Ships – Mooring device – Having ship-mounted turret
Patent
1997-12-23
2000-10-31
Swinehart, Ed
Ships
Mooring device
Having ship-mounted turret
1142301, B63B 2100
Patent
active
061385980
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a method and apparatus for directing a floating structure against the direction of the waves, where the structure is anchored or moored to a buoy at its fora end (in front of the midship area). A floating structure may here include any kind of ship, vessel, boat or floating construction that is designed for use in open waters.
Oil and gas obtained from underground reservoirs at sea, for instance the North Sea, are at present commonly transported to installations on the shore, such as refinery and storage tanks, by means of pipelines arranged on the sea bed. In addition, significant quantities of oil and gas are transported by ship, in particular oil and gas produced at small, distant fields that are not brought into communication with the existing pipe system on the sea bed.
When using a ship for this kind of transport, the ship is connected or moored to a buoy that is anchored close to a platform or a subsea storage installation where the oil or the gas is stored. The oil or gas is transferred from the storage installation to the ship by means of one or more pipe lines provided through the buoy.
Storage and production ships have been gradually employed for storage and production of oil and gas from small fields at sea, or fields where the depth of the sea makes the use of installations resting on the sea bed inconvenient or impossible. Ships of this kind are anchored by means of a turret that most commonly is arranged in the fore end of the ship hull.
In bad weather with strong winds, sea currents and heavy seas, the forces acting on the ship, buoy and moorings may become extremely strong. In particular, strong forces act upon ships that are allowed to swing freely about a mooring point (buoy, anchor or the like) with large amplitudes from one side to the other.
In the open sea, the dominant forces acting on a ship that is moored to swing freely are normally sustained by wave forces. The larger the amplitude of the swinging motion becomes, the more the ship will be influenced by the waves. This is followed by large horizontal movements and forces, and also heave and roll motions that cause heavy loads, resulting in wear and damage of the ship and mooring.
Previously, it was known to direct an anchored ship against the direction of the waves by means of side thrusters arranges in the aft end of the ship. However, such installations are expensive, and represent additional costs in connection with maintenance and repair works.
Furthermore, it is common knowledge in connection with boats, in particular in connection with small fishing boats equipped for fishing with lines or nets, to employ a spanker. A spanker is a sail that is supported by a mast at the aft end of a boat, and it serves to keep the boat against the direction of the wind, and to reduce the rolling motion of the boat. When hauling fishing gear such as nets or lines, it is important to keep the boat against the direction of the wind to avoid the boat drifting across the fishing gear. Thus, a spanker is a sail that is arranged in a direction normally (except when sailing) parallel with the boat.
While a ship is anchored or moored to a buoy or the like in the open sea to load or to produce oil or gas, the primary task is to keep the shop against the direction of the waves in a stable manner, as previously mentioned, to avoid having the ship start swinging (yaw motions) with large amplitudes that may cause heavy loads on the moorings. In addition, large amplitudes of rolling motion may be avoided when the ship is positioned with little directional variation.
SUMMARY OF THE INVENTION
The present invention provides a method and a device that solve the above problems. According to the present invention, the method is characterized in that the floating structure is provided with a wind rudder at its aft end that is adjusted versus the wind direction such that the floating structure is directed against the direction of the waves.
Furthermore, according to the invention the device is chara
REFERENCES:
patent: 1582391 (1926-04-01), Flettner
patent: 3191201 (1965-06-01), Richardson et al.
patent: 3774562 (1973-11-01), Dean, III
patent: 4089287 (1978-05-01), Kranert et al.
patent: 4273066 (1981-06-01), Anderson
patent: 4848258 (1989-07-01), Priebe
Askestad Sigmund
Nielsen Finn Gunnar
Norsk Hydro ASA
Swinehart Ed
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