Another novel feature was in the method of controlling the depth of submergence when navigating between the surface and waterbed.
Built to further demonstrate the possibility of navigation over the waterbed of seas or the ocean.
1610s, "a bed on board a ship," from water (n.1) + bed (n.). As a water-tight mattress filled with water, it is recorded from 1844, originally for invalids. Reinvented c.1970 as a hip furnishing.