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Old 20-01-2015, 06:49   #1
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Converting DECCA readings

Appologies for above. I have been unable to post on here for some time.

I have some old DECCA readings for fishing grounds in the North Sea. They are for chain 2A and are for the green and purple lanes. They read something like

B 34.76
C 63.97 for example.

I would like to convert these to Lat/Long and wonder if anyone knows of or can find a suitable bit of software online. I found a link to one but it would not work!.

Having converted to Lat Long I will need to determine the datum used which might be OSGB36 or possibly ED50 then I will convert to WGS84.

I am thinking the more complex part of the problem is the initial conversion from DECCA 2A to Lat Long

Any ideas?

Thanks

Mike
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Old 20-01-2015, 11:51   #2
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Re: Converting DECCA readings

Your best bet would be to find an old Decca chain 2A chart. We shut down the UK chains in 1997 so I would expect all the company information to have been lost by now, especially as Racal (who bought Decca in 1980) were absorbed into Thales in 2000/2001. Latterly the chains were run on behalf of the GLA so you could try Trinity House or perhaps the Royal Institute of Navigation. Several past RIN presidents are ex Decca men so they may be able to help.

Hyperbolic to Cartesian coordinate conversion routines were iterative and really only understood by the companies designing plotters and nav/survey systems.

I hope this is helpful.

Paul
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Old 20-01-2015, 13:16   #3
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Re: Converting DECCA readings

I have a couple of old Deccan charts from days of crab fishing will find them out but from memory I am pretty sure they only cover English channe and channel Island.when I change fromdecca too lat and long the navigator I had actually converted gps lat and long to Deccan at the push of a button , for the love of me I can not remember the make ,but there is a navigator that did the hard work for you, ( if they are still made) alternative find chart and convert yourself
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Old 20-01-2015, 13:36   #4
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Re: Converting DECCA readings

Carl's charts are likely to be 1A or 5B. Converting from Lat Lon to Decca was mathematically/computationally relatively straight forward. In fact, the iterative process did the calculation in that direction, checked the error, applied a correction, and recomputed until the error was within acceptable limits.
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Old 22-01-2015, 07:07   #5
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Re: Converting DECCA readings

test test test test
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Old 22-01-2015, 07:15   #6
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Re: Converting DECCA readings

Thanks,

I do have a Decca chart 2A and can enter the decca readings on the chart and take a Lat Long but I am afraid however sharp my eye or pencil is I am unlikely to be able to get close enough to find the marks unless by good luck.

I too had a couple of Decca/gps units which would happily convert back and forth. I can remember one of these was called a Vigil (I think). However they got turfed out when I went over to GPS. I am still pinning my hopes on a converter being available online.

Mike
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Old 26-01-2015, 11:35   #7
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Re: Converting DECCA readings

I did find a link to a website:

Decca Navigator

There is a link to a page that has collections, don't know where you are located but suspect UK or Scotland, maybe you can find someone with a chart who can look it up for you.

Good luck!
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