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While a VHF radio is one of the best signaling items, it does not replace other equipment and is not a Coast Guard approved signaling device. There are a few small waterproof VHF radios in the $250-$350 price range. A few years ago we were using an Apelco 510. This is a compact, (advertised as) waterproof model with most of the features you would want. The 510 meets the Coast Guard standard for waterproofness at CFR-46. The standard calls for a VHF radio to withstand a multidirectional stream of water shooting 65 gallons per-minute for five minutes without leaking. This does not mean a radio is submersible, but it will stand wind driven rain and a small waves or two washing over your deck. It will not withstand constant rolling or surf waves. All of our 510s have died at one time from water damage, but they come with a three year warranty which covers water damage, but not submersion damage. Remember we use our equipment much harder than most paddlers. We have had a few other high quality non waterproof radios that we kept in waterproof VHF bags, but they didn't hold up as well as the Apelco 510. Most waterproof radios should be kept in a waterproof container when not in use. It would help to keep the radio in a waterproof VHF bag. The Apelco 510 has been replaced by the Ray 100 (waterproof) and Ray 102 (submersible).
After each use in a salt water environment, it should be washed with fresh water and fully dried. The battery should be removed regally to be checked for water damage. We now put electrical tape around the battery seal to help with waterproofness. Check with the manufacturer to see if you should put silicon o-ring grease on the battery o-ring (most waterproof cameras use o-ring grease). Salt water is very destructive and only the best (expensive) radios which are well treated and maintained will survive for the long haul. If the radio doesn't work when needed properly in bad conditions what good is it.
We have also used the Navico Axis 200. Navico has a version of this radio which meets GMDSS. Since 1999 all large ships operating internationally must comply with the Global Maritime Distress and Safety System (GMDSS) carriage requirements. These include specifications for survival crafts hand held radios. We have been told that the Navico Axis 200 is identical to the GMDSS version, but hasn't been tested or certified as GMDSS. While the Axis 200 cost over $600 (discounted) it is the best rated radio in that price range. The Axis 200 is more waterproof and drop resistant, but is also large and very heavier. What good is a warranty when you are in a survival situation. If this radio holds up, it is well worth the price.
Each year the radios are getting better, more waterproof and less expensive. What we would like is a totally waterproof, drop resistant, small sized radio with a twelve hour battery and all the scanning features available.
Standard HX460 may come closest to what we are looking for in a VHF radeo. Read the specs for this radeo.
"Extraordinary toughness with a tiny package barely 3 1/2" tall. The Lithium Ion battery is good for over 12 hours of use, rechargeable at any time without damage or reduction in capacity. Includes 12V power cord and unique cell phone style swivel clip.
The advantage of a radio is that you can call the Coast Guard or other boats for help. If you must cross a channel in the fog, you can send a message to all other boaters of what you are doing and where you are. The distance a VHF radio can transmit is line of sight. In a kayak, this is only a few miles if you are talking to another kayak. The Coast Guard antennas are high, which will increase the transmittable distance. To increase your transmittable distance use a telescoping antenna. A telescoping antenna will increase transmittable distance much more than increasing the output power. The problem is that most radios come with a non-telescoping antenna and the optional telescoping antenna is not waterproof. You can always carry a telescoping antenna and put it on in situations where you need to transmit further, but where the radio wont get wet.
Most VHF radios now come with six to eight hour battery so you can keep the radio on for an extended period. This is the amount of time you can have the radio on receive. Transmitting takes more power and will drain the battery much faster. All VHF radios have a high/low power transmitting switch. You should always use the low setting in non-emergency situations. If the party you are calling can hear you on low, it is only going to interfere with other people if you use the high setting. Typically rechargeable batteries will drain about 1% a day when not in use. Some batteries have "memory" and you need to drain them totally every few charges.