A heavy-lift ship is a vessel designed to move very large loads that cannot be handled by normal ships. They are of two types: * Semi-submersible ships that take on water ballast to allow the load—usually another vessel—to be floated over the deck, whereupon the ballast is jettisoned and the ship's deck and cargo raised above the waterline. * Project cargo ships that use at least one heavy-lift crane for handling heavy cargo and sufficient ballast to assure stability and sea-keeping properties.