To connect floating units, such as vessels, to a mooring buoy several proposals are known from the prior art.
U.S. Pat. Nos. 3,823,432 and 3,908,212 both disclose a single point mooring buoy having a buoyant body which is small with respect to the floating unit, and around which the floating unit can weathervane. The vessel and buoy are interconnected by a rigid arm. This arm has a horizontally disposed hinge interconnecting the floating unit and the buoyant body so that they can achieve an angular displacement at need with respect to each other in a vertical commonplane of symmetry. The size and thereby the mass of the buoyant body is chosen so that it offers very little resistance to the action of waves thereon. Vividly the mooring buoy will follow the motions of the floating unit as well as the motions of the sea surface. The amplitude and frequency of the primarily cyclic motions of the floating unit and the sea surface differ substantially from one another. Such different motions may result in heavy loads exerted on the catenary anchor lines as well as the hinge mentioned above.
The above mentioned known arrangements of a small buoy which by means of a rigid arm is held by the vessel like a barrow does already reduce the loads under the majority of circumstances. However, it may occur that the combination of forces on one hand of the vessel through arm and buoy on part of the catenary lines, in particular if already drifted away from its proper location, and on the other hand of the waves leads to unexpected overloads. These loads appear to be that heavy that the maximum allowable tensions in the catenary anchor lines and in the hinge will be exceeded easily causing line failure and breaking of the pivot respectively.
Moreover, structures of both buoyant body and interconnection means may not the best for use in ice-infested waters. The body of the buoy may strike ice floes during said movements causing even more heavy loads to be exerted on the catenary anchor lines and the hinge.
Alternatively, large semi-submersible mooring buoys are known, for instance from U.S. Pat. No. 4,784,079. Such large structures are particularly indifferent to the motions of the sea surface because of their size being relatively large in view of the amplitude of the waves. These structures are indifferent also to the motions of a vessel interconnected thereto because of their size and mass which may be equal to or even larger than those of said vessel. In U.S. Pat. No. 4,784,079 a rather complex structure for interconnecting the buoyant body and the vessel is shown, primarily to cope with the motions of the floating unit relative to the buoyant body. To this end the connecting means are designed to act like a spring.
The object of the invention is to minimize the loads exerted on both the catenary anchor lines and the hinge caused by the motions of the sea surface and the floating unit relative to the buoyant body.