Bridge mock-up for ocean towing
Birds eye view of the installation (simulator run)
tugs for more than 3,000 km to the final destination. On arrival, six tugs manoeuvred the structure in the right position where it was ballasted down to the seabed in about 28 m of water, within 55 cm off the target.
MARIN was contracted by Aker Marine Contractors (AMC) to set-up and execute a dynamic vessel handling and manoeuvring simulation to train and familiarise personnel involved in the marine operations of the Adriatic LNG terminal prior to the actual tow-out, transport and installation. The overall purpose of the simulation was to train and ensure quality of communication between the operators during the actual marine operations. MARIN had to provide training for the most important parts of the operation, including the out-of-dock operation, the ocean towing, installation and station keeping.
Realistic behaviour The biggest challenge for MARIN was to set-up a simulator embodying the realistic behaviour of the structure under tow and on the other hand, one that had the possibility to work with 15 people at the same time (seven tug captains, five winch operators, a pilot, a tug coordinator and a tow master).
As well as ensuring the quality of communi- cation, MARIN was responsible for training and familiarising the personnel with opera- tions, procedures, equipment capabilities, geographical and weather limitations. MARIN’s contribution focussed on the evaluation, assessment and verification of mooring and towing configurations. The contract also addressed emergency situations and it identified the risks and hazards during operational procedures.
Direct control Initially, the sideways and rotational movement of the structure during tow-out was going to be controlled with the shore lines and then the connected harbour tugs would be used as back-up. Three anchored ocean tugs towed-out the structure. During the first runs, the main observation was that it was very difficult to control the movement with the shore lines, so there was a decision to change the primary control, using the harbour tugs instead and using the shore lines only for back-up. Tension in the warping lines was kept to a minimum and the harbour tugs were used for control. This resulted in more direct and accurate control.
When wind and current were increased, the harbour tugs were not sufficient to control the structure. Therefore, it was
decided to use two of the three ocean tugs as free sailing tugs, to give them the possibility to swing out and this resulted in firm control.
Other important observations were: - Once the structure is turning, the rotation is difficult to stop. It is important to recognise deviations from the track at an early stage and react immediately with small corrections;
- In the case of a jammed winch, the line should be cut immediately and the structure should be controlled with harbour tugs;
- Communication should be by fixed and short sentences to avoid misunderstand- ing and replies to messages must be confirmed.
On completion, AMC stated that there was no doubt that the training had made a very big contribution to the successful outcome of the operation.
And Fairmount, the towing subcontractor, expressed its appreciation by stating that all the personnel who had attended the simulations in Wageningen, agreed that the training was very helpful in understanding the behaviour of the structure and its limitations at the various stages.
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