|Although most heavy lifts are done with the ship’s own equipment, some ports have a floating crane. This is the Canute at Southampton which has a 200 tonnes capability
This is is a semi-submersible vessel. As the term semi-submersible implies, the vessel can load and unload main-deck cargo by sinking low enough to allow cargo to float on and off. This is accomplished by a process known as ballasting, taking on water in special internal tanks which can lower the ship up to 26 feet below her normal draft in about six hours. It takes about the same amount of time to return the vessel to her normal draft. Though semi-submersibles were designed primarily to move large and unwieldy off-shore oil rigs, they soon proved equally adept at transporting small naval vessels and other military hardware.