A method of using a floatable offshore depot, the method comprising: a. providing a sheltered area inside a buoyant hull configured as a tunnel for safe and easy launching or docking of a watercraft, wherein the tunnel comprises a first tunnel side and a second tunnel side between which the watercraft is received; b. providing an internal dock side within the tunnel for embarkation or debarkation of personnel, wherein the first tunnel side is located at a first side of the internal dock side and the tunnel further comprises a lower tapering surface located at a second side of the internal dock side opposite to the first side; c. providing the sheltered area inside the buoyant hull configured as the tunnel with the internal dock side for transferring equipment between the watercraft and the floatable offshore depot; wherein the internal dock side allows the personnel to step off like a dock, or the equipment to be stored; wherein the floatable offshore depot comprises: (i) the buoyant hull with a hull planform that is circular, oval, elliptical, or polygonal; (ii) a matching keel and a main deck, wherein the main deck and the matching keel are configured for offshore stability; (iii) a plurality of dynamic movable tendering mechanisms (24a-24h) disposed within and connected to the first tunnel side and the second tunnel side, wherein the plurality of dynamic movable tendering mechanisms (24a-24h) is arranged spaced apart from one another along at least part of the first tunnel side and the second tunnel side; and (iv) at least two connected sections engaging between the matching keel and the main deck, the at least two connected sections joined in series and symmetric about a vertical axis with the at least two connected sections extending downwardly from the main deck toward the matching keel, the at least two connected sections comprising at least two of: 1. an upper cylindrical side section; 2. a transition section; and 3. a lower cylindrical section; and wherein the tunnel of the buoyant hull formed within the buoyant hull for receiving the watercraft when the buoyant hull is at a floating operational depth, the tunnel comprising: a tunnel opening in the buoyant hull opening to an exterior of the buoyant hull and dimensioned so as to receive the watercraft; and further wherein the floatable offshore depot is configured to be floatable to transition from the floating operational depth or a floating transit depth to resting on a seabed. a. providing a sheltered area inside a buoyant hull configured as a tunnel for safe and easy launching or docking of a watercraft, wherein the tunnel comprises a first tunnel side and a second tunnel side between which the watercraft is received; b. providing an internal dock side within the tunnel for embarkation or debarkation of personnel, wherein the first tunnel side is located at a first side of the internal dock side and the tunnel further comprises a lower tapering surface located at a second side of the internal dock side opposite to the first side; c. providing the sheltered area inside the buoyant hull configured as the tunnel with the internal dock side for transferring equipment between the watercraft and the floatable offshore depot; (i) the buoyant hull with a hull planform that is circular, oval, elliptical, or polygonal; (ii) a matching keel and a main deck, wherein the main deck and the matching keel are configured for offshore stability; (iii) a plurality of dynamic movable tendering mechanisms (24a-24h) disposed within and connected to the first tunnel side and the second tunnel side, wherein the plurality of dynamic movable tendering mechanisms (24a-24h) is arranged spaced apart from one another along at least part of the first tunnel side and the second tunnel side; and (iv) at least two connected sections engaging between the matching keel and the main deck, the at least two connected sections joined in series and symmetric about a vertical axis with the at least two connected sections extending downwardly from the main deck toward the matching keel, the at least two connected sections comprising at least two of: 1. an upper cylindrical side section; 2. a transition section; and 3. a lower cylindrical section; and 1. an upper cylindrical side section; 2. a transition section; and 3. a lower cylindrical section; and