P2, can you expain to us "non-divers" how does this happen: 2 people left from a diving trip? Shouldn't the dive boat be searching for them? I don't know because I am not a real diver, just a club/resort diver.
azbob,
it's easy to lose divers as they get on/off a dive boat. The more people onthe boat, the easier it gets. Many operators will "tag" each diver as they get into the water. As an example, they'll assign each tank with a number tag and record those numbers as the divers get into the water. Then, after everybody's been down for a half hour or so, divers start getting back onto the dive boat and the divemaster checks to see that everybody who got off gets back on.
The first time I saw this was during a night lobster dive with about thirty divers. Some divers blew through their air quickly and were back on the boat right away, while others hunted lobsters methotically and conserved their air, getting back to the boat after an hour. The divemaster kept track of everyone and the operation had a rescue plan that could be implemented if anyone got lost that night.
Now, other operations count heads in other ways or not at all. In Cozumel, for example, several divers are lost every year. The Gulf Stream is born there, in the straights between the Yucatan and Cuba. It's easy to lose divers in the current, and it happens more often than you'd think.
Once, while diving off Bali, we came upon a monster dive boat sponsored by Quicksilver, the Australian swimwear manufacturer. There had to be at least 100 divers on this barge. I can't imagine how they kept track of everybody.
Myself, I carry an EPIRB. That's an emergency locator beacon, the same gizmo that is installed in every aircraft and life raft. If I go missing, I can fire up the beacon and my chances of drifting for days are drastically reduced. It's the best $100 I ever spent on safety equipment.
Dan