Note: Descriptions are shown in the official language in which they were submitted.
9~2~
This invention relates generally to methods of
launching pipelines from an on-shore site into a body
of water and of retrieving support means used in ]aunching
the pipeline. The pipeline is maintained above a floor
of the body of water during the launching procedure.
The construction of off-shore oil or gas
production facilities often requires the placement of
a long pipeline on or near the ocean floor~ for example,
to connect a satellite well to a central producing
platform.
The most common way of manufacturing the pipe-
lines and placing them on the ocean floor is to constrl~ct
the pipeline on a lay barge and to lower the constructed
pipeline frorn the lay barge onto the ocean floor as the
pipeline is constructed.
In some situations, however, it i5 not possible
to construct the pipeline on a lay barge and simultaneously
lower it onto the ocean floor because of the severe
environmental conditions present. This is often the case
when production facilities are being constructed in the
North Sea area. ~lso, some flowline bundles are too
complex to construct on a lay barge.
It has been proposed that an entire pipeline be
constructed at an on~shore construction site and
subsequently be launched from the on-shore construc-tion
site and into a body of water and then towed through the
body of water to the installation site.
2~
Summary of the Invention
-
In some geographic locations particular problems are
presented to the launching of a pipeline from an on shore
site due to of-shore shallow water depths, sandy bottom
conditions which create a very high drag on any tow cable
which is allowed to engage the bottom of the ocean floor,
and large boulders located off-shore in the launching area.
The present invention provides a very much improved method
of launching long pipelines which holds the pipeline above
the ocean floor during the launching procedure and allows
it to be immediately towed away rom the launch site in a
catenary configuration, and which provides for retrieval of
support means after launching.
This method includes the supporting of the pipeline at
the on-shore site with a plurality of floatable ground en-
gaging movable support means spaced along a length of the
pipeline, said means of said plurality of support means
being connected together by a support connecting line.
A shallow draft barge is positioned off-shore from the
launching site. A main launching line is deployed seaward
from a seaward end of the barge to a main buoy located at a
posi-tion in the body of water where the body of water has a
depth sufficient to allow a launch vessel to approach the
main buoy. The main launching line is pro~ided with suffi-
cient buoyancy means to hold the launching line abo~e thefloor o~ the body of water.
A pipeline launch line is connected between a landward
end of the barge and a seaward end of the pipeline. A sup-
port means launch line is connected between the landward end
of the barge and a seaward end of the support connecting
line.
The seaward end of the main launching line is discon-
nected from the main buoy and connected to the launch ves-
sel. When the body of water is at substantially its high
tide mark, the launch vessel then steams seaward and tows
-the pipeline and support connecting line into the body of
water. This towing is done at a speed sufficient to tow
the entire length of the pipeline into the body of water
6;~
--3--
while the ~ody of water is at substantially its high tide
mark. As the~ pipeline is towed into the body of water, a
retarding force is applied to the pipeline to thereby main-
tain a tension force on the pipeline sufficient to hold the
pipeline above the floor of the body of water. This retard-
ing force is preferably supplied by a known frictional force
between the ground engaging support means and the ground
~ ~, between sled runners and a pair of rails), or it may
be supplied by a retarding line attached to a landward end
of the pipeline and/or the support connectirlg ~ine.
Once the landward end of the pipeline reaches a posi-
tion in the body of water sufficient that a trailing tow
vessel may approach the landward end of the pipeline, a
trailing tow line is connected to the trailing tow vessel
and a tensional retarding force is applied to the trailing
tow line and the pipeline by means of the trailing tow ves-
sel to hold the pipeline above the floor o~ the body of
water. Then the retarding line means is dlsconnected from
the landward end of the pipeline. A leading tow line is
then connected between a leading tow vessel and the seaward
end of the pipeline and the pipeline launch line is discon-
nected from the pipPline.
The floating support means and support connecting line
are then retrieved.
At this point the pipeline is suspended in a catenary
fashion between the leading tow vessel and the trailing tow
vessel an~ may be immediately towed to the installation
site. This entire launching pxocedure is accomplished with-
out the pipeline engaging the ocean floor so as to avoid
the problems previously mentioned.
It is therefore a general object of the present inven-
tion to provide an improved method of launching a pipeline
from an on-shoxe site.
Another object of the present invention is to provide
a method for launching a pipeline from an on-shore site
while holding the pipeline above the ocean floor.
Yet another object of the present invention is the pro-
vision of a method for launching a long pipeline from an
1~962~DO
on-shore site where shallow off-shore conditions prevent a
leading tow vessel from connecting a tow line directly to a
seaward end of the pipeline to launch the same.
Still another object of the present inven-tion is the
provision of a method for launching pipelines wherein all
tow cables are kept above the ocean floor so as to prevent
problems created by the drag of tow cables on the ocean
floor.
Yet another object of the present invention is the pro-
vision of methods for launching long pipelines wherein thepipeline will be launched at relatively high speeds to take
advantage of tide changes.
And another object of the present invention is the pro-
vision of methods for launching pipelines at high launching
speeds wherein the launching speeds are controllable through
a braking system.
A further object of the present invention is the provi-
sion of a method for launching pipelines, wherein support
means for the pipeline are floatable and may be easily re
trieved after the pipeline is launched.
Other and further objects, features and advantages of
the present invention will be readily apparent to those
skilled in the art upon a reading of the following disclo-
sure when taking in conjunction with the accompanying
drawings.
Br1ef Description of the Drawings
FIGS. 1-5 comprise a sequential series of schematic
plan drawings illustratiny the method of -the present inven-
tion.
FIG. 6 is a schematic elevation view of a pipeline
being towed in a ca-tenary fashion between a leading tow ves-
sel and a trailing tow vessel.
FIG. 7 is a side elevation view of a pipeline system
supported by a plurality of ground engaging movable support
means.
FIG. 8 is a front elevation view of the system of FIG.
7 taken alony line 8-8 of FIG. 7.
bCI
FIG. 9 is an exploded view of an alternative form
of ground engaging support means which includes a floatation
means so that the support means will float once it is dis-
engaged from the pipeline.
FIG. 10 iS a graph describing the buoyancy of the
sys-tem of FIG. 9 in relation to the depth of submergence of
the float.
FIG. 11 is a schematic plan view illustra-ting
several alternative methods of retrie~ing the floating
support means of FIG. 9 after they are disengaged from the
pipeline.
Detailed Description of the ~referred Embodim nt
mhe methods of the present in~ention are particularly
adapted for use with a pipeline system such as is disclosed
in U.S. Patent No. 4,363,566 of Arthur W. Morton, dated
December 14, 1982, and for use with subsequent methods of
towing such a pipeline as also disclosed in said prior
application, which application is assigned to the assignee
of the present invention.
Referring now to FIGS. 7 and 8, a pipeline system
10 includes a pipeline 12 ha~ing a plurality of chain weights
14 attached thereto. As can be seen in FIGo 6 I the pipe-
line system 10 also includes a leading pipeline sled
assembly 16 defining a seaward end of pipeline 12~ and
includes a trailing pipeline sled assembly 18 defining a
landward end of pipeline 12. Pipeline system 10 is
constructed in accordance with the teachings of Application
Serial No. 048,316. Pipeline 12 itself has a positive
buoyancy. Chain weights 14 give the entire system 10 a
negative buoyancy~ so that in the absence of any lifting
forces from outside sources pipeline system 10 will assume a
position with pipeline 12 floating off bottom and chain
weights 1~ engaging the bottom of body of water 30.
As shown in FIGS. 7 and 8, the pipeline system 10
is supported at an on-shore construction site by a plurality
of ground engaging support means 20 which are spaced along a
length of the pipeline system 10. The support means 20 are
~:~9~
connected together by a support connecting llne 22 which may
be a steel cable. The connecting line 2~ may be a continu-
ous cable being attached at intermediate points to the vari-
ous support means 20, or it may be comprised of a plurality
of cable segments having their ends attached to adjacent
support means 20.
The support means 20 are movable relative to the ground
surface so that when the pipeline system 10 is -towed into
the ocean, support means 20 will move with the pipeline sys-
tem 10.
One manner of construction of the support means 20 isshown in FIGS~ 7 and 8, and includes a plurality of sleds
having runners 24 slidably engaging a pair of parallel rails
26 and 28 extending into a body o~ water 30. Thus, sleds
having runners engaginy rails, which rails are mounted on
the ground, may be generally referred to as ground engaging
support means.
The support means 20 of FIGS. 7 and 8 each includes a
frame 31 supported from runners 24. Attached to frame 31
are a pair of spaced parallel cylindrical buoyancy tanks 33.
The pipeline 12 rests on cushions 35 attached to the tanks
33, and the ohain weights 14 are supported in a chaImel 37
attached to frame 31 between tanks 33. The tanks 33 have a
buoyancy less than the weight of support means 20 including
tanks 33, therefore support means 20 will not float when it
is disengaged from pipeline system 10.
Each of the runners 24 includes a wooden skid 25. The
skids 25 are attached to runners 24 by bolts (not shown)
which are countersunk into the bottom of the skids so that
30 they will not engage the rails 26 or 28 as the skids 25
wear down.
The rails 26 and 28 are covered with tallow so that a
wood on tallowed steel friction factor is provided between
the sleds 20 and the rails 26 and 28. The wooden skids 25
preferably are oak, and this friction factor for tallowed
oak on steel rails has been determined to be in the range
of about 0.12 to 0.18. Since the weight of the sleds and
the loads carried thereby may be determined this provides
7--
a predetermined ~rictional force between the sleds and the
rails based upon this friction factor.
Other advantages are also pxovided by the use of sup-
port means 20 with runners as shown in FIGS. 7 and 8 as com-
pared to support means 86 with wheels as shown ln FIG. 9.
If the rails 26 and 28 are worn, or for other reasonsare not uniformly and accurately positioned, support means
86 with wheels 92 can sometimes "jump" the rails at high
speed. The inverted channel shape design of runners 24
with downwardly depending flanges 23 allows some lateral
movement of runners 24 xelative to rails 26 and 2~ thus al
lowing the sled to function satisfactorily on rails which
would not provide a satisfactory track for a wheeled appa-
ratus.
Also, the combination of properly sized runners 24 and
buoyancy tanks 33 provides a support means 20 which can be
pulled across the ocean floor without digging into the ocean
floor. This is generally not provided by a wheeled appara-
tus because the ~heels dig into the ocean floorO To pro-
vide this proper combination it is necessary to know the
bearing pressure which can be supported by the ocean floor.
The bearing area of the runners 24 is dependent on their
size. The submerged weight of the support means 20 can be
controlled by modifying the volume of water displaced by
buoyancy tanks 33.
Referring now to the sequential series of FIGS. 1-5,
and heginning with FIG. 1, the method of the present inven-
tion is described below.
FIG. 1 illustrates a portion of an on-shore site 32.
The rails 26 and 28 have their seaward ends extending into
the body of water 30 to a point 34 defining the low tide
markof the body of water 30. Sand dunes 27 and 29 are shown.
The rails 26 and 28 extend landward through a construc-
tion facility 39 and then further landward for a distance of
approximately one mile. The pipeline system 10 is construc-
ted in the construction facility 39 and is stored on the
rails 26 and 28 prior to launching.
z~
Located near the rails 26 and 28 are an on-shore winch
36 and first a~d second turning blocks 38 and 40.
In E'IG. l, a shallow draft barge 42 has been positioned
off-shore from the site 32 and is anchored by means of an-
chor lines 44 and 46. Barge 42 may also be referred to as
an intermediate floating vessel 42.
A main launching line 48 is deployed seaward from a
seaward end 50 of barge 42 to a main buoy 52.
The floor 54 (see FIG. 6) of body of water 30 is at
such a shallow depth at the location of barge ~2 that it
would not by possible for a typical launch ves~el to reach
that location because there is insufficient draft to float
the launch vessel. The main buoy 52 is located at a posi-
tion in body of water 30 sufficient to allow a launch ves-
sel to approach main buoy 52.
The main launching line 48 is provided with sufficientbuoyancy means 56 to hold main launching line 48 above the
floor 54 of body of water 30. It will be appreciated by
those skilled in the art that the buoyancy means 50 may
either be separate detachable elements attached to an other-
wise non-buoyant line 48, or the line 48 may be constructed
in such a manner and of such materials that the line 48 has
an inherent buoyancy.
Also illustrated in FIGo 1 is the high tide mark 58 of
body of water 30. The present invention is particularly
adapted for launching the pipeline system 10 at high tide,
and is adapted for launching at high speeds so that the en-
tire launching procedure can be accomplished while the body
of water 30 is at or substantially near its high tide mark
58.
Preferably, support means 20 with runners 24 having
wooden skids 25 running on tallowed rails 26 and 28 are
utilized so that a known friction force is provided between
the support means 20 and the rails 26 and 28 to apply a re-
tarding force on pipeline 12 sufficient to hold it in ten-
sion and hold it above the ocean floor as the pipeline 12
is towed into the body of water. When that system is used
` - 9 -
there is no need to initially attach a retarding line to
the landward end of the pipeline 12.
If, however, a wheeled support means 86 like that shown
in FIG. 9 is used, it may be necessary to attach a retard-
ing line 60 (see FIG. 1) to the landward end 18 of pipelinesystem 10 and to the landward end of the support comlecting
line 22. Retarding line 60 is mounted upon a retarding
winch 62. This retarding line 60 is then used to hold pipe-
line system 10 in tension as it is towed into the body of
water.
Referring now to FIG. 2, the pipeline system 10 has
been moved seaward from the position shown in FIG. 1 to a
position wherein the seaward end 16 is located near the high
tide mark 58. This movement is preferably accomplished by
used of the win~h 36 and a pulling line (not shown) extended
from winch 36 around turning block 38 and connected to sea~
ward end 16 of pipeline system 10.
When the pipeline system 10 is in approximately the
position shown in FIG. 2, a pipeline launch line 64 is con-
nected between a landward end 66 of barge 42 and the seaward
end 16 of pipeline system 10. A support means launch line
68 is similarly connected between barge 42 and a seaward end
of support connecting line 22.
Referring now to FIG. 3, a launch vessel 70 approaches
main buoy 52 and a seaward end 72 of main launching line 4a
is disconnected from main buoy 52 ~nd is connected to the
launch vessel 70 as shown in FIG. 3. Next, as illustrated
in FIG. 4, the launch vessel 70 moves seaward and thereby
tows the pipeline system 10 and the support connecting line
22, with attached support means 20, into the body of water
30. In FIG. 4, only the pipeline system 10 is shown to sim-
plify the illustration. The support connecting line 22 and
support means 20 are generally still located below the pipe-
line system 10 and are submerged in the body of water 30.
As the pipeline system 10 and support connecting line
22 are towed into the body of water 30, a retarding Eorce is
applied thereto to maintain a tension on the pipeline system
62~3~
~10--
10 sufficient to hold the pipeline system 10 above the floor
54 of body of water 30.
This retarding force is preferably applied by provid
ing a known friction force between support means 20 and
rails 26 and 28 through the use of wooden skids 25 engaging
tallowed rails 26 and ~8~ This frictional force should be
of a magnitude such that it is greater than any gravita-
tional forces present due to inclines in rails 26 and 28.
In that manner the known frictional orces also provide a
braking force sufficient to hold the pipeline system 10 in
place if the towing operation is terminated.
With the arrangement just described the launching force
which must be provided by launch vessel 70 is determined
by the frictional forces between skids 25 and rails 26 and
28. As the pipeline system 10 is towed int~ the body o
water the total of the frictional forces continually de-
creases so that a contlnually decreasing towing fo~ce is
required. The pipeline system 10 is preferably towed at a
substantially constant speed in the range of about 250~300
feet per minute, which is approximately the fastest speed
at which a man can walk beside the moving pipeline and per-
form manual operations thereon. Preferably contact is main-
tained by radio between an observer monitoring the speed of
the pipeline and the operator of the launch vessel 70.
~5 If the retarding line 60 is used the retarding force is
applied to retarding line 60 by means of retarding winch 62
which retarding force is sufficient to maintain a tension on
the pipeline system 10 suf~icient to hold the pipeline sys-
tem 10 above the floor S4 of body of water 30. ~lso the
retarding line 60 and retarding winch 62 provide a bxaking
system for controlling the high launching speed of pipeline
system 10.
With either method of applying the initial retarding
force, when the landward end 18 of pipeline system 10
reaches approximately the position illustrated in FIG. 4 a
polypropylene seagoing retarding line 74 is connected to
the landward ends of both pipeline system 10 and support
~6~.3~
connecting line 22, and the first retarding line 60 (if
used) is disconnected. The tensional force on pipeline
system 10 and support connecting line 22 is maintained by
seagoing retarding line 74.
Referring now to FIG. 5, the launch vessel 70 has con-
tinued to tow the pipeline system 10 into the body of water
30 until the landward end 18 of pipeline system 10 has
reached a position in the body of water 30 wherein the body
of water 30 has a depth sufficient to float a trailing tow
vessel 76.
~ pennant buoy 78 is then picked up by trailing tow
vessel 76 and a trailing tow line 80 (see FIG. 6~ is con-
nected between the landward end 18 of pipeline system 10 and
the trailing tow vessel 76.
Then, trailing tow vessel 76 applies a tensional re-
tarding force to trailing tow line 80 to hold pipeline sys-
tem 10 above the floor 54 of body of water 30, and the sea
going retarding line means 74 is disconnected from the pipe-
line system 10.
A leading ~ow vessel 82 is then connected to seaward
end 16 of pipeline syst~m 10 by a leading tow line 8~ and
the pipeline launch line 64 is then disconnected from the
pipeline system 10. At that point, the pipeline system 10
has the appearance shown in FIG. 6 where it is suspended in
2S a catenary fashion between leading tow vessel 82 and trail-
ing tow vessel 76.
FIG. 9 illustrates an alternative manner of construc-
tion of the support means. The support means of FIG. 9 is
designated by the numeral 86, and is a floating support
means 86. The floating support means 86 includes a struc-
tural frame 88 having a saddle member 90 extending upwardly
therefrom for engagement with pipeline 12. Attached to the
frame 88 are a plurality of wheels 92 for engagement with
the rails 26 and 28. It will be understood by those skilled
in the art that skids or runners such as runners 22 could be
substituted for the wheels 92.
Attached to the support means 86 is a float 94. The
float 9~ is preferably a toroidal shaped inflatable elasto-
6;~
-12-
meric member. The ~loat 94 may be an innertube from a pneu-
matic tire or the like, and thus is relatively inexpensive.
The float 94 is attached to -the frame 88 by an annular
wooden support piece 96. Float 94 is attached to support
piece 96 by a plurality of straps 98. The support piece 96
is itself attached to frame 88 by a plurality of brackets
100 the lower ends of which are welded to Erame 88 and the
upper ends of which are bolted to wooden support piece 96.
As can be seen in ~'IG. 9, the toroidal float 94 fits around
the saddle member 90.
Referring again to FIGS. 7 and 8, it is seen that each
of the support me~ns thereshown, supports a portion of the
weight of the pipeline 12 and also supports one of the chain
weights 14 which is piled up on top of the support means 20.
Similarly, the chain weight 14 is layed on top of the wooden
support piece 96 of support means 86.
Each of the floats 94 has a buoyancy greater than a
combined weight of the float 94 plus the support means 86
to which it is attached, and less than a comkined weight of
the float 94, plus the support means 86 to which it is at-
tached, plus the portion of the total weight of the pipeline
system 10 supported by the support means 86, so that when
the portion of the total weight of pipeline system 10 car-
ried initially by support means 86 is removed from the sup-
port means 86, the support means 86 will float to the surfaceof body of water 30.
As can be understood by viewing FIGS. 7 and 8, once the
pipeline system 10 is in the body of water 30, the support
means 86 will begin to submerge. As soon as support means
86 has moved slightly downward away from the pipeline 12,
the only portion of pipeline system 10 then being supported
by the support means 86 will be the weight of chain weight
14. As the depth of submergence of support means 86 below
pipeline 12 increases, the portion of chain weight 14 being
supported by the support means 85 will also decrease.
Thus, the float 94 preferably has a buoyancy less than
a combined weight of the float 94, plus the support means
-13-
86, plus the chain weight 14, so that so long as the sup-
port means 86 is supporting a substantial portion of the
chain weight 14, the support means ~6 wilL be held under
water.
When using an inflatable elastomeric float like the
float 94, the overall design of the system must take into
account the fact that as the inflatable elastomeric float
94 is submerged to deeper depths within the body of water,
the external pressures acting upon the inflatable float in-
crease thus decreasing the volume of water displaced by the
~loat and thus decreasing the buoyancy of the floatO For
any given inflatable elastomeric float attached to a support
means having a fixed submerged weight, it is possible to
submerge the assembled float and support means to a depth
such that the buoyancy of the float is decreased to a value
less than the total weight of the float and the support
means, so that the float is no longer capable of buoying
the support means and at that point the entire assembly will
sink to the bottom of the body of water. Thus, the design
of the system must be such that the float 94 will not be
submerged to this critical depth during the proces~ of
launching the pipeline.
An example o~ such a design is illustrated in FIG. 10,
which is a graph plotting the weight supported by float 94,
and the buoyancy of the float 94, as a function of the depth
to which the float is submerged.
In FIG. 10, the horizontal axis represents the submer-
gence depth of the float 94 and the vextical axis is scaled
in pounds and both weight and buoyancy are plotted on the
vertical axis.
The curve 102 on FIG. 10 represents the buoyancy of
float 94 as a function of depth of submergence. The posi
tion of curve 102 may be moved, fox example, to the position
shown in dotted lines, by varying the inflation pressure of
float g4. It can be seen that for the particular example
plotted in FIG. 10, the buoyancy of the float at the surface
is equal to 334 pounds. A second curve 10~ of FIG. 10 is a
i62~
_14W
plot of the total of the weight of the support ~eans 86,
the float 94, and the portion of weight chain 14, if any,
supported by support means 86 for a given submergence depth
of float 94.
For a pipeline system 10 like that disclosed in the
present application, the chain weight 14 has a length of
6.8 feet and a weight of about 18.4 pounds per foot in salt
water, so that the chain welght 14 has a total weight of
approximately 125 pounds. The combined weight of the sup-
port means 86 and the float 94 attached thereto is approxi-
mately 220 pounds. It will be understood that in the embo-
diment disclosed herein the weight of the float 9~ itself is
negligible so it can be said that the support means 86 weighs
approximately 220 pounds. It is, however, possible that
otner ~ypes of float means might be attached to the support
mean~ 86 wherein the 1Oat itself would have a substantial
weight, so it will be understood that in order for the float
to support the entire apparatus to which it is attached
after it is disengaged from the pipeline system 10, the
float must have a buoyancy sufficient to overcome th~ weight
of the support means and any weight of the float itself.
The combined weight of the support means 86 and the
chain weight 14 is thus approximately 345 pounds as is re-
presented by the left-most end of second curve 104.
It can be observed for a pipeline system 10 like that
disclosed in the present applicationt that the pipeline 12
will float off the support means 86 when the float 94 is
submerged to a depth of approximately three feet. Thus, the
left-hand flat portion 106 of second curve 104 represents
the first three feet of submergence of float 94 wherein the
support means 86 s-till is supporting the entire 345 pound
combined weight of chain 14 plus the support means 86. From
a submergence depth of three feet to a submergence dep-th of
9O8 feet, the support means 86 will support a linea.rly de-
creasing portion of the weight of the chain weigh-t 14. Thus,
the combined weight of the support means 86 plus the portion
of the weight of chain weight 14 being supported thereby for
- -15-
depths of sub~ergence between three feet and 9.8 feet is
represented by the downwardly sloped portion 108 of curve
104.
At any submergen~e depth of greater than 9.8 feet, the
chain weight 14 is no longer supported by the support means
86 so that the right-hand horizontal portion 110 of second
curve 104 represents the weight of support means 86 of 220
pounds.
It can be seen in FIG. 10 that the second curve 104
first crosses the first curve 102 at a point 112 represent-
ing a submergence depth of approximately 7 feet for the
float 94. Thus, at a submergence depth o~ 7 feet the buoy-
ancy of float 94 is equal to the weight of support means 86
plus the portion of the weight of chain weight 14 being sup-
ported thereby, and the support means 86 will thus not sink
ar.y further. At this depth of about 7 fee~ any sideways
thrust exerted on the float 94 will cause it to move side~
ways from under the chain weight 14 and the float 94, thus
disengaging pipeline system 10, and the support means 86
will pop to the surface of the body of water 30. It will be
understood that some of the support means 86 may disengage
themselves from pipeline system 10 before the entire pipe-
line 12 is towed into the body of water 30.
Thus, it is seen that it is important that the overall
system design be such that the float 94 will never be sub-
merged to a depth below the depth at which its buoyancy is
greater than the weight of the support means. In the ex-
ample shown in FIG. 10 this means that the float 94 should
never be submerged to a depth greater than approximately 17
feet Eor if it is, then it will continue to sink due to de-
creasing buoyancy.
The summation of the forces acting upon the support
means 86 due to its weight, supported weight, and buoyancy
of float 94, may generally be described by looking at the
relationship between the two curves 102 and 104. At the
left-hand side of FIG. 10, the second curve 104 is above the
first curve 102 thus representing the sinking of float 94
-16-
from a depth of zero ~eet to a depth of approximately 7
feet. This is a zone 114 of negative buoyancy wherein the
weight exerted downward is greatex than the upward buoyant
force. At depths of submergence for float 94 between appro-
ximately 7 feet and 17 feet, the float 94 has a buoyancygreater than the weight being supported by support means 86
and thus there is a zone 116 of positive buoyancy. For
depths of submergence greater than 17 feet, the buoyancy
once again becomes less than the weight which is exerted
downward upon support m~ans 86 thus there is a second zone
118 of negative buoyancy.
Preferably the entire system is designed such that the
chain weight 14 has a length such that when pipeline 12 is
located substantially at the surface of ~ody of water 30 and
the chain weight 14 is extended downward substantially its
entire length with the support means 86 located below and
engaging the lawer end of the chain weight, the float 94
attached to support means 86 has a buoyancy greater than the
combined weight of the float 94 and the support means 86.
This eliminates any possibility of the float 94 being suh-
merged into the second negative buoyancy 20ne 118~
Referring now to FIG. 11, several methods are there
schematically illustrated for retrieving the floating sup-
port means 86 after the pipeline system 10 has been launched.
As previously described, one of the final steps in the
launching of the pipeline system 10 is the disconnection of
pipeline launch line 64 from the seaward end of pipeline
system 10. At the same time the support means launch line
68 is disconnected from support connecting line 22. If a
non-floating type of support means such as support means 20
is utilized, then when it is disconnected from barge 42, the
support connecting line 22 and all of the attached support
means 20 will sink to the ocean floor. If, however, float-
ing support means such as support means 86 are utilized,
then the support connecting line 22 and all of the support
means 86 will float to the surface of the body of water 30.
The floating support means 86 and support connecting
;2~
-17-
line 22 may then be retrieved in any one of several manners.
FIG. 11 simultaneously illustrates these various methods.
A first manner of retrieving the ~loating support means 86
is to connect the support connecting line 22 to a retriev-
ing winch 120 located on shore. Then the support connecting
line 22 may be reeled into shore by the winch 120 thus also
pulling the floaking support means ~6 onto shore.
A second method of retrieving the floatin~ support
means 86 is to connect small boats, such as boats 122 and
124, to the support connecting line 22 and the floa-ting sup-
port means 86 and to tow the support connecting line 22 and
floating support means g6 to shore.
A third method of retrieving is illustrated on the up-
per portion of FIG. 11 wherein a boat 126 is anchored in
the body of water 30 by anchor lines 128 and the support
connecting line 22 is connected to a retrieving winch 130
on the boat 126. Then the support connecting line 22 is
reeled into the boat 126 by means of winch 130 thus pulling
the support connecting line 22 and floating support means
86 into the boat 126.
Thus it is seen that the present invention readily
achieves the ends and advantages mentioned as well as those
inherent therein. While certain specific arrangements of
parts and steps have been illustrated for the purposes of
the present disclosure, numerous changes in the construc-
tion and arrangement of steps and parts may be made by
those skilled in the art, which chan~es are encompassed with~
in the scope and spirit of the present invention as defined
by the appended claims.
