METHOD AND SYSTEM FOR FLUID TRANSPORT BETWEEN SHIPS

SYSTEME DE TRANSPORT DE FLUIDES ENTRE NAVIRES, ET METHODE CONNEXE

English Abstract

A method and a drift anchor system (7) for fluid transport
between two ships (1) in the open sea. At least one of the
ships is at its stern provided with a loading hose (2), a reel
or similar for said hose, and a mooring hawser (4).
The drift anchor system (7) is arranged forward on the
ship and is designed for providing breaked aft driftage. The
system comprises a bottom weight (8) having rounded shape, a
drag chain (9), an anchor wire (10), a winch (11) on the deck
and a vertical or inclined chain shaft (12) form the deck and
down to the ship bottom.
The method incorporates activating of the drift anchor
system (7), manoeuvring of the second ship (5) towards the
first ship (1), mooring of the ships to each other by means of
the mooring hawser (4), and activating of a bow loading system
(6) on the second ship to establish fluid transfer by means of
said loading hose (2).

Claims

WE CLAIM:
1. Drift anchor system (7) to allow fluid transport
between two ships (1, 2) in open sea and according to the method
of one of the preceding claims, characterized in:
a bottom weight (8) having rounded shape and without
anchor hooks,
a drag chain (9) secured to the bottom weight (8) at
its lower free and,
an anchor wire (10) having a considerable length and
being secured to the upper end of said drag chain (9),
a winch (11) on the deck for reeling of said anchor
wire (10), and
a vertical or inclined chain shaft (12) from the deck
of the first ship (1) and down to its bottom.
2. Drift anchor system according to previous claim
characterized in that said bottom weight (8) at least at its
upper portion is conical or spherical, and that the shaft mouth
(14) of said chain shaft (12) in the ship bottom is shaped
complementary to the conical or spherical form of said bottom
weight (8).

Description

CA 02578769 2007-03-01
Method and system for fluid transport between ships
There are several reasons to transfer fluid such as oil
or gas between two tankers in the open sea, and by having
available good and flexible solutions for a such fluid or load
transfer, a better employment of the fleet will i.a. be
possible. A good load transfer flexibility will particularly
be valuable for a fleet in which the individual ships have
different types of loading/discharging equipment on board.
Until now known methods to transfer fluid between tankers
in the open sea have turned out problematical during so-called
marginal weather conditions (by significant wave heights over
6 feet [2m]). The reason is as follows: If two ships to be
interconnected for load transfer are moving by their own
forward machinery to keep a minimum steering speed (the
machinery in position "forward, slow"), the forward or rearward
speed still may be at least approx. 5 knots, and therefore it
will not be.recommendable to make the connection and carry out
the subsequent load transfer between the ships, since the risk
for collision would be too great. If, on the other hand, the
ship machinery is deactivated, the ships could easily break
adrift in an uncontrolled manner and end up being laterally
exposed against waves and wind, and even then it will most
often be problematic to arrange a load transfer from one ship
to another.
-Different ways of transporting fluid, such as by fuel
supply to military vessels neither can be used advantageously
for tankers, because the dimensions of ships and tankers and
their loading hoses are far heavier, thereby leading to more
serious consequences in the event of a possible direct contact
between the ships.

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In a broad aspect, the present invention relates to a
method for fluid transport between two ships in the open sea,
at least one of said ships having forward machinery and having
at its/their stern a loading hose, a reel or a corresponding
storing device for said loading hose, and a mooring hawser, and
forward a drift anchor system to allow breaked aft driftage due
to the prevailing weather forces, and said at least one other
or second ship having machinery for forward movement and having
a bow loading system for fluid transfer to or from said first
ship, said method comprising: stopping of the forward machinery
of the first ship; activating of the drift anchor system of
said first ship until its driftage is becoming stable;
manoeuvring of said other ship towards the stern of said first
ship and to a position ahead of it, in relation to the aft
driftage of said first ship, the bow of said second ship being
faced against the stern of said first ship; mooring of said
other ship to said first ship by means of the mooring hawser
in the stern of the first ship; and activating of the bow
loading system on board the other ship and establishing of a
fluid transport connection between the ships by means of said
loading hose.
In the following description the invention will be
described more closely with reference to the

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acoompanying drawings, wherein:
Fig. 1 dsmonetratee a connection between two tankers in
order to carry out fluid transport according to the invention,
Fig. 2 illustrates a drift anchor system on one of the ships, and
6 Fig. 3 ehowe schematically the drift anchor system in activated
condition.
Referring to Fig. 1 there is shown a fi.rst ship 1
having a loading hose 2 at its stern and a reel 3 or a similar
storing device for the loading hoee, which also may be stored in
1e a horizontal support. At the stern there is also provided a
mooring hawser 4. Further is illustrated the bow portion of a
second ship 5, moored to the first ship 1. The second ship is
preferably, a buoy loading ship having excellent manoeuvring
properties due to a system for dynamic positioning (DB) for the
is control of trugterg forward and aft and turnable main propellers.
When the pP system is activated the mooring hawser 4 haa the
funotion of an extra safety mechanism between the ehips. A
typical distance between the ships may be 80 - 100 m during
mutual mooring.
20 The free gnd of the Toading hose 2 from the first ship
is connected to a bow loading system 6 of traditional type on the
other, second ship S.
At its bow portion the first ship I is provided with a
drift anchor system 7 (Fig. 2) comprising: A bottom weight having
as a rounded shape, without anchor hooks and secured to the lower
free end of a drag ohein 9, an anchor wire 10 having a consider-
able length, for example 1000 - 2000 m and being secured to the
upper end of said drag chain, a winch 11 mounted on deck and
adapted for reeling of the anchor wire, and 4 vertical or
3o inolined chain shaft extending from the ship deck and down to its
bottom.
When the drift anchor system is inactivatea, the winch
11 is keeping the anohor wire 10 reeled, while the drag chain 9
is hanging vertically and extended within the chain shaft 12. The
35 winch pull on the wire may be slightly greater tha,n the combined
weight of bottom weight 8 and drag chain, or the upper end of
said chain may be seoured under tension by means of a$topper 13
on the deck, in which case the winch is relieved. In both aitu-
ations the bottom weight 8 will be drawn with a certain force

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against the shaft mouth 14 in the ship bottom in order to close
the shaft. For this reason the bottom woight may be conical or
spherical at least at its upper portion, and the shaft mouth 14
will be correspondingly complementary shaped.
During use the first ship forward machinery is stopped,
the drag chain with bottom weight connected is lowered down to
the sea floor, and the anchor wire is reeled out gradually when
the ship breaks adrift and turns into the direction of the wind
and sea current. The turning will partly be under control due to
io the friction of the drift anchor system. Fig. 3 illustrates this
situation, and it is obvious that also a portion of the anchor
wire will be positioned along the sea floor and slowly being
dragged forwards. it is of importance that the bottom weight is
not designed as an anchor but instead is rounded to be drawn
15 alongside the sea bottom under resistance, together with the drag
chain. The drag resistance acting upon a ship having a such drift
anchor system will depend upon the weight and length of the drag
chain and its connected anchor wire. if a particularly great drag
resistance should be wanted, for example if a hip serving as a
zo barge vessel has a considerable tonnage, a coarse drag chain and
a corresponding large and heavy bottom weight 8 may be used. The
,
drag resistance may also be varied within certain limits by
adjusting the length of the portion of the anchor wire being
dragged along the sea floor.
25 Preferably the drift anchor system of the ship is
provided with two sets of wire/chain equipment, as illustrated
in Fig. 3. Thereby is given the possibility to adjust the ship
heading or deviation direction to a certain extent by arranging
a different length of the wire/chain equipment along the sea
30 floor on the steerboard and port side of the ship, respectively.
By letting the ship heading in this way be under
control of the drift anchor system, the angular or azimuth
direction of the ship during its aft driftage will approximately
become in line against the prevailing weather forces. In this way
35 the wind influenoe can be kept relatively small due to that the
wind facing area will be far lesa than if the ship should be
allowed a free driftage, since it then probably would end up in
an azimuth perpendicular to the wave and wind direction. A such
uncontrolled driftage therefore would be considerably greater and

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could lead to a driftage speed of for example 4 - 5 knots when
the wind strength is, say 50 knots. By the method and drift
anchor syetem of the invention is assumed that a barge operation
may be executed under minimum risk even during great wind speeds
6 and at wave heights (given as significant wave height H.) up to
around 5 - 6 m.
A loading operation for fluid transport between two
ships in open 8ea, for exambrle the transfer of oil/gas from a
first to a second tanker will follow these steps:
io a) The first ship stops its forward machinery and
activates its drift anchor system, whereafter it is allowed to
break adrift and turn into a position with ite bow towards the
prevailing weather forces (waves, wind and current). Alter-
natively and to save time the ship may first be turned against
25 the wind, thereafter the forward machinery is reversed so that
the ship by own means starts its aft driftage, then the machinery
ia switched on and the drift anchor system is activated.
b) When the aft driftage (rearward movement) of the first
ehip 1 has become stable, the second ship 5 is manoeuvred with
ao its bow against the stern of the first ship and is positioned
ahead of the bow (the "preseion "ahead of" here meeLning: in
relation to the direction of movement of the first ship). The
manoeuvring may for example be effectuated in the same way as is
common by mooring/connection to an offshore buoy installation.
zs Thereafter the ships are connected together, and the second ship
may keep an approximately constant distance to the first ship by
means of its DP system.
v) The bow loading system 6 is activated and made to
Bstablieh a fluid transport connection between the ship by means
30 of the loading hose 2, and the fluid transfer may start.
d) At the and of the loading operation the ships are
digaonneoted, the first ship is heaving in the loading hose and
the mooring hawser and winching the anchor wire until the bottom
weight is lifted to close the shaft mouth, thereafter the ships
35 may navigate to their destination sites.
Carried out in this way, hydrocarbon fluid may be
traneferred faster and more secure from one ehip to another out
at sea, compared to known methods, even by marginal weather
cnnditions.

Representative Drawing