Mary,

With regard to the EPIRB, (I should probably research this a little - I know some work with stationary satellites) but I believe they work periodically as a satellite screams across the sky. It gets the information from the EPIRB and sends it to the emergency services. Naturally, there would be some delay in this information getting to the Coast Guard and if it is periodic in nature (because of the satellite orbits), if Larry was still moving at 15knots, by the time they got to where the signal said they were, they would be long gone. That's probably why they had difficulty finding them.