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Scenario - GPS loss offshore


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#1 marinheiro

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Posted 02 April 2018 - 12:30 PM

We have all become very dependent on GPS both at sea and as part of our lifestyle, but what if you were offshore and your ability to receive signals was lost. This could be due to a "local" condition such as
- power loss on board
- a lightning strike
or a GPS system problem eg
- it being switched off by US military
- a technical issue with the GPS constellation causing it to fail
- a solar storm
This article prompted these thoughts:
https://www.passagem...al/stormy-skies
and this provides a more wide ranging scenario
https://www.theatlan...s-fails/486824/

Cat 1 no longer requires proficiency in Celestial Navigation. I am curious to know what preparations people are making for such eventualities considering things such as
- hand held GPS (preferably in a metal container with spare batteries)
- manual GPS (grey plastic sextant) or similar
- favorite celestial nav book
- Nautical almanac data, site reduction tables, plotting sheets etc
- a reasonable watch (a cheap Casio F91W is surprisingly accurate, needs to be in the same metal container as the hand held GPS
- having some idea what to do with all of the above
- knowing your compasses may be stuffed

Thinking about what would happen in a power loss situation, even with sails available had one "gulp" moment, no Autopilot
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#2 Steve Pope

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Posted 02 April 2018 - 01:47 PM

We don't have an auto pilot, wind vane only, otherwise manual steering, or sheet to tiller, + various bungy assistants. We carry a sextant and a Sharp PC1248 with "Merlin" sight reduction tables loaded, Ok untill 2028 + spare batteries. 3 x handheld GPS's, (Garmin / Lowrance) a shitload of AA batteries. D cell battery operated multi frequency radio reciever, WWV for accurate time signals, C cell battery chronometer, havn't checked accuracy recently though. + sun rises in the east and sets in the west. No faraday cage although I believe the stove is a good substitute, ;-)

PS. I believe the Russians have their own GPS system, maybe it can be accessed??


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#3 darkside

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Posted 02 April 2018 - 03:15 PM

Coming into Nelson from Brisbane in 2000 there was a downgrade of the GPS system and we lost the two main GPS's. The little handheld strapped to the EPIRB never missed a beat which was appreciated closing on Farewell Spit at some pace. I now have a USB GPS which I imagine would survive a lightning strike if not plugged in.

We did lose a GPS aerial from a lightning hit once but the GPS was fine. I can't imagine you would ever lose a compass from lightning. I haven't pulled the sextant out for 20 years so not sure if I could use it in anger.


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#4 Black Panther

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Posted 02 April 2018 - 03:55 PM

DR and a latitude shot at noon?


I still have the sextant aboard. Must get tables and almanac
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“If we don’t change our direction, we will end up where we are headed.”

 


#5 Island Time

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Posted 02 April 2018 - 04:53 PM

The russian GPS system is called GLONAS it is available now and quite a few modern GPS units can access it. Check your system manuals to see if your does. There is also the European Galileo system, and now the BeiDou-1 Chinese GPS system, currently experimental and technically different from the others;

 

BeiDou-1 consists of four satellites (three working satellites and one backup satellite). ... Unlike the American GPS, Russian GLONASS, and European Galileo systems, which use medium Earth orbit satellites, BeiDou-1 uses satellites in geostationary orbit.  

 

Its pretty unlikely that all these would be down at once. However, I carry a perpetual Almanac and reduction tables, along with a plastic sextant. 

Note that OpenCPN has a celestial plugin, that will do site reduction for you, simply tell it what celestial body, time and altitude, and it plots the position line directly on your electronic charts. Cool. 


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There is nothing, absolutely nothing, half so much worth doing, as simply messing about in boats


#6 Steve Pope

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Posted 02 April 2018 - 08:54 PM

Didn't realise that Open CPN had that, cool!


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#7 marinheiro

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Posted 02 April 2018 - 11:53 PM

DR and a latitude shot at noon



I still have the sextant aboard. Must get tables and almanac


Don't forget midday longitude from Meridian by equal altitudes, just need sextant, Nautical Almanac and a clock

This is a good site for Nautical Almanacs and sight reduction tables

https://thenauticalalmanac.com/

I have found this book a useful "easy" reference guide
http://minitransat65...ers_GuideV6.pdf


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#8 Black Panther

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Posted 03 April 2018 - 08:26 AM

Excellent. Thank you.
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“If we don’t change our direction, we will end up where we are headed.”

 





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