Note: Descriptions are shown in the official language in which they were submitted.
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1. Field of the Invention
This invention relates to a reel pipelaying vessel.
More particularly, the invention pertains to a new type of ship,
specifically a self-propelled, dynamically-positionable reel
pipelaying ship, in which a pipe spooling reel and associated
pipe handling equipment are integrated into the ship's
construction.
The vessel of this invention has been specifically
designed to accommodate a permanently mounted pipe spooling
reel substantially larger than any other pipe spooling reel
heretofore known or used and capable of spooling substantially
larger size pipe than any heretofore used.
2. History of the Prior Art
In laying offshore subsea pipelines for such uses
as the gathering of oil and/or gas from offshore subsea
wells, as, for example, in the Gulf of Mexico, it has been
conventional to use one of two main methods to lay the pipe.
In the first, or "stovepiping'l method, a pipeline is
fabricated on the deck of a lay barge by welding together
individual lengths of pipe as the pipe is paid out from
the barge. Each length of pipe is about 40' or 80' long.
Thus, the pay-out operation must be interrupted periodically
to permit new lengths of pipe to be welded to the string.
The stovepiping method requires that skilled welders and
their relatively bulky equipment accompany the pipelaying
barge crew during the entire laying operation; all welding
must be carried out on site and often under adverse weather
conditions. Further, the stovepiping method is relatively
slow, with experienced crews being able to lay only one to
two miles of pipe a day. This makes the entire operation
subject to weather conditions which can cause substantial
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1~21~()7
delays and make working conditions quite hars~l.
The other principal conventional method is the
reel pipelaying technique, in this method, a pipeline
is wound on the hub of a reel mounted on the deck of a
lay barge. Pipe is generally spooled onto the reel at a
shore base. There, short lengths of pipe can be welded
under protected and controlled conditions to form a continuous
~ipeline which is spooled onto the reel. The lay barge is
then towed to an offshore pipelaying location and the pipeline
spooled off the reel between completion points. This method
has a number of advantages over the stovepiping method, among
them, speed (one to two miles per hour); lower operating
costs (e.g., smaller welding crews and less welding equipment
must be carried on the lay barge); and less weather dependency.
Historically, the technique of laying undersea
fluid-carrying pipelines had its rudimentary beginnings in
England in the 1940's. In the summer of 1944, 3" nominal bore
steel tubes, electrically flash-welded together, were coiled
around floating drums. One end of the pipe was fixed to a
terminal point; as the floating drums were towed across the
English Channel, the pipe was pulled off the drum. In this
manner, pipeline connections were made between the fuel supply
depots in England and distribution points on the European
continent to support the allied invasion of Europe. (See
Blair, J. S., "Operation Pluto: The Hamel Steel Pipelines",
Transactions of the Institute of Welding, February 1946).
The broad concept of reel pipelaying was also
disclosed in British Patent No. 601,103 (Ellis) issued
April 28, 1948, wherein it was suggested that lengths of pipe
be joined together at the manufacturing plant and coiled onto
a drum, mounted on a barge or ship; the loaded barge would
~121607
then be moved to the desired marine location and the pipe un-
wound from the drum by fixing one end of the pipe and towing
the barge away from the fixed location.
While the concepts described in British Patent 601,103
and those actually used in Operation Pluto were adequate for
wartime purposes, no known further development work or commer-
cial use of the technique of laying pipe offshore from reels
was carried out after World War II. After a hiatus of about
fifteen years, research into the re~l pipelaying technique
was renewed and was carried on by Gurtler, Hebert ~ Co. Inc.,
of New Orleans, Louisiana; by 1961, Gurtler, Hebert had suf-
ficiently ad~anced the reel pipelaying technique to make it
a commercially acceptable and viable method of laying pipe in
the offshore petroleum industry, able to compete with the
traditional stovepiping technique. The first known commercial
pipelaying reel barge, called the U-303, was built by Aquatic
Contractors and ~ngineers, Inc., a subsidiary of Gurtler,
Hebert, in 1961. The U-303 utilized a large vertical axis
reel, permanently mounted on a barge and having horizontally
oriented flanges (generally referred to in the trade as a
"horizontal reel"). A combined straightener-level winder was
employed for spooling pipe onto the reel and for straightening
pipe as it was unspooled. The U-303 first laid pipe commercial-
ly in September, 1961, in the Gulf of Mexico off the coast of
Louisiana and was used successfully during the 1960's to
lay several million linear feet of pipe of up to 6" diameter.
The U-303 reel pipelaying barge is described in U.S. Patent
3,237,438 (Tesson) and U.S. Patent 3,372,461 (Tesson), both
assigned to the assignee of the in~ention hereof.
The successor to the u-3a3, currently in use in
the Gulf of Mexico and known in the trade as the "Chickasaw",
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112-1607
also utilizes a large horizontal reel, permanently mounted to
the barge such that it is not readily movable from one carrier
vessel to another. Various aspects of "Chickasaw" are
described in the followin~ U.S. Patents, all assigned to the
assignee of the invention hereof:
Sugasti, et al. No. 3,630,461
Gibson No. 3,641,778
Mott, et al. No. 3,680,432
Key, et al. No. 3,712,100
Commercial reel pipelaying techniques require the use
of certain pipe handling equipment in addition to the reel.
Among such pipe handling equipment essential to any commercial
reel pipelaying system is a straightener mechanism. This may
take the form of a series of rollers or tracks, or any other
arrangement which imparts sufficient reverse bending force
to the pipe to remove residual curvature so that after unspool-
ing, the pipe will lay substantially straight on the sea bottom.
No such pipe-conditioning apparatus was used in Operation
Pluto or contemplated by the British Ellis Patent.
U.S. Patent 3,982,402 (Lang, et al.) describes an
apparatus for laying pipe from a vertical reel in which the
pipe conditioning apparatus is pivotable to adjust the
lift-off angle of the pipe relative to the horizontal ~e.g.,
the deck of a ship) as a function of the water depth in which
the pipe is being ~aid. This has distinct commercial
advantages, especially where the reel pipelaying system is
incorporated into a self propelled ship, such as that of the
present invention, capable of traveling to different job
sites, having different pipe size and/or lay depth require-
ments.
An early concept for a reel pipelaying ship is
'7
described in Goren, et al., "The Reel Pipelay Ship - A New
Concept" Offshore Technology Conference Proceedings, May 1975
(Paper No. OTC 2400). This paper (hereafter the Goren, et al.
1975 OTC Paper) describes advantages and operating features
of a proposed reel pipelaying ship. However, the cost of
construction of a ship as described there was estimated to be
on the order of $100,000,000; by contrast the ship of the
herein described invention is currently under construction
at less than one-third that estimate. The research and
development work for the ship described in the Goren et
al paper, (done at great expense by or on behalf of the
assignee of this application) was subsequently materially
revised in numerous major respects, and substantial changes
and improvements were made to achieve the design of the
substantially different reel pipelaying ship described
hereinafter; this new reel ship is or will be materially
different in concepts, construction features, mode of oper-
ation and results compared with the ship described in the
Goren et al paper.
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SUMMAR~ OF THE INVEI~TION
There is an increasing need in the offshore petroleum
industry to lay pipeline in deep and rough water, singly
and in multiple pipeline bundles, and in remote areas far from
supply bases. The dynamically-positioned pipelaying reel ship
of this invention represents a new and different approach to
meeting these needs.
The fact that the reel ship of this invention is
self-propelled substantially eliminates the need for support
vessels, such as tugs and supply boats, required by known
pipelaying barges of either the stovepiping or reel laying
type. In addition, the reel ship is highly mobile and has
the capability of laying pipe in remote areas far from any
supply base.
The reel ship also has an advantage in being able
to discharge pipe in deep water where it is extremely difficult
or impossible for conventional stovepiping or reel barges to
operate. This is due to the adjustable ramp assembly which
mounts the pipe conditioning apparatus at the stern of the
ship; the ramp assembly is adjustable to allow pipe to enter
the water at very steep angles (up to about 60) while con-
ventional barges are limited to about a 15 entry angle. This
allows the reel ship to work without a stinger, which is
required by conventional barges; elimination of the stinger
contributes to the ability of the reel ship to work in rough
weather.
A principal feature of the reel ship of this invention
lies in its hull construction. In order to support the load
of the reel and its full complement of pipe, the ship utilizes
a novel design which increases its longitudinal strength,
supports the reel at a height to accommodate the largest
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permitted reel size, and increases the covered deck storage
area.
Another feature of the reel ship is its use of the
reel hub as a ballast compartment. In order to keep vessel
roll motion to a minimum and to ensure that the main pro-
pellers and thrusters are submerged sufficiently to allow
efficient and non-cavitational operation, the draft must be
maintained constant at or near the load line draft as pipe is
spooled off. To achie~e this, ballast water must be added
to the hull during the unspooling op2ration. If the water
is added to ~he ballast tanks in the double bottom, the overall
center of gravity of the ship (KG) is lowered with a resulting
increase in statical stability, conveniently represented by GM.
Increasing GM, and thus increasing ship's stability, decreases
the natural period of roll and hence increases the roll motion
that will be experienced in sea conditions in which it is
desirable to be able to operate. In order to minimize this
increase in GM, as pipe is unspooled from the reel, water
ballast can be added to a ballast compartment located within
the reel hub in such amount as to partically or wholly compen-
sate for the weight of pipe being offloaded.
In accordance with one broad aspect, the invention
relates to a reel pipelaying vessel, comprising:
a hull composed of a plurality of longitudinal port and star-
board side primary structural members; a pipe-carrying reel;
port and starboard side reel support structures, each having
a substantially box-beam cross-section extending upwardly
from said port and starboard side primary vessel structural
members and above a main deck level of the vessel in the mid-
ship section thereof to increase the section modulus of the
vessel in the midship section, said reel support structures
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llZi~(17
extendin~ upwardly to a height sufficient to accommodate the
largest permitted reel diameter, based on maximum pipe diameter
and length to be carried by the vessel; and reel mounting means
for mounting the reel to the respective reel support structures
for distributing the load of the reel downwardly and longitu-
dinally outwardly through said reel support structures and
primary vessel structural members to maintain the stress on the
vessel's primary structural members within the maximum allowable
stress limits for the materials used in the construction of the
vessel's primary structural members.
For convenience, the following terms may be employed
in the description of this invention:
1. A "turn" is that length of pipe wound through
one complete revolution of the reel;
2. A "wrap" comprises a plurality of turns
making up a layer of pipe wound on the
reel across the full or substantially
full width of the reel.
Other features and advantages of the reel ship of this
invention will become apparent from the following detailed
description of a preferred embodiment.
BRIEF DESCRIPTIQN OF THE DRAWINGS
FIG. 1 is a starboard side elevation of a preferred
embodiment of the reel ship;
FIG. 2 is a top plan view of the reel ship of FIG. l;
FIG. 3 is a plan view of the main inner bottom hull
structure of the embodiment of FIG. l;
FIG. 4 is a profile of the main hull structure
of the embodiment of FIG. 1 with the shell plating removed;
FIG. 5 is a midship cross-section of the reel ship
hull through e.g., frame FR 25, in FIGS. 3 and 4;
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FIG. 6 is a perspective of the skeletal structure of
the reel ship hull with main deck and 'tween deck plating
removed between frames FR 9 and FR 49;
FIG. 7A is a starboard elevation of the pipelaying
reel partly in section to show internal bracing; taken along
lines A-A in FIG. 7B;
FIG. 7B iS a part sectional view of the reel looking
aft, through lines B-B of FIG. 7A;
FIG. 8A is a top plan view of one embodiment of the
vent conduit system of the reel ballast system;
FIG. 8B iS a view along lines B-B in FIG. 8A;
FIG. 8C is a view along lines C-C in FIG. 8A;
FIG. 9A shows a sectional view of the reel shaft
with its associated piping for a second embodiment of the
reel ballast system;
FIG. 9B shows a sectional view of the venting valve
arrangement mounted on the reel hub for the second embodiment
of the reel ballast system;
FIG. lOA is a top plan view of the starboard reel bear-
ing assembly and an embodiment of a starboard side reel bear-
ing unloading mechanism;
FIG. lOB iS a sectional elevation of the unloading mech-
anism taken along lines B-B in FIG. lOA;
FIG. lOC is a partial section of the starboard side
bearing unloading mechanism looking forward, taken along
lines C-C in FIG. lOB;
FIG. llA-B show plan and side views of the support
ramp assembly located near the stern of the vessel in FIGS.
1 and 2;
FIG. 12A is a side elevation of one level wind track
shown in box 12 in FIG. llB;
ilZ16~7
FIG. 12B is a view of the starboard portion of the ramp
and level wind track looking aft, taken along line B-B in
FIG. 12A;
FIG. 12C is a section of the level wind track taken
along line C-C in FIG. 12B;
FIGS. 13A and 13B show top plan and starboard side
elevations of the level wind truss assembly;
FIG. 14A is a starboard side elevation of one level
wind roller carriage assembly shown in ~ox 14 in FIG. 13B;
FIG. 14B is a view of the level wind roller carriage
assembly looking aft, taken along line s-s in FIG. 14A;
FIG. 14C is a plan view of the level wind roller
carriage assembly taken along line C-C in FIG. 14B;
FIGS. 15A-15C show plan, side, and end elevations
of the level wind drive assembly;
FIG. 16 is a schematic of the skeg and props of the
ship;
FIG. 17 is a graph which represents the relationship
between a reel ship's beam and GMT;
FIG. 18 is a perspective view looking forward of the
pipe handling equipment.
FIGS. 1-5, 7A, &B, 10A-lOC, llA, llB, 12A-12C, 13A,
13B and 14A-14C are taken from construction layout drawings
and are drawn substantially on scale. Within each of these
figures, the component parts or elements are su~stantially
in proportion.
DESCRIPTION OF THE PREFERRED EMBODIMENT
1. Hull Construction (FIGS. 1-6)
The reel ship, generally designated 10, is designed
to carry a main pipe-spooling reel system and its associated
support and drive assemblies, generally designated 20, and
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` 1121~07
pipe conditioning equipment, generally designated 40, located
aft of the reel system assemblies 20.
The ship's hull, generally designated 110, comprises
a forward section 112, a midship section 114, and a stern
section 116. The ship construction is referenced primarily
to frames (designated FR) which locate hull structural members
in transverse planes. The forward section 112 is defined
approximately between frames FR 0 and FR 17; the midship
section 114 which carries the reel assemblies 20, lies approx-
imately between frames ~R 17 and FR ~1; and the stern section
116, which mounts the pipe conditioning equipment 40, lies
approximately between frames FR 41 and FR 59.
The stern section 116 preferably includes, on its under-
side a skeg 118 which serves to increase stern buoyancy, to
protect the main propellers 128, such as from floating or sub-
merged objects or from grounding in shallow w~ter, and to
provide housing for a stern thruster or thrusters 122; and
to improve directional stability of the vessel. The skeg, which
consists of a substantially wedged shaped structure after part
of the ship's keel, is an advantageous but not essential feature
of the reel ship. It is particularly useful to increase stern
buoyancy at relatively shallow draft, on the order of about
13' - 15', and where the size of the ship may be limited by
economic and/or practical considerations, such as the need to
be able to negotiate canals or ship channels of relatively
limited size.
Advantageously the skeg is so sized that, at high
draft, it contributes between about 1.41% and 2.1% of the
ship's buoyancy; at low draft, it contributes between about
1.04% and 1.48% of the ship's buoyancy (see Table I below)
112~6C~7
_ ......... . .. ., . , . ,,_ . ___ ____ _ , . _ , . . . . .
SHIP DIMENSIONS SKEG BUOYANCY
(as % of total ship buoyancy)
Ship Length (L) Skeg Width(WS) Hlgh Draft Low Draft
(13') (18')
_ __ _
385' 16' 1.48 1.04
400' 16' 1.41 0.99
400' 24' 2.1 1.48
_ ,
TABLE I
The skeg also ~adv~ntageously houses one or more thruster
tunnels 120 for stern thrusters 122. The bow section 112 houses
one or more thruster tunnels 124 for bow thrusters 126. One
embodiment contemplates the use of two bow and two stern
thrusters. The bow and stern thrusters, which are reversible,
assist in course and station keeping by gi~ing the r~el ship
lateral or transverse positioning capability, while main props
128 provide fore and aft drive and, in conjunction with the
shipls rudders, positioning capability.
As an alternative to tunnel-mounted thrusters, as
shown, 360 rotatable aximuthal thrusters may be utilized;
such as aximuthal thrusters are extendable below the hull for
use and are retracted into tihe hull when the vessel is under-
way or entering shallow draft areas. Aximuthal thrusters
would be likely alternate when a skeg is not built into the
ship.
It is intended that the thrusters (whether of the tunnel
or aximuthal type) be manually controllable to allow the
operator to maintain the ship on a desired course, especially
during a pipelaying operation. If the operator determines
that the ship is too far to the right or left of the desired
course, he can apply a manual correction using the thrusters;
the result is a manually controlled dynamic positioning of the
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ship. By the addition of suitable equipment, the dynamic posi-
tioning control maybe made automatic.
The location of the propellers with respect to the
hull bottom provides advantages in terms of efficiency of opera-
tion as well. In particular, referring to FIG. 16, the propel-
lers must be so located with respect to the load line to avoid
cavitation; this is a function of the prop diameter (D, in feet)
and the distance (H, in feet) from the mean water line at a
given ship's draft to the center of the prop. A second factor
relates to the location of the prop with respect to the hull
bottom to minimize vibration; this is a function of the prop
diameter (D) and the distance (a, in feet) between the hull
bottom and periphery of the prop.
It has been found that H should be 1.125D; preferably
the ratio H:D is in the range of about from 0.625:1 to 1.125:1
between vessel high and low draft conditions, respectively.
The distance "a" between the hull bottom and the tip of the
propeller blades should be not less than 0.2D; "a" is preferably
between about 0.2D and 0.4D, and more preferably is about
0.2125D.
FIGS. 3-6 show the primary structural arrangement of
the ship. The reel pipelaying ship of this invention utilizes
a novel reel support structure and multiple bulkhead box-beam
construction in the midship section of the vessel to support
the weight of the fully loaded reel.
American Bureau of Shipping (ABS) regulations require
that primary structural elements be continuous for the length
and/or breadth and/or height of the vessel. In the reel ship
of this invention, such primary structural elements include
outer longitudinal hull walls 130 (corresponding elements on the
starboard and port sides are designated "S" and "P", respective-
ly) and a double longitudinal bulkhead arrangement comprising
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longitudinal bulkheads 134 and 136 which lie interiorly of a
single bulkhead 132 between frames FR 17 and FR 41.
Longitudinal bulkheads 136 run substantially the
length of the ship between frames FR 5 and FR 59. Hull walls
130 and bulkheads 134, 136 extend vertically from the baseline
(hull bottom) to the main deck level except between frames
FR 19 and FR 39 where midship portions, generally designated
130', 134' and 136', respectively, extend upwardly to the
top of the reel support structure. Bulkheads 130', 134', and
136' taper to the main deck level at their fore ends between
frames FR 19 and FR 17 and at their aft ends between frames
FR 39 and FR 41.
Single bulkheads 132 which are not generally considered
as primary structural members, lie interiorly of and are spaced
from the outer hull walls 130 between frames FR 13 and FR 49
(which includes the midship section between frames FR 17 and
FR 41). Longitudinal bulkheads 132 extend vertically from the
baseline to the main deck level throughout their length.
In the transverse direction, primary ship structural
members which also form part of the reel support structure
include web frames FR 17, FR 21, FR 25, FR 37 and FR 41.
Additional fore and aft primary transverse structural members
include web frames FR 5, FR 9, FR 13, FR 49, and FR 59. Web
frames FR 5 - FR 59 extend vertically from the baseline to
the main deck level of the ship. All of the transverse
bulkheads, except those comprising frames FR 29 and FR 33,
extend across the entire beam of the ship. The bulkheads
comprising web frames FR 29 and FR 33 extend transversely
only between the outer hull walls 13Q and the innermost longi-
tudinal bulkheads 136. A space or well 152 in the midship
section is thereby defined for receiving a pipe carrying the
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1121~(~7
reel 210; this reel well 152 is bounded by the bulkheads
comprising web frames FR 25 and FR 37 fore and aft, respec-
tively and longitudinal bulkheads 136S and 136P.
In normal ship construction, the frame spacing is
maintained substantially equal throughout. In the reel ship
of this invention, the mid-section frame spacing is shortened
between frames FR 25 - FR 37 to accommodate the large weight
of the reel. In one embodiment, for example, the reel weighs
about 800 tons and is capable of carrying a full load of
between 1,500 and 2,000 short tons of pipe.
Horizontal members of the hull structure include the
baseline 138, the tank top 140, the 'tween deck 142, and the
main deck 144. The tank top 140 extends across the entire
beam of the ship and longitudinally between the bow and about
frame FR 52.
A pair of horizontal midship structural members 146
and 148 extend transversely between the outer hull wall 130
and inner double longitudinal bulkhead 136 above the main deck
144; midship structural members 146 and 148 extend longitudinal-
ly bétween frames FR 19 and FR 39. Upper member 148 also
advantagously comprises the lifeboat deck.
The main deck 144, lower and upper midship horizontal
structural members 146 and 148, respectively, and the portions
130', 134' 136' of outer hull wall 130 and outer and inner
double longitudinal bulkheads 134 and 136 respectively, between
main deck 144 and upper midship horizontal structural member
148 comprise a box-beam reel support structure, generally
designated 150, which sits atop the main deck level in the
midship section between web frames FR 19 and FR 39, with the
ends tapering to web frames FR 17 and FR 41, respectively.
The box-beam reel support structure 150 comprises
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a highly advantageous feature of this invention. One of
the primary problems of a reel ship relates to the large
concentrated load applied at the middle of the ship by the
main reel. Substantially the entire reel load is concen-
trated in two bearings, one on each side, which covera relatively small part of the ship's length. If the ship
is considered as being poised on two wave crests, one at each
end of the ship, the reel load concentrated on the bearings
creates a large sagging or bending moment at the middle of
the ship which drops off rapidly in the fore and aft
directions. It is necessary to counteract this large bend-
ing moment in the center. Normally, at least a substantial
part of this bending moment would be counteracted by the
main deck and 'tween deck hull structure However, the
continuity of main deck 144 and 'tween deck 142 in the reel
ship is lost due to the reel well 152 located in the middle
of the ship just in the region where the bending moment counter-
acting forces are required. Due to this discontinuity in the
main deck and 'tween deck structure, there is insufficient
section modulus in the ship to react the bending moment created
by the reel.
The problem of adequately reacting the bending moment
due to the reel imparted load is solved in the present invention
by the box-beam reel support structure 150. The overall
structure of a vessel can be considered as a composite long-
itudinal I-beam in which the double bottom of the hull
comprises the bottom flange and the main deck is the upper
flange. In the reel ship of this invention, the bottom flange
is continuous, whereas the upper flange is broken by the reel
well. The upper flange at the point of maximum bending moment
has been moved up to the top of the box section 150 and the
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)7
webs are comprised of hull walls 130 and double bulkheads 134,
136; the latter distribute the shear load of the reel down-
wardly and outwardly in the planes of the bulkheads 134, 136
to the bottom flange.
Because the bending moment due to the reel load is
so peaked and drops off rapidly in the fore and aft directions,
the box-beam support structure 150 need not extend more than
the minimum required by classification society (e.g., ABS)
regulations. In particular, the box-beam 150 need not extend
the entire leng~h of the ship. The length of the box-beam
150 (in this case the distance between frames FR 17 and FR 41)
need only be at least about 0.4L, where L is the length of
the ship. This is a highly advantageous feature of this
invention because it reduces the amount of space required for
the support system (which space is useable ~or other purposes)
and reduces the overall cost of the vessel substantially.
By virtue of the fact that the support structure
150 comprises a box-beam located above and resting on the
main deck level, the shear load is spread out ~rom the reel
into' the structure of the ship in the fore and aft directions.
The box-beam structure 150 in conjunction with the other hull
members transmit the shear load from the reel 210 efficiently
into the rest of the hull and ultimately into the shell plate
(baseline 138) in such a way as not to exceed the load limits
of the shell plate and so that the shear forces can be resisted
by the buoyancy forces on the shell plate.
The double bulkhead - box~beam construction used in the
reel ship of this invention has a number of advantages, includ-
lng:
1. Increasing the section modulus of the ship in the
middle by the use of xelatively little additiona] structure;
ll.Zl~)7
the box-beam distributes the reel load through the ship so as
to maintain the stress on the primary structural members well
within maximum allowable stress limits for the materials used,
according to pertinent classification society requirements.
As a corollary, for the sagging condition the.b0x-beam 150
maintains the compressive stress in the top flange and tensile
stress in the bottom flange of the composite longitudinal
beam of the vessel structure within maximum allowable limits.
2. Supporting the rotational axis of reel 210 axis
at the height required to accommodate the largest permitted
reel size (based on maximum pipe diameter and length to be
carried by the ship). This avoids construction of a much
larger ship and results in substantial cost savings.
3. Providing a longitudinal passageway between
bulkheads 134 and 136 for access to compartments such as
storage and/or personnel cabins located between the bulkheads
134 and bulkheads 132.
4. Creating additional enclosed spaces for winches
and other equipment, including, for example, the diving equip-
ment. This additional space was made available by the discoverythat it was not necessary to extend bulkhead 132 vertically
to the full height of the box-beam structure 150. Rather, it
was disco~ered that by advantageously having longitudinal bulk-
heads 134, 136 span the reel bearing support blocks (described
below) substantially all of the effective load is transmitted
through bulkheads 134, 136 to the lower composite beam flange
(i.e., the double bottom of the ship's hull). Thus, a vertical
extension of bulkhead 132 became superfluous.
In addition to the above-discussed advantageous features
of the construction of the reel ship, other new and desirable
features, as follows, are also apparent and are useable in pre-
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~lZ1607
ferred embodiments.
One of the advantageous features of the reel ship is
its ability to operate in relatively shallow draft areas.
The ship is designed to draw as little as 13' - 14' of water,
thereby enabling it to operate in essentially unlimited areas,
including such as Australian waters, where sand bars limit
vessel drafts to about 13 feet. Equally, or more important,
the reel ship can operate out of shallow water ports, such as
assignee's reel pipelaying shore base at Houma, Louisiana.
Generally, a reel shore base requires a fairly large expanse
of dock area. The land at deepwater ports is generally at a
premium; shallow water port land is much less costly. Thus,
there are economic and commercial advantages to a ship which
can operate out of a shallow water base.
lS As a consequence of its shallow draft capability,
provision must also be made for ballasting the ship down
to its operating draft. This is advantageously accomplished
by the double bottom hull design, in which the tank top 140
is spaced about twice the normal distance from the baseline
138 (normal spacing is about 3.5'; whereas in a preferred
embodiment of this ship, the spacing is on the order of 7').
Space is thereby created for sufficien~ ballast to sink the
ship to its desired normal operating draft (e.g., about 18 feet).
The space between bulkheads 132 and outer hull members
130 is void so that the construction of the major part of the
vessel is equivalent to a double hull arrangement, at least
between frames FR 13 and FR 49. This provides good reserve
damage stability to the ship.
la. Vessel Characteristics
An important hydrostatic characteristic of the reel
ship that affects its hydrodynamic characteristics (i.e., that
--19--
:112i~07
has an effect on its motion in waves) is its GMT (i.e., the
vertical distance (in Eeet) from its center of gravity to the
transverse metacenter of the ship). GMT changes with changes
in the vessel load; generally GMT increases as the ship
becomes lighter, i.e., as vessel load and draft decrease.
If the GMT of the vessel is too small, the vessel
becomes statically unstable; slight shifts in weight, e.g.,
as the booms of cranes mounted on the vessel are swung around,
will cause the vessel to heel a substantial and highly undesir-
able amount, possibly up to 10. On the other hand, if the
GMT of the vessel is too large, the ship becomes too stiff and
the roll will be too great for acceptable operating conditions
for personnel and equipment in prevailing seas.
In the reel ship of this invention, over 2,000 tons
of pipe may be offloaded during a laying operation. ~s pipe
is payed out from the ship, and the ship becomes lighter,
the GMT will increase. If no adequate compensation is made
for the removed pipe weighb the GMT could increase to the
point where the pipelaying operation may have to be terminated
prematurely because of excessive rolling action of the ship.
In other words, without appropriate compensation, the reel
ship would be limited to a more restricted range of operating
sea conditions.
For example, consider vessel displacement at full
load to be about 13,000 tons with an operating draft of about
18 feet. If no ballast is added after offloading the pipe,
the vessel displacement will be around 11,000 tons and the draft
will be 15 feet, resulting in the vessel being raised 3 feet
out of the water. The GMT of the vessel changes from about 5.5
feet to about 13.3 feet, an increase of about 7.8 feet. (See
Table II below, which compares the approximate GMT of the vessel
-20-
11~1S~07
under full load, half load and empty reel conditions, where
no reel ballast is added and where ballast is added to the
reel hub (or core) as pipe is unspooled). This increase roll
stability of the vessel so that the ship becomes stiffer about
the roll axis and increases the rateOf roll o~ tbe vessel. equally,
if not more importantly, such decrease in draft reduces the
efficiency of the main props and thrusters and increases the
cavitation problem, as noted above.
The change in GMT of the vessel, from about 5 feet
to nearly 14 feet as the pipe weight goes from 2,000 tons to
0 tons, would be a large change for a vessel of this type and
size. In practical effect, this would be detrimental to the
safety and comfort of personnel, to on-deck equipment, to over-
all ship operations, to the pipelaying operation in particular,
and to the reel itself (due to excessive loading of the bearings
and other reel support elements).
In order to maintain relatively constant displacement
of the ship as pipe is payed out, ballast can be added in a
conventional manner to hull ballast tanks (e.g., between the
baseline and tank top). Although such bottom ballast will keep
the draft at about 18 feet, the center of gravity of the vessel
will shift downwardly as ballast is added. The result will be
a change in GMT which may be outside acceptable commercial op-
erating limits for the safety of personnel and equipment in pre-
vailing seas.
In order to maintain commercially acceptable motion
characteristics, it is a requirement that the GMT of this vessel
be maintained within 25% of its initial height, which for
commercial purposes, should not be more than about 7 feet,
although a change of between 25~ and 30% can be tolerated
during the unreeling operation, and a greater change tolerated
llZ~16~7
in calm sea conditions. Once a nominally optimurn GMT for
the vessel is determined, it is then desirable to maintain
the change in this GMT as small as possible and at least
within acceptable limits to avoid the overstability and
excessive motion problems noted above.
For sea conditions in which normally expected maximum
wave periods are in the range of about 5-8 seconds, the GMT
(in feet) of such a reel ship should be no greater than
0.00194B , where B is the beam (in feet) of the vessel. FIG.17
shows the relationship between GMT and beam B for a natural
vessel period Tn of 10.0 sec., a commercially advantageous
minimum period. The shaded area under the curve represents
maximum commercially acceptable values of GMT for a reel ship
of this invention. Advantageously and preferably, the GMT of
the reel ship should be between about 3 feet and 8 feet under
all significant offshore operating conditions. In order to
maintain the GMT range, it has been found highly advantageous
and preferable to provide ballast compensation at the level of
the reel, and particularly in the reel hub, as pipe is unspool-
ed (see Table II below).
GMT (in feet)
Reel Load without with core
core ballast ballast
.
Full 5.51 5.51
one-half 10.22 6.68
_ ~
empty A~ I 7.60 ¦
It is desirable that the hub be sufficiently large to
accommodate enough ballast to maintain the change in GMT
within commercially acceptable limits. In one preferred embodi-
ment, the reel has a capacity to spool up to about 2,000 tons
-22-
l~,f~L607
of pipe; the hub can hold up to about ],600 tons
of ballast. The remaining necessary ballast can be added to
conventional hull tanks without adversely increasing the
change in GMT of the ship.
In addition to the above-mentioned advantage of minimiz-
ing the change in GMT as the pipe is offloaded during a layoperation, the use of reel or core ballast has other advan-
tages to the ship of this invention. For example, if the
ship is carrying only a partial load of pipe, ballast can be
added to or removed from the reel core to change the natural
roll period of the ship and thereby reduce its roll motion.
In this way, the GMT of the ship can be changed to adjust for
varying sea conditions; in particular, the natural roll period
of the ship can be changed, as necessary, with respect to
prevailing wave periods to prevent resonance conditions from
occurring.
The reel ship, with no reel load but with sufficient
bottom ballast to achieve its operating draft of about 18
feet, has a very high GMT (with a concomitant short natural
period). This results in a tendency of the ship to whip with
high acceleration and deceleration forces. By adding ballast
to the reel core, the GMT of the ship can be decreased to
detune the vessel and create longer, slower roll periods,
i.e. the natural period of the ship is increased.
Additionally or alternatively, the vessel roll may be
damped by the use of bilge keels 156 and/or flume tanks
(not shown). The bilge keels 156 are provided along the paral-
lel mid-body of the vessel on the turn o the bilge as an aid
in cutting down on ship's roll; preferably these keels should
not extend beyond the outer projected horizontal and vertical
vessel surfaces at least in part as protection agains-t
breaking off.
-23-
1~16~)7
With respect to other vessel characteristics, it has
been found that ~he length of the ship should be preferably
between about 385' and 410'; the beam is preferably between
about 60' and 80' and more preferably between about 68' and
73'. The ratio of beam (B) to draft (D) is preferably in
the range of about 2.25:1-4.00:1 and more preferably in the
range of 3.5:1-4.0:1.
2. Reel Assembly (FIGS. 7-10)
The pipe spooling reel system 20 comprises a reel 210
located near the longitudinal center of buoyancy, which is
near the longitudinal geometric center of the vessel.
Reel 210 (see FIGS. 7A-B) is comprised of a central axial
shaft, generally designated 212. Axially opposite flanges,
generally designated 214S, 214P, extend radially outwardly from
15 shaft 212. A hub, generally designated 216, co-axial with
shaft 212, extends between flanges 214S and 214P. Each flange
214 is composed of a plurality of radial arms 218 extending
from the shaft 212 outwardly to the flange rim. Typically,
- radial arms 218 may be spaced 30 apart around the circumference
of the shaft 212. A further plurality of shortened radial reel
arms 220, which extend radially outwardly from the surface of
hub 216 to the flange rim, are located between adjacent arms
218.
The reel hub 216 comprises a circumferentially and axially
continuous outer surface covering 222 extending between flanges
214S and 214P. A plurality of annular spacers 224 extend from
the interior face of hub surface covering 216. The other ends
of annular spacers 224 are secured (e.g., by welding) to trans-
verse bracing members 226 which extend between opposed flanges
30 214S and 214P. ~eb plates 228 lie in radial planes between the
interior surface of hub covering 216 and transverse bracing
-24-
6(~7
members 226 and between adjacent annular members 224. This
interior construction of the reel results in a criss-cross
or honeycomb structure under the plating 222 of hub 216. Such
construction produces a reel with great strength necessary to
accommodate large back tension forces which may occur during
pipe laying and/or pipe retrieval operations. Such back tension
forces produce a wedging action between adjacent turns of pipe
in a wrap which cause large splitting forces to develope in the
reel flanges 214.
Advantageously and preferably the ratio of the diameter
of the reel (at the flange rim) to the width of the reel hubs
for the reel ship is in the range of between about 3:1 and
4:1, more preferably, this ratio is in the range of about
3.5:1 - 3.8:1; still more preferably such ratio is about 3.7:1.
In the preferred embodiment designed for construction, the
reel diameter is about 82 feet and the hub width is about
22 feet.
2. Reel Ballast System
An important and advantageous feature of this invention
lies in the fact that the interior of the hub 216 comprises a
water-tight compartment to which ballast may be added as pipe
is spooled off the reel. This ballast system requires means
for supplying ballast, advantageously sea water, to the reel
hub while the reel is rotating, at the same time providing means
for venting the hub.
A first embodiment of such a ballast system is shown in
FIGURES 7A-7B. In this embodiment, shaft 212 comprises machined
end portions 230, each having a central axial bore 232. End
portions 230 extend from a tubular central portion 234 which has
support plates 236 spaced from each other on the inside of
tubular portion 234. Shaft ends 230 and tubulax central
~lZ~G~)7
portion 234 together act as unitary shaft element 212.
A fill and drain conduit 238 extends exially into the
reel through one axial shaft bore 232 (e.g., bore 232P);
inside the reel, conduit 238 makes a 90 bend and extends
radially outwardly toward the interior surface of hub 216.
The end portion of conduit 238 may be secured to a transverse
member 226. A second or vent conduit 240 extends exially
into the reel through the other shaft bore (e.g., bore 232S).
Inside the reel, conduit 240 makes a 90 bend and extends
radially outwardly toward the inner surface of hub 216; the
end portion o~ conduit 240 may be secured to a transverse
bracing member 226. Advantageously and preferably, conduits
238 and 240 extend in opposite radial directions from each
other.
15In one relatively simple embodiment, the fill and drain
conduit 238 may be connected through a swivel connection to
a T conduit, connected in turn through valve means to a pump
which pumps ballast into the reel and to a drain conduit which `
pipes ballast overboard. Closing the outlet valve and opening
the inlet valve permits sea water ballast to be supplied to the
interior of the hub 216i opening the drain valve and closing the
inlet valve allows the ballast to drain out of the hub and over-
board.
Referring now to FIGS. 8A-8C, vent conduit 240 may be
connected through a conduit 242, having an exterior cammed
surface 246, to a swivel connection 244. The other side of
swivel 244 is connected through conduit means to a vent dis-
charge. The arm of a switch mechanism 248 contacts cammed
surface 246 on conduit 242 to control the opening and closing
of valves in the vent discharge line. The switch mechanism 248
is adjusted so that the valves are open for only a short period
-26-
6C~7
of time, e.g., when the opening of vent conduit 240 is within
plus or minus 30 of its apex of rotation. This arrangement
prevents a discharge of ballast water when the vent pipe
rotates a sufficient distance to be submerged within the hub.
In an alternate arrangement, shown in FIGURES 9A-9B,
tubular section 262 between shaft end 230 and a sealing plate
264 contains a number of openings 266 which communicate the
interior of the tubular shaft portion 262 and the reel hub
interior. The outer end of shaft portion 230 may be sealed
by a flange 268 through which a pipe 270 extends. The outer
end of pipe 270 may be connected through a swivel joint 272
and a gate valve 274 to a fluid supply conduit 276. A spring-
loaded pressure relief valve 278 may be provided to avoid
excessive fluid pressures from building up.
During the course of a pipelaying operation using this
alternate arrangement, as the pipe is unspooled from the reel,
water ballast is pumped into the reel hub through the valve 274,
swivel joint 272, conduit 270, and openings 266 in shaft portion
262. As water is pumped in, air in the hub is vented to the
outside through venting valves, generally designated 280
(FIG. 9B). At least two such venting valves are provided approx-
imately 180 apart on one or both of flanges 214. Vent valves
280 comprise a gravity-operated scupper valve 282 and a lever-
operated butterfly valve 284. The disc 282a of the scupper
valve i5 gravity operated. Thus, as the reel rotates and the
valve travels downwardly, at a certain point the disc 282a will
be pulled closed, aided, if necessary, by the pressure of the
ballast water in the hub as the valve moves below the water
line; the escape of water ballast from the reel is thereby
prevented (other than a possibly minimal amount which may
escape before the valve is fully closed). As the reel
-27-
1'1'~16C~7
continues to rotate and vent valve 280 moves up, it will
eventually reach a point where the scupper valve 282 is above
the water line and gravity pulls disc 282a down. This opens
the vent valve 280 to vent air out of the reel hub interior.
The butterfly valve 284 is normally kept open and is used
essentially as a manual closure.
2b. Reel Support System (FIGS. lOA-lOC)
The reel shaft 212 seats in a pair of axially opposite
bearings 290. The bearings 290 can be any commercially avail-
able shelf bearings (e.g., FAG Model No. 539948 roller bearing).
The bearings 290 rest on bearing support blocks 292. Bearing
support blocks 292 in turn are secured to the upper midship
horizontal structural members 148 comprising the top of the
reeI support structurelso.A5 noted earlier, the bearing blocks rest
on bulkheads 134, 136, which distribute the reel and bearing
load downwardly and longitudinally outwardly through the reel
support structure 150 to the baseline 138.
Preferably and advantageously, the reel may be horizon-,
tally located within about -5% of the longitudinal center of
buoyancy. In the preferred embodiment of the vessel as
designed for construction, the ship has a length of between
about 385'-410'; the reel may be located within a range of
about 20' fore and aft of the longitudinal geometric center.
When at sea, the reel ship will sometimes encounter
heavy sea conditions which cause the vessel to roll from side
to side, thereby placing large loads on the bearings. It
may therefore be desirable to unload the bearings when the
ship is traveling between pipelaying operations, particularly
if smaller bearings than those presently contemplated are
used or if the reel size and capacity are increased relative
to the bearing size. For this purpose, means may be provided
-28-
)7
for unloading the bearings, preferably by jacking up the reel
shaft to raise it off the bearing seat. An added advantage of
this bearing unloading capability is that the bearings can be
repaired or removed while the vessel is at sea.
One such unloading mechanism which could, if desired,
be incorporated into the reel ship is shown in FIGURES 10A-lOC.
In this embodiment, a portion 154 of the reel well bulkheads
are recessed between frames FR 27 and FR 35. This recess pro- -
vides space for mountin~ a reel shaft support mechanism,
generally designated 300. The support mechanism 300 includes
a support truss 302, having wedge-shaped bottom portions 304,
306, between which is a generally flat bottom section 308.
The upper face of the support truss 302 contains an arcuate
recess 310. A pair of gussets 312, having arcuately shaped
inner faces co-radial with the arc of surface 310, are located
on the upper face of support trust 302 to continue the arc of
surface of 310. An arcuate plate 314 is secured at its ends
to gussets 312 and completes the circle which surrounds shaft
212. One or more hydraulic cylinders 316 mounted on the reces-
sed deck portion 154 engage the bottom surface portion 308 of
support truss 302. In the preferred embodiment, up to four
hydraulic cylinders, each having a 400-ton lifting capacity,
are employed with each of the port and starboard side reel
shaft support mechanisms 300. A pair of longitudinally opposed
movable end wedges 318a, 318b rest on the recessed deck portion
154 and are slideable under wedge-shaped bottom portions 304,
306 of truss member 302. Wedge members 318 are driven by
respective hydraulic jacking screws 320a, 320b. Wedges 318
co-operate with hydraulic cylinders 316 to lift the support
truss 302 and shaft 212, and to retain the truss 302 and shaft
212 in their elevated positions. By this arrangement, a strong
-29-
,16C~7
adjustable s-tructural support is provided for the shaft 212 and
reel 210 which allows the bearings 290 to be unloaded for
extended periods, such as under heavy seal conditions when the
ship is traveling between jobs, or when bearing repair is
required.
2c Reel Drive System
The reel drive system includes a drive gear 330 mounted
around the outer rim of one or both flanges 214. In the embodi-
ment shown, the drive gear is located on and circumferentially
around the rim of starboard flange 214S. The reel is driven
by one or more motors, as shown, for example, in the afore-
mentioned Lang, et al. patent and~or Goren, et al. 1975 OTC
paper. 332. Such motors are advantageously hydraulic motors
(e.g., Hagglund Hydraulic Motor Model # ~18385 with Brake Model
# FBC-80-2-D or equivalent). The invention is not limited to
the use of hydraulic drive motors; D.C. motors are also suitable
because of their high torque capability at low speed. The reel
drive mechanism also incorporates an automatic tension control
feature which maintains a relatively constant tension on the
pipé, particularly during lay and/or retrieval operations.
3. Pipe Conditionlng Equipment (FIGS. 11-15)
The pipe conditioning equipment, generally designated 40,
is mounted sternward of the reel assembly 20. The pipe condi-
tioning equipment 40 includes, inter alia, a main support ramp25
assembly 410 and a level wind assembly 450 and a level wind
assembly 450. The level wind assembly 450 has various pipe
handling equipment mounted thereon, including a pipe bending
radius controller 490, pipe straightening equipment 510, a
tensioning assembly 520, a pipe clamp assembly 53Q, a stern pipe
guide assembly 540, and various fixed and/or movable work plat-
forms.
-30-
3a. Support Ramp Assembly (FIGS. 11-12)
The support ramp assembly 410 preferably comprises
an open truss framework of a type shown, for example, in
FIGU~ES llA-llB. The ramp support assembly 410 comprises
upper and lower longitudinal frame members 412 and 414,
respectively. These longitudinal frame members are advanta-
geously interconnected by vertical, horizontal and/or diagonal
bracing members for additional strength. Upper frame members
412 are longer than lower frame members 414; the upper and lo~er
frame members are longitudinally offset from each other and
are connected at their forward end by structural members 416
and at their aft end by structural members 418.
The support ramp assembly 410 mounts a plurallty of
tracks 420 extending transversely across the support ramp
assembly. Tracks 420a-420d are mounted on upper frame members
412 so as to be substantially co-planer with each other. Track
420e is located on connecting member 416 at an angle relative
to the plane of tracks 420a-420d.
FIGURES 12A-C show details of a typical ramp mounted
level wind track 420. A track base support member 422 extends
approximately orthogonally from each of upper frame members
412S and 412P. A track base plate 424 extends between and is
secured (e.g., by welding) to each of track base su~port
members 422. A T-shaped track member 426 having flared ends
428 extends upwardly from track base plate 424 and transversely
between upper ramp frame members 412. The axially opposite ends
of track members 426 are secured (e.g., b~ welding) to end
support plates 430 which, in turn, are secured to the upper
frame members 412 and track base suppoxt members 422. Addition-
al intermediate track support members 432 may be provided to
give the track 426 additional strength.
-31-
The support assembly 410 is mounted to the stern
portion of the vessel at pivot points 411. Advantageausly,
a jacking truss 550 may be pivotably connected at one end to
the support ramp assembly 410 and at the other end to a
jacking mechanism 552 mounted on tracks 554 secured to ~he
vessel deck. The jacking mechanism may be moveable along
the tracks to pivot the ramp support assembly 410 about pivot
points 411. This allows adjustment of the pipe path through
the pipe handling assemblies to thereby adjust the exit or
lay angle of the pipe relative to the water.
3b. Level Wind Assembly (FIGU~ES 13, 14)
The level winder 450 consists of a main frame 452.
A level wind frame section 454 extends from the forward end
of main level wind frame 452 and at an angle thereto which
essentially follows the angle of ramp frame connecting member
416.
A plurality of level wind roller carriages 456 extend
from the underside of level wind truss 452. The basic con-
struction of each carriage 456 is the same and comprises down-
wardly extending fore and aft carriage members 458 connected
at the top by transverse frames 460 and at the bottom by
transverse frame 462. The carriage is located so that a trans-
verse frame member 464, comprising part of the level wind truss,
lies intermediate transverse carriage frame members 460a, 460b.
Each of carriage members 460 mounts a roller 466 e.g. r Hilman
Roller Model No. 5XTDW 200-ton capacity) which rides on a corres-
ponding flared end 428 of T~shaped track member 426. A third
or top roller 468 (e.g., Hilman Roller Model No. 6X 300 ton
capacity) is mounted to transverse frame member 464 and rides
on the flat top surface of T-shaped track member 426. An
optional fourth or bottom roller 470 tsimilar to rollers 466)
-32-
6~7
is provided, especially on carriages 456c and 456d; battom
roller 470 is mounted to bottom frame member 462 and co-operates
wlth the track base plate 424.
It will be seen that the level wind roller carriages
456 essentially surround the level wind tracks 420 while per-
mitting the level wind structure 450 to traverse the width
of the support ramp 410.
The level wind drive system may employ, in one contempla-
ted embodiment, a hydraulic motor 472 connected through a chain
drive to a drive shaft 474 which is mounted through bearing
supports 476 to one of the ramp support frame members 412.
Beveled gears 478 connect the drive shaft 474 with a plurality
of jack screws 480 which extend transversely across the ramp
assembly 410 between frame members 412S and 412P. The external-
ly threaded jack screws 480 are threaded through complementary
threaded openings in do~rdl~r extending leyel w~nd d$ ~e connect-
ing members 482. The hydraulic motor 472 rotates the drive
shaft 474 which, through beveled gears 478, rotates jack screws
480. Such rotation of the jack screws 480 produces a traversing
motion of the level wind assembly 450 across the width of the
ramp support structure 410.
3c. Pipe Bending Radius Controller
At its forward end, the level wind assembly 450 mounts
a stress uniformizer or pipe bending radius controller 490.
The radius controller assembly may comprise a plurality of
rollers 492 mounted to curved frame members 494, whi~h are
secured to the level winder frame 452. The radius controller
is connected to the level winder through pivot mounting
assemblies 496. A jacking mechanism 498 (e.g. a hydraulic
screw jack) is advantageously coupled between the level wind
forward frame members 454 and the radius controller frame 494.
-33-
llZ~607
Through operation of the jacking mechanism 498, the radius
controller can be pivoted about pivot mounts 496 as needed
to adjust for the size of pipe and support ramp angle. In
this manner, the amount of curvature to be imparted to the pipe
before it enters the straightener 510 can be properly estab-
lished for varying operating conditions.
The radius of curvature of radius controller assembly
490 is advantageously and preferably approximately the same
as the minimum radius of curvature to which the inner wrap
of the largest diameter pipe capable of being spooled on the
reel 210 can be bent. The radius controller 490 imparts a sub-
stantially uniform stress and subs~antially constant radius
of carvature to pipe as it is unspooled and prior to lts entry
into the straightener apparatus 510. The ratio of the radius
of the reel hub ~ to the radius of the radius controller ~C
lies in the range of between about 1.2:1.0 and 1:1.2; more
particularly, the prefered ratio is about 1.0:1Ø
3d. Straightener Assembly
A straightener assembly 510 is mounted to the level wind
assémbly 450 downstream of the radius controller assembly 490
(in the direction of pipe unspooling). The purpose of the
straightener assembly 510 is to impart a reverse bending force
to the pipe sufficient to overcome the curvature set by the
radius controller 490. For this purpose, th~ee reaction points
are required to be exerted on the pipe, the two end points
acting in one direction and the intermediate point acting in the
opposite direction, such that all 3 forces are substantially
coaligned in the plane of pipe bending. A two-roll straightener
can be used in which the radius controller is considered as one
reaction point. Advantageously and for greater flexibility of
operation, a "three-roll" straightener apparatus 510 is used;
-34-
the straightener rolls may, in fact, comprise tracks of the
type described ~or example in assignee's U.S. Patent 3,680,342.
Advantageously in the preferred embodiment designed for
construction, the straightener assembly 510 comprises a first
track assembly 512 a second track assembly 514 and a third
track assembly 516. For convenience hereafter the straightener
track assemblies 512, 514, 516 will be referred to generically
as ~straightener rolls", it being implicit therein that the
track assemblies can be replaced by individual rollers, if
desired.
The irst straightener roll 512 is mounted to and between
radius controller frame members 494 and is pivotably movable
therewith as controlled by jacking assembly 498. Straightener
roll 514 is mounted in a straightener frame assembly 518 car-
ried by the level wind 450. Straightener roll 514 is located
on the opposite side of the pipe passage from straightener roll
512 and is adjustable in a direction substantially perpendic-
ular to the nominal longitudinal axis of pipe passing through
the pipe conditioning apparatus 40. The third straightener
roll 516 is also mounted in the straightener frame 518 on the
same side of the pipe passage as the first straightener roll
512; straightener roll 516 is substantially fixed in position.
One of the features of the three roll straightener
apparatus of this invention is that both of the first and
second straightener rolls 512 and 514, respectively, are
adjustable relative to each other and to the nominal pipe
passage to thereby maintain the actual pipe path as close
to the desired nominal as possible for varying pipe sizes
and ramp angles.
The straightener assembly also incorporates the
tensioner apparatus 520. Specifically, in the presently
preferred embodiment, the tensioner may comprise a track
~35-
l~LZ~ 7
or roll 522 mounted in the straightener Erame 518 and adjust-
able in a direction substantially perpendicular to the nominal
pipe path in a similar manner as straightener roll 514. Once
such suitable tensioner mechanism is used on the aforementioned
"Chickasaw" and is described in one or more of the above
referenced Sagasti et al, Gibson, Mott et al and Key et al
U.S. patents.
3e. Additional Equipment
Additional pipe handling equipment, including a movable
clamping assembly (not shown), a fixed clamping assembly 530
and a stern pipe guide assembly 540 are also located on the
level winder assembly 450. This additional pipe handling equip-
ment is not germane to the present invention and no further
details thereof are described herein.
The pipe coming off the reel 210 should make sufficient
contact with the radius controller 490 at a tangent thereto
to bend the pipe sufficiently so that each wrap of pipe being
unspooled will have the same amount of curvature as it enters
the straightener.
One way which has been suggested to accomplish this
uniformity would be to pass the pipe through a preferably
vertically adjustable set of rollers 562 located on a tower
560 aft of the reel 210. The rollers 562 force each wrap
of pipe to have a sufficiently large radius of curvature to
be tangent to the radius controller 490 as the pipe is unspooled.
Absent rollers 562 or some similar mechanism for imparting the
desired bending moment to the pipe, each wrap of pipe unspooled
would have a different set; that is, the inner wraps have a
smaller radius of curvature than the outer wraps so that the
curve on the free pipe between the reel and the pipe condition-
ing equipment would change as a function of the wrap being un-
-36-
1~2~6()~7
Spooled; this, in turn, would cause the pipe to contact the
radius controller at a different location for each wrap, there-
by altering the effect of the radius controller and its ability
to impart a uniform radius of curvature to the pipe before it
passes through the straightening assembly 510.
As an alternative to the tower shown, it is considered
that a "free floating" roller assembly may be used. Such roll-
er assembly would ride on the upper surface of the pipe and be
tied to the deck of the ship by cable, thus, the pipe and cables
together act as the roller support, with the pipe exerting an
upward force and the cable a downward ~orce on the rollers.
The roller assembly 562 whether tower-mounted or cable
tethered, increases the ability of the reel to impart larger
hold-back tensions on the pipe than would be possible without
such roller assembly 562. This factor increases the capability
of the ship of this invention to lay larger pipe in deeper water
than might otherwise be the case.
4. Portable Reels
The reel ship of this invention is capable of carrying
spooled pipe on "portable" reels, that is, reels which do not
form part of the basic ship construction, but which are mounted
on, e.g., skids, and may be offloaded at the shore base. This
advantageous feature permits the shore base to prespool pipe on
such portable reels and store the spooled reels in the yard
while the reel ship is at sea. When the ship returns to port,
any empty portable reels on board can be removed and the pre-
spooled waiting reels be loaded on board, thereby reducing down
time in port.
Advantageously, one or more such portable reels, general-
ly capable of carrying up to 6'` diameter pipe, may be mountedon the clear deck space forward of the main reel 210. This
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secondaxy pipe may be passed over the main reel to the pipe
handling apparatus 40. The secondary pipe may bypass the
straightener assembly 510 and be bundled with the main pipe
upstream of the stern guide assembly 540 so that it enters
the water at the same lay angle as the main pipe.
5. General Characteristics
In a preferred embodiment of this invention, the reel
210 has a diameter of about 82 feet. Pipe capacity is about
2,000 tons. Capacities in terms of pipe size and length are
shown below:
Nominal Pipe Size Approximate Capacity
(Inches)(Feet) (Miles)
4 267,000 50.5
6 160,000 30.2
8 104,000 19.7
73,000 13.8
12 54,000 10.3
14 45,000 8.5
16 30,000 5.7
Capacities shown are for typical projects in medium to deep
water. The vessel is also capable of carrying two portable
ree~s with total capacity of 500 tons. The portable reels
are positioned so their pipes may be payed out as a bundle
with the primary pipe.
Other characteristics of the preferred embodiment of
the reel ship of this invention are (approximately):
Length overall 405 feet
Beam70 feet
Depth 28 feet, 6 inches
Draft, operating 18 feet
6. Applications
Below are discussed a number of uses for the reel ship
in the offshore construction industry.
6a. Subsea Completions
Of the many potential uses employed by the reel ship,
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one of the most important applications is in subsea completions
and subsea tie-ins. Major advantages include:
1. Pipe is welded and tested on shore before laying
offshore. This is especially an advantage for
through flow lines, which can be drifted before
laying.
2. Speed of laying pipes offshore substantially
reduces delays due to weather and minimizes
interference with field operations.
3. Since the vessel can dynamically position itself
next to platforms, wellheads, etc., the danger
to underwater pipelines or other bottom equipment
is minimized. The reel ship is also much faster
in setting up, moving away from, and moving
between locations.
4. Except on the largest of projects, one load of
pipe is all that is required to complete pipe-
lines to subsea wellheads.
5. The reel ship can lay bundled configurations
made up of pipes or combinations of pipe and
cable as desired.
6b. Bundled PipPlines
In the "stovepiping" method of laying pipeline offshore,
a new section of pipe must be welded (added) every 40 or 80
feet. This method re~uires one "welding line" for one pipeline.
If it is desired to lay pipe in bundles, then, in effect, a
"welding line" must be set up for each pipe in the bundle.
Since most standard pipelay barges are designed for just one
pipeline, finding enough room for one or more additional pipe
"welding lines" is difficult.
Furthermore, most pipeline vessels apply tension to the
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pipe with the use of a tensioner, specifically designed to
handle one pipe, and not two or more.
These problems are overcome by the reel ship of this
invention with the use of the main reel and one or more port-
able reels. A typical bundle, for example, could consist ofan eight inch pipe coming off the main reel and four inch and
two inch pipe coming off separate portable reels. It is also
possible to have more than one pipe bundled together on a reel.
Pipes for different lay operations can be carried
together on the reels. The experience of the assignee and/or
its predecessors-in-interest in laying pipe by the reel method
has shown that different size pipes can be spooled over other
pipes without damage.
Because of the large spooling capacity of the reel ship
of this invention on the main and portable reels, pipe can be
carried on one trip for a number of separate lay operations,
such as those required on a subsea completion project.
6c. Operation in Congested Areas
In an area which is congested with many platforms, pipe-
lines, subsea completions, construction barges, supply boats,
etc., the vessel which can operate without the use of a con-
ventional anchoring system will have a great advantage.
One example of this application would be in a developed
field which already has many operating pipelines. If the need
arose to bring an adjacent field's production into this facility
by pipeline, it could be effectively accomplished with the
dynamically positioned reel ship. With the pipe already loaded
onto the reel, the ship would dynamically position itself next
to the platform in the developed field,~ feed out the end of
the pipe to the platform and lay away from the structure, thus
requiring only a minimum time in the congested area.
2~607
Another application of the dynamic positioning capabil-
ities of the reel ship would be pipeline tie-ins at platforms,
subsea completions or manifold centers. Besides the reduced
risk by not using anchors, the speed at which the ship can
set up on location, move between locations, and move off
location at the end of the job, will allow the maximum time
to be devoted to completing the project during favorable
weather periods.
6d. Laying Pipe in Shipping Lanes
Modern pipeline barges can lay more than two miles of
pipe in a 24-hour period by the "stovepiping" method; present-
day reel barges can lay same amount of pipe in a fraction of
that time. In each case, the barge anchor patterns in doing
this may cover an area approximately three miles long and one
mile wide. If this area is located in a major shipping lane,
such as the English Channel, unnecessary delays to shipping
could be expected.
In contrast, the reel ship could lay the two miles in
a few hours, and, since no anchoring pattern is Used the
vessel would occupy only a nominal width of the shipping lane
during any particular period of time. The reel ship's unique
pipelaying operation offers a means of reducing inconvenience
to shipping when pipelines must be installed in areas with
heavy commercial shipping traffic.
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6e. Remote Locations ~ Worldwide Operations
Certain areas of the world, such as the Beaufort Sea,
allow very little time each year for offshore construction.
Similarly, land support bases and the logistics associated
with the base operations, offer difficulty in supporting
offshore operations.
The reel operation of the reel ship offers advantages,
of which a few are listed below:
- The speed at which the reel ship can
tra~el to such locations.
- The large pipe capacity the reel ship can
carry in one trip.
- The speed in laying offshore.
- Minimum shore support if complete require-
ment of pipe can be carried in one load.
The reel ship will be able to mobilize from the Gulf
of Mexico to offshore areas such as the North Sea, California,
Brazil, and the Mediterranean in approximately 2-l/2 weeks;
the North Sea to the Mediterranean will take only one week.
Since the reel ship has a large carryin~ capacity for
smaller pipes, it will be able to operate from a base, for
example, in the North Sea, and mobilize to an area like the
Mediterranean. This eliminates the need to set up bases
in eYery area where pipe is laid.
In short, the reel ship is able to mobilize, complete
the job, and demobilize in a short period of time.
7. Operating Example
The following example is presented to illustrate the
basic reel method laying procedure.
A. Pipe size - 10-inch nominal
B. Pipeline length - 25 miles
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The basic operation begins with coated pipe delivered
to the spooling yard. The pipe is welded into approximately
1,700 foot lengths. All welds are X-rayed and coated before
spooling onto the reel ship.
At the time the reel ship arrives, approximately 12.5
miles of pipe is ready for spooling. Thirty-nine 1,700 foot
lengths of pipe are spooled aboard, stopping o~ly to weld,
X-ray and coat joints at the end of each new length.
The reel ship, now loaded with pipe and necessary
anodes, mobilizes to location.
Once at location, the ship is dynamically positioned
next to the first platform and a cable tied to the platform
is attached to the pipe.
The lay operation now commences.
Anodes are added at the sterm of the ship during laying.
The ship is normally stopped for 3-5 minutes to add each anode
as required.
At the end of the 12.5 mile lay, the pipe is secured
in a clamp at the stern of the ship.
An abandonment head is welded on and the pipe lowered
to the seabed with a winch. The lowering/pick up cable is
attached to a buoy.
The ship then returns to the yard to spool up the second
load of pipe.
Upon returning to the laydown point, the pipe is picked
up and again clamped. The ne~ pipe is welded-on/ the joint
is X-rayed and coated, and the lay operation commences again.
At the second platform the pipe is pulled in and secured at
the platform. The pipeline is then tested and the reel ship
is demobilized.
Additional features of the reel ship and its operation
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~2i~0~7
are described in a paper co-authored by Kenneth R. Friman,
Stanley T. Uyeda and Herman Bidstrup, entitled "First Reel
Pipelay Ship Under Construction - Applicàtions Up to 16-inch
Diameter Pi~e 3000 Feet of Water" (OTC Paper No. 3069) to be
presented at the Offshore Technology Conference in Houston,
Texas, May 8-11, 1978 and contained in the proceedings thereof.
8. Summary
It will be seen from the foregoing description that the
reel ship of this invention represents a new and different
advance in the art of offshore reel type pipelaying techniques.
In particular, the ship represents a new type of vessel con-
struction which is advantageously suited for carrying large
pipe spooling reels to conduct subsea pipelaying operations
quickly and economically for a world market.
The invention may be embodied in other specific forms
without departing from the spirit or essential characteristics
thereof. The embodiment described above is therefore to be
considered in all respects as illustrati*e and not restrictive,
the scope of the invention being indicated by the hereafter
appénded claims rather than by the foregoing description, and
all changes which come within the meaning and range of equiv-
alency of the claims are therefore intended to be embraced
therein.
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