Q&A: Radar Reflectors and/or AIS Transponders?

imageQuestion [Edited for brevity]: We have been upgrading the safety equipment on board our boat and are thinking of installing radar reflectors to amplify and enhance the radar signal we create to alerting oncoming vessels of our position during offshore sailing in bad weather and heavy seas.

The Echomax Active-XS-Dual Band reflector seems very good, though at a high price. We’re also considering mounting a passive reflector, Echomax 230 or 305, in case of electrical failure.

What do you think?

Answer: We have an old Firdell Blipper mounted just above the top of the staysail stay on the mast. However, I think that the Echomax passive is a better reflector and probably a good idea for your boat. In fact, I have just added replacing our Blipper with an Echomax to our never-ending/ever-growing boat project list.

AIS—A Better Deal

I would not bother with an active radar reflector (transponder) but rather install an AIS transponder. Just about everyone out there that has radar probably at least receives AIS too and it will tell them a lot more about you and what you are doing than an active reflector. Also, you will get an invaluable AIS receiver in with the price. Of course, both radar and AIS transponders would be nice if you have a big budget and lots of time for electronic installations.

Don’t Rely on Any Transponder

Having said all that, I strongly believe that we in small boats should assume at all times, even if our boats are equipped with both radar and AIS transponders, that ships have not seen us.

For example: Some years ago I did a single handed passage from the Virgin Islands to Bermuda. At the time Morgan’s Cloud was fitted with a radar detector. Over the course of seven days I saw at least half a dozen large ships that did not trigger my detector. On three occasions I called the ships in question on VHF and asked them if their radar was on. All three assured me that it was. But in each case a few seconds after my call my radar alarm sounded, indicating that the watch officer had just pressed the transmit button, taking the radar out of standby. (If the radar had been off completely I would not have received an alarm for at least two minutes while their unit warmed up.) My guess is that these ships were leaving the radar in standby to conserve the expensive magnetron.

And an AIS transponder will not save you from this kind of thing either, since commercial plotters and radars have the ability to filter out signals from the Class B AIS transponders typically carried by yachts. As more of us fit these transponders it is likely that more ships will filter us out in crowded waters. Conscientious watch officers will turn off those filters while at sea but, in the real world, how many will actually remember to do so?


In summary, all these devices are great, but the most useful of them is the AIS receiver, which supplements the Mark I Eyeball and our own radar units (highly recommended if you don’t have one) in helping us get out of the way of ships.

Note that we will be doing a review of our new AIS system soon.

What do you think: radar transponder or AIS transponder, or is it worth the expense and complication to have both? Please leave a comment.

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Meet the Author


John was born and brought up in Bermuda and started sailing as a child, racing locally and offshore before turning to cruising. He has sailed over 100,000 miles, most of it on his McCurdy & Rhodes 56, Morgan's Cloud, including eight ocean races to Bermuda, culminating in winning his class twice in the Newport Bermuda Race. He has skippered a series of voyages in the North Atlantic, the majority of which have been to the high latitudes. John has been helping others go voyaging by sharing his experience for twenty years, first in yachting magazines and, for the last 12 years, as co-editor/publisher of AAC.

16 comments… add one
  • Chris May 3, 2011, 4:29 pm

    We have a tri-lens mounted at the masthead.

    We put it there to prevent mast shadowing, which can kill a return through as much as 60deg. Since we sail in the vicinity of many fishing boats which actively use radar and practical AIS for boats our size was unavailable at the time, no real thought was required.

    Of course the radar reflector is like a silent dog whistle. Maybe the dog heard it, and maybe she was just going to come anyway.

  • David Nutt May 4, 2011, 7:55 am

    No matter how many pieces of electronic gear you have aboard there are two organic items that are of utmost importance – your right eyeball and your left eyeball. We had a close call with a ship while en route from Panama to the Galapagos. After finally contacting them via VHF they assured us they had us on radar. Amazing radar they had because none of the three scanners were rotating. It is up to us out there and electronic aids, and I have many, are just aids.

  • David Head May 4, 2011, 9:07 am

    This is a critical subject, and well worth deep analysis + comment. I have always believed that no matter what rights of way etc the best practice is to remain vigilant, and be prepared to avoid any close encounter. Regarding so called radar reflectors: The Quinetic report commissioned by the MAIB after the Ouzo / Pride of Bilbao accident looked into the dubious claims made of the various styles and came to a damning conclusion. They were all virtually condemned as being largely ineffective offering a poor reflection when vertical and all but none when heeled. My experience with AIS is less than good. Discounting the vast numbers that do not transmit and the vessels that carry no transponder I have found that of those that offer an AIS response the information can be limited, often with a very slow refresh rate that is so vital at the time of an early contact. This technology still has a long way to go before it replaces ‘eyeball’ / common sense / self preservation! I do have some respect for ‘Marpa’ which, when viewed on a well tuned radar screen, offers much that AIS was supposed to provide. My words of warning about radar concern the need to be very conversant with your set BEFORE the need to use it in anger.

    • John May 5, 2011, 9:49 am

      Hi David,

      We had exactly the same refresh problem with AIS until we started using our mast head antenna, instead of a rail mount, and a really good receiver.

      Now with the new rig we are getting very fast refresh rates and no target drops.

      On our just completed trip north from Charleston to Nova Scotia we found that pretty much all commercial vessels were now transmitting AIS. The only exceptions being US naval vessels and fishing boats.

  • Brian Lockett May 4, 2011, 11:45 am

    Radar reflector of any kind is unlikely to be picked up on ship radar in a heavy squall, making the case for AIS. But a radar reflector is not subject to electronic failure on your boat while AIS is vulnerable. Do both if you can afford it.

  • Tim Allen May 4, 2011, 1:20 pm

    I fitted an AIS transponder last year, and found it invaluable — but mainly for the receiver capability. None-the-less, I am very glad to be transmitting as well! (FWIW, I am of the opinion that concerns about class B filtering are overblown — my AIS receiver has very powerful filtering capability and I use it to reduce clutter and avoid alerting me to things that are not a potential hazard. But even the things I am filtering will become un-filtered if they do become a real hazard, and as I understand it the same thing applies to sets that can filter signals based on class.)

    This year, I have fitted an active radar target enhancer (the EchoMax Active-X; the XS model wasn’t available at the time I purchased mine). My boat doesn’t go in the water for another week, so I can’t yet comment on how well (or not) it works. I sprung for it for two reasons: 1. having previously read the Quinetic report commissioned by the MAIB after the Ouzo / Pride of Bilbao accident noting that passive reflectors are of limited effectiveness (though I still hoist my Davis echomaster, believing that something is better than nothing); and 2. the Active-X also serves as a radar detector. I believe this could be useful as many of the vessels I might encounter where I sail probably do transmit radar but not AIS signals.

    I do not yet have my own radar due to issues of cost, complexity, and power consumption, but it is on my list.

    I also want to strongly concur with the sentiment that these electronic aids are just aids, and reinforce the notion that watchstanders need to rely most heavily on their primary senses of sight, hearing, smell, and anything else that might alert them to the presence of other traffic.

    • John May 5, 2011, 9:43 am

      Hi David and Tim,

      A really good point on how poorly radar reflectors did in the testing you reference. Echomax, aside from selling an active radar transponder, claim to have significantly improved passive reflectors. Does anyone have any information to confirm or refute that?

  • Tom Hildebrandt May 4, 2011, 4:45 pm

    Ditto what everyone else is saying, radar is good, AIS is good, but, eyeball is the best. Of course in bad weather, squalls, heavy seas, and the like radar becomes less viable, AIS is great, but not all vessels are fitted with the equipment.

    For me, I fitted Juno two years ago with a used (but with only light use) radar unit a couple years after my origianl died. Better than nothing, but only marginally. I will keep it as long as it works and see what new products are available when it does bite the bullet; this summer I plan to install a new VHF radio that includes an AIS as one of its functions.

    But still, except in the bad weather situations, I am thinking that the eyeball is still the best bet for avoiding the dreaded close encounter of the wrong type!

  • John May 5, 2011, 9:35 am

    Hi All,

    Thanks for all the well reasoned comments, great stuff. Lots of stuff that I had not thought of that will help the sailor that asked the original question and all the many others who will read the full thread.

    All particularly relevant to me today since we just spent two days motoring in thick fog across the Bay of Fundy and along the Southwestern Shore of Nova Scotia, dodging scores of fishing boats out taking advantage of the last month of the lobster season.

    In this case AIS was not much use since few fishing boats carry it. Also, I would not rely on a distracted skipper trying to pick up a tiny buoy in the fog while being swept around by three knot tides seeing and avoiding us, no matter what radar reflector (active or passive) we had.

    Bottom line, to be out there in those conditions without your own radar and a lot of experience using it would be really dangerous.

    • Chris May 5, 2011, 9:55 am

      John, one thing that did not get mentioned, and I’m not trying to stretch the thread, is radar tuning — mostly for sea state and rain. But we have also found in the Fundy type conditions you mention increasing echo stretch helps. The false target count can go up if you don’t tweak for sea state (STC). I’d rather have a few false targets than miss a few real ones.

  • Dick May 8, 2011, 3:20 am

    Pertaining to the Firdell Blipper vs Echomaster: the picture makes it look like the mounting brackets for the FB are the same as the EM. Is this the case and is the footprint the same? I dislike putting more holes in the mast. Thanks Dick

    • John May 8, 2011, 9:25 am

      I’m with you, Dick. One of the advantages of the Echomaster is that they designed it to have the same mount pattern as the Blipper. Just make sure you get the right model. See their site for more.

  • Gianca May 9, 2011, 10:59 am

    I think my favorite system to avoid collisions is a simple stand alone AIS receiver only, with VHF antenna splitter. I rate Vesper Marine to be the best, easy to read, and very low power needed compared to chart plotter or pc interfaced black box.
    The Sea Me active radar reflector proved to be totally not detected by a German cargo ship who almost sunk my best friend single handing from Argentina to Europe. With this I’m not saying the system did not work, I’m just reporting what happened that horrible night.
    One consideration regarding a more complex, see expensive, AIS class B, there is the possibility that big ships have their AIS set not to display small or slow boats, so it becomes useless.

  • Terradagua May 16, 2011, 3:50 pm

    Hello to all,

    Sorry if the question is dumb!? But thought I should ask….
    Do you still use a radar reflector even if your boat is made out of aluminum?
    Thanks to all for always great and informative comments and a big thanks to the Morgan’s Cloud crew for having the website up and sharing all this valuable stuff!

    • John May 18, 2011, 8:14 pm

      Hi Terradagua,

      Not dumb at all. I have wondered the same thing myself. We have a reflector, even though we have a metal hull, in the hopes that it will do some good. Also, at 2/3 of the way up the mast it is less likely to be obscured by big seas than the hull. Having said that, some recent studies, as cited in the comments above, have been pretty damning about the effectiveness, or lack thereof, of passive radar reflectors. Having a metal hull is a comfort since there is no question that we see metal fishing boats way further away with stronger radar returns than those built of fiberglass or wood.

  • Richard Phillips Dec 22, 2018, 4:37 pm

    Presumably you have seen this review – a somewhat scientific review of reflectors – with strong results for the Echomax 230


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