Submersible drydock

Claim 1

A drydock system comprising, (a) a shore-based stationary dock having an upper face and an outer side wall, (b) a submersible platform having an upper support face, a front end and an underside, said front end being disposed opposite said outer side wall of said shore-based stationary dock, a buoyancy cavity formed in said underside and opening downwardly therefrom, vent means adapted to open to vent said cavity and to close to make the cavity airtight, said platform being capable of submerging under its own weight when said vent means is open and said buoyancy cavity is flooded and being sufficiently buoyant to float and raise a vessel of a predetermined weight from the body of water when said vent means is closed and said cavity is filled with air, (c) foundation means underlying said platform and disposed adjacent said outer side wall of said stationary dock, (d) guide means for guiding said platform along a predetermined path extending in an arc from a raised position in which said front end of said platform is juxtaposed, said outer side wall of said stationary dock to a submerged position spaced outwardly from the stationay dock, said platform moving in a first direction when moving from said lowered position to said raised position and a second direction moving from said raised position to said lowered position, said guide means comprising a parallelogram linkage system interconnecting the platform and the foundation means, said parallelogram linkage system being arranged over top dead center in said first direction when said platform is in said raised position, whereby a loss of buoyancy in the platform would result in the movement of the platform to a position in which the front end thereof bears against the outside wall of the stationay dock thereby preventing significant lowering of the platform, (e) buoyancy control means communicating with said buoyancy chamber for varying the amount of air within said chamber to effect raising and lowering of said platform relative to said foundation means, (f) means for securing said platform against movement with respect to said shore-based stationary dock when said platform is in said raised position.