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    Re: Rdf
    From: David Pike
    Date: 2021 Feb 8, 10:51 -0800

    Bill Lionheart you wrote: I was talking to former and future skippers on the Golden Globe Race. They are allowed to use RDF and many took one and found it useless. This is a single handed solo unassisted circum navigation race around the great capes without GPS.   So if there were Air NDBs or broadcast stations for a position line how would they use that? For example I was thinking approaching Cape Horn if you had had dense cloud  for a few days it would seem to be handy? 


    Technically what you suggest is possible, but you would require up to date information on non-directional beacons (NDBs), a decent receiver, and a lot of preparation and practice.

    First, you’d need to find a list of suitable beacons in the area you’re intending to operate.  Looking at Cape Horn Area on Google maps, it stretches for hundreds of miles and is very remote, so that might be quite a struggle.  It would be worth checking for marine NDBs, but you are unlikely to find any.  Most, if not all, have disappeared.  A few were converted to DGPS stations, but most of those are scheduled for closure.   There are still aviation NDBs of varying strength, mostly low power, but I bet the RAF on the Falklands Is. have a powerful one (try looking here https://www.pilotnav.com/browse/Navaids/continent/South%20America).  There are of course national long wave broadcasting stations.  Radio 4 198HZ (formerly ‘The BBC Light Programme on 1500M) is still going strong like the ravens at the Tower of London, or the barbary apes on the Rock of Gibraltar.  You’d need to know frequency, operating times, and characteristics.  I.e. continuous, or timed sequence like the old North Sea coastal lighthouses, call-sign, and transmission characteristics: identify and take bearings on ‘voice’, identify on ‘voice’ and take bearings with ‘BFO-On’, or identify and take bearings with ‘BFO-ON’.  

    You’d need a decent receiver, preferably with its own magnetic compass.  Otherwise, you’d have to note the yachts heading at the moment you took the bearing, not easy or very accurate with the yacht healed or in a chop.  Using headphones would probably reduce weather noise.  You’d need to correct for magnetic variation and deviation, so you’d need to have swung your observing position.  Deviation, of course, would change with latitude and possibly longitude, so you’d need to have been using check headings.  You’d also need to have tested for quadrantal error from your mast and rigging bending the incoming radio wave.

    Possible Errors and Plotting your Position Line.
    You’d need to be aware of the usual NDB errors before selecting and relying on a beacon. E.g. night effect, terrain effect, thunderstorm effect, coastal bending, interference from nearby stations, and meaconing. Then, at 56S, if plotting on a Mercator chart, you’d have to apply ‘conversion angle’ at relatively short ranges, greater than 60nm say.  Finally, don’t forget, if you manage a bearing as close as 5 degrees, which would be pretty good, for every 60 miles you are from the NDB, you’d have a 5nm error in the position of your PL. Interestingly, until about 40 years ago, all this was normal and accepted by yachtsmen.  DaveP

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