When an emergency situation is encountered, a communication strategy to get help must be initiated immediately. When near shore or other boats, a properly registered VHF/DSC that is connected to the GPS should be used. The boats nearby will hear your call and the nature of distress and can be the quickest to arrive to give assistance.
When offshore, deploying a 406 MHz EPIRB is the most reliable signal to initiate a search and rescue. In addition, the VHF/DSC, and SSB if you have one, should be used in case there is a vessel nearby that can hear your distress call and offer prompt assistance.
Whether near shore or offshore, the 406 MHz EPRIB should be deployed in any MayDay (life-threatening) situation.
Having a properly registered EPIRB on board your boat is just as an essential a piece of equipment as your up-to-date set of flares. One should not think that VHF/DSC, cell phones, Sat phones, etc. can replace an EPRIB. They are complementary tools to the EPIRB.
Anne D. Glenn