Fixed radar reflector vs inflatable

[Oscarpop]

Off the back of my last post about ais, we need to think about radar reflectors.

I am still not sold on the passive ones as I don't see that the reflector will add a jot to my 20 m high aluminium mast.

If someone can please explain the science to me then I am more than happy to be corrected.

So I read somewhere that inflatable ones are better as you can hang them off the windward spreader, which gives better results .

Again, I am still not sold on this.

I understand active reflectors are best but not in a huge position to have one of these.

The final thing I would like answered is this.

When my friends used to sail sir 30ft yacht ( without any radar reflector) across the channel, they used to call Dover coast guard who would pick them up on their radar and keep an eye on them.

Surely they must have had enough of a radar profile to be picked up, or does Dover have a much more sensitive one.


Ta

 

[rob2]

Well, your mast is near circular in cross section and any reflection will be dispersed rather than returned to whence it came. The design of a passive relector is to offer flat plates acting like a mirror, usually in a corner configuration so that three relections will send the signal back alonga reciprocal path. It's the same principle in three dimensions as playing a cue ball into a corner of the table so that it returns along a close parallel path. Of course, there is a limit to the angle that will achieve this and ideally the reflector should be hanging upright, so maybe dangling it from the spreaders improves the return (rather than rigidly mounted on the mast when heeling).

For myself, I'm one generation behind the technology as I fitted an X-band RTE and carry a hoistable passive reflector in the hope of improving the return if I'm painted by an S-band system. In good vis I don't bother with either in coastal waters, but I think I'd switch on the RTE if crossing a major traffic system.

In good weather, a yacht may give a good return without any added reflectors, but who is to say what the radar is detecting? It could be the engine block or even the hole the yacht makes in the water, but in rough water or rain the clutteris likely to hide your return. In particular the set may only pick you up intermittently and will not activate any automated alarms and most watch keepers are unlikely to be studying the screen and tweaking it for best reception!

Rob.