BoatsExplained.com - Radar Reflectors on sailboats

Radar Reflectors on sailboats
The most obvious single factor that makes one reflector more efficient than another is size. Generally speaking, the bigger the reflector the more energy it will intercept, so (assuming it's well-designed) the more energy it can return.
Shape is also important, because although the best possible reflector is a flat plate, it can only work when it's perpendicular to the illuminating radar, so would be useless on a moving boat! At the other extreme, a sphere is a pretty dreadful reflector but its reflection is constant no matter what angle it's at. The problem for the reflector designer is to make a reflector work at a range of angles in both pitch and yaw. There's no 'rocket science' involved: the secret is in optimising the geometry to give the best possible result over the range of angles and radar frequencies required. This always involves compromise, because increasing the 'evenness' of the return is likely to involve reducing the peak return. .
This compromise inevitably makes multiple corner type reflectors inefficient and hence large. The better ones may give a big, even return but they're still only reflecting a fraction of the energy that's hitting them.
Lens reflectors can be much more efficient, but their problem is the weight of the solid dielectric lenses. In radar reflectors, as in life, there's no such thing as a free lunch - you have to choose between windage and weight.
The big question, I suppose, is what sort of reflector you should fit to a small boat to give the best possible chance of being seen on a
ship's radar. The answer depends on a lot of different factors, including the size, construction, and type of boat concerned, the weather conditions in which you sail, and the level of risk you're prepared to accept.
In calm weather even a small yacht will give a reasonable radar return, so you could well argue that it doesn't need a reflector.
As soon as the weather gets a bit lumpy, however, the hull will tend to get lost among the waves, thereby disappearing from the radar screen. A reflector up the mast may not give such a strong return, but it's likely to be visible more of the time simply by virtue of its height.
This causes a problem if you think about the kind of conditions in which you most want the benefit of a reflector. In fog, when it may well be flat calm, a small reflector may reduce your chance of being seen on radar by cancelling out some of the return from the boat itself, but in rough weather that same small reflector might be all that's visible.
In theory, the return from most GRP or wooden boats could probably be improved. For instance, you might consider adding a layer of metal foil behind the cabin lining, especially in the upper areas and internal bulkheads. Fitting small trihedral comer reflectors fore and aft could improve matters, and even something as simple as stowing a CQR anchor on deck with its pointed end aft might make a
measurable difference. The snag is that the effects could only be verified by doing a series of costly and time consuming tests on each individual boat, before and after each modification.
As a small boat sailor myself, I would want the best bit of kit I could sensibly get up the mast - ideally a small, light, but very effective reflector combined with some form of radar-warning receiver. I like the idea of the radar target enhancers that are available now, except that they cost a lot and depend on electrical power. I remember being becalmed at night, with no engine, in the middle of a shipping lane. We had no navigation lights because the battery was flat, so a target enhancer wouldn't have done us much good!

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