Mobile marine platform and method of installation

A mobile marine drilling assembly has a horizontally disposed pontoon which floats on or is submerged below the surface of a marine environment. A first vertically disposed column is secured to the pontoon and extends upwardly therefrom. A work platform has an opening through which the column extends, and the platform overlies the pontoon and is vertically movable relative thereto along the column. A jack system is operably connected with the work platform and with the column for jacking the work platform along the column between a first position wherein the pontoon floats on the surface of the marine environment and a second position wherein the pontoon is disposed a substantial distance below the surface of the marine environment. An anchor is secured to the floor of the marine environment. A plurality of resilient tendons extend between and are secured to the pontoon and the anchor, and the tendons are under tension when the pontoon is in the second position so that wave and current induced horizontal movement of the pontoon and thereby of the column and the work platform is permitted, and vertical movement is resisted.

BACKGROUND OF THE INvENTION 
A tension leg platform, or TLP, is a marine platform having economic 
potential for use in drilling in deep water locations. A typical tension 
leg platform is similar to a semi-submersible platform by having a number 
of large, vertical cylinders close to the periphery for providing 
stability during the transportation phase from shore to the drill site. 
The platform has a lower structure tieing the cYlinders together at the 
bottom thereof in order to provide some buoyancy. It also has an upper 
structure tieing the upper ends together, and providing space for 
equipment, supplies and the like. 
At the drill site, the tension leg platform is connected by a plurality of 
tendons to a heavy anchor secured on the sea bottom. The tendons are 
vertically oriented, and are always under tension. The tendons are quite 
slender and flexible, and act essentially as strings to permit the tension 
leg platform to move relatively freely in the horizontal plane while 
substantially preventing upward and angular movement. The tension leg 
platform provides considerable advantage over a semi-submersible platform, 
because the wellhead may be above water and drilling and work over may be 
done in the conventional surface fashion. 
The hydrodynamic behavior of a tension leg platform has certain 
characteristics during the construction and installation phase which are 
at odds with the characteristics desired in the on-location phase. These 
characteristics impose conflicting design requirements. When on-location, 
it is desirable to reduce the vertical wave forces as much as possible, 
and thereby to reduce the strength, weight, number and cost of the tendons 
and the anchor. In order for this to be done, the buoyancy should be well 
below the surface of the water. Thus the cylindrical columns should be as 
deep in the water and as small in diameter as possible. Such a 
configuration, however, results in a very tall structure which is unstable 
when floating to location, and also has excessive draft during 
construction. Stability while floating to location is an absolute 
requirement, with the result that the goal of minimizing the on-location 
wave forces is normally sacrificed. 
A further limitation on the prior art tension leg platform has to do with 
the buoyancy effect resulting from wave motion. Passage of a wave beyond a 
column causes that portion of the column normally disposed above the sea 
surface to be covered, thereby increasing the buoyancy thereof. Those 
portions normally disposed below the sea surface, on the other hand, 
suffer from reduced buoyancy when this occurs, on account of the motion of 
the water particles resulting from the cyclic nature of the wave. The net 
result is that the buoyancy may be adversely affected by wave action, 
particularly by waves of substantial amplitude. 
The disclosed invention is one which overcomes the conflicting design 
requirements normally presented by a tension leg platform. The disclosed 
invention combines the advantages of a jack-up drilling platform with 
those of a tension leg platform in order to provide a mobile marine 
platform which has a first geometry during the construction phase and a 
second geometry during the on-location phase. In the first geometry the 
work platform is closely spaced to a pontoon system floating on the 
surface of the water and with the pontoon system substantially providing 
stability because no tendons are connected. In the second geometry, the 
work platform is spaced a substantial distance above the pontoon on a 
column carried by the pontoon and stability is substantially provided by 
the tendons connected to the anchor. The dimensions resulting from this 
two geometry system permit columns that are much smaller in diameter and 
extend to a much deeper operating draft than heretofore possible. 
A further advantage of the invention involves the relationship between the 
buoyancy provided by the column and that provided by the pontoon. It is 
theoretically possible to size the two elements so that the theoretical 
wave forces cancel. The disclosed invention permits such dimensional 
configurations to be more easily taken into account, with the result that 
full advantage can be obtained of this phenomenon. 
OBJECTS AND SUMMARY OF THE INVENTION 
The primary object of the disclosed invention is a mobile marine platform 
having optimum stability during the construction and transportation 
phases, as well as optimum stability during the on-location phase. A 
further objective of the invention is a method for shifting the mobile 
drilling platform from the first geometry, which is suitable for the 
construction phase, to a second geometry, suitable for the on-site phase. 
An intermediate geometry may be used during transportation. 
Yet a further object of the disclosed invention is a method for connecting 
the tendons of the mobile platform to a marine anchor secured to the sea 
floor. 
A mobile marine platform according to the invention comprises horizontally 
disposed pontoon means for floating on or being submerged below the 
surface of a marine environment. At least a first vertically disposed 
column is secured to the pontoon means and extends upwardly therefrom. A 
work platform has at least a first opening through which the column 
extends, and the work platform overlies the pontoon means and is 
vertically movable relative thereto along the column. Jack means are 
operably associated with the work platform and with the column for jacking 
the work platform relative to the column between a first position wherein 
the pontoon means float on the surface of the marine environment, and a 
second position wherein the pontoon means are disposed a substantial 
distance below the surface of the marine environment. An anchor is 
provided for being secured to the floor of the marine environment. A 
plurality of resilient tendons are provided for extending between the 
pontoon means and the anchor means, and the tendons are under tension when 
the pontoon means are in the second position so that wave and current 
induced horizontal movement of the pontoon means and thereby of the column 
and work platform is permitted and upward and angular movement thereof is 
resisted. 
A well drilling assembly comprises a floating platform comprising pontoon 
means submerged below the surface of a marine environment, at least a 
first vertically disposed column is secured to the pontoon means and 
extends upwardly therefrom and terminates above the marine environment 
surface, a work platform has at least a first opening through which the 
column extends and the platform overlies the pontoon means and is movable 
along the column relative thereto, and jack means are operably associated 
with the platform and with the column for jacking the platform relative to 
the column between a first position wherein the pontoon means float on the 
marine environment surface and a second position wherein the pontoon means 
are submerged therebelow. An anchor means is secured to the floor of the 
marine environment, and a plurality of resilient tendons extend under 
tension between and are secured to the anchor means and the pontoon means 
so that wave and current induced horizontal movement of the platform is 
permitted and upward and angular movement thereof is resisted. 
A jack-up tension leg platform comprises a generally horizontally disposed 
pontoon means for floating on or being submerged below the surface of a 
marine environment, and the pontoon means are X-shaped in plan. A first 
vertically disposed cylindrical column is secured centrally to the pontoon 
means and extends upwardly therefrom. A work platform has a central 
opening therethrough and through which the column extends, and the work 
platform overlies the pontoon means and is vertically movable relative 
thereto along the column. Jack means are operably associated with the work 
platform and with the column for jacking the work platform between a first 
position wherein the pontoon means float on the surface of the marine 
environment and a second position wherein the pontoon means are submerqed 
therebelow. 
The method of assembling a tension leg platform comprises the steps of 
providing a well drilling platform comprising pontoon means floating on 
the surface of a marine environment, at least a first vertically disposed 
column is secured to the pontoon means and extends upwardly therefrom, a 
work platform has at least a first opening through which the column 
extends and the work platform is movable along the column, and jack means 
are operably associated with the work platform and with the column for 
jacking the column relative to the work platform between a first position 
wherein the pontoon means float on the surface of a marine environment and 
a second position wherein the pontoon means are submerged therebelow, an 
anchor means is secured to the floor of the marine environment, and a 
plurality of resilient tendons are provided. Each of the tendons is 
secured to the pontoon means so that the tendon means are suspended 
therefrom in the marine environment and terminate a selected distance 
above the anchor means. The column is jacked relative to the work platform 
and thereby causes the tendons to terminate at or below the anchor means. 
The tendons are connected to the anchor means and the buoyancy of the 
platform is increased, thereby causing the platform to rise relative to 
the floor of the marine environment so that a tension is applied to the 
tendons. 
These and other objects and advantages of the invention will be readily 
apparent in view of the following description and drawings of the above 
described invention.

DETAILED DESCRIPTION OF THE INvENTION 
Mobile marine well drilling platform P1, as best shown in FIG. 1, comprises 
a pontoon assembly 10 floating on the surface 12 of marine environment 14. 
Cylindrical column 16 is secured to pontoon assembly 10 and extends 
upwardly therefrom. Work platform 18 is mounted above pontoon assembly 10 
and about Column 16 on account of opening 19 and is longitudinally movable 
relative thereto. Derrick 20 is mounted to work platform 18 adjacent 
column 16, while quarters 22 are positioned on work platform 18 on an 
opposite side thereof adjacent to column 16. Derrick 20 is movable on 
rails 21. 
Pontoon assembly 10, as best shown in FIGS. 3, 4 and 9, is X-shaped in plan 
and has equiangularly disposed legs 24, 26, 28 and 30 extending uniformly 
outwardly from the base of Column 16. Each of the legs 24, 26, 28 and 30 
is rectangular in plan and cross-section, and the legs 24, 26, 28 and 30 
have uniform dimensions, although other configurations are possible. Each 
of the legs 24, 26, 28 and 30 terminates in an end member 32, 34, 36 and 
38, respectively, which is disposed generally transverse to the length 
dimension of the associated leg. 
The legs 24, 26, 28 and 30 likewise have upper members 40, 42, 44 and 46, 
respectively, which lie on a common plane and are uniformly spaced from 
parallel lower members 48, 50, 52 and 54, respectively. Side leg members 
56 and 58 extend between upper and lower members 40 and 48 and between 
column 16 and end member 32, while side leg members 60 and 02 complete leg 
26. Likewise, leg 28 has side leg members 64 and 66, while leg 30 has side 
leg members 68 and 70. The legs 24, 26, 28 and 30 are hollow and provide a 
multi-compartment ballast tank system for admitting sea water through 
valve 72 or causing same to be expelled as a result of air pressure 
supplied by a compressor or otherwise. 
A plurality of tendon receiving connector assemblies 74 are secured to each 
of the end members 32, 34, 36 and 38 adjacent the associated lower 
surfaces thereof, as best shown in FIGS. 8 and 9. The tendon receiving 
connector assemblies 74 are all substantially identical, and permit 
pivotal movement of a secured tendon 76. Those skilled in the art 
understand that the tendons 76 are long, multi-element tubular assemblies 
which are resilient but substantially non-elastic in the vertical 
direction. The tendon receiving connector assemblies 74 are uniformly 
spaced apart both relative to each other, and to the associated end 
members from which they depend. 
It can be noted in FIG. 2 that a pivot connector 78, provided by a 
resilient bushing or the like, is mounted within or at the top of each of 
the tendon receiving connector assemblies 74 and is secured to the 
associated tendon 76 in order to permit pivoting of the tendons 76 during 
flexing thereof as may be caused by wind, wave or current conditions. 
Cylindrical column 16 has an annular chamber 80 defined by outer wall 82 
and inner cylindrical member 84 having central opening 86, as best shown 
in FIG. 9. Cylindrical column 16 and its annular chamber 80 are closed at 
the base thereof by end member 88, a best shown in FIG. 4, and at the 
upper end by end member 90, as best shown in FIG. 3. In this way, annular 
chamber 80 likewise provides a ballast tank system which, through valve 91 
and in combination with pontoon assembly 10, permits the buoyancy of 
platform P1 to be regulated as may be needed. 
FIG. 1 illustrates the platform P1 in the construction geometry. In this 
geometry, the work platform 18, which interiorly may include crew 
quarters, storage and the like, is lowered in order to be adjacent pontoon 
assembly 10 so that floatational stability is provided mainly by the 
pontoon assembly 10. Once deeper water is reached, then platform P1 may be 
appropriately ballasted so that pontoon assembly 10 is submerged, and 
platform 18 floats on surface 12, as best shown in FIG. 2. Stability in 
this transportation geometry is important because it is common for the 
platform P1 to be constructed at the shore, and to thereafter be towed or 
otherwise transported to the drill site. The drill site can be some 
distance from the shore, with the result that stability must be maintained 
for quite some period and distance, particularly during storms. 
FIG. 7 discloses the platform P1 in the on-location geometry. In this 
geometry, the work platform 18 has been raised to an operating elevation 
along the column 16 relative to the pontoon assembly 10. Stability is 
provided by appropriate control of the ballasting of the chamber 80 and 
the pontoon assembly 10 so that the tendons 76, having substantial length 
and secured to and extending between pontoon assembly 10 and anchor 92, 
have a sufficient tension applied thereto. It can be noted in FIG. 7 that 
the platform assembly P1, as clearly illustrated on the right side 
thereof, has been horizontally shifted as a result of wave W1. The 
string-like effect of the tendons 76 permits the platform P1 to be 
horizontally shifted but substantially prevents upward and angular 
displacement, and also causes the platform to be returned to the vertical 
orientation illustrated on the left side of FIG. 7. 
FIG. 2 illustrates the platform P1 in the transportation and installation 
geometry as the tendons 76 are suspended from hook 94 carried by crane 
assembly 96 secured to crane mount 95. Installation of the tendons 76 in 
the associated tendon receiving connector assemblies 74 can proceed fairly 
straightforwardly, because the pontoon assembly 10 is rotatable relative 
to the work platform 18. There is no pressure between the work platform 18 
and the column 16, because both are floating on account of their own 
buoyancy. Receipt of a tendon 76 in one of the tendon receiving connector 
assemblies 74 and securement thereto by its pivot connector 78 can be 
rapidly effected. Rotation of the pontoon assembly 10 or the work platform 
18 can then occur, in order to align the crane assembly 96 with the next 
tendon receiving connector assembly 74. 
Once the tendons 76 have all been mounted in their respective tendon 
receiving connector assemblies 74, then it is necessary to have the 
downwardly suspended ends thereof secured to the anchor 92, followed by 
jacking of the platform P1 into the second geometry illustrated in FIG. 7. 
FIGS. 5 and 6 illustrate the jack assembly J utilized for shifting the 
work platform 18 relative to the column 16 in order to cause the suspended 
ends of the tendons 76 to be positioned at or below the anchor 92, as well 
as to jack the work platform 18 to the elevated operating position once 
the tendons have been appropriately secured to the anchor 92 and the 
pontoon assembly 10 and chamber 80 deballasted. Since the work platform 18 
is movable relative to the column 16, the upper end of the column 16 can 
be positioned substantially flush with the work platform 18. At this 
position, the derrick 20 may be moved in a position overlying the column 
16, since the derrick 20 is movable on rails 21, as best shown in FIG. 3. 
Once the derrick 20 is overlying the column 16, the derrick 20 may be 
aligned with the central opening 86. 
The jack assembly J is positioned on the top of the work platform 18 and 
comprises an upper annular yoke 98 mounted about the column 16 and free to 
slide along the column 16. A lower annular yoke 100 is similarly mounted 
about column 16 and is free to slide relative to the column 16. The yokes 
98 and 100 have uniform inner and outer diameters, and the lower yoke 100 
is secured to upper wall 104 of work platform 18. It is necessary that one 
of the yokes be secured to the work platform 18, while the other be free 
to move relative to the work platform 18. 
A plurality of pin receiving openings 106 are equiangularly disposed about 
the column 16 for substantially the length thereof. The openings 106 are 
also disposed in a series of layers, with each layer having the same 
number of openings 106, and with the openings 106 of each layer 
longitudinally aligned with the openings 106 of the other layers. Each of 
the openings 106 is closed interiorly of the column 16 by a pin closure 
108 in order to prevent the entry of water into chamber 80, as well as to 
prevent leakage from the chamber 80 and to maintain the proper ballast. In 
this way, each of the pin receiving openings 106 resembles a detent which 
is adapted for receiving an associated pin or jack element 110 or 112 
carried by the yokes 98 and 100, respectively. There are sixteen sets of 
pins 110 and 112 disposed about the yokes 98 and 100 for assuring positive 
securement of the work platform 18 in a selected geometry, as well as to 
minimize the load on any individual pin 110 or 112 during jacking. While I 
have illustrated the pins 110 and 112 as being manually operable, those 
skilled in the art will understand that numerous mechanisms can be 
provided for driving the pins into the openings 106, as well as for 
removing them therefrom. It is preferred, however, that each of the pins 
110 and 112 extend generally perpendicular to the axis of column 16 in 
order to minimize bending forces. 
Interdigitated between the pins 110 of the yoke 98 and the pins 112 of the 
yoke 100 are a plurality of hydraulic cylinder and piston assemblies 114 
The cylinders 116 thereof are secured to the yoke 100, and the pistons 118 
thereof are secured within the yoke 98. In this way, extension and 
retraction of the pistons 118 will cause corresponding movement of the 
yokes 98 and 100 along the column 16, provided that the pins 110 or 112 of 
one of the yokes 98 and 100 are removed from the associated openings 106. 
Movement of the work platform 18 along the column 16 can be readily 
accomplished by appropriate manipulation of the pins 110 and 112, in 
cooperation with extension and retraction of the cylinder and piston 
assemblies 114. Because the cylinder and piston assemblies 114 are secured 
to and extend between the yokes 98 and 100, then the weight of the work 
platform 18 will be carried by the yoke 98 as the yoke 100 is moved in 
response to operation of the cylinder and piston assemblies. In this way, 
once the pins 110 have been properly secured in their associated openings 
106, then the pins 112 can be removed from their openings and the piston 
118 caused to retract relative to the cylinder 116 so that the yoke 100 is 
caused to move toward the yoke 98, and thereby the platform 18 to be moved 
upwardly. Once the platform 18 has been moved sufficiently upwardly, then 
the pins 112 are inserted into their associated openings, and the pins 110 
removed, thereby permitting the yoke 98 to again be moved upwardly 
relative to the yoke 100. After a sufficient distance, then the pins 110 
are again inserted into their associated openings, and the process is 
repeated. Those skilled in the art will understand that the work platform 
18 can similarly be moved downwardly through like cooperative action of 
the pins 110 and 112 with the cylinder and piston assemblies 114. 
Anchor 92, as best shown in FIG. 10, is, preferably, a torus comprised of 
concrete having a hollow interior to which is connected valve 120. The 
anchor 92, because of the buoyancy provided by its hollow interior, will 
float on the surface of marine environment 14 and can therefore likewise 
be towed from shore to the drill site. Although configurations other than 
a torus are possible, I prefer a torus because it provides maximum 
strength for withstanding the pressures applied at extreme depths. Opening 
of the valve 120 will cause the anchor 92 to be filled with water such 
that the decreased buoyancy will cause the anchor 92 to sink to the sea 
floor 122, as best shown in FIG. 7. Anchor 92 may then be secured to the 
sea floor by suitable pilings, subterranean anchors and the like 124, 
although the weight of anchor 92 in certain instances may be sufficient to 
preclude the need for pilings 124. 
Anchor 92 has girders 126 and 128 extending in spaced parallel relation 
from one side to the other. Beams 130 and 132 extend between the girders 
in order to form a box-like structure 134 through which risers 136 extend. 
The risers 136 extend upwardly from box structure 134 into aperture 86 of 
column 16 and are used to extract oil or gas, supply drilling fluids and 
the like. Preferably, each of the risers 136 has a pivot joint 138 
slightly below end member 88, as best shown in FIG. 4, in order to permit 
the risers 136 to pivot as the platform P1 is shifted, as best shown in 
FIG. 7, and similar pivot joints may also be provided at anchor 92. Anchor 
92 preferably has pivot joints 140, provided by resilient bushings or the 
like, for connecting the lower terminal end of each tendon 76 with the 
anchor 92. This prevents the respective tendon 76 from breaking during 
horizontal movement of the platform P1. 
FIG. 15 discloses an alignment mechanism particularly useful during 
rotation of the work platform P during installation of the tendons 76. In 
this regard, ring 142 is secured to column 16 and fork 144 is slidably 
received within member 146 secured to platform 18. The fork 144 is movable 
generally transverse to the axis of column 16 with the result that 
engagement of the tines around the ring 142 prevents the column 16 from 
tipping or otherwise being shifted out of proper alignment. Conventional 
drive means 147 rotates the column 16 relative to the work platform 18, as 
best shown schematically in FIG. 15. 
INSTALLATION OF PLATFORM P1 
The platform P1, when configured in the geometry of FIG. 1, has sufficient 
stability to permit the platform P1 to be towed for a substantial distance 
from the shore. Once the water is sufficiently deep, then appropriate 
ballasting submerges the pontoon assembly 10 to the geometry of FIG. 2, 
and platform P1 remains in this geometry for the rest of the distance to 
the drilling location. Similarly, the anchor 92 likewise has sufficient 
buoyancy to permit it to be towed. Once the platform P1 has reached the 
location, however, then it is necessary to transform it to the on-site 
geometry illustrated in FIG. 7. The jacking system J permits this 
transformation to occur with relative ease, without sacrificing the 
stability attributable to a tension leg platform. 
The anchor 92 is first caused to sink within marine environment 14 until it 
comes to rest on sea floor 122. Pilings 124 may then installed to secure 
the anchor 92 to the sea floor. After the anchor 92 is appropriately 
secured to the sea floor 122, then the tendons 76 are installed. 
FIG. 2 illustrates the platform P1 during installation of the tendons 76 
through utilization of the crane assembly 96. Each of the tendons 76 is 
appropriately secured within its associated tendon receiving connector 
assembly 74 and caused, thereby, to hang downwardly in marine environment 
14. The tendons 76 are normally comprised of a series of interconnected 
pipe-like assemblies which together, necessarily, are quite long because 
the tension leg platform P1 is normally most suitable for water depths in 
excess of 500 feet. 
Once all tendons 76 have been appropriately secured by pivot connectors 78 
within their associated tendon receiving connector assemblies 74, then the 
pontoon assembly 10 may be jacked downwardly relative to surface 12 in 
order to cause the lower, suspended terminal ends of the tendons 76 to be 
disposed at or below the pivot joints 140 of the anchor 92. Appropriate 
manipulation of the pins 110 and 112 in combination with the cylinder and 
piston assemblies 114 will jack the column 16 and its pontoon assembly 10 
relative to work platform 18, with the result that the pontoon assembly 
will be sufficiently further submerged. 
The lower, suspended terminal ends of the tendons 76 may then be connected 
to the pivot joints 140. Once all tendons 76 have been appropriately 
secured to the anchor 92, then the platform P1 is shifted to the geometry 
of FIG. 7. This is accomplished by an upward stroke of the jacking 
assembly J in order to pull the platform 18 down into the water, thus 
creating a tension in the tendons 76. The specified initial design tension 
may then be achieved by pumping ballast from the pontoon assembly 10 and 
the column 16, as well as by simultaneously raising the platform 18 
through appropriate manipulation of the jacking system J because the 
tendons 76 prevent the pontoon assembly 10 and column 16 from being moved 
vertically upward. Once the platform 18 has been jacked clear of the 
marine environment 14, and the ballast in the pontoon assembly 10 adjusted 
for proper initial tension of the tendons 76, then the platform 8 may be 
raised to its final design elevation through use of the jacking system J. 
Once at the operating elevation, then platform 18 is secured by the pins 
112 of yoke 100 to column 16. 
The single column platform P1 is an advantageous configuration because 
wind, wave and current forces are reduced on account of the reduced 
surface area of the single column 16. Furthermore, because of the central 
orientation of the column 16 relative to the pontoon assembly 10, the 
upper portions of the risers 136 are not exposed to wave forces because 
they pass upwardly through the aperture 86, and this aperture is normally 
submerged. The single column platform P1 is furthermore advantageous 
because of the X-shape of the pontoon assembly 10, and its ability to 
widely space the various groups of tendons 76. The tendons 76 are 
connected to the pontoon assembly 10 outwardly thereof such that, when the 
platform P1 is caused to be horizontally shifted on account of wave W1, as 
best shown in FIG. 7, then the tendons 76 are not struck or otherwise 
contacted by the pontoon assembly or related parts of the platform P1. 
This is also attributable to the fact that the tendon receiving connector 
assemblies 74 are positioned along the respective lower surfaces of the 
legs 24, 26, 28 and 30, and furthermore permit pivoting as may be 
required. 
The single column platform P1 has improved performance not only because of 
the reduced surface area provided by the column 16, but also because the 
pontoon assembly 10 is appropriately dimensioned relative thereto to 
minimize turbulence, wave forces and the like which would occur as a wave 
W1 of substantial magnitude passed beyond the platform P1. As earlier 
noted, the relative dimensions of the column 16 to the pontoon assembly 10 
can be appropriately selected so that the oppositely oriented buoyancy 
effects caused by the wave W1 are cancelled in a manner which enhances and 
increases stability. 
FOUR COLUMN EMBODIMENT 
FIGS. 11-14 illustrate a four column marine platform assembly P2 which 
utilizes a jack system J2, which corresponds to the jack system J, for 
shifting the pontoon assembly 148 and work platform 150 between the 
construction geometry of FIG. 11 the transportation geometry of FIG. 12 
and the on-site geometry of FIG. 14. Platform P2 has columns 152, 154, 156 
and 158 extending upwardly from pontoon assembly 148. The pontoon assembly 
148 is a centrally open system, resulting from the interconnection of 
peripherally disposed hollow tubular legs 160, 162, 164 and 166 and has 
valve 167 for ballast control purposes. 
Tendon receiving connector assemblies 168, which correspond to the tendon 
receiving connector assemblies 74 of the platform P1, are secured to the 
rounded, corner portions of the pontoon assembly 148 adjacent the 
associated lower surface thereof. The tendons 170, which correspond to the 
tendons 76 of the platform P1, are pivotally secured by pivot connections 
172 within the associated tendon receiving connector assemblies 168. In 
this way, as with the platform P1, the tendons 170 are outwardly disposed 
relative to the pontoon assembly 148 in order to prevent them from being 
struck or otherwise contacted by the pontoon assembly 148 as the platform 
P2 is shifted from the normal, floating position illustrated to the left 
in FIG. 14, to the horizontally shifted position illustrated on the right 
side of FIG. 14. 
Platform P2 has a well derrick 174 which is secured to the work platform 
150. The work platform 150 has a central opening 176, as best shown in 
FIG. 13, in order to permit risers 178 to extend upwardly from anchor 180, 
which corresponds to anchor 92 of platform P1, to the top of work platform 
150. Because the legs 160, 162, 164 and 166 are spaced apart relative to 
each other, then there is a central opening in the pontoon assembly 148 
which avoids the need for a pivot connector for the risers 178 prior to 
their passing through the pontoon assembly 148. 
The platform P2 is connected to the anchor 180 much as discussed with the 
platform P1, with the exception that the platform 150 cannot rotate 
relative to the pontoon assembly 148 because of the four columns 152, 154, 
156 and 158 which are fixed to and extend upwardly from the pontoon 
assembly 148. Once on location, however, the tendons 170 are secured 
within the associated tendon connector assemblies 168 and the pontoon 
assembly 148 is jacked by a plurality of jacking systems J2, each of which 
corresponds with the jack system J of the platform P1, and each of which 
is disposed about one of the columns 152, 154, 156 and 158 and carried by 
the platform 150. 
FIG. 12 discloses the work platform 150 after it has been jacked 
intermediate the construction orientation of FIG. 11, and the operating 
orientation of FIG. 14. In this transportation and installation geometry, 
the tendons 170 are illustrated during the process of being lowered toward 
the anchor 180 in order to permit connection thereto. 
Much as with the platform P1, the platform P2 has the work platform 150 
normally disposed a substantial distance above the surface 182 of marine 
environment 184, as best shown in FIG. 14. Should a wave W2 pass through 
the platform P2, then the tendons 170 will again permit the platform P2 to 
be horizontally shifted relative to the normal vertical orientation, but 
will prevent upward and angular displacement. The columns 152, 154, 156 
and 158 are sized relative to the pontoon assembly 148, as with the 
platform P1, in order to have the oppositely oriented buoyancy effects of 
the wave W2 cancelled in a manner which minimizes stress on the tendons 
170. 
While this invention has been described as having a preferred design, it is 
understood that it is capable of further uses, adaptations and/or 
modifications of the invention following in general the principle of the 
invention and including such departures from the present disclosure as 
come within known or customary practice in the art to which the invention 
pertains, and as may be applied to the central features hereinbefore set 
forth, and fall within the scope of the invention of the limits of the 
appended claims.