Note: Descriptions are shown in the official language in which they were submitted.
~075999
I 1 Thi~ invention relates to improvements in the
2~l transfer of materlals mined or conveycd to a location on or
3 1l below ~he bottom o~ a bo~y of watèx to above-surface recep-
41 tacles and, more part~cularly, apparatus and method for
transferlng ~uch material~ along a generally vertical path
6 through the body o~ water even under extreme wave and
7 ¦ weather cond~tion at the ~urface.
8 11
g!
In the handling of crude oil pumped from off~hore
oil wells, a number of offshore terminal~ have been d~veloped
11 over the year~ for use in tran~ferring the production from
12 such wells to tankera at berth or to other receptacles or
13 ¦ vessels. Among these are the following: the artific~al
14 ¦ offshore island made up of ~te~l constructisn or preca~t
15 ¦ concrete pil~ngs fixed to the sea bottom and supporting
16 steel, precast or cast-in-place concrete structures; thQ
multiple-buoys-mooring sy~tem consi~ting of several moor~ng
18 buoys anchored around a tanker berth; the tower mooring
20 ~ system con3isting of a steel structure f~xed to the ~ea
bottom by pilea and having a turntable fitted on the top of
211 the 3tructure from which a mooring rope is connected to a
tanker at berth ad~acent thereto; and the single point
23 ¦ mooring ~ystem which can be of one of two types, namely, a
¦i catenary-chain type, single buoy mooring system or the
single anchor leg mooring unit, both of which allow a tanker
to rotate freely and to take the posit~on o~ lea~ rQslstance
1~ to combined external ~orces, such as those due to waves, sea
!! currents, wind and other types of rotating mooring All of
- I the~e various sy3tems can only be compared by select~ng a
30lj
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1~ partlcular ~ite where such ~ystem~ may be installed. At any
2 ~uch site, water depth and qea and weather conditions are to
3 be conRiderad along wlth the moorihg forces between each
4 system and a vessel to be as~oclat2d therew~th.
5 I All of the foregolng ~y9tem3 have certsin drawbacks,
6 I especlally when the same are used in region~ of the ~aa
7~ whlch have extreme wave actlon at certain times of the year.
8l For instance, at certain locatlon3 in the North Sea where
9 much offshore drilling now take~ place, a 100-y~ar wave i~
estimatad to have a height o~ 95 to 105 feet but such esti-
11 mates have latoly been ~hought to be erroneous in that a
12 more correct e~timat~ is lS0 feet. Under such extreme wave
13¦~ conditions, it is virtually impossible to maintain a moorlng
14 I between a ves~el and any one of the aforesaid offshore
15 ~ terminal~ without causing damage to both ~he vessel and the
16~ terminal. A1YO, to disengage and re-engage the vessel
17l relative to the terminal in ~uch extreme wave conditions,
181 special ~tructures and time con~uming procedure~ are required.
19~ The above-ment~oned offshore terminals also have
20¦ other drawback~ including restrictive water depth and excessive
21~ cost3 of con~truction and maintenancQ due to their complexity
221 o~ ~tructural detail. For instance, the artificial offshore
23l island i~ 80 c08tly that lts use seems ju~tified only when
24 ¦I tha oil production handled thereby or throughput i9 very
25~ high, such a~ above 200,000 barrels per day, and only when
26l very large va~sel~ are available for u3e with lt. Also, the
27 1I water~ around the i31and ~hould be well protected; otherwice,
28 1ll a breakwater ha~ to be constructed at high co~t. Furthe~more,
291 the depth at which the aforesaid svstems are operable do not
30l exceed about 300 feet.
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The multiple-buoy~-mooring ~ystem finds it appli-
~I cation only in protected shallow waters ox exposed locations
j~ with m~ld wave climate and or relàtively small tankar~. It
othe~ise too ea~ly damased; thus, it cannot withstand
~I the extre~e weather conditions mentioned above whlch occur
76j ln the North Sea.
The tower mooring system i~ c03tly to erect and to
8 operate and presents collision ris~s. It is believed to
find it~ best application only in relatively shallow waters
which are proteated from extreme wave action; thus, it i8
11 not suitable at all for the open North Sea opexations discu3sed
above.
43 The ~in~l~ point mooring sy~tem i~ not suitable
for use under extreme wave conditions because, in the case
o~ the ~ingle buoy mooring system, the hawsexs which anchor
16 the tanker or vessel break due to i~pact tension caused by
17 ~ wave forces exerted on tho system. These waves also cau3e
1 1 the buoy to separate from the vessel and then to slam into
19 it to cause damage to either or both of them. In the case
I o f the single anchor leg mooring system, an anc~or chain
22 connects a buoy body to a generally rigid ~ertical riRer
¦ standing upwardly from the sea bottom but this chain al30
¦~ breaks due to extreme wave action and separates the ~uoy
24 11
i from the riser, causing sufficient damage to the system to
il re~uire replacement of the buoy, all of which requires a
Il long shutdown time for repair3.
27 1l In view o~ the problems associated with the off-
I ~hore oil terminals mentioned above, a need has arisen for
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1075999
an improved offshore terminal which is simple and rugged in
construction, is relatively inexpensive to produce and
maintain, can be easily moved to other locations, can be
used to keep a vessel coupled thereto even under extreme
wave conditions yet the vessel can safely engage with and
disengage from the terminal without special assistance or
procedures, and can operate at depths of up to 2,000 feet or
more.
The present invention satisfies the aforesaid need
by providing an improved materials delivery system for
transporting materials from the bottom of a body of water to
the surface and to a receptacle, such as a vessel coupled
with the system itself. The present invention is especially
suitable for handling offshore oil well production although
it is suitable for other applications as well. For instance,
it can be used to deliver natural gas from such offshore
wells, and it can also deliver particle material, such as
manganese nodules and ore, and can also deliver refrigerated
fluids and slurries of various types. In the case of
slurries, ocean mining can be carried out which would allow
dredging marine deposits of tin, diamonds, gold or high
value commodities under sea conditions in which conventional
dredges are impractical or impossible for use.
More specifically the present invention is a
materials delivery system for the transfer of mined materials
from the bottom of a body of water to the water surface
comprising: a spar having means at one end thereof for
mounting the same in a generally upright position on the
bottom of said body of water with the spar having a length
1075999
sufficient to permit it to extend to a location adjacent to
the water surface, there being a material delivery line
capable of transporting said materials and extending along
the spar from a location adjacent to said mounting means to
a location adjacent to the upper end of the spar, said
delivery line adapted to be coupled to a materials receiver
near the water surface when the spar is in said position;
and means coupled with the spar near the upper end thereof
for coupling the spar to the materials receiver and for
applying a generally upward force to the spar when the spar
is in said position, the upper end of the spar being movable
laterally when the spar is mounted in said upright position
and as said upward force is applied thereto, whereby the
spar can move laterally with the materials receiver.
The materials delivery system of this invention
may use a spar having a relatively small cross section and
provided with means for applying an upward tension force
thereon when the lower end of the spar is anchored by a
suitable mass anchor base or is pile anchored or hydro-
anchored to the bottom of a body of water. The coupling
between the mass base and the spar can be a ball joint, a U-
joint, an elastic joint or other structure permitting
articulation of the spar relative to the base so that the
spar, when coupled to a vessel on the surface of the water,
can move with the vessel due to wave action without becoming
separated from the vessel. It is also possible to make the
spar flexible and to attach it by a rigid connection to the
anchor base. This latter feature would be advantageous in
deep water. The base can either be permanent or of a
removable type, the latter being much more economical to
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16175999
relocate to another site than presently existing structures.
Tension is applied at all times to the spar by,
for example, a buoyancy chamber carried by the spar adjacent
to but below the upper end thereof. When a vessel is
adjacent to the spar, it is coupled by tensioning means to
the spar, and the tensioning means applies an additional
tension force to the spar in a manner such that a lateral
tension component is exerted on the spar at all times during
the vessel-spar connection to hold the spar against the
vessel. This feature virtually assures that they will not
separate from each other even during periods involving
extreme wave and wind conditions on the water surface. This
will prevent impacting of the spar and the vessel together
to thereby eliminate any structural damage to either or both
of them due to this cause. The connection of the tension
means to the spar is by way of a swivel so that the vessel
can windvane without causing rotation of the spar about its
longitudinal axis. Any of several embodiments of the
tensioning means can be used to carry out the teachings of
the present invention.
1~75~9~
llj The nor~al or rcst pO3itiOIl will ordinarily be
2I generally vertlcal. ~owever, it can ~e normally tiltcd by
3 !! ad~usting the amount of buoyancy ~rovided by either or both
4~l of the buoyancy chamber and the tenqioning means.
5 11 The spar c~n be provided with ono or more exter~al
6¦ or intornal material deliv~ry lines, Ruch as fluld flow
7 llnes or conveyors for particle matorial, coupled at their
8l lower end6 to a materi~ls source near tho ma~s anchor base,
91¦ the delivery lines extending to swivel means near the upper
10l end of the spar, whereby the material delivery from the
11 ¦ delivery lines can be transferred by material delivery means
12¦ to the vessel or other receptac~es regardless of the locat~on
13~ of the vesQel or receptacle about the spar. Control means
14i can also extend through the core and the spar to operate
151 control equipment on the bottom of the body of water. If
16 ! the delivery lines are comprised of fluid flow lines, the
17l buoyancy chamber itself can be provided with a manifold to
18 I permit a decrea~e ~n the fluid pressure of the flow lines
19 ll and to reduce the number of flow lines to swlvel cou~led to
20 ~ he delivery hoses connected to the vessel.
21 1l If material conveyors are used, they c~n be bucket
22 ll conveyors or hydro-pneumatic (airlif~) or pneumatic conveyor3,
23 11 'or delivery of particle materi~l, such as ~anganesa nodules
24 1 or ore, to ~he water ~urface. Such materials can be raised
25 ll in slurry form through ~luid flow lines as an alternative
26 ~ approach. I
27 'I The system i-~ suitable for depths f.om 250 feet to
28l more than 2,000 feet below the water surface and can be used
29 to r~place all existing offshore terminals of the conventional
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" 1C1 75999
types described above. It is simple in construction,
readily installable in place, and requires a minimum of
maintenance.
The swivel at the top of the spar can be con-
structed to handle segregated products, such as crude oiland natural gas or particle materials of several different
~inds. Such products would not be co-mingled at the swivel
and they could be transferred by respective flexible delivery
hoses or conductors to a vessel or other receptacles and
into segregated storage areas thereon.
Thus this invention provides materials delivery
apparatus and method for the transfer of mined materials
from the bottom of a body of water to a receptable on the
water surface wherein a spar having tension exerted thereon
is used to support material transfer means extending from
the bottom of a body of water to the water surface in a
manner to permit transfer of materials to the receptable
even during extreme wave action on the water surface, yet
the spar can be engaged with and disengaged from the recep-
tacle under such conditions without the need for special
assistance or procedures to carry out this purpose.
Several embodiments of the invention are illus-
trated, by way of example, in the accompanying drawings, in
which:
`
1~7~g99
2 ~11 Fi8. 1 i~ a ~che~tic view of the artlcul~ted
3 1I te~810~ spar of thii3 invenelon showing one of saveral ui~e~
4l of the sa~e, n3~Qly, for trani3ferrlng crudc oll from an
5l; ~nderwator wcll to a ves~Ql at bcrth near the uppcr ~nd of
I the spar;
7 I Fig. 2 i8 a ~ide clevatlonsl view of the upper ent
8, of the spar, sho~ing the way in whlch tens1on ig applied
Il there~o when the same i8 coupled to laterally proJecting
lO,j horns on the bow of the veqsel;
Flg. 2a i~ a fragmentasy view of the ~psr and
2,~ tensio~ing synte~ when tne &par i~ in lts vertical po~itlon;
! Fig. 3 i0 a top plan view of the spar tens~oning
14 syste~ of Fig. 2;
I! Fig, 4 i3 a fro~t elevat~onal view of the spar
16~ tenslonlng system of Fi8. 2;
171¦ F~g. 5 18 a perspectlve vlew of a ?referred
I embodlment of the mass anchor base for the spsr;
19l Fl~ 6 i8 a alde elevatlonal view~ partly ln
201, section, of the mass anchor base when the same 18 embedded
in the botto~ of a body of wster, showlng the spsr mountet
Il by a ball Jolnt on the base; - I
23 11 Flg. 7 19 a view slmllar to Flg. 6 but ~howlng
24 11 anoth~r embodlment of the base ~ul~able for use whcn thc
bottom of the body of water ls covered by a lsyer of soft
,I mud;
27i1
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~ot75999
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l ll
1 I Fig. 7a i~ a view ~imilar to Flg8 . 6 and 7 but
2 ~ ~howing another way in whlch the spar 1 coupled to the
3 base;
4 1I Fig. 7b i~ a view similar to Fig. 7a but showing a
5 1I tripod or a pyramidal ~tructure coupling the spar and the
6~ base;
71 Fig. 8 i~ an enlarged, fragmentary, view of the
8 upper end of the ~par showing the way in which fluid flow
9 I line~ through the spar are coupled by mean~ of ~wivels to a
10 ~ fluid swivel core and one or more deli~ery ho~e~ or con-
11 ductor~ ts a vessel or other xeceptacle;
12 I Flg. 9 is a cross-sectional view taken along line
13 9-9 of Fig. 8;
14 Fig. lO i8 a view similar to Fig. 2 but Rhowing
15¦ another tensloning system between the spar and a vessel with
16¦ the spar in a substantial windvane position relative to the
17¦ vessel;
181 Fig. ll is a view ~imilar to Fig. lO but ~how$ng
19l the spar in a sub~tantial override position;
20~ Fig. 12 i3 a top plan vlew of the ~ystem of Fig.
21~ 10;
l Flg. 13 is a view similar to Figs. 2 and 10 but
23~ showing a third embodiment of the tensioning sy~tem between
24~ the ~par and the ve~el, the spar being in a substantial
25l~ windvane position relat~ve to the ve~sel;
26l F$g. 14 is a view similar to F~g. 13 but showing
27l the ~par in a ~ub~tant$al override po~ition;
i
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321~ 1
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~ 107599g
1 Fig. 15 is a top plan view of the system of Figs.
23~ 13 and 14;
l Fig. 16 is a schematic vlew of the spar and vessel
4~ of Figs. 13-15 at the crest of a wave;
6 ~ig. 16a is a fragmentary view of the spar showing
l the wave and tension forces exerted thereon at the crest of
7j a wave when the wave moves in the direction shown in Fig.
8~ 16;
9¦ Fig. 16b iq a ~iew similar to Fig. 16a but showing
10¦ the forces on the spar at the trough of a wave when the wave
11 ¦ moves in the direction shown in Fig. 16; and
12~ Fig. 17 is a view similar to FigO 16 but showing
13l the spar and vessel at the trough of a wave.
14
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27 11
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1075999
~ ~ For purpo~es of illustration only, the material~
3 delivery system of the present invention will hereinafter be
4 described as a mean~ for transEerring cruda oil or gas
through fluid flow lines from a base manifold coupled to one
or more wells drilled into the bottom of a ~ody of water to
a ves~el floating on the surface at a location above the
wells. Crude oil wlll hereinaf~er be described as the fluid
l to be handled ~y the system of the present invention. The
91 invention is, however, broader in ~cope than this illustrative
example, since it can be used to ral3e partlcle material,
2 such as manganese nodules or ore, to the surface of a ~ody
13 of ~ater by the use of conveyors.
I ~he concept of the present invention is illustrated
141 schematically in Fig. 1 wherein the delivery system, denoted
16~ by the numeral lO, includes an elon~ated, tubular, spar 12
17~ mounted on a base 14 on the bottom l6 o~ a body of water
18~ which will hereinafter be considered a~ a sea so that
19 bottom 16 will be referred to as the sea bottom. Spar 12
extands upwardly from the base to and above the upper surface
21 18 of the ~ea and terminates near the bow 20 of a vessel 22,
which will hereinafter be described as a tanker, although
22l ~uch a vessel can include any type of marine craft, such as
23l a barge, ore ship, floating pier and the like.
25¦ Base 14 is positioned on the sea bottom in the
26 vicinity of one or more oil wells, typically six in number,
27 which may be spaced from each other a~ varying distances.
I! Fluid flow llnes from the various we~ls and the associated
28ll
equipment, such a~ valves, regulators, controls, p~nps and
!! the like, are provided ~o direct the crude oil from the well
3 0 11
I headq to a ba~e manifold 27 and then into spar 12 for transit
31l
I through one or more fluid flow linas extending through the
32
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1075~5~9
spar to its upper end and then, by way of other conduit
means, to the tanker as hereinafter described.
sase 14 is shown in its preferred embodiment in
Figs. 5 and 6. The base can have any suitable shape but~
for purposes of ill~stration~ it comprises a generally
square, octagonal or round hollow housing 24 having a top 26
provided with a pair of tubes 28 and 30 communicating with
the interior thereof. Tubes 28 and 30 extend either into
spar 12 or extend upwardly to upper surface lô along the
outer surface of the spar. They are used for directing a
ballast into housing 24 when it is desired to anchor the
same on sea bottom 16.
A typical ballast is a slurry of iron ore, magnetite,
sand, or some other heavy material in slurry form to he
pumped from the surface into housing 24. This type of
ballast will allow good control of the submergence of base
14 since no compressible gas or fluid is used for this
purpose. Also, by using tubes 28 and 30, the ballast can
later be fluidized within housing 24 and ejected if it
becomes desirable to move base 14 to another job site.
Typically base 14 is made slightly positive in buoyancy to
facilitate its transport to a job site. A typical ballast
weight is lS00 tons or more.
Housing 24 may be of one or several compartments
either connected to or independent of each other. In the
latter case, each independent compartment would have its own
tubes 28 and 30. The compartments may be tubular and may be
set up in the particular geometric configuration to suit the
sea and soil conditions of the site.
Housing 24 has a continuous penetration skirt 32
secured to and extending from the bottom of the housing as
shown in Figs. 5 and 6. This skirt is adapted to penetrate
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107S9~
the sea bottom to provide a positive anchor for the base.
The skirt provides a hydraulic seal for the bottom of housing
24, and relief tubes 34 and 36 extending outwardly from
opposite side of the housing and through the bottom thereof
can be used to provide a reduced pressure or suction in the
space surrounded by the skirts to permit differential,
hydraulic pressure to force skirt 32 into the sea bottom.
Tubes 34 and 36 are connected to a suitable suction force,
such as on the vessel which is used during installation of
the base.
To disengage housing 24 from the sea bottom, the
region below the bottom of the housing can be pressurized
through tubes 34 and 36 to assist skirt 32 to move out of
the sea bottom. Then, by ejecting the ballast from housing
24, the base can then be moved to a new job site. The
ballast can be ejected from the housing through either the
bottom of the housing or other tubes through the housing by
conventional means.
In some cases, the sea bottom in deep water comprises
a layer 38 (Fig. 7) of soft, fine sand and silt bottom, the
layer being 15 or more feet thick and resting on a good
bearing bottom 40. In such a case, the footing of layer 38
is too weak to support base 14. In such a case, the base
will have a different construction from that shown in Figs.
5 and 6 and will include a continuous sidewall 41 (Fig. 7)
secured to a housing 43 and extending downwardly therefrom.
A continuous penetration skirt 42 will extend downwardly
from the sidewall 41 as shown in Fig. 7, housing 43 being
hollow and provided with tubes 44 and 46 for the same purpose
as tubes 28 and 30 of Figs. 5 and 6. Continuous sidewall 41
10~$~
is used to increase the pressure on layer 38 so that skirt
42 can more effectively penetrate the layer and then extend
into the good bearing material 40 below the layer. The
interior of the space surrounded by sidewall 41, denoted by
the numeral 48, can be exhausted by a pair of tubes 50
connected to a suitable suction source. Space 48 can be
pressurized when it is desired to remove base 14 from the
sea bottom and to move it to another job site.
One way of mounting spar 12 on base 14 is by the
use of a ball joint 54 (Figs. 6 and 7) with the ball of the
joint being mounted on a suitable pedestal 56 on top 26 of
base 14 and with spar 12 having a socket member 58 at its
lower end for coupling the spar with the ball. The spar is
thus able to articulate relative to the base 14 in all
directions about hori~ontal axes through the ball; however,
the coupling is provided with means (not shown) for preventing
rotation of spar 12 about its longitudinal axis relative to
the ball joint. In lieu of a ball joint, a universal joint
can be used for this same purpose.
Other embodiments of the action between the spar
and the base are shown in Figs. 7a and 7b. In Fig. 7a,
pedestal 56 is provided with an elastic ring or elastic
blocks 60 which rest upon and are connected to the flat
upper surface 62 of the pedestal and which support and are
connected to the bottom of spar 12. To limit the compression
of blocks 60 when spar 12 has a tendency to tilt with respect
to the vertical, a number of limit bars or springs 64 may be
used and, if used, are secured between pedestal 56 and re-
spective lateral ears 66 on the lower end of spar 12. Limit
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bars 64 prevent the deformation of blocks 60 beyond its
elastic limit. In any case, blocks 6Q allow spar 12 to
articulate relative to base 14 in all directions about
generally horizontal axes through the block, and limit bars
64 prevent spar 12 from rotating about its longitudinal axis
relative to the base.
To enhance the structural behavior and the economics
of a very long spar in deep waters, base 14 could be fabricated
to contain a tripod or a pyramidal structure of three or
more legs 67 as shown in Fig. 7b~ All of the flow lines
could be made to extend through the base and legs 67 and
into spar 12. At the top of the pyramid is a platform 69 to
mount pedestel 56, 54, and socket member 58. This feature
will allow the use of a relatively short spar since legs 67
can be made relatively long.
Spar 12 is of relatively thin-wall steel construc-
tion, such as a 2-inch wall thickness, and is relatively
small in diameter, typically about 10 feet in diameter. In
the alternative, the spar could be of concrete and steel or
other suitable material. The length of the spar typically is
from 250 to 450 feet but can be as long as 2,000 feet or
more. The length will be such that the upper portion of the
spar will extend upwardly from upper surface 18 and through
the space 70 (Fig. 3) between a pair of spaced, generally
parallel bow horns 72 mounted in any suitable manner on bow
20 of tanker 22. The upper end of the spar terminates above
the bow horns as shown in Figs. 1 and 2~ for instance.
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Spar 12 has a buoyancy tank 74 (Fig. 1) mounted
thereon near the upper end thereof and below surface 18.
Tank 74 provides buoyancy for spar 12 and provides a tension
force which is exerted on the spar in an upward, axial
direction at all times even when tanker 22 is separated from
the spar. Thus, the spar can be of relatively small diameter.
When the tanker is in berth, the spar is further tensioned
by a spar tensioning system in a manner hereinafter more
fully described.
Buoyancy tank 74 can be designed with either or
both air and buoyant material-filled buoyancy chambers.
Also, it can be somewhat enlarged so that it can enclose one
or more flow line manifolds to allow reduction in flow line
pressures from about 3,000 psi to about 300 psi. When a
large number of flow lines are being brought into the spar,
one or more manifolds at this location will reduce the
output lines to one or more from the spar to the tanker.
Under certain conditions, spar 12 may have a
ballast tank 75 (Fig. 1) near its lower end for receiving
ballast to assist in putting the spar in place. Ballast
tank 75 reduces the upward forces on base 14 and assists in
keeping spar 12 in an upright position if, for some reason,
the spar separates from the base. Ballast tank 75 can have
a number of compartments and can be helpful in towing the
spar to a job site since tank 75 will be buoyant with no
ballast in it and can cooperate with base 14 when the latter
is free of ballast to provide a buoyant force on the lower
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end of the spar so that the spar can be towed in a generally
horizontal position, the front end of the spar being buoyed
by tank 74.
a first embodiment of the spar tensioning system
is shown in Figs. 2-4. In this embodiment, the spar has a
collar 76 rotatably mounted thereon at a location either
above or below the surface of the water. A pair of tension
members 78, such as cables or chains, couple collar 76 to
the tanker. Specifically~ one end of each tension member 78
is connected to an eyelet 80 near the outer end of the
corresponding bow horn 72 and the opposite end of the
tension member is coupled to a constant tension device 82
mounted on the tanker near the rear end of the corresponding
bow horn. Each tension member 78 passes down and about a
sheave 84 mounted on a respective side of collar 76 (Fig. 4);
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thus, the two portions of each tension member extending
upwardly from the corresponding sheave 84 are at acute
angles relative to the longitudinal axis of spar 12. Also,
members 78 extend upwardly and laterally outwardly (Fig. 4)
to provide equal and opposite lateral force components on
the spar to keep it substantially centered between the bow
horns to prevent impact therewith.
Under maximimum storm conditions, a typical tension
applied to the spar by tension members 78 is 300 ~ons. Such
a load requires a heavy-duty construction for each tension
member. A suitable chain for this purpose is 4-inch, super-
strength, Di-Lok. Each link of such a chain is 24 inches
long and 15 inches wide. Proof tests of this chain include
the application of loads up to 600 tons. All sheaves used
with this type of chain will be shaped to fit these links as
commonly used in a wildçat windlass. This chain size should
be satisfactory for resident tanker service3 i.e., where the
tanker remains permanently connected to the spar by way of
the chains. If a transit tanker is to be coupled to the
spar, the chain will need only a small fraction of the
strength required for resident tanker service since a transit
tanker will be in berth only under less severe sea conditions.
Also, the average transit tanker will be smaller than the
average resident tanker.
As wave loads exerted on the spar increase, the
tanker, because it is coupled to the spar by tension members
78, puts a greater load on the spar which, in turn, becomes
more resistant to transverse wave loads to minimize bending
of the spar. ~nis spar design tends to compensate for wave
loads on the spar itself and reduces resulting stresses
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thereon. Moreover, the spar tends to remain upright because
of the buoyancy of buoyancy tank 74 and the geometry of the
tension system. When the spar is in its upright position
~Fig. 2a), the portions of each tension member 78 extending
away from the corresponding sheave 84 make substantially the
same angle with the longitudinal axis of the spar so that
the resultant tension force T is generally vertical.
The main purpose in allowing spar 12 to articulate
is to allow it to follow horizontal movements of the tanker
rather than moving relative to and out of phase with the
tanker and then impacting with it which would cause damage
to either or both of them. For instance, if the spar is
caused to articulate or tilt slightly toward the tanker as
shown in Fig. 2, sheaves 84 will move a short distance along
respective tension members 78 so tha~ there will be an
unbalanced force in the forward direction, i.e., to the
right when viewing Fig. 2, which will contribute to the
buoyant force of buoyancy tank 74 to return the spar to its
normally upright position~ Similarly, if the spar tilts in
the direction opposite to that of Fig. 2, the opposite
effect will occur.
The tensioning system of Figs. 2-4 also operates
to position and keep the spar centrally between and spaced
from bow hor~s 72 and forwardly of and spaced from bow 20.
The tensioning system also allows the tanker to pitch rela-
tive to the spar yet the tanker and spar remain coupled
together and the spar remains substantially centered between
the bow horns~ Also, the spar can be disengaged from and
re-engaged with the ~anker without assistance from additional
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~075999
marine craft. Differential vertical forces exerted on the tanker are
compensated for by the tension system supplied by tension members 78.
The spar needs both anchorage and buoyancy to keep it in an
upright position. Base 14 provides the anchorage as mentioned above
to achieve the desired negative buoyancy. By balancing the buoyancy
force of the buoyancy tank 74 and the anchorage supplied by ballast
in base 14, the spar can be designed for towing, submerging and final
positioning with little or no recourse to air chambers.
While the tensioning means 82 has been described as a con-
stant tension device, this is only for purposes of illustration
because there are other ways of providing the constant tension for
tension members 78. For instance, a counterweight can be mounted on
the tanker bow or spar and coupled to tension members 78 so as to
provide the desired tension thereon, such as about 300 tons. This
value of tension should be adequate to deal with 50-year recurrence
storms but is far in excess of normal requirements. The counter-
weight could possibly be of the variable type, such as one filled
with seawater or other fluid so that it could be adjusted to changing
sea conditions.
A variable tension could be applied to tension members 78
by way of one or more air cylinder and piston assemblies. Such an
assembly might typically be about 50 feet long, 30 inches in diameter,
and operate under a pressure of 1,000 psi under extreme weather
conditions.
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10~759~
Motion compensators are also commercially available
for applying constant tension to tension members 7~. These
devices a}e commercially available from suppliers to the
offshore drilling industry. Some types of motion compensators
involve multiple cables and sheaves; thus, they are not as
practical for use as constant speed winches or a counterweight.
Under the constant motion of a tanker in the open sea, the
movement of cables over sheaves would possibly result in
excessive wear of the sheaves and the cables. However,
cable type motion compensators might possibly be suitable or
adequate.
In some instances, heavy nylon hawsers could be
used to maintain tension on the spar. The overall length of
nylon hawser would be such that maximum elongation does not exceed
25 percent. Within this limit, nylon is resilient.
A swivel unit 90 (Figs. 8 and 9) is mounted on the
upper end of spar 12 to allow rotation of tanker 22 about
spar 12. Swivel unit 90 includes an elongated tubular
swivel core 92 mounted by spaced upper and lower bearings 94
and 96 to the upper part of spar 12 so that core 92 can
rotate relative to the spar. A number of delivery hoses 98
(only one af which is shown in the drawings) communicating
with the interior of core 92 are connected to a support 100
(Fig. 2) mounted on the bow of the tanker. The support has
flow lines (not shown) coupled to hoses 98 to direct crude
oil from respective flow lines on the spar to the gas-oil
process facilities on the tanker or to a storage tank therein.
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- ~ ( l
1~7599~
1 A well-control condule 102 exte~ds downwardly
2 through the center of core 92 a~d can carry as many as 60 or
3 more high-pres~ure, ~mall diameter hydraulic line~ and 8iX
4 electrlc downhole pressure lndicator llnes. Condult 102 1~ ¦
flxed relatlve to the spar BO that core 92 rotate~ about
6 conduit 102. A well-control ~wivel 104 i~ ~ounted on the
7 upper end of conduit 102 and has an umbllicsl cable 106
8 whlch extends to the tanker. Cable 106 i~ coupled to the
9 varlous llnes ln conduit 102.
There may be ~everal flow lines from subsea wells
11 extend~ng upwardly through the spar to a reglon ad~acent to
12 core 92. Typlcally, there wlll be seven hydraulic flows
13 through the swivel, slx of which wlll be for use in dlrecting
14 crude oll upwardly and lnto core 92 for translt through plpe
98 to the tanker. The seventh llne wlll be used for well
16 test purpo~es and wlll be used to dlrect natural ~as or
17 crude oil back down the spsr and then to a nearby transit
18 tanker berth or by plpellne to a recelvlng ter~lnal on the
19 shore. For purposes of lllustration, three such flow lines
are coupled by respective swlvels to core 92 at corre~pondln8
21 locatlons along the len~th of the core. As shown in Fig. 8,
22 there 18 an upper swivel 108, a mlddle ~wlvel 110 and a
23 lower swlvel 112, all three swlvels belng rotatably mounted
24 on core 92 and havlng sultable seals at the core-swivel
Junctions to assure a fluidtlght connectlon eherebetween.
26 Any number o f flow systems can be accomodated uslng thi~
271~ general arrangement. Flow llnes 114, 116 snd 118 are coupled
28 1I to respectlve swlvels 108, 110 and 112.
291'
33
32 -23- i
~1
I
~(~7~
Core 92, for purposes of illustration, is divided
into three compartments, 120, 122 and 124, compartment L24
communicating with flow line 118 as shown in Fig. 9. Flow
lines 114 and 116 are similarly in tommunication with com-
partments 120 and 122? respectively~ Well-head pressure, if
sufficient, will cause crude oil to be pumped through flow
lines 114, 116 and 118. Pumps can also be used for this
purpose. There will be respective delivery hoses 98 in
fluid communication with the three compartments 120, 122 and
124. Thus, regardless of the angular position of the tanker
relative to the spar, there will be a flow of crude oil
through hoses 98 to the tanker. In the alternative, the
spar could have a flow line manifold. In such a case, only
one hose 98 would be required.
An access man-way 126 is provided in the upper end
of the spar as shown in Figs. 8 and 9. The depth to which
the man-way extends generally will be at least to buoyancy
tank 74 and possibly below the same.
Another embodiment of the tensioning system of the
present invention is shown in Figs. 10-12 wherein the upper
portion of the spar is provided with a morring swivel 130
rotatably mounted thereon above buoyancy chamber 74 on spar
12 as shown in Fig. 10. The spar also has a slip ring 132
rotatably mounted thereon between a pair of bow horns 134 on
the bow 20 of the tanker. A first pair of tension members
136 are secured at their lower ends to respective sides of
mooring swivel 130, and tension members extend upwardly to
and over a common sheave 138 on bow 20 and then pass to a
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1(~'7S5'~5~
constant tension device 140, such as a constant tension
winch. Thus, members 136 exert a tension force on spar 12.
The location of mooring swivel 130 along the length of spar
12 is such that angle A (Fig. 10) between each tension
member 136 and the longitudinal axis of spar 12 is quite
shallow, such as 10 to 15~ Tension members 136 are located
at this angle relative to the spar so that there will always
be a lateral component 137 of the tension force T exerted
along each tension member 136 to urge the spar toward the
tanker. In this way, the spar and tanker are kept from
moving out of phase with each other so as to avoid damage
due to impacting of the two together.
A second pair of tension members 142 is coupled at
the front ends thereof to respective sides of slip ring 132,
then to respective sheaves 144 near the outer ends of
respective bow horns 134, then to respective constant tension
devices 146 on opposite sides of the bow as shown in Fig.
12. Tension members 142, when cooperating with slip ring
132, maintains the spar centrally located between bow horn
134 and spaced forwardly of the bow of the tanker to prevent
impact of the spar and the tanker itself. Also, tension
members 142 allow the tanker to pitch relative to the spar.
The buoyancy force of buoyancy tank 74 is aided by the
tension force of tension members 136 to bias or urge the
spar into its normally upright position.
Fig. 10 shows a substantial windvane position of
the spar relative to the tanker~ and Fig. 11 shows a substantial
override position of the spar relative to the tanker~
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1~75999
l Typlcally~ ~he inclination of the gpar ln the wlndvane
2 posltlon 19 about 20 and ln the overrlde position 18 about
3 10-. In both ca~es, the spar r,emains centered between and
4 spaced from the bow horn~ by te~nslon members ~42 and tenslon
members 136 continue to be at an angle relael~e to the
6 longltudlnal 8xi8 of the ~par.
7 The embodiment of Flgs. 13-lS 18 very slmllar to
8 that of Flgs. 10-12 ln that lt has a rotatable ~oorlng
9 swivel 130 above buoyancy tank 74 and a palr of tenslon
members 136 whlch extend upwardly to snd over a common
ll sheave 138 on the bow of the tanker and then to a constant
12 tension devlce 140. Inetead of slip ring 132 and ten~ion
13 membQrs 142 of Figs. 10-12, the embodiment of Flgs. 13-lS
14 has a motlfled bow horn structure 148 in whlch a V-~haped
notch or recess 150 (Flg. 15) i8 provlded at the forward
l6 extremlty and three or more angularly spaced rollera 152 are
l7 mounted on structure 148 near the rearmost portlon of the
l8 notch for rotatlon about respective horlzontal axes. The
l9 rollers operate to engage the ad~acent part of the spar at
20~ all times. Spar 12 1Q held in rolling contact with rollers
21~ 152 by the lateral component 137 of ehe tension force T
22¦ applied by angled tension member~ 136 to ~ooring swlvel 130,
23~ yet the spar i~ biased in a normally npright po~itlon by the
241 buoyancy force of buoyancy tank 74. Flg. 13 ~how3 a a~bstan-
251 tlal windvane posltion of the spar relative to the tanker;
26 and ~ig. 14 sho~is a substantial override posltion of the
27 spar.
281
29
3~ -~6-
1~75~
The way in which wave action affects the relative
positions between the spar and the tanker is illustrated in
Figs. 16, 16a, 16b and 17. The tensioning system of Figs.
10-12 is assumed to be the coupling means for purposes of
discussion hereinafter. In Figs. 16 and 16a, the effects
will be considered at the crest of a wave, and Figs. 16b and
17 illustrate the effects at the trough of a wave.
The crest of the wave (Fig. 16) is denoted by the
numeral 210 and the direction of the wave is from right to
left as indicated by arrow 208. Thus, as conventionally
considered~ the wave particle motion will be circular as
indicated by circles 214, 216 and 218 and of progressively
decreasing diameter as the circles extend downwardly and
away from crest 210.
In practice, the wave will have its greatest force
at the surface 18, the wave force being less intense as the
water depth increases. The force of the wave action will be
exerted at various locations along the spar, the individual
forces at such locations being denoted by arrows 220 extending
to the left.
Fig. 16a shows the resolution of the various
forces exerted on the spar when the spar is in the inclined
attitude of Fig. 16, assuming the wave crest is passing and
wave direction is from right to left as denoted by arrow
208. In this case, the forces exerted on the spar by the
wave action and the component 137 of the tension force of
each tension member 136 exceed the lateral component of
force 139 due to the buoyancy force 141 of buoyancy tank 74.
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t--
~ 7S999
2 Thus, th~ ~par 1~ malntained ln lts normal coupled relstlon-
3 shlp with the bow of the tanker and there is substant1ally
4 . no problem of tanker separaeion from the spar due to wave
actlon (Flg. 16~.
6 When che wave trough i~ passing and wave directlon
7 ¦ 1~ ln the dlrection of arrow 208, the wave forces on the
8 ~ spar are in the dlrectlon of arrows 222 (Fig. 16b) and the
9 spar may a~sume the inclined attitude opposlte to that of
10 ~ Flg. 16a. In the alternative, the spar may remain gen~rally
11 I uprlght althou~h, in general, it will be sllohtly inclined
in one direc~ion or another. Assumlng that the incllnaelon
23 ¦ f the ~pa~ i~ a~ shown in ~ig. 16b, lateral co~ponent~ 137
14 ¦ of the tenslon force due to tension members 136 and lateral
15 ¦ component~ 139 of the buoyancy force 141 of buoyancy tank 74
16 ~ must be at lea~t as great as the sum of the force~ of the
17 I wave actio~ denotPd by arrow 222. Since the tension of the
18 I ten~lon memberR 136 1~ relatively large, such as 300 tons or
19 ¦ ~ore, the lateral component 137 will be relatively large ~o
20 ¦ as to keep the spar effectively coupled to the tanker e~en
21 ~ during e~treme conditlon3, such as being subJected to the
22 ¦ trough of a 60-foot wave in the dlrectlon of arrow 208 of
23 ¦ Fig. 16. Even assumlng thst the spar i9 in a generally
24 ¦ upri~ht position when the wave strikes the ~par, lateral
25 ~ component 137 will continue to counterbalance the force of
26 the wave or even exceed the force of the wave wlthout the
27 assistance of component 139, for in the uprlght po~itlon,
28 co~ponent 139 will not exist becau~e the buoyancy force 141
29 will be coincident wlth the }ongitudinal a~is of the spar.
2 -2~-
Il ~
.
1075999
1 I In considerlng the rlelatlonshlp to the tanker and
2 ¦ the Qpar at the trough 230 of R wave moving ln the dlrectlon
3~ of arrow 208 (Flg. 17~, the wave action i9 assumed to rotate
4 ~n the d~rection of srrow 232 and thereby exert lsteral
5 ¦ fQrces 234 along varlous locntlons of the spar. ln sueh a
6 case, the lateral component 137 of the tenslon due to member
7 136 must counterbalance the~e force~ 234 as well as the
8 later~l component 139 of buoyancy force 141 If ~par 12 i~
9 lnclined to the left as shown in Flg. 16a. If incllned to
the rlght a~ shown in Fig. 16b, lateral components 137 and
11 139 are ln the ~ame dlrectlon and are addltlve, the sum of
12 these co~ponents then serving to counterbalance wa~e forces
13 234. The tension of members 136 wlll be sufflclently great
14 such that component 137 will have a magnltude st least equal
to or greater than the sum of the forces comprlsed of com-
16 ponent 139 and forces 234 due to the wave aetion.
17 For wave actlon at the trough for waves moving ln
18 the dlrectlon opposlte to arrow 208, the lateral forces 236
19 will be the forces due to wave action and these lateral
20 ¦ forces wlll be in the same dlrection a~ lateral component
21 137. Thus, thls will be a condltion ln whlch there wlll be
22 substantlslly no tanker separatlon problems and the spar and
23 the tanker wlll remaln effectively coupled together. This
24 conflguratlon allows the tanker to dlsengage from the mooring
25 ~ under severe weather condltion~ wlthout as~lctance from
26 ¦ other marlne craft and without ha~lng workmen exposed on the
27 tanker bow by slmply releasing the connectlng csble.
28
29
31
32 -29-
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