A mono hull vessel for retrieving and deploying equipments in offshore region comprising a deck box with an upper deck (2) at its top said upper deck having a lifting and lowering device (3,3′), a hull/pontoon (1) at the base of said vessel, the vessel is characterized in that said hull/pontoon (1) is connected to the deck box by a plurality of columns (4) and said hull/pontoon (1) is made in one piece and is continuous to form the platform for a lower deck (5), the upper and lower deck being configured to allow lifting and lowering of equipment therefrom and thereon respectively.