Animation thruster exchange


BigLift Shipping and MARIN in joint aNySIMpro operations


Olaf Waals o.waals@marin.nl


In the past few years BigLift Shipping has been operating in shielded waters to replace thrusters on DP vessels and semi-submersi- bles. In a joint aNySIMpro study we are now investigating the limiting sea states for these operations, in order to optimise the thruster replacement procedure.


BigLift Shipping has performed several thruster exchange operations. But some rigs only have a system to lower their thruster to a certain depth and need assistance to lift the thruster above the water surface. BigLift can provide such a service by coming alongside and performing a so-called “wet handshake”. BigLift’s Tra type vessels are perfectly suited to this type of operation.


In October 2007, BigLift performed its first exchange operation with Ocean Rig’s semi- submersible “Leiv Eiriksson” in the sheltered waters of the port of Las Palmas. Since then


18 report


BigLift has carried out several other exchange operations but there is a trend towards these being carried out further offshore and in deeper waters. As a consequence, it be- comes more important to study the dynamic interactions between the floating bodies in varying environmental conditions in order to get more insight into the workability of this type of operation.


MARIN’s pro concept allows clients to use the aNySIM program on a project-by-project basis. Depending on the client’s needs, these studies can be completely carried out at MARIN or partly at the client’s offices. In this case, BigLift requested an initial model of the thruster replacement in which three floaters, the thruster and a crane are simu- lated in waves, wind and current. After a few initial runs and checks at MARIN the program was delivered in February. In a second stage BigLift will use aNySIMpro to optimise the configuration of the mooring lines and fenders. This can easily be done by changing the line stiffness, attachment


points and line lengths in the input file. Furthermore, the behaviour of the lifting configuration can be validated against observations that were made offshore.


Once a realistic numerical model is obtained, aNySIMpro can be used to run many cases in different Sea States. By comparing results with long-term wave statistics the opera- tional uptime can be estimated for a certain location or season.


Thruster exchange at Las Palmas (MV Tramper)


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