Means for raising vessels by use of semi-submergible docks, nearly all of which are floating vessels and constructed to receive the vessel upon its bottom or upon a platform or equivalent way, the dock being raised by changing the line of flotation through buoyancy by ejecting or pumping water from the water-tanks or by changing ballast.
(1) Note. Compare with this class, subclasses 258+.
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49, and 53, for structures that are to be entirely submerged.
