Ships – Anchor – With means driving the anchor into the sea bed
Patent
1980-01-02
1982-08-31
Blix, Trygve M.
Ships
Anchor
With means driving the anchor into the sea bed
114301, B63B 2126
Patent
active
043466630
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a new anchoring system.
The anchoring system according to the invention is in particular, suitable for securing in position floating structures such as chips, offshore drilling and hydrocarbon production platforms, etc. This anchoring system is also suitable for anchoring structures on land.
Conventional anchoring system of positioning a plate, or hook in the ground, to which a horizontal pull is subsequently applied by means of a rigid rod or shank connected to a chain by means of an eyelet.
The weight of this anchor is high so as to permit the initial penetration of the flukes or hooks into the ground, this penetration being only slight when the anchor is just laid onto the ground and subsequently increasing as the anchor is dragged. Ahead of the buried fluke of the anchor, the ground acts as an abutment and a wedge similar to the Coulomb's wedge is formed: the anchor and the ground wedge would have a tendency to glide upwardly in the absence of the anchor weight which maintains the anchor fluke or flukes buried at a certain depth, thus providing for a kinematic equilibrium, so that it is often assumed that the holding power of an anchor, (i.e. the highest admissible horizontal pull F), is proportional to the anchor weight P. Depending on the anchor shape, the ratio (F/P) comprises a value of between 5 and 15 for a sandy water bottom, and between 8 and 20 for a clayish bottom.
Thus high capacity anchors are very heavy, weighing up to 10 or 15 tons.
An additional requirement is that the anchor must always be positioned correctly for gripping the ground when it is laid, irrespective of the configuration of the water bottom. This has lead to anchor shapes generally having two planes of symmetry, such as the very conventional and well known grapnel type anchor or anchors having hinged mechanisms allowing pivoting about a shaft at the end of the anchor shank and perpendicular thereto, such mechanisms providing for symmetrical positions of the anchor.
Moreover, since the anchor must be weighed at the end of the mooring period, additional devices are sometimes used to facilitate this operation.
SUMMARY OF THE INVENTION
An object of the invention is to provide an anchor of substantially reduced size and weight as compared to the conventional anchors of the same holding power.
Another object of the invention is to provide an anchor which can be more easily placed in position.
French Pat. No. 1,562,678 already discloses an anchor comprising a curved plate having a plane of symmetry with a circular arc cross-section, as well as the same type of cross-section along planes parallel thereto. A suitably adapted device permits connection of this plate to a chain or to an anchor cable, with the connecting device located in the plane of symmetry of the plate and secured thereto so that the anchor chain or cable exerts at its connection point, a pull directed outwardly from the convex side of the plate.
This connecting device is preferably positioned at the center of gravity of the plate, or in the vicinity thereof.
However such an anchor suffers from the drawback of penetrating into the ground along a circular path, the average inclination of the plate, relative to the horizontal, increasing progressively as this plate is buried more deeply.
This characteristic is detrimental to the stability of the anchor because it prevents the latter from being buried very deeply, any reduction in the burying depth tending to facilitate the release of the plate from the ground.
U.S. Pat. No. 2,721,530 describes an anchor comprising a plate to which the anchor line is secured by means of chains connected to a plurality of points of the plate, and connected to the anchor line through a ring. Such an anchor is capable of penetrating only into soft muddy soils.
The invention provides an anchoring system which is free of the above-mentioned drawbacks.
The anchoring system according to the invention comprises an anchor including at least one plate, at least one anchor line conn
REFERENCES:
patent: 305186 (1884-09-01), Herman
patent: 1838745 (1931-12-01), Croney
patent: 2721530 (1955-10-01), Vorenkamp
patent: 2735394 (1956-02-01), Walpole
patent: 3305984 (1967-02-01), Borcuk
patent: 3570440 (1971-03-01), Pot
patent: 3685479 (1972-08-01), Bruce
patent: 3961451 (1976-06-01), McCain
patent: 4173938 (1979-11-01), Colin
Habib Pierre
Luong Minh P.
Avila Stephen P.
Blix Trygve M.
Institut Francais du Pe'trole
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