The system uses standard Long BaseLine (LBL) techniques to position both the ship and the diver. In order to meet high levels of accuracy, three sets of positional data have to be obtained; the diver relative to the seabed, the ship relative to the seabed and the diver relative to the ship.

This is achieved using a lightweight transceiver fitted to the diver, a seabed array of miniature transponders and three transceivers attached to the vessel hull at known locations; usually two on the keel and one on the side.

The seabed array forms the basis for positioning the ship and diver relative to each other and the seabed. In addition, this enables the position of the hull to be determined in three dimensions relative to the seabed array. The position of the diver is similarly determined and the co-ordinates transformed into co-ordinates in the vessel frame of reference. All the positional information is updated once a second.

A PC running the Underhull Inspection software application is used to monitor the progress of the survey. A central chart display shows the position of the ship and diver along with quality information so that the operator can see how well the system is working.

Features :-

• Allows hull inspections to be completed without drydocking
• Provides full hull coverage including area around rudders and propellers
• Operates under any type of vessel of any size
• Positions divers to better than 150mm
• Simple and quick to deploy
• Based on proven acoustic principles