In-situ thruster repair limits downtime

This enables work teams to access the thruster tunnel and remove or repair the thruster within the tunnel in complete safety.

Hydrex has since then developed this technology further using lightweight flexible mobdocks. These modernized mobdocks, which are designed to be easily transported around the world, are used to close off the thruster tunnel on both sides. This allows divers to work in a dry environment around the unit and enables them to reinstall the propeller blades of an overhauled thruster inside the thruster tunnel after the unit has been secured. They can also replace the blades or seals and perform repair work on a specific part without removing the unit. These operations are carried out in partnership with Dutch thruster specialist AEGIR-Marine Propulsion Service.

There is no need to send the vessel to drydock as all operations can be carried out in port or while the vessel is stationary at sea. Normal commercial activities can therefore continue without disruption.

In the last few years Hydrex divers have used the flexible mobdock technique on numerous occasions for bow thruster operations around the world, winning the Ship Repair and Conversion Award at Lloyd’s List Global Awards 2009.

When one of the four 40 ton swing-up azimuth thrusters of an offshore crane barge which was servicing rigs on an oil field off the coast of Gabon malfunctioned, Hydrex was called in to remove the thruster and perform the necessary repair work while the unit remained at anchor just outside the field.

While it is possible to maintain location with three thrusters, the fourth needed to be repaired straight away. This had to be done in the short timeframe in between two scheduled operations, which was the only time the barge could leave the oil field. All repairs and other servicing work needed therefore to be carried out before the start of the next operation.

A similar operation had been planned and carried out by Hydrex three years ago. Just as with the recent operation, going to drydock had not been an option as the nearest suitable location was South Africa and this would extend the repairs far beyond the available timeframe.

For this reason a large mobdock measuring 9m by 6m by 2m and weighing over 25 tons was constructed under Hydrex supervision in Belgium and transported to Gabon. There it was stored after the repair to beused at short notice whenever future repairs were required on the thrusters.This allowed for a very fast mobilization and execution of the operation carried out at the beginning of 2010.