Chart positions transfered from minutes to decimal to wgs

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ean_p

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Maybe a question for the pro navigators etc out there....have obtained a list of HO wreck positions off the Yorkshire coast of about late 80's date. The positions are given in minutes and seconds of arc, generaly Hi Fix and Syledis in origin and based on a 'NG' horizontal datum which I take to be OSGB36. To bring them forward into a useable wgs format I intend to convert to decimal and assume OSGB36 and then convert using relevent chart correction for changing OSGB36 to WGS84. Does this sound the right way and if so what level of error might be introduced and where. Also how accurate were Hi Fix and Sylidis ?

cheers

Ian P
 
Hyperfix has hyperbolic range patterns (its like high accuracy Decca) , so it depends how far off the baselines the surveys were, but assuming reasonable coverage geometry accuracy in the order 8-15m
Syledis should be better with a well configured chain, which the east coast ones were usually accuracy of the order 5 to 10m.
 
I think you would get more accurate datum conversion using a program such as PCTrans (http://www.hydro.nl/pgs/nl/pctrans_nl.htm) than using the corrections on a chart, The latter are an average to cover the whole area of the chart so the accuracy of conversion can depend on the scale of the chart. Also, as already provided, Syledis positioning is likely to be more accurate than HiFix but one has to ask what area does the wreck cover and which part of the wreck is in the stated position? With a wreck possibly covering quite a wide area, ultimate position accuracy cannot be that critical and the position data from these sources is likely to be more accurate than you can plot on anything but a very large scale chart.
 
The real question is what was the datum of the original positions. I would be surprised if they are OSGB, as charts of the early 80's were mainly in WGS72 format.
 
If the list of positions is from the HO (Hydrographic Office, I presume) then they should be able to tell you exactly what datum was used. Even better, they might be able to give you an up-to-date list using current datums.
 
Slightly off subject but can anyone throw some light on the different OSGB36 systems/standards?

My MLR GPS offers about 8 versions, but my Folio charts simply refer to OSGB36. I simply use the first one, but I don't know if that is correct. Any thoughts?
 
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