Abstract: The semisubmersible drilling vessel has two spaced, parallel, horizontal, elongated submersible hulls which support a deck and a deck mounting structure. The deck has a central opening overhanging the space between the two hulls and is surmounted by a derrick. The mounting structure includes at least two vertical columns which connect the ends of the hulls to the deck and at least two hollow columns facing and spaced from one another substantially in the center of each hull. These central hollow columns form caissons on the interior of which is provided pipe manipulation apparatus which accommodates the handling and vertical storage of pipes associated with drilling a well.