10
STRUCTURES IN THE OFFSHORE ENVIRONMENT
rigs and construction barges are used in water depths of up to 2000 m. An
example of an early and successful drilling rig is the Océan Victory installed at
a water depth of 450 m. This rig employed 12 anchors, each with a holding power
of 200,000 newton (N) or about 45,000 1b. Each catenary line was about 2500
m long and consisted of two equal segments: one of 8.9 cm diameter steel wire
cable and the other of 8.3 cm diameter chain. Newer génération rigs designed
for deep water hâve ten times the anchor-holding capacity of the Océan Victory.
An anchor design based on suction is shown schematically in Figure 1.7.
Figure 1.7 A suction anchor showing water flow during embedment.
Platform Pile and Single-Point Moorings
For installing piles for platform moorings, specially fitted derrick barges
may use hydraulic hammers, drilling equipment, or possibly a jetting System.
In jetting, seawater is forced around the base of a pile, blasting away the soil
to make way for pile embedment. When installing mooring piles for tension leg
platforms, template structures are carefully positioned at the site, and piles are
hammered through the template that serves as a pile guide. Suction piles are
employed in deep water where the use of hydraulic hammers is impractical or
too costly. Suction piles employ hydrostatic pressure to push the piles to full
pénétration.
Single-point mooring (SPM) Systems are designed to accommodate deepdraft tankers while they transfer crude oil and fuel oil to and from shore. Two
typical designs are shown in Figure 1.8: the single anchor leg mooring (SALM),
and the catenary anchor leg mooring (CALM). By the year 2000, there were
about 50 SALM Systems and 150 CALM Systems in operation throughout the
world. Their common features are the rotating head on the buoy and the vertu al chain that anchors the buoy to the sea floor. While a few SALM Systems
ma> ha\e taut mooring lines for added buoy stability, ail CALM Systems hâve
multiple catenary lines (anchor legs). A third type of SPM System, the articulated column, has been designed and laboratory-tested but has yet to be
installed offshore.
STRUCTURES IN THE OFFSHORE ENVIRONMENT
rigs and construction barges are used in water depths of up to 2000 m. An
example of an early and successful drilling rig is the Océan Victory installed at
a water depth of 450 m. This rig employed 12 anchors, each with a holding power
of 200,000 newton (N) or about 45,000 1b. Each catenary line was about 2500
m long and consisted of two equal segments: one of 8.9 cm diameter steel wire
cable and the other of 8.3 cm diameter chain. Newer génération rigs designed
for deep water hâve ten times the anchor-holding capacity of the Océan Victory.
An anchor design based on suction is shown schematically in Figure 1.7.
Figure 1.7 A suction anchor showing water flow during embedment.
Platform Pile and Single-Point Moorings
For installing piles for platform moorings, specially fitted derrick barges
may use hydraulic hammers, drilling equipment, or possibly a jetting System.
In jetting, seawater is forced around the base of a pile, blasting away the soil
to make way for pile embedment. When installing mooring piles for tension leg
platforms, template structures are carefully positioned at the site, and piles are
hammered through the template that serves as a pile guide. Suction piles are
employed in deep water where the use of hydraulic hammers is impractical or
too costly. Suction piles employ hydrostatic pressure to push the piles to full
pénétration.
Single-point mooring (SPM) Systems are designed to accommodate deepdraft tankers while they transfer crude oil and fuel oil to and from shore. Two
typical designs are shown in Figure 1.8: the single anchor leg mooring (SALM),
and the catenary anchor leg mooring (CALM). By the year 2000, there were
about 50 SALM Systems and 150 CALM Systems in operation throughout the
world. Their common features are the rotating head on the buoy and the vertu al chain that anchors the buoy to the sea floor. While a few SALM Systems
ma> ha\e taut mooring lines for added buoy stability, ail CALM Systems hâve
multiple catenary lines (anchor legs). A third type of SPM System, the articulated column, has been designed and laboratory-tested but has yet to be
installed offshore.