DEEPWATER MOORING: Two mooring lines per winch

Santa Fe International contracted Bodewes Winches in The Netherlands to provide combined chain/wire rope mooring sys-tems for two new deepwater semisubmer-sibles under construction in Singapore.

Santa Fe International contracted Bodewes Winches in The Netherlands to provide combined chain/wire rope mooring systems for two new deepwater semisubmer-sibles under construction in Singapore. Two years ago, a comparable combined mooring system was delivered for the Transocean Sedco Forex semisubmersible Deepwater Nautilus. This rig recently established a world record through mooring successfully in 2,380 meters of water in the Gulf of Mexico.

The two new systems for Santa Fe will operate in slightly lesser depths (up to 2,290 meters). Both packages will include eight traction winch/windlass units managing a chain/steel wire rope configuration, using as many as two mooring lines per winch frame.

Uniquely, the system will allow the new semisubmersibles to be connected to either eight, 12, or 16 anchor lines on a pre-laid or conventionally moored system, providing redundancy and greater flexibility during stormy conditions.

Sixteen instead of eight

According to Bodewes sales engineer, Bas Oskam, Santa Fe's requirement to moor with up to 16 points instead of the conventional eight-line arrangement necessitated modifications to the storage winch frames (mounted inside the columns), with four fairleads to be accommodated per column, instead of the normal two. Oskam said it was a challenge.

The fairleads had to be positioned to avoid interaction with the winch drums and interference with the mooring lines. This problem was solved during a live, five-hour design session with engineers from Santa Fe and the rig designer Friede Goldman Halter.

The new semisubmersibles are designed to work in milder deepwater environments such as Brazil, West Africa, and the Gulf of Mexico.

"We are putting two mooring lines on one winch, versus the conventional one line per winch," he said. "The in-line set-up of winches and tractor winches on one frame allows us to do this. This also saves up to 25% deck space for Santa Fe, compared with the traditional arrangement based on traction windlasses.

Other advantages

Other advantages claimed by Oskam are that the design of the drum allows for better feed-out of the line and flexibility of "playing" with the fairleads. He claimed that the Bodewes system was designed "not to break, so we don't need spares." On bearing changeout, modularity makes it easier for such a replacement maneuver, when needed.

The Bodewes system is gear-driven and computer controlled, with constant back pressure applied on the traction winch. Wire rope/chain connections and disconnections are performed using the company's QuickLink system.

Bodewes is scheduled to complete testing, delivery, and installation of the system for the first Santa Fe semisubmersible soon. Work on the second system is due to be completed by the end of 2002.

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