Note: Descriptions are shown in the official language in which they were submitted.
CA 02293328 1999-12-06
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PATENT APPLICATION
TITLE: DOUBLE POINT MOORING SYSTEM
BACKGROUND O>= TH[,~ INVENTION
Cross Reference To Related A~~lication
This application claims the priority filing date of U.S. Provisional
application 601051,959 filed 07/08/97.
Field of the Invention
This invention relates in general to mooring arrangements for vessels
and in particular to a spread mooring arrangement for a permanently moored
storage vessel to which a shuttle tanker is tied up along side during product
transfer.
Description of the Prior Art
A shuttle tanker tied up beside a permanently moored storage tanker
needs clearance between its hull and the anchor legs of the storage tanker.
There are many permanent mooring arrangements for storage tankers
yet, a possibility exists for shuttle tanker entanglement with anchor legs of
the
permanently moored vessel, especially if anchor legs are secured mid-way
between its stern and its bow or if anchor legs are secured mid-way between
its stern and its bow or if anchor legs extend from the deck via the side of
the
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vessel.
Identifrcation of Objects of the Invention
it is an important objective of the invention to provide a mooring
arrangement for permanently mooring a storage tanker in deep water
(greater than 200 meters) which substantially prevents the possibility of
entanglement of the shuttle tanker with the anchor legs of the storage tanker.
Another object of this invention is to provide a spread mooring at the
bow end and the stern end of the vessel to allow large shuttle vessels to be
tied up alongside the storage vessel in moderate environments for offloading
of hydrocarbon product without the potential to entangle the permanently
installed anchor legs of the storage vessel
Another object of this invention is to provide a double point mooring
system for large vessels to be tied up together in moderate environments for
offloading product from one vessel to another while providing space on the
side of the storage vessel for the securement of production risers, work over
risers or control umbilicals.
SUMMARY OF THE INVENTION
In shallow water, spread mooring systems have been used. The
anchor legs of such spread mooring systems have normally been deployed
from a top deck of the vessel from its sides, bow or stern. Placement of such
spread anchor legs is likely to cause entanglement of a shuttle tanker when
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it is maneuvered for tying up the side of the storage vessel.
According to the invention, a double spread mooring system is
provided, one at the stern, the other at the bo~ni of the storage vessel for
deep
water (greater than 200 meters) applications. Such placement of anchor legs
away from mid-way between stern and bow provides a certain level of
clearance of a shuttle tanker tied up to the side of the storage vessel. The
bow and stern anchor legs enter the vessel not from the deck of the bow or
stern or from its sides, but rather from beneath the vessel via a mooring
insert tube through which anchor chains are pulled in from winches on the
deck of the vessel. Because the anchor legs approach the vessel from the
bottom of its keel, a further level of clearance is provided for deep water
applications, which substantially insure that a shuttle tanker will not become
entangled with the anchor legs.
BRIEF DESCRIPTION OF THE DRAWINGS
The various objects and advantages of this invention will become
apparent to those skilled in the art upon an understanding of the following
detailed description of the invention, read in light of the accompanying
drawings which are made a part of this specification and in which:
In the Drawings:
Figure 1 is a plan view of a permanently moored vessel with a double
point mooring arrangement according to the invention with a shuttle tanker
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tied up along its side;
Figure 2 is a cross sectional view taken along sections lines A-A of
Figure 1 which illustrates anchor legs at the stern of the vessel entering a
mooring insert tube of the vessel; and
Figure 3 illustrates the mooring insert tube of the mooring arrangement
of the invention.
DESCRIPTION OF THE PREFERRED
EMBODIMENT OF THE INVENTION
A plan view is presented in Figure 1 of a permanently moored storage
vessel 10 having a shuttle tanker 20 (shown fully loaded) tied up along its
side for loading of product. Rubber fenders 50 protect the vessels from
damage while being tied to each other. Flexible hoses 60 provide product
flow paths from the permanent storage vessel 10 and the shuttle tanker 20.
The storage vessel 10 is moored to the sea bed by a double spread
mooring arrangement comprising anchor legs 30 at the bow and anchor legs
40 at the stern rather than a single anchor leg pattern connected mid-way
between bow and stern. The anchor legs are terminated at the sea floor by
anchors. Such anchors may be of any of several known types in the art of
mooring systems. Anchor legs 30 may include lengths of chain and wire or
synthetic rope as well known in the art of mooring systems.
Anchor legs 30 at the bow are secured to vessel 10 by entering at a
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bottom end of a bow insert tube 100 which is placed on the longitudinal
center line of the hull of the vessel and extends from the vessel deck 15 (or
a chain pull-up deck) to the keel of the vessel. Each anchor leg 30 is pulled
in and secured to the chain pull-up deck 15 of the vessel 10 by a double
drum winch 17. Likewise, anchor legs 40 at the stern are secured to vessel
by entering at a bottom end of a stern insert tube 120 which is similar in
construction to tube 100. Each anchor leg 40 is pulled in and secured to the
chain pull-up deck 15 of the vessel 10 by a double drum winch 19. Different
chain pull-up decks may be used under certain circumstances.
10 Figure 2 illustrates the two vessels 10 and 20 in a cross-section view
along lines A-A of Figure 1. Because anchor legs 40 enter the insert tube
120 from beneath the permanently moored vessel 10, rather than from its
side or the top of its bow or stern, and because the anchor legs 30 and the
anchor legs 40 are connected to storage vessel 10 at its bow and stern, not
mid-way between bow and stern, the shuttle tanker 20 has sufficient
clearance from anchor legs 40 and anchor legs 30 to insure that there will not
be entanglement.
The section view of Figure 2 further illustrates a riser porch 65 provided
along the side opposite that to which the shuttle tanker 20 is tied up. Riser
porch 65 provides a structure where production risers and control umbilicals
70 may be run and secured to the permanently moored vessel 10. Such riser
porch 65 may be provided mid-way between stern and bow.
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Advantageously, the riser porch placed to the side of the permanently
moored vessel 10 provides a large area for the combination of risers for
production, re-injection or control umbificals. This allows great flexibility
and
adaptability for the installation of such equipment in the event that
production
methods for the oil field were to change during its lifetime or in the event
that
adjacent production wells were to be required to be serviced by the vessel
10.
Figure 1 illustrates that a large deck space 16 is available for
production processing equipment even where two mooring insert tubes 100,
120 are provided.
Figure 3 illustrates an anchor leg 30 being spooled onto the vessel by
a drum winch 17. Each mooring insert tube assembly 100, 120 is welded into
an existing tanker 10 structure, typically at an intersection of longitudinal
and
transverse bulkheads. The internal diameter of the mooring tubes may be
three meters, for example. Typically four anchor legs per tube are provided
as illustrated in Figures 1 and 2. This arrangement maintains the integrity of
the tanks of the vessel and provides a way to introduce mooring loads into
the tanker.
The drum winches 17, 19 are preferably double drum winches to
facilitate the hook up of the anchor legs 30 or 40 as the case may be. A
chain-wire-chain anchor leg arrangement is illustrated in Figure 3, but of
course other arrangements may be provided.
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Although, the preferred embodiment of the double point mooring
arrangement of Figures 1-3 is for a shuttle tanker 20 to be tied up along the
side of the permanently moored vessel 10, the arrangement may be used for
offloading systems at the bow and or stern of the vessel to better facilitate
off
loading. The same advantages of providing large clearance distances
between the anchor legs 30, 40 and the off loading shuttle vessel reservoirs
are achieved.
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