Re: Gps versus locator.
I agree if your radio has a DSC button then you can hook up most GPS systems to the radio. Then get a MMSI number and your all set. When you hit the Red DSC buttom your radio will transmit your MMSI number and position to any station in range. It transmits on channel 70 on 1 watt.
The MMSI Number give then your name an boat information and the GPS provides your position.
http://www.boatus.com/mmsi/
Before your buy a GPS Or Radio check the specs to make sure they are compatable.
Their are several formats and they must match between the radio and the GPS to work.
EPIRB (Emergency Position Indicating Radio Beacpm) works with sattelites in orbit to indicate your position.
Their are also PLB (Personal Locator Beacon) that you can wear on your person and they cost from $300 to $400 that will also give your GPS position. Some float and even have a built in strob light.