Non farming question “Satellite and Transponder”?

[Pilatus]

I have been tracking the Sir D Attenborough research ship on its journey to Antarctica via the Falkland Islands.
It is now so far South I get the impression it is now out of reach of the AIS system that uses transponders on ships to give their position, the Vessel Finder app implies that the only way to track ships that far away is by Sattelite.
How do transponders transmit position information back to vessel monitoring organisations, how come they can’t relay the same information when they get so far away, from in this case the Uk?

 

[Steevo]

I think transponders need a receiver somewhere (or perhaps another transponder) to pick up the signal. Perhaps they are too far from a land based receiver, or even another ship that could pick up the signal also and pass it on.

 

[ollie989898]

AIS primarily works using radio base stations situated around the coasts of certain parts of the world. These are what do the business. If you go out of range of these then the ship is no longer picked up by the AIS network unless it is routed via satellite. I don't know if it still is but I understood that it was AIS base stations that were used to enhance the accuracy of many commercial GPS systems by using the AIS network as a correction signal.

Obviously the idea of AIS was to enhance the safety of ships at sea in busy or confined shipping areas. Way out at sea ships still rely on navigational radar and the risk of collision is much reduced anyway so there is less need for AIS.