watercraft is weight. The overall weight of such a hydraulic cylinder and the hydraulic fluid needed to lift the requisite distance will be a burden to many a watercraft and even if the watercraft is large enough to support the weight, the excess weight will impact fuel economy and the ability to bring the watercraft up on plane.
Another reason why a garage-type lift will not function in a watercraft is stability. Such a lift operates well on stable ground, but in a watercraft, wave motion and winds create instability. When operating certain payloads on a garage-type lift within a watercraft, stability is often required. For example, when extending a hoist to lift a dingy out of the sea, sudden movement of the hoist due to movement of the lift mechanism is often disastrous. Certain movement results in damage to the dingy and/or sinking of the dingy.
Other lift mechanisms are not suited for watercraft for similar or different reasons. For example, elevators are not practical because such require overhead pulley systems which are not feasible on most watercraft.
What is needed is a lift system that will quickly deploy and retract a payload while occupying minimal vertical space and adding minimal weight to a vehicle such as a watercraft.