Spot on, but still a little harsh on the Hydrographic Office. In UK waters they produce charts based on surveys supplied by port authorities, more recently the offshore industry, but mostly those sponsored over the years by central government (so you and I pay!), and surveying at sea is a very expensive business. A little less expensive and much more accurate these days thanks to modern technology, but surveying is not a speedy process and still eats up the money in large quantities. Repeat surveys, to update accuracy, therefore have to be justified on cost grounds and need. Do I really want to give the Government another large wadge of my money to re-survey the UK coast with GPS? Not really.
Diff GPS has only been around since the late 80s, so much will have been surveyed without it – check out the ‘source data diagrams’ provided on each chart, so at least the user can make a judgement on the accuracy of the information.
For its day, Decca was great for repeatability of position but not for absolute accuracy – hence the need to apply corrections (where they had been established). Anything found by means of Decca had a good chance of being relocated. Take Decca away, which is what has happened with the introduction of GPS, and the flaws in Decca’s absolute accuracy are laid bare. Depending on the the area being worked, the difference between the two systems can easily be up to half a mile.
The Hydrographic Office produces charts for safe navigation at sea. The requirements of divers are somewhat different. In the last decade or two, modern technology has provided divers with a tool that previous generations of sea surveyors could only have dreamt of.
Finally, and I suppose it had better be that as we are veering way off topic, I share in your disappointment, but divers have been spoilt by these new hand held devices and must put things into context. Give the Hydrographic Office a break, it’s not their fault. Blame it on the rapid advances in technology.
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