There are a lot of things that vary here. Is the vhf radio a handheld or a fix mount? A fixed mount will ALWAYS transmit further then a handheld for 2 reason's, 1 is power output, a fixed mount is more powerful and can transmit further for that reason, and a handheld is going to be lower in the boat then a fixed mount antenna. The higher up your antenna the further it will transmit. This is why some boats put their antennas on top of towers, or mount them on arches or hardtops. Other factors involve how good of a connection you have, corrosion will cut down on transmission distance, as will weather. Inclimate weather will cut down on a waves traveled distance. At some point, you have to take into account the curvature of the earth, depending on how high the antenna is off the boat, you might get anyways from 30-50miles of range from a fixed mount. A hand held will be about 20miles roughly. I have 8' antennas ontop of my hardtop on my 265 Express and I can radio somewhere from 35-45miles out and still catch convos at inlets that are straight in from me. It really depends on sea state and weather conditions. On rougher or overcast days my transmission distance drops a little bit. I've been on large sportfishermen where we've heard convo's 50 miles out, but these are antennas on BIG tower's on 60-80ft boats, you won't get that distance from any Grady.
As for transmitting emergencies, some coast guard stations have repeater antennas that are mounted really high in the air so if your inlet or port has a station near by your range for emergencies will increase since the antenna your transmitting to is maybe 100-200ft in the air. Last season we had to make a call to the CG after we saw a flare shot off on our way out tuna fishing, we were about 45 miles offshore at the time on a clear day, but before sunrise and had a perfect 45min long convo with the USCG giving them details of the event, countless bearing numbers, speeds, angles of sight, gps and loran coordinates as well as other pertainent information. After going through that, I know just how much effort the CG puts into a search and how maticulous they are with records and tracking.
It is a shame what happent o this crew. If your venturing more then 10 miles offshore on a regular basis, you really need something more then a handheld vhf as your back up. You should ahve one anyways since a fixed mount might become useless if the boat capsizes and now can nolonger transmit. An Epirb is the best bet, but if it is not in your budegt, a PLB can help for elss money, but understand with one you get a cheaper version of a piece of equipment that could save you. A PLB will have trouble broadcasting while floating in rough seas unless your nearby, this is why they are great for man overboard situations, but for a crew, you want something you can have float next to you and transmit perfectly without worrying if the signal is getting out. Just about every PLB I have seen reviews on need to be held 3 ft in the air to transmit without any intermitance, try holding anything over your head while floating...not something I'd want to do. Another cheaper tool is a SPOT, they are good, but have the same issue as the PLB, they have issues sometimes transmitting all the time, but the benefit is ou can not only send out an emergency signal, you can message family or friends who know where you are who can notify authorities, now you have 2 pieces of information to help them search, your given location and where you should be, might give the CG a better idea of what they are dealing with and how to deal with it best. Other important things to have are flares, night strobe beacons, and good PFD's. A night beacon can help the CG find you at night much easier, and flares can get you noticed when communication is difficult. I carry 2 sets of flares, one in my ditch bag and 1 in the boat with a float attached so I can dive under and retrieve it if necessary, storing them in your cabin is a bad idea, you want them somewhere you can dive under to quickly and retrieve, last thing you want is to be in a cabin underwater. In addition to PFD's, add glow sticks to each by a tag line, this will give you light to atleast see underwater or to keep the crew close together at night.
When I venture offshore, i always know other boats going, I have a large database of buddies who fish, some I have known for years, other's I've met 1 or 2 times, but if I know any are going out those days as well, I call them before, give them my rough trip itinerary as well as theirs and make sure we make contact out on the water, even if we leave from different ports. Not only does this help you find fish easier having more guys out there, but if something goes wrong you have someone who knows your there and can radio you. When we leave to head in, we all let each other know, and soon as we hit the dock we call to make sure they made it, if not we would radio authorities of details.
