EPIRBs use 406 MHz COSPAS/SARSAT satellite communications which includes your GPS position information, the 406 MHz transmission burst goes out approximately every 52 seconds and generally updates GPS position information with each burst. They also use 121.5 MHz homing beacons for the search and rescue crew to home in on, the 121.5 MHz signal is continuous (with brief interruption during 406 MHz transmission). The C/S system uses LEO, GEO and now MEO satellites. The location of the EPIRB can also be determined by the LEO and MEO receiving satellites even without GPS information being encoded in the signal. The C/S system does have models for drift so once the 406 MHz signal stops they can predict location. The 406 MHz satellite signal is active for 24 hours after the transmission is initiated. The 121.5 MHz homing beacon will run for as long as the battery holds out but is supposed to last 48 hours at least (I believe this duration is accurate, I work on aircraft ELTs and the maritime EPIRBS may be different, some homing beacons have a 150 hour requirement).I am interested in the technology the EPRIB/PLB broadcasts your GPS at the moment you push the button after that I believe it puts out 121 MHZ for a radio direction finder equipped searcher. But in this case another yacht picked them up 10 hours later. Is somebody estimating current and wind drift from the initial fix and updating the searchers? If the searchers get within a few miles then flares or a handheld radio could pull them in.
From what Ive read, the rescue boat (a Leopard 45 “Rolling Stone”) was using Starlink for communication (WhatsApp). Apparently the initial coordinates were relayed from a boat the mishap crew called (via Iridium Go) just after abandoning ship. When the mishap crew saw the lights from the Leopard they called them on VHF and activated the PLB AIS.Suspect the rescue boat was equipped with SSB which is used on open ocean to communicate. Once close you have to search. It is fortunate for them that the Pacific was placid.
VHF is line of sight. It is a big ocean.