19/07/01 - Day 18
Combing the search box
Rob White reports
As the sidescan sonar 'Ocean Explorer' travels deep into the ocean, it has a very precise
duty to carry out - derived from the equally deep research carried out over the last 6 years by our Search Director David Mearns.
David's researches have taken him on a long journey into British, American and German archives, to find the best information he can to work out where we should search for the wrecks of both 'Hood' and 'Bismarck'. He uses every piece of data he can to tell him where he should go - especially any positions reported by nearby ships (though of course in those days they didn't have 'global positioning by satellite' to help them.)
David monitors the sonar
Using that information - which includes details from ship's logs showing how they approached the site of the sinking - David creates a "search box".
Then parallel courses are plotted to give 'lines' for the sonar to travel up and down, sweeping the seabed below with electronic pulses that get a return signal from large objects - especially metal ones. Late last night we began our third line of the 10 David has fixed.
The search box (click to enlarge)
Each 'line' is 60 kilometres long, and the whole box is 600 square miles in area. At the end of each line 'Northern Horizon' must turn in a long arc, taking up to 5 hours, to allow the six thousand (or more) metres of cable paid out to the sonar to turn too.
Gently does it. That cable is literally our lifeline.