In another thread folks have been telling what they carry to assist being seen on the surface. Most are carrying things that are great for helping a nearby boat spot them. You may be interested in the range of these devices in the open ocean as well. (distances vary greatly depending on the height above water of the lookout and the sea state - these figures are typical for a small boat - larger boats with higher lookout positions can see further, if they're looking - except for the whistle, of course)
Day...
Whistle - typically 100 yds or less (maybe 300 on a flat calm day with nobody talking and all engines & generators shut down)
Lift bag - 150-250 yds
Safety sausage - depending on size, 200-300 yds
Signal Smoke - 2-3 miles
Mirror (glass, not metal - a real signal mirror used properly - sweep aiming spot along the horizon) - over 50 miles (search plane on a clear day)
Radio - up to 100 miles
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Night...
Whistle - about the same as day
Lift bag - probably around 100 yds
Safety sausage *with reflective tape* - about the same as day
Dive light or strobe - 500 yds
Flare - surface - up to a mile
Flare - pistol - 5-10 miles or so for a boat, about 15-25 from a plane.
Radio - up to 100 miles
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Whistles, safety sausages & such are fine for your dive boat looking for you at the end of a dive. If you want to have a device that'll work in an open ocean search, however, as in a "left behind" situation, at least carry a signal mirror, and train enough to know how to use it.
Rick
Day...
Whistle - typically 100 yds or less (maybe 300 on a flat calm day with nobody talking and all engines & generators shut down)
Lift bag - 150-250 yds
Safety sausage - depending on size, 200-300 yds
Signal Smoke - 2-3 miles
Mirror (glass, not metal - a real signal mirror used properly - sweep aiming spot along the horizon) - over 50 miles (search plane on a clear day)
Radio - up to 100 miles
--------
Night...
Whistle - about the same as day
Lift bag - probably around 100 yds
Safety sausage *with reflective tape* - about the same as day
Dive light or strobe - 500 yds
Flare - surface - up to a mile
Flare - pistol - 5-10 miles or so for a boat, about 15-25 from a plane.
Radio - up to 100 miles
---------
Whistles, safety sausages & such are fine for your dive boat looking for you at the end of a dive. If you want to have a device that'll work in an open ocean search, however, as in a "left behind" situation, at least carry a signal mirror, and train enough to know how to use it.
Rick