These radios can be used to call fellow paddlers independent of any local rescue entities that may be or may not be reachable via VHF. But they will be of little use to your paddling partners if you do not turn yours on at the beginning of your paddle outing.
if you want to increase your competence and confidence in your ability to use your VHF, consider taking and completing a course.
Line of sight - effective limitation of VHF radio communication range on water (maybe only a couple of miles from surfski to surfski). But coastal radio rescue networks or ships may pick up signals from a greater distance.
US Coast Guard Distress Network Coverage these maps assume your signal is 2 meters above water level - the reception of your signal from a surfski may not reach as far although sometimes reception occurs over surprisingly longer distances.
DSC Digital Selective Calling - automatic broadcast of your GPS location (another reason to turn radio on at beginning of paddle - it can take a minute or two for radio to initially lock on GPS satellites)
“Waterproofness” - the weak point on some VHF radios can be the covering over charge ports (make sure they are completely closed and if you need to - cover the closure with tape). Trouble has been reported with some models that have a cover (possibly due to forgetting to make sure the cover is on correctly). Some models like the Horizon HX40 have solid exposed pins for charging which may provide a more reliable water tight seal.
Jeff Hegedus <jhegedus@…>11/06/11 #11683 “I rinsed my IPX7 rated waterproof handheld after every paddle, and the two copper electrodes between the gasketed snap-in rechargeable battery pack and the main unit still fully corroded (they are spring loaded for a good connection, and the spring failed). Its something that you wouldn't normally notice until failure occurs; I had it serviced, and now keep the radio in a dry bag when in my pfd pocket. The dry bags can be purchased at West Marine. Handhelds are not really designed for daily immersion, but rather for boaters that occasionally get them wet…”
Caution: Toasted VHF Radio
10/14/12 #13446 GEAR CHECK TIME. Crap, my waterproof IPX7 rated VHF radio, always carried in a dry bag in my PFD pocket, was destroyed. The dry bag had a pin hole leak; I end each paddle with a swim, and the bag stored the unit in water. The bag was three years old and had a ton of wear, not its fault. The radio is not designed for continuous immersion, not its fault. Glad I checked.