The present invention relates to apparatus for mooring a floating vessel in open sea, using a semi submersible floating dock. The apparatus is particularly suitable for tankers carrying liquid natural gas in cryogenic form which can be a dangerous substance to handle and hence offshore terminals are preferred. The apparatus comprises a semi-submersible floating dock (1) for receiving a vessel (10) and a single point mooring system (5), with a rigid arm (3) between the two. The dock (1) is pivotally connected to the arm (3). The single point mooring system (5) comprises a mooring buoy (17) secured to the seabed by a compliant anchoring system such as a number of catenary anchor legs (15). This allows vertical movement of the mooring buoy (17) but constrains the movement to a relatively small column of water.