offshore safety - page 7
4.7 Communication & location equipment
Emergency Position Indicating Beacons (EPIRBs) transmit a distress message from anywhere in the world to Marine Rescue C0-ordination Centres (MRCC) on the 406MHz radio frequency. Each EPIRB has a Unique Identification Number which is registered to the user so that MRCCs can identify who is in trouble.
The EPIRB signal is transmitted via satellites and give a basic indication of position, accurate to a few miles. Precise location is also possible because EPIRBs also transmit a homing sugnal on 121.5 MHz.
Many EPIRB's have a built in GPS receiver (sometimes called GPIRBS) to provide a higher level of positional accuracy. By including a GPS receiver, the search area is redused from around 5 km to 100 metres aiding quicker location. This allows an MRCC to broacast this information to other vessels in the area.
EPIRBs on large vessels are often fitted to 'float-free' should the vessel sink. This has caused many false alerts, since yachts frequently encounter waves, which activate the EPIRB. More often than not, EPIRBs are kept near the companionway, deck locker or in the grab bag. 24 or 48hr battery packs are the norm. The choice depends on your area of operation and distance from rescue.
EPIRBs explanation from U.S. Coast Guard
Flares are used for distress signalling, attracting attention and illumination. They are coloured orange and red for distress signalling, and white for illumination and attention.
Red Handheld Flares. A short-range distress signal used to pinpoint position during day or night. It burns with a light intensity of 15,000 candela for a duration of 60 seconds. Hold over the side of the boat and downwind to stop red hot sparks falling onto your vessel. Visibility is about 3 miles.
Float Smoke Flares. This is a small and compact distress signal for daylight use only. Smoke Signal that floats on the water for position marking during rescue operations. Indicates wind direction. Safe for use on oil or petrol covered water.
Red Rocket Flares. Longer range than a handheld, it ejects a red flare on a parachute at 300m (1000ft), burning for 40 seconds at 30,000 candela. This gives the flare around 30 miles of visibility allowing vessels over the horizon and out of line of sight to potentially see your distress signal. Point the flare downwind. Fire a second flare aminute or so after your first. This gives the observer a chance to confirm the sighting and gain a bearing to your location.