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32 | Oilfield Technology January 2015

A careul eye and steady hand rom the winch operator became the motto

during deployment to prevent rupturing the cover and exposing the core

ropes and ibres to the environment.

Installation vesselJoshua Chouest  is a 288 f long AHV with a 66 f beam and a 29.5 f height.

It has a deadweight tonnage o 4744 t. Equipped with two Caterpillar diesel

engines, each with a brake horse power o 15 200 bhp, the Joshua  has a

bollard pull o 200 t. There are also ive winch drums, o which two are anchor

handling drums and two are storage reels. The main tow drum has the largest

capacity.

In order to develop procedures that work or an offshore installation, it

is important to survey the proposed vessel(s) to ensure that the equipment

is capable o handling the mooring components effectively. For Delta House,

this survey took place over a year in advance o the installation.

The chain segments were test itted in the proposed whelps to ensure

that lowering o the connection between the messenger chain and the

topsides chain could be perormed saely. While writing the procedures to

install the very large chain proposed or Delta House, it became clear that

the chutes delivered rom the shipyard when the Joshua  was built were too

small to accommodate the 18 in. girth o each link. The capacities o the chain

lockers were also examined to ensure that they could accommodate the

proposed lengths o chain.

Equipped with a remotely operated vehicle (ROV), the Joshua  was

technically suited or the subsea connection o the SMC-III which links the

anchor chain to the ground chain and ultimately the FPS. The ROV was usedto ‘arm’ the connector or locking prior to joining.

Custom installation aidesIn order to make the assembly o the chain and shackle components more

efficient and to reduce the risk to personnel on the back deck, an A-rame

was manuactured with chain hoists on the top rail. These were used to

help position the pin and shackle such that the chain or polyester could be

connected. Additional measures were taken during the mobilisation o the

equipment at the dock to urther expedite the offshore assembly.

The weight o the chain attached to the male end o the SMC-III connector

was so great that the chain had to be lowered rom a synthetic lowering line

to share the load and not rupture the jacket o the polyester mooring rope.To ensure adequate back-tension was kept on the lowering line during

recovery afer deployment o the preset lines on the seabed, a section o

stud-link chain was added between the ROV hook and the lowering line.

This made it necessary to develop some methodology to secure the smaller

diameter chain in the shark jaws. An insert was designed and abricated to

help reduce the spacing between the shark jaws and the smaller stud-link

work chain.

Synthetic rope slings made rom HMPE ibre ropes were also used or

the deployment and recovery slings on the top chain to lay it on the sea loor.

In addition, similar slings were used or the connection between the anchor

chain and the ROV hook on the end o the lowering line.

Conceptual designs or additional assembly aides to support greater

efficiency on uture systems have also been created by InterMoor engineers.

Figure 3. Employees review rigging and procedures one last time beforeover-boarding a suction pile for installation in the Delta House mooring system.

Figure 2. The intersection of vessel capabilities, mooring component size, and workable installation procedures is where the work gets done.

Figure 4. Chain handling on AHV Joshua Chouest. Note the modifiedchain chutes (in burgundy instead of dark orange), which routed thechain from the lockers to the whelps and back deck. Figure 5. Connecting large polyester rope segment to mooring chain segments.