Abstract: A drilling tender (2) has a pair of laterally spaced buoyant hulls (4) with ballast chambers to permit the hulls to be moved between a submerged condition and a surface floating condition. Each hull (4) supports a row of columns (8). The columns (8) support a working platform (10) including a main deck (12) and a pipe rack deck (30) above the main deck (12). A bow deck (48) above a forward portion of the pipe rack deck (30) has mounted on a corner portion thereof a main heavy duty crane (50). The support structure for the crane (50) extends downwardly through the decks (12, 30, 48) and down into one of the columns (8). Between the main and pipe rack decks, the support structure is formed by a plurality of bulkheads. These bulkheads have portions extending down into the column (8) to transmit forces created by operation of the crane (50) to the column (8).