Bob F Posted March 13, 2004 Report Share Posted March 13, 2004 Here's a post I made on another forum, in answer to a question a guy had about "would it improve my visibility on a radar if I lined the cuddy with tin foil"? Thought it would be a useful reference for here, also. I' not an expert on Marine radar but used to work on airborne radar systems. You are right in thinking that tin foil will be a better medium that GRP for getting a better radar reflection, but, in general, lining the inside of your cuddy with tin foil is not going to help much, if at all. The size and shape of the material you use is very important to improve your radar reflection. Ideally the size needs to be a mutiple of the wavelength on the radar signal (marine radar use X-Band 9.32 - 9.5GHz). You might have seen the ticker-tape tin foils strips that aircraft in WW2 used to drop out of the plane to confuse the enemy radars??? Well, these tin foil strips were cut to a certain length to match the freq on the enemy radars. The other thing about lining the inside of the cuddy is that it has not raised the profile on your boat on the water. A radar reflector should be mounted high so that it can be seen by the radar. The biggest problem with our small cuddy boats is that we sit too low in the water and can be hidden by the waves, and GRP is a very poor reflector of radar signals. My advice would be to fit a radar reflector IF you can install it high enough to be effective. They are not very effective if they are just mounted on the roof of the cuddy. Radar reflectors WILL improve your radar signature IF fitted properly. But on a small boat their effectiveness is reduced by the heel of the boat as it rocks in the waves. Modern ships use a computer controled Radar system called ARPA (Automatic Radar Plotting Aid) which steers the ship to avoid targets it has detected. Unfortunately for us, it relies on getting a signal back from a target at least 50% of the time it scans it, to avoid false alarms. So, even with a radar reflector you could still be missed by a big ship. If you are looking for the best solution, and can afford it, an active radar target enhancer is the way to go. These are light, slim, low power units that are mounted on a standard antenna mount. It detects the radar signal, amplifies it and re-transmits so you send out a super strong, consistent signal. Well thats probably totally confused everyone or sent you all to sleep. cheers Bob F Quote Link to comment Share on other sites More sharing options...
Bob F Posted March 13, 2004 Author Report Share Posted March 13, 2004 And a follow-on question about the new tube-like radar reflectors. The tube-like radar reflectors are supposed to be pretty good for their physical size, and much better than the old octahedral types. They come in different versions and have one type that mounts nicely on the roof of a small boat. And they are not a bad price either at about Quote Link to comment Share on other sites More sharing options...
shytalk Posted March 13, 2004 Report Share Posted March 13, 2004 there has been a bit of a debate going on about active reflectors big ship captains saying that in congested waters such as the solent they become a liability because they increase the radar signature of a 30fter to the size of the QE2 this causesthe problem that the ship will react differently to a 30fter than the qe2 if there were say 30 boats in the solent with active reflectors all switched on a big ship radar would show it as solid and inpassable where in fact there is plenty of room the suggestion was to only use said units in open waters !!!! Quote Link to comment Share on other sites More sharing options...
great white Posted March 13, 2004 Report Share Posted March 13, 2004 Hi all, A while ago I lost the blipper reflector off of the cabin roof in a gale.[ boat on mooring] I was going to replace it with one of the cylinder type that are smaller and much cheaper, untill I read a review in one of the yachty mags that said they were very little use, in fact the old type were much more effieciant. I have yet to replace mine so will be interested in your views, we should all have one [if we venture out among the ferrys as we all do]. Charlie Quote Link to comment Share on other sites More sharing options...
shytalk Posted March 13, 2004 Report Share Posted March 13, 2004 another lesson learned not only must the reflector reflect well but must also be installed well !!!!!!!!!!!!! Quote Link to comment Share on other sites More sharing options...
Coddy Posted March 13, 2004 Report Share Posted March 13, 2004 Hi all I am sorry but I have to disagree with Bob, regarding the effectivness of the "tube" type reflectors. In fact following a number of tests both here and in the USA they have found that they are one of the least effective. In fact old octahedrals came out the best. see a good report of reflectors http://www.ussailing.org/safety/Studies/ra...lector_test.htm The Practical Boat Owners mag did a similar test and came up with similar results. In fact they had to repeat the test as many of their advertisers were suppliers of radar reflectors and they were about to slate their products! I was going to buy one of those tube reflectors but I am going to get one of the octahedral type and mount it on a shower rail to gain some hieght, the important bit is the angle of the reflector to get most effectiveness out of it. <off my soap box now> Quote Link to comment Share on other sites More sharing options...
Bob F Posted March 13, 2004 Author Report Share Posted March 13, 2004 No, no need to get off your soap box Codfather, that's exactly what a good forum is about. Like I said, I have not seen the spec on the tube types, so I couldn't make an informative recommendation on them, apart from the little bits that have been mentioned in other articles. The article you have referenced is great, but we have to bear in mind the date it was written. It clearly shows that the tube-like reflectors they tested offer much less that the 2.5 m sq RCS that is recommended. Shame they didn't test the newer models of the EchoMasters. As far as I could tell, this article was written back in 1995, so it has not taken into account any of the more recent advances in reflector technology, like the newer Echomasters, and maybe even the tube-like reflectors now perform better??? Perhaps the Practicle Boat Owner tests were done more recently?? Can you check? What is clear is that although the octahedral peformed the best in this test, it still has large holes in it's reflection map, which is exactly why the Admiralty have slammed them. I'd still like to see the spec sheet for the modern tube-like reflectors before consigning them to the bin. But my concerns about them are their physical size (perhaps too small to be effective) and the price (why so cheap?). Good debate, Codfather. Bob F Quote Link to comment Share on other sites More sharing options...
Bob F Posted March 13, 2004 Author Report Share Posted March 13, 2004 These are snippets from some of the articles I had read on the tube-like or Mobri reflectors. I also notice that Mobri now produce a larger diameter reflector called the M3, which should address some of the issues with the older, smaller diameter units. The Mobri was first tested in 1980 by designer Mogens Pederson with fishermen and yachtsmen in Denmark. Tests were also carried out at the Admiralty Research Department in England with favorable results. To date many thousands have been sold worldwide to sailors, power boaters, and fishermen, as well as to the U.S. and Canadian Coast Guards for use in navigational buoys. A personal recommedation from a boater, not scientific, but... Our first line of defense in making our presence known is our radar reflector. We have a Mobri radar reflector mounted on our upper shroud just above the spreader. The Mobri has gotten some bad press from West Marine and Practical Sailor. Both are responsible testers but our experience is that we show up extremely well on small boat and ship radar. We have the 4 inch diameter model. We felt the Mobri was better constructed than other reflectors so it would keep its good performance longer and as it is up in the rigging it is something you forget about easily. We highly recommend the Mobri. Here's a 2002 update on the 1995 report. They don't really say much about the Mobri but infer that it is still inferior. But they haven't tested the new M3 Mobri. Having done a bit more reading on the Mobri's what I like about them is their practicality to my own situation which is a small boat that does not have a mask. The Mobri's will sit nicely on top of the cuddy, which is not as good as mounting them up a mask, but that it never going to happen on my boat. I'm not advocating the Mobri, but just trying to bring the choices into perspective. http://www.tri-lens.com/practical_sailor.txt http://www.euromarinetrading.com/Mobri.htm Bob F. Quote Link to comment Share on other sites More sharing options...
Coddy Posted March 14, 2004 Report Share Posted March 14, 2004 Hi Bob I think the PBO artical was early last year. As some of you may know I belong to the Internet Angling Club and we are having a 2 day fish in over the Witsun week-end in May. A number of boats have radar reflectors of differant sorts and I know of one boat who has a radar so we will hopefully do some checks when out and about. It seems most reports are based on yachts, who of course have a big metal stick thing to which they hang their sheets on for the wind to dry them. These metal sticks do help a lot to be picked up on a radar screen. It is also worth looking at what the charter boys use on their boats. I have seen a number of differant versions, of course the majority of charter boats are GRP they to suffer the same problems as us. Regards Cod Quote Link to comment Share on other sites More sharing options...
shytalk Posted March 14, 2004 Report Share Posted March 14, 2004 there is another side to the debate , it does tend to rely on the radar operator knowing how to use the radar , last year i came pretty close to being hit by a bulk carrier in the middle of the channel because i hadnt tuned the radar in well enough the ship was not sounding his horn as he should but never the less if the radar had been tuned in better we may have had more warning to move, these days the electronics we use have so many features you need adegree to understand them Quote Link to comment Share on other sites More sharing options...
Coddy Posted March 14, 2004 Report Share Posted March 14, 2004 Hi all, I found out the artical which carried out the tests. It was "Motor Boats Monthly" July 2001, a copy of which can be purchased for Quote Link to comment Share on other sites More sharing options...
Bob F Posted March 14, 2004 Author Report Share Posted March 14, 2004 Coddy, Testing the various reflectors out at sea is a nice idea. Let us know how you get on. Bob F. Quote Link to comment Share on other sites More sharing options...
Nipper Posted March 14, 2004 Report Share Posted March 14, 2004 so bob what one do us small boat owners buy for our boat . mark b Quote Link to comment Share on other sites More sharing options...
Bob F Posted March 14, 2004 Author Report Share Posted March 14, 2004 Ah, the million dollar question. That's what we are trying to determine. I like the idea of the Mobri tube-like reflectors but I'd like to see on tested out at sea to see if they do increase the radar signature. That's what Coddy is going to try to do. Or we might be able to talk to a local Chandler and ask to borrow one for testing. If we like it we would then recommend other clubs members to buy them. Tom and Pete have radars. Bob F. Quote Link to comment Share on other sites More sharing options...
great white Posted March 14, 2004 Report Share Posted March 14, 2004 It gets more interesting this subject. it will be good to see which ones are good. Once you have picked one and bought it do not do as I did. I was rigging every trip while awaiting annual maintenance to fit it properly. Then at the end of a trip I left it up on the plastic Ties, after that it was left up and the permenent fitting got forgotten. I expect the Ultra Violet got to the plastic, and it dissapeard in a gale. Only one person to blame, ME very expensive bit of kit to chuck away. Charlie Quote Link to comment Share on other sites More sharing options...
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