Perhaps I should have explained better how radar range alarms work in practise. With the sea return and rain return dialed back to minimum settings the collision avoidance system will acquire and track waves and rain squalls. If the close range alarm does not drive you batty the lost target (target?) alarm will. Adjusting the radar gain, as well as sea and rain suppression, so as to eliminate the false returns results in a radar setting that will only pick up the Globetic London, 500,000 gross tons, and so, while they seem like a good idea from an engineering standpoint they do not perform in real world conditions.
Proper radar operation involves continual fussing with sea/rain clutter setting, depending on conditions. By doing so it is possible to determine if one is looking at a sailboat mast, or submarine periscope, or merely a dense spot of a passing squall. In my experience, on over twenty sea-going vessels, both the sailboat and periscope show up, on average, at six miles and often substantially less (if at all). I have picked up sailboats at ten miles and those must have had a reflector from what I was able to tell. Bearing in mind that the average sea-going merchant ship is travelling at 17 knots, he will have approximately 20 minutes to "see" you. If you happen to run into the Sealand MacLean at sea speed, the mate on watch will have approximately 2 minutes to "see" you. Obviously, anything that increases the distance that he can "see" you on radar is of benefit.
It is quite likely, if you are keeping a decent watch, that you will see the merchant ship long before he sees you. After all, you are on a white boat, with white sails, there are whitecaps on the water, and whiteish/gray rain squalls about-and you're awfully small. If you feel that a merchant ship has not seen you, and I'm referring to offshore primarily, it is entirely appropriate to make a VHF call, if only for a radio check. Believe me when I say that a voice coming over the VHF, that sounds like it's transmitting from right alongside you the signal is so loud and clear, will get the attention of the mate on watch who previously thought he was alone in his little section of ocean! If you're well offshore, he'll probably appreciate the conversation too. As always, female voices elicit quicker and more inquisitive responses!
Naval vessels are to be feared at all times for the following reasons: They often do not monitor the VHF radio as well as they should, being pre-occupied with six other radios squawking, and the sense that it is "merely" a civilian radio and of little consequence to them. Their radar is no better at picking up your sailboat than the merchant ship's. (Don't Tom Clancy me on that one. I've sailed with Navy ships in just such situations and while they may be tracking something 50 miles away, they can't "see" you any sooner or better than that rusty Greek tramp can.) And Naval vessels, due to the nature of their work have two nasty habits; they tend to change course for no obvious reason, often with a large increase in speed, and they think nothing of being in close quarters situations due to formation steaming and re-fueling at sea operations. Aircraft carriers are particularly to be feared. Remember that the captain of an aircraft carrier is a naval aviator and you can guess where most of his experience and training has been concentrated.
It would be a boon to all if a reasonably priced and sized radar transponder were available. Much like those found on the sea-buoys of major ports, they give an excellent radar return at an appreciable distance.