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Hi John,
I appreciate your mining these data-based informative reports. Thanks.
I suspect that: if the Mobri reflector does poorly that the venerable take-apart aluminum reflector (Davis?) one puts up in a “catch rain” orientation would also do poorly as they seem to be a similar design.
Any thoughts?
My best, Dick Stevenson, s/v Alchemy
Hi Dick,
Actually those simple reflectors do relatively well, but the key word is “relatively” since the bottom line is that none of the radar reflectors tested, except one large commercial one too heavy for yachts, make much of a difference, at least consistently.
Hello,
Our sailboat came with a spherical radar reflector mast head mounted called “Diabolo High Seas” it was factory installed by Hallberg Rassy.
The documentation specifies that it is not to affected by healing.
Could post a picture if needed.
Best regards
Denis
Hi Denis,
That’s interesting, but I would guess (could not find it with a search) that’s a Luneburg device. If so, it is better in heeling to about 18 deg, and then quits working altogether. See the Honey study. Point being that a lot of claims get made by radar reflector manufactures, but few stand up well to real scientific testing.
Many years ago (early nineties) I worked with an ex senior RAF Engineering Officer who had developed a variation on the ‘Windows’ strips that were used in WWII to confuse enemy radar. He had some samples woven into sailcloth and we hoisted them glues to the mainsail of a wooden Folkboat that the the radar return signal of a child’s pram. We also had examples of the various reflectors available at that time as well as the old single reflector in the ‘catch-water’ position, and we hoisted them all individually and tested them at 3 marked ranges on the radar on my boat ( a good one). The ‘Windows cloth’ was very impressive, especially when compared to the others, most of which hardly registered at all.The big Octahedron was the next best.
He conducted further trials at a much higher standard, with specially made fabric with the help of a major manufacturer, but not one sailmaker was interested.
So big is best, and most aren’t big enough by half in my experience.Sea-me seems a good idea – as long as someone is watching (see other comments!) and AIS must send as well as receive, which is what we have.
‘Heal’? Hopefully that’s what happens if all your efforts to avoid a collision fail….!
A good call, however; the MAIB report was the reason my boat had a Sea-Me fitted some years back. It would be interesting to hear from any current Bridge Watchkeeper about how much attention is paid to X as opposed to S-band when away from coastal waters these days. Although I’m pleased I invested in a decent AIS transponder, the thing once died in lumpy seas immediately on entry to a very busy TSS in the English Channel. This was just a faulty connection but the event showed me the importance of an effective ‘layered defence’.
The watch officers who might be inclined to respond to such a question will say that they keep an eye on both radars plus the AIS and also maintain a visual lookout.
The ones you need to worry about aren’t going to answer the question. They’re on Facebook while the autopilot does the work, and aren’t going to look up from their phones unless something sets off a CPA alarm. All the engineers who design ships’ bridges in the last 20 years know that you can’t trust the watch officer to actually keep a lookout. Hence, automation.
Radar reflectors are nice for making sure that, if you’re in fog and nearby vessels are relying on radar, you’re a bit easier to track. But there’s no guarantee they’ll make you stand out from the clutter at any significant distance when the other ship’s controls have been adjusted to suppress the waves, rain, etc.
So, yeah. The reflector is of some value in a foggy close-quarters situation. But if you want the ships to actually see you, you need to transmit AIS.
Hi Matt, as an ex- navigator I can confirm (albeit from 40 years ago) what you say is pretty much what I would expect today, and maybe worse. In my time, as “stand on vessel” I had to avoid “give way vessels” (large ships that didn’t respond to my ship’s horn blasts) at least a dozen times, and so yachts should expect worse.
A caution about relying on AIS that is subject to electrical / system failure, plus any delay between GPS updates (up to a minute in my experience), which at close quarters in fog can be problematic.
Whilst even old style radar reflectors are surprisingly effective in slight seas if well mounted, and very effective in calm foggy / misty conditions when sea clutter is minimal. Places like Nova Scotia that can have fog AND strong wind / bigger seas together are more problematic.
By way of example, I was on early watch steaming at about 22 knots towards the Caribbean off the South American coast, on a calm night with a slight left-over swell. I perceived a very faint and occasional white light, absolutely dead ahead in the distance. Turning radar on from standby quickly confirmed a solid target at about three nautical miles.
Altering course, I simultaneously heard a security call on channel 16 from a very relieved American yacht who said they were using their handheld VHF and madly waving a torch. They were becalmed, with a dead engine and equally dead batteries.
They were keen to know if I could see them on radar – they said they had an old style Davis reflector low down on their backstay.
Hi Rob,
Thanks for the real world report, very useful.
Like you, I have had to alter for many ships that were burdened but oblivious. That said, as a general rule I have found ship’s officers to be both professional and helpful. That might be partly because even when stand on I have general offered to alter for a ship since they are working and I’m playing. That said, only if I have established comms and we are both clear about what’s going on.
Over the years I guess I would put the proportion of pros to the others at 80/20 to the good side.
On your experience with the yacht, having read both radar reports I do wonder if you were mostly getting a return off the hull and spars, not the reflector. No way to know, of course.
Hi John,
Yes, hard to be sure if it was mainly the reflector or the vessel – it’s always a combination of both. Big ship’s radars are powerful and in slight seas, even a tiny constant echo will show up over sporadic wave clutter, which is more often the case in restricted visibility.
Steel or aluminium boats will show up much better than wood or fibreglass boats. Small steel fishing boats show up better again with their bulky topsides and accommodation blocks.
So my own take on this is the more reflector(s) we have the better, for our fibreglass boat. On passage in good visibility, we don’t need to be seen on radar as we trust our watch keepers. Fog and misty conditions, or heavy rain downpours are our concern.
We have two of the 4″ Plastimo cylindrical types that came with the boat installed on the shrouds like in your picture above. Reading the MAIB report (10 years ago or more), we removed these and installed an Echomax 230 on our mast, which performs OK if we are not heeled like in fog / mist where we might sail, or be at anchor.
But we still keep those two cylinder reflectors in our bosun’s locker, which can be hoisted to the spreaders, then aligned to vertical using our twin flag halyards. This will help to some extent, especially with vessels approaching from astern where our Echomax will be hidden by our mast. The aluminium mast itself is of course a great reflector, but being rounded in section, will show up only sporadically.
From my experience, it’s the constant echo that gets us noticed on big ship radar.
Hi Rob,
I would suggest reading the Honey report, if for no other reason than you will get some space back in your bosuns locker. Both tests showed those cylinder reflectors to be fundamentally useless. And even the Echomax was not great, but better than nothing.
John,
WRT keeping clear of working ships this is my take too. In fog we would usually be running at reduced speed burning diesel and could make an alteration of speed, but in mist and heavy rain we would more usually be running on heavy oil and slowing the ship was problematic.
So collision avoidance usually involved altering course and if I was officer of the watch on a give-way ship on passage, I would be taking action under Rule 16 and Rule 8 (a,b,c) before or at five nautical miles. But if I hadn’t identified a small target in time like in my account above, then by three nautical miles as an absolute minimum.
So on our yacht, if a give-way ship hasn’t taken action by 5 nautical miles, then applying Rule 7(a), we assume a risk of collision exists and take our own avoiding action, even as stand-on vessel as provided for in Rule 17(a) (ii).
As a general rule, I will not try and make contact on passage with another vessel large or small by VHF (then or now), as this can lead to confusion in my experience, especially if English is a barrier – plus it wastes valuable time.
If the other watch keeper hasn’t seen me, then they probably won’t hear me either.
For clarity, in shipping lanes, narrow channels or other special navigation areas, I do believe well executed VHF contact has its place. Here it is more likely the captain and or pilot are on the bridge, and not just some under-paid and often under-qualified watch keeper.
Hi Rob,
I agree on taking avoiding action early, even if stand on, and that has always been my practice. And when I mentioned VHF contact I was referring to confined waters, For example, when transiting New York harbour, as I have done at least six times, it’s vital, and standard practice, to communicate intentions. Also, before AIS, I often contacted ships at sea to clarify and in many cases that worked well because they had not seen me. To me that’s no different than a crew shining a torch on the sails, as in your example.
This is the sort of professional feedback I was hoping for in my original comment; many thanks. Until John wrote the article I’d thought my ‘Sea-Me’ was the best there was but it spurred deeper research; I’ve found that Echomax now make an RTE that functions on both X and S bands. Rob’s point about a constant echo being the key factor in getting noticed is of great value.
https://www.echomax.co.uk/active-xs
Very curious of your opinions regarding an active reflector like the EchoMax D/S mounted on an aluminum hull sailboat. I suspect the answer is, “well, it can’t hurt, but it might not help.“ With an aluminum hull I’d expect the natural reflectivity is by and large going too far exceed any artificial enhancements that I can add. And yet… Well, if it can’t hurt…
Hi Zac,
Although I cruised in a metal boat for some 30 years I was never really able to get any solid data on how good, or not, a radar target we were. So I think that if sailing in a high fog area one of the new Active XS units might be a very good idea…can’t hurt…sorry, couldn’t resist.
Hi Rob,
Thanks for the heads up on who’s likely to be on the bridge of working ships depending on navigation circumstances, as well as your 5 NM range practice. It helps those of us that have not worked on a large ship visualise the operations. I’ll keep that in mind.
When sailing in conditions that do not make it easy for me to manoeuvre (solo or short-handed, heavy seas, spinnaker etc.), I check on the give-way vessel’s intentions early and have found them very accommodating. Otherwise I take avoiding action well before the risk of collision can be deemed to exist.
JL
this seems to be https
https://www.ussailing.org/wp-content/uploads/2018/03/radar-reflector-tests.pdf
Hi Ignat,
Great, I will change that. Thanks
This is a classic example of new technology seeming better than the outgoing Refresh rate of AIS class B is supposed to be 30 seconds when travelling over 2 knots, however it’s is often over a minute. In a congested waterway the “real location of an ais target is not what is showing on your chart plotter, it’s old news Radar wins here.
That particular issue should improve now that AIS-B using SOTDMA (or “AIS B+”) is a thing.
AIS-B using CSTDMA has to wait until it senses a clear channel, then transmit its burst, then wait at least 30 seconds before trying again. If the channel isn’t clear at that instant, it might wait quite a long time before succeeding.
AIS-B+ using SOTDMA can transmit at higher power (5 W instead of 2 W) and participates in the same self-organizing transmission schedule as AIS-A, varying its update rate to match vessel speed.
Even so, radar is always going to yield the most current & correct target data, assuming you actually get a return from the target.
I carry a four-inch mobri type reflector with a claimed RCS of 4.0 m2. I suspect its true RCS accounting for heel angle etc. is less than a third of that. I’m under no illusions that it’ll light up a 600 foot ship’s S-band display from eight miles out with a sea running. It absolutely won’t, and it’d be irresponsible to assume otherwise. But it does make us more visible to the X-band pulsed and FMCW units on the car ferry and the pleasure powerboats from a mile or two away, especially when the fog’s rolled in, and when their auto-gain control has sensed the lack of sea clutter and cranked itself up to match.
Radar can provide more current target information than AIS, but if the watchkeeper is relying upon ARPA to acquire and track radar targets, the radar information could be as much or more out of date than A(S-B.
Hi Mark,
Hum, why do you say that? As I understand it good quality ARPA like that provided by Furuno is updated on every sweep. Sure it takes time to detect a course change, but then so do all systems. Even if AIS was updated say every 5 seconds it would still take time for the plotter to stabilize the plot to a course change, I think.
That’s a question of whether you are looking at a recent implementation of ARPA or the standard definition. ARPA is allowed to take as long as a minute to establish a target, but recent radar systems do considerably better than that.
Either way, it is worth recognizing that target acquisition and tracking requires multiple sweeps, whether it is a human doing it or an automated system. If that target isn’t showing up on most sweeps, acquisition and tracking is much more difficult, and the target may not show up as an ARPA track at all.
Hi Mark,
Absolutely true. I was thinking more about after the target is fully acquired and locked in. And don’t get me started on the B&G implementation! Eric has a two part series on radar use in fog all written and just waiting to get to the top of our publishing queue.
Hi Matt,
Good point on AIS B+.
On the mobri I would suggest you read the Honey report. Their claims are pretty much proved to be totally bogus. That’s also confirmed by the British report. I was too kind in my headline. I should have said useless. In my view the cylinder reflectors are actually worse than useless because they give a false sense of security.
I quote Stan:
John,
Yes, I read the reports. Hence:
“I’m under no illusions that it’ll light up a 600 foot ship’s S-band display from eight miles out with a sea running. It absolutely won’t.”
Honey’s recommendation for a minimum RCS of 2.5 m2 is based on the ship using both X- and S-band pulse radar, with the controls set for a moderate sea clutter state, such that the ship (when using S-band on 24 mile range and X-band on a shorter range) will see a consistent, repeatable return from at least three to six miles out. This is a very reasonable recommendation; 2.5 m2 is roughly equal to one 1970s fighter jet head-on, and should usually provide enough return for a MARPA algorithm using data from either band to lock on from 3 to 6 miles out.
When you are closer and the sea is not so rough, the situation is different. Most X-band pulse radars should be able to show a 0.5 m2 target from 1 to 2 miles away when in low to moderate sea clutter. Modern FMCW is much better at short range; these are known to pick up individual pilings and lamp posts (<0.1 m2) on the shoreline.
We should be careful about mixing literary exaggerations with quantitative data. The F-22 and B-2 stealth planes both have RCS on the order of 0.0001 m2. The F-35 is about 0.005 m2, similar to the F-117 (0.003 m2). By comparison, the mini (useless) mobri is 0.07 to 0.22 m2 on X-band depending on angle, and the larger mobri is 0.37 to 1.08 m2 on X-band, i.e. 100 to 10,000 times more visible than a stealth plane.
I would not recommend spending money on a mobri type reflector. But, IF AND ONLY IF the main concern is foggy close-quarters situations (in which case the sea state is probably low and the other vessels are probably on X-band) then I would not remove a large mobri on a boat that already had one. I’d leave it above the spreader 24/7, and would hoist something better and *much* larger when visibility from more than a mile or two away is required. (This is my own situation: on our part of Lake Ontario we are never in the main commercial shipping lanes; the concern is small craft within less than two miles which are using MARPA on X-band pulsed or FMCW.)
The trouble with a reflector large enough to reliably give >2.5 m2 from all angles is that it’s a heavy, bulky, high-windage thing that has to be suspended from a halyard. You can’t realistically fly it all the time. Whereas, in Canada, vessels of non-metallic construction must by law have radar reflectors hoisted at all times when in waters used by radar-equipped boats (see TP 511E page 19 https://tc.canada.ca/sites/default/files/2024-03/tp_511e.pdf ). Keeping a mobri tied to a shroud 24/7 satisfies this legal requirement, which is by extension an insurance requirement, even if we all know that it’s ineffective at any great distance and that we must hoist something better when we want to be seen from a distance.
Hi Matt,
Do as you like, obviously, but if it were me and having known Stan for many years, and having huge respect for him as both a scientist and very experience sailor, I would take his recommendation and not rely on the Mobri at all, other than possibly to provide a regulatory and insurance fig leaf, which is a use I can understand.
This article brings a lot of connections for me. 1) I worked at SRI just before this study was conducted there. 2) I worked closely w/ Dick Honey, Stan Honey’s uncle. I sailed a lot w/ Dick on San Francisco Bay. Dick was a first rate scientist and knew his way around electro-magentic radiation (radar). You can trust the data presented. And I ran the engineering group at Davis Instruments some years later (maker of the Echomaster.). We did not have the radar facilities at SRI but were happy to support their efforts there. And finally, as a user of the Echomaster, I can attest that I’ve seen targets on my radar in low visibility conditions make dramatic corse corrections when we came w/in their radar range when flying the Echomaster at spreader height in the rain catch position (no angle of heal). I think we looked far bigger to them than we would otherwise. Can’t hurt. But no substitute for your own carful watch-keeping
Hi Jeffrey,
Wow, that’s interesting, and I totally agree with your last sentence.
For other’s. One of the fascinating things that came out of the Honey/SRI report is that the simple and relatively cheap Davis units did very well, and better than more expensive and larger units like the Firdell Blipper.
I had the Davis-style reflector mounted on my backstay, but AIS was definitely the go-to. Even though we transmit and receive, when offshore, I would act as if my transmit was not seen: when I saw a ship on AIS, I would get its name from my chartplotter, and if I was at all concerned that we would pass close, I would make VHF contact at least 5nm out. I would usually just make “small-talk” about the weather forecast, but I would start my transmission with “good evening Maersk Giantship, this is the sailing vessel Merdeka, 5 miles off your port bow…” Then I always knew the watch-stander would be glancing at their AIS and radar screens right after that.
Hi James,
That’s always been pretty much my practice and experience, as well.
We opted for a Davis style reflecter, which I hear is better but similarly useless… but it’s cheaper. You are legally required to have one in Canada, so that’s the reason why we have one at all!
Hi Kerri,
Good point on the legal requirement. That said, the Davis did amazingly well in the Honey/SRI report.
The now out of print book “Radar Reflectors for Cruising Sailboats” by Philip G. Gallman (2005) is a good technical introduction to the subject. I have found it useful. https://www.amazon.com/Radar-Reflectors-Cruising-Sailboats-Limitations/dp/1930580738/ref=sr_1_1?crid=22OL4LXGUTLNZ&dib=eyJ2IjoiMSJ9.Lr2mhP08orUa5dAqmPlL3g.idPRpXiLRriPKyUyhJbjvDPIDJ8kzrQioB_UbASS00A&dib_tag=se&keywords=radar+reflectors+for+cruising+sailboats&qid=1728307222&s=books&sprefix=radar+reflectors+for+cruising+sailboats%2Cstripbooks%2C92&sr=1-1