22/07/01 - Day 21
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'.
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.
George Holmes at work
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.
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.
The radio mask on board Northern Horizon
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.