Ships – Mooring device – Boom type
Patent
1997-03-31
1998-10-06
Swinehart, Ed L.
Ships
Mooring device
Boom type
441 4, B63B 2152
Patent
active
058161830
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a Catenary Anchor Leg Mooring (CALM) buoy comprising a body with buoyancy, means for connecting the buoyant body to catenary anchor chains to anchor the body to the seabed, a turntable being rotatable with respect to the body with buoyancy, said turntable having mooring means for a floating unit such as a vessel, a swivel and means for connecting at least one hose between at least one swivel and a submerged pipe structure extending over or into the seabed to any subsea well or the like, as well as means for connecting at least one hose between at least one swivel and at least one vessel.
A CALM buoy serves for mooring a floating unit, such as a vessel, and for connecting said floating unit to a submerged pipe structure extending over or into the seabed to any subsea well or the like.
BACKGROUND OF THE INVENTION
CALM buoys are well known as being buoys with buoyancy floating at sea level. Because of said floating at sea level the CALM buoys are affected by severe loads caused by forces exerted upon the hawser lines by the vessel floating to and from the buoy forces exerted on the means connecting the buoy with the vessel, and forces exerted upon the catenary chains anchoring the buoy to the seabed, by the action of waves to the buoyant body of the buoy. As a rule they have own stability and therefore volume.
To connect floating units, such as vessels, to a mooring buoy and to a submerged pipe structure extending over or into the seabed to any subsea well or the like, several proposals are known from the prior art.
To solve the problems of these forces U.S. Pat. No. 3,823,432 and U.S. Pat. No. 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. The 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 common plane of symmetric. 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.
However, 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 said 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.
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 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. Said large structures involve high cost to produce and to maintain these structures.
U.S. Pat. No. 4,617,000 discloses a much smaller buoy not being co
REFERENCES:
patent: 3750723 (1973-08-01), Schirtzinger
patent: 4516942 (1985-05-01), Pedersen
patent: 5288253 (1994-02-01), Urdshals et al.
Braud Jean
Brown Paul Anthony
O'Nion Geoffery
Single Buoy Moorings Inc.
Swinehart Ed L.
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