Faced with the challenge of installing one of southeast Asia’s largest offshore platforms, all without damaging a complex network of existing pipelines and subsea equipment, anchor lines made with Dyneema® were the only solution.
To prevent any issues arising with anchor lines, Dockwise concluded that they needed ropes made with Dyneema® fiber to meet the tough challenge to come. With sensitive subsea structures to contend with, and a tight deadline to meet, the company required strong yet light lines it could trust not to damage anything, and not to break.
Dockwise, the world's biggest seagoing heavy transport shipping company, operates a fleet of 23 ships and semi-submersible vessels. For this job the company called up the Black Marlin, an open-stern heavy transport vessel.
The ship, and the company, faced some significant requirements. First they would have to safely load and transport the topside platform to the transportation site. At 18,900 metric tonnes (t) and 124 meters (m) tall, the topside was one of southeast Asia’s largest offshore platforms. Second, the float-over installation needed to be carried out without damaging the existing, and extensive, underwater infrastructure in a field that dates back to 1978.
*Equipped with fixed casing at starboard.
These factors led Dockwise to replace the Black Marlin’s normal complement of steel wire anchor lines with synthetic lines made with ultra-high-molecular-weight polyethylene (UHMWPE). “The operation was in the vicinity of pipelines and other subsea assets,” explains Aart van den Hoonaard, Senior Project Manager at Dockwise. “In such demanding and precise operations, it might be possible to use steel wire rope with mid-line buoys, but it would have required more installation time.”
The company initially chose lines made with UHMWPE from another manufacturer. However, when one of those failed, Dockwise opted for Oliveira X-Trema Line 12 Strand Rope made with Dyneema® SK78 fiber. Mooring lines made with Dyneema® are as strong as steel wire rope of the same diameter, yet they are less than one-seventh the weight. In addition, a rope made with Dyneema® is about 60% of the diameter and 30% of the weight of an equally strong polyester or nylon rope.
As the loading window approached, the Black Marlin was outfitted and prepared for the skid-out operation that would slide the topside onto the Black Marlin. Two days’ sailing later, and the team executed a flawless float-over installation.
The float-over involved the use of a four-point anchor mooring arrangement. The four mooring lines held the Black Marlin in position during the operation. But instead of the usual steel wire rope, the mooring system this time used anchor lines made with Dyneema® to prevent damage to the existing field layout. Three tugs assisted in the topside’s installation on the jacket.
And what was it like using lines made with Dyneema® in such a challenging operation? “Generally, the crew found that handling the stored rope is easier, although it needs more attention,” comments Aart van den Hoonaard. “We could have done the same thing using steel wire rope and mid-line buoys [to prevent the rope from hitting the seabed and possibly damaging pipes and other subsea infrastructure], but it would have been much more time-consuming to install.”
When Dockwise was planning how to install the topside, the company knew that with sensitive subsea structures to contend with, and a tight deadline to meet, it would require strong yet light lines that it could trust not to damage anything, and not to break.
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