Keeping in position

Rob White reports

The ROV is now travelling over the wreck site - searching out the best pictures of the wreck of HMS 'Hood'.

George Holmes at work

But it would have a job getting any of them if it weren't for the technical wizardry of 'Global Positioning by Satellite'. 'Northern Horizon's G.P.S. signal comes down into the ship through an equipment array above the bridge - fixing where she is so that once we have a site to work on we can stay on it.

All the time of course wind and wave are doing their best to push us OFF that position. That's where George Holmes, Dynamic Positioning Operator, and his 'D.P.' kit come in.

The ship has side and bow thrusters, controlled by a computer programmed with the position we need to be in. If we move from that, the D.P. computer instructs the thrusters to put her back on the spot.

The radio mask on board Northern Horizon

But getting the D.P. to work properly is still down to human experience. For a start, judging the best direction to point the ship for the ROV to work well is down to a seaman's judgment.

And even G.P.S. has to be fine-tuned. That's done by cross-checking where the satellite SAYS something is against where it ACTUALLY is, on a good old-fashioned chart. Then our navigator, Chris Jones of Thales Geosolutions, will measure the difference between the two positions, adjust the fix we want to use accordingly.

"One Hundred and Eighty!" - you're on the bullseye and ready to get to work.