Ships – Anchoring arrangement
Patent
1990-05-23
1992-03-24
Swinehart, Edwin L.
Ships
Anchoring arrangement
B63B 2124
Patent
active
050977873
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a tensioning device for pretensioning spread mooring line systems having spaced opposed anchor members lodged in a mooring bed and anchor cable means connected to each anchor for attachment to a vessel or other floating marine structure to be moored. It is to be understood that the term "cable" covers link chain cable in addition to wire cable and, indeed, all line constructions equivalent to such wire and chain cables.
It is present practice to pretension the cables of such mooring line systems to set the ground-engaging portions of the cables into the soil when the anchor members comprise driven piles and, additionally, to cause penetration of the anchor members themselves when the anchor members comprise drag embedment fluke anchors. A common method of pretensioning involves simply hauling in on opposed cables using a winch mounted on a floating vessel. This has the disadvantage of requiring a large and costly high-powered winch when large anchor members are deployed. This disadvantage can be mitigated substantially by adopting a method involving the well-known tension-in-a-bight purchase principle wherein an increment of tension applied to a first cable attached at right angles to the middle of a stretched second cable deflects it and so induces an increment of tension in the second cable which by resolution of forces, may be several times greater than that applied to the first cable. The component of tension at right angles to the first cable that is induced in the second cable is equal to the tension in the first cable divided by twice the tangent of the angular deflection of the second cable at the attachment point. Thus, the power and cost of the tensioning winch required to pretension a mooring line system may be reduced greatly by pulling vertically on a riser cable attached at a joining point between two lengths of anchor cables stretched out horizontally over a mooring bed between two anchor members to benefit from the multiplication of tension obtained from the tension-in-a-bight purchase principle.
It is an object of the present invention to provide an improved tensioning device for pretensioning mooring line systems when using the tension-in-a-bight purchase principle.
According to the present invention there is provided a tensioning device for use in pre-tensioning at least first and second cables of a mooring line system when the device is attached thereto, at least one of the cables including link chain cable, the tensioning device comprising a body member including at least first and second cable holding means, and passage means located between the cable holding means to enable the one cable including link chain to pass through the body member to define a riser cable portion, at least one of the cable holding means comprising releasable catch means for engaging the link chain cable, the releasable catch means being arranged such that a link, referred to as the caught link, of the link chain cable extending through the passage means is caught by the releasable catch means when the riser portion is tensioned and released from the releasable catch means when the riser portion is relaxed, the body member including structure defining slot and clearance means in the body member whereby when the caught link is engaged by the releasable catch means during chain tensioning a downline chain link threading the caught link and a following link can move into the slot and clearance means, and the downline chain link can swing to form an angle in the range 0.degree. to 27.degree. with a plane containing a line connecting the first and second cable holding means, defined as the cable holding means connecting line, without a portion of the body member contacting the downline chain link.
Preferably the body member includes land surface means adapted to support only said caught link of link chain adjacent said releasable catch means, and preferably said land surface means support the caught link in a plane inclined at an acute angle to the horizontal when the caught link (L
REFERENCES:
patent: 2448482 (1948-08-01), Woolslayer et al.
patent: 3386407 (1968-06-01), Mount
patent: 4090462 (1978-05-01), Mount
patent: 4727819 (1988-03-01), Pollack
patent: 4889065 (1989-12-01), Vanden Haak
BruPat Limited
Swinehart Edwin L.
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