The latest exchange was accomplished in just three days under on-site management from a UMC Project Manager and Mr Alan Jones MBE from the Ministry of Defence. Despite strong winds and poor weather the task was completed without a problem or delay to the ship's planned operational schedule.

The procedure extends the British Royal Navy's ability to reduce the dependency of its ships on docking for maintenance.

The procedure to replace the VSP has four phases. Phase One is the underwater installation by a diver of a large cofferdam that encloses the entire VSP unit and seals against the surrounding hull. Weighing 600kg in air, the cofferdam has been designed for variable buoyancy so that once it has been lowered from the jetty into the water, it can be safely and easily manoeuvred into position.

Phase Two is the removal of the VSP unit, which begins with the installation of a VSP lifting frame on the upper deck and the removal of a soft patch located over the VSP in the ship's propeller room. Rigging from the lifting frame and associated lifting beam are then attached to the VSP unit.

The VSP unit is prepared for removal and lifted out of the ship onto the jetty. The underwater cofferdam provides a watertight seal over the 2m diameter opening that has been temporarily created in the ship's hull.

In Phase Three the new VSP unit is installed. Having been prepared on the jetty, it is lifted onto the ship by a crane, transferred to the VSP lifting frame and lowered into position in the propeller room.

In Phase Four the specialist VSP exchange equipment is removed from the ship to allow preparations to commence on board for the basin trial. Once removed, the specialist equipment is inspected and stowed in its dedicated ISO container ready for transport worldwide to support the next Royal Navy VSP replacement afloat.

MJ Information No: 19244