Much can be done without leaving the office and this winter has seen me sat in front of the screen for hour after hour. I have English and French Hydrographic reports going back years, some of it on the early green lined computer paper which I am now having to scan and copy as the print is fading. It is very interesting to compare old data with the new and the marks I am particularly interested in are the ones that disappear after a few years as in subsequent surveys they can’t be found. This is due primarily for three reasons: the target was never there just a spurious reading, the target has decayed and become more difficult to locate and finally and in my experience the most common reason, positional inaccuracy. Most positions today are recorded using datum WGS 84 (World Geodetic System 1984) but in the past the French used E 50 (Europe 50) the British used Hyperfix which was in degrees minutes and seconds and there were other variations such as British charts used to use the datum OSGB 36 (Ordnance Survey Great Britain 1936). So to get a latitude and longditude from say the seventies to today’s decimal position you have to take the last two numbers from the north and south fixes divide by six and times by ten then when you have done that it is quite likely that then gives you an old Decca position which equates roughly to OSGB 36. To then get that to WGS 84 You add three numbers to the last number on the north and then add nine numbers to the last number on the west position. When you start involving Europe 50 it gets worse and you can be over half a mile away from the original position with ease. Finally navigation systems were nowhere near as accurate as they are today. I now have a chart with all the dead positions and the can’t find comments from more recent surveys.

Kingfisher charts are compiled by fisherman with the aim of identyfing wrecks, obstructions, areas of ground etc that may cause trawls or dredges to snag. What to a fisherman is just a snag could be a long lost wreck, either way the trawlermen avoid the area or eventually through constantly running over the obstruction reduce it to nothing, this has been the fate of many aircraft sites. Going through old Admiralty charts, Kingfisher charts, Hydrographic information etc can be rewarding in that sometimes an obstruction shows again and again often in slightly different positions. This this gives me the basis for a search area, an area with a high concentration of possible targets is what I am looking for.

A Kingfisher chart dating from the 1980's

Some of the small print