Mike, waterproofing and size is a red herring, it's whether or not the beacon is activated *by* water.
There are two different types of emergency beacons used on boats, EPIRBS and PLBs. It may be -and that's one of the unknowns for me - the crew here only had, or had access to, PLBs or personal EPIRBs, which is why they let them off in sequence. This explains a bit more:
http://powerboat.about.com/od/safetyandeducation/a/epirborplb.htm