The Offshore Voyaging Reference Site

Can We Really Be Seen By Ships at Night?

Some days ago we made an overnight passage from Nova Scotia to Newfoundland. At about 2:00 am, Phyllis picked up a slow-moving target at about 2.5 miles on radar.

Despite it being a dark and clear night, with a tiny sliver of waning moon low in the sky, we could see no lights, even through our high-quality Steiner binoculars, and they suck light.

Finally, when the target was just 1.5 miles on the beam, and against the blackness of the land, we were able to just barely discern a very faint white glow that we finally recognized as a steaming light reflecting off the target’s headsail—indicating a sailboat motorsailing—but during the whole encounter we never saw red or green sidelights, and we only saw said glow because the radar was giving us the exact bearing to direct the Steiners on.

I gave them a call on VHF and was immediately answered with the information that they were indeed a sailboat motorsailing.

And then, when the range had closed to about a mile, an AIS target came up on our plotter for the very first time. Said target only showed the other boat’s name for a moment or two and then reverted to an MMSI number before blinking out completely at about 1.5 miles.

I took two important lessons away from this encounter:

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Hi John, for sure an interesting and vital topic. And of course AIS visibility of a vessel always depends on the AIS being switched on at all … in the Med, for example, trawlers who are either actively fishing or moving to their hunting grounds tend to deactivate AIS as to not give their location away to other fishing boats. And in Greece I once had a Superfast ferry (one of these really fast and huge ferry boats running at 25+ m/h) having the AIS switched off as it took a shortcut that is forbidden for commercial traffic.
AIS can also be an issue esp. in Croatia when you are not navigating exactly or don’t take the country border line into account – crossing the border line with your AIS active might present you with a nice surprise when back in port where the harbour police will fine you for crossing the border without clearing out first. They charge up to 2k EUR per peron for this. So a lot of recreational boaters turn off their AIS when navigating near the border.


Actually there is a remote rocky island called Palagruza which belongs to Croatia, thus extending the 12mi border. The topology of this island creates a “dent” in this (imaginary) line, so navigating correctly is a bit tricky, some boaters simply take the straight line and thus leave and reenter the croatian waters, albeit only for approx. 2nm. Which makes for some nice extra income for the tax office.


Interestingly short sighted behavior for officials.
They are not only compromising security at sea because they effectively encourage people to switch off their AIS, they are also compromising their own growing yachting industry by discouraging people to visit.

Francisco Moreno

That the Croatian authorities specialize in tracking boats via AIS and then fining them for any number of reasons based on their AIS track is a well-known fact.

They are even said to come to your boat with a printed track of your boat when they approach to charge the fines!

Marc Dacey

There’s other reasons to switch off AIS transceivers and even lights as well. Going through the Sunda/Malacca/Singapore Straits is going through pirate waters, although most of this is directed to commercial vessels. An added issue are unlit fishing boats which may be easier to avoid from a deck made as dark as possible. The Red Sea has quieted down of late, but more than once I read of sailing yacht “convoys” going dark, transceivers off and radio traffic very limited to pre-arranged channels so as to make their detection by pirates as difficult as possible.

While this is not the case described by John, the result is the same: don’t count on the traffic you meet at sea being lit up in several frequencies. There are reasons beyond “bad coax” why they may not be. Interestingly, however, despite the fact our boat is exactly one cm. short of 12 metres LOD for now-obscure tax purposes, I have always upsized the lights to the greater than 12 metre standard. When I want to be seen, I want no ambiguity about it. Tiny 10 watt lights (as are legal below 12 metres LOD in Canada) at night are very hard to make out on smaller boats.


When we last had our mast down for re-rigging, I went ahead and installed an led tricolor light at the masthead. The thought was that the added height would be beneficial in rough seas when the conventional sidelights might be obscured by wave action, but after reading this, I’m inclined to use the tricolor more regularly when offshore. I am aware that one cannot legally use both sets of light simultaneously. We do not have radar and only have an AIS receiver and while we do appreciate the data sets it produces, for our situation, an alert pair of eyes is still our best line of defense.

Peter Mahaffey

Well that article hasn’t exactly done a lot for my confidence in the McMurdo S20 personal AIS beacon which I wear at night when on watch during offshore passages. Its supposed to have a range of 5-7 miles at sea level, with its fragile little antenna. Now we hear that even on a 14 m yacht with antenna mounted several metres above sea level, the range might only be a mile of two.

Marc Dacey

That matches with the height of the antenna at the masthead combined with the compartively low wattage. I did some tests a while back using a SH HX850 handheld (six watts on high power) taken out into the lake and used to reach my wife on our boat with a masthead antenna on a pre-arranged channel. Six miles was about the workable limit where I could be heard above the static, under “best conditions”. So I generally cut that in half for “average conditions”. Given that AIS beacons/tags operate on the same frequencies, your numbers make sense. On a fast boat, that doesn’t give a lot of time to react, come about and try to find someone in the dark in the water. That’s why I like those beacons that set off a big alarm if the wearer gets more than 20m (or whatever) away from the VHF. Of course, how many people keep the VHF on 24/7 on passage? Some do not.


We use our tri-light when motorsailing, as does pretty much every other sailboat we see out here. It may not be legal,but is a lot more visible and therefore safer. Our Vesper watchmate has worked brilliantly for the two years that we have had it. The fishing fleets here in the South Pacific, mostly Chinese or Japanese, do not show AIS and can be a significant hazard


To be honest, I’d rather be illegally seen than legally run over.


It was mainly for the obvious pun – and as you said, today’s LEDs are quite bright.


A “legal” alternative is also the masthead allround red over green in addition to the nav side lights (COLREGS Rule 25.(c)).


Hi Ernest
In my understanding of the colregs a sailingvessel that is motorsailing is legally a powerdriven vessel which means that rule 23 applies. That means no red over green is allowed. Correct me if I’m wrong.


Of course you’re correct – I meant it for sailing vessels. A vessel motoring shows the steaming light which is already well above the side nav lights and _should_ make it visible. Which unfortunately is not always the case given Johns story above…


This is true, but the white steaming light is the solution here, as it gives the visibility whilst motoring or motor sailing. The issue in the story is not that they didn’t have a steaming light, but most probably where it was mounted. For some reason I can’t understand, sailing yachts now come with the steaming light mounted about 2/3 of the way up the mast. This has been the case as long as I can remember (about 30 years), and I can’t find any reason for it in Colregs. When mounted at this height, and motor sailing, it is sometimes obscured by the sails.

Colregs doesn’t dictate a maximum mount height for the steaming light, only a minimum. Thus it makes absolute sense to mount it at the masthead. This provides greatest distance and minimum disruption by sails when motor sailing.

Unfortunately almost no sailboats come with a masthead steaming light as standard: it’s almost always fitted 2/3 up the mast. So such a light is a retrofit, which almost nobody does.

I have no idea why this is the case.

We refit our boat with Lopolights about 7 years ago. Not withstanding earlier posts about Lopolight reliability, we have had no issues. We have the all round red over green, and our steaming light is part of our masthead anchor light: when anchored it’s an all round, when steaming it’s just the front portion lit. I think it’s the best solution.


Matt Marsh

I’m strongly in favour of setting up the boat to follow both Rule 23a and Rule 25c precisely. That is:
– red, green, and white sector lights at deck / cabin level, used all the time
– red over green all-round lights at the masthead, used when sailing
– white masthead light (excluding aft sector), used when motoring

I honestly don’t like masthead tri-lights, by comparison, although they are better than minimal deck-level sector lights. From a distance, either type appears as just a single dot of one colour. The full Rule 25c setup, by comparison, makes it pretty easy to tell that I’m looking at a sailboat, that it’s about yay big, and that it’s about yonder far away.

Skimping out on lights sorta-kinda made sense when batteries were limited, incandescent bulbs were hungry, and the seas were mostly empty. These days, I can think of no reason not to use the full Rule 23a / Rule 25c setup.


For a sloop there seems to be no reason to not have the steaming light mounted on the mast top as to Rule 23.a.i ( A power-driven vessel underway shall exhibit: a masthead light forward) – no min/max height specified here. Rule 21.a defines ” “Masthead light” means a white light placed over the fore and aft centreline of the vessel showing an unbroken light over an arc of the horizon of 225 degrees” which basically would make a position that keeps the light partially obscured by sails illegal (“unbroken”).
Any ketch, yawl or schooner might choose to show a second steaming light (even if not obliged to, Rule 23.a.ii) which again must be located higher than the forward one, thus dictating to mount the forward light lower than the mizzen height.
If I had a two master I’d certainly opt for two bright LED steaming lights.


I have had issues with several AIS transponders. One from heat issues, one from a bad automatic antenna switch and the last from a damaged coax cable installed on a brand new trawler. Imagine traveling through N. Y. harbor and seeing only five AIS targets.

My mother in-law checks the the performance of our transponder using the Marine Traffic network. I find out quite quickly if something is not working properly.

Marc Dacey

I have a father-in-law who was a one-time yacht designer. I think he can be relied upon to perform a similar function. It’s a great way to self-check.


Interesting article and presented a number of issues that I may need to check on our AIS. Last winter passages across and returning from Cuba to Key West we experienced both a lot of traffic, as well as problems both with lights and AIS. While we carry max light requirements, we found a lot of sailing vessels that had little or no lights. One claimed that they saw us on AIS, were running parallel to us, but we saw no lights nor AIS signal. Large commercial vessels were clearly visible, we could track them through the night, and even alter course to avoid them. We also had a tug, with a barge tow, he called us to tell us he had a 1200 ft cable on the tow and not to cross behind him. He claimed to be in front of us moving west to east and saw us on AIS. We spent 20 minutes searching for him, no lights, even though he claimed he had them on, no AIS target, and nothing on radar ! Twenty minutes later after repeated conversations he suddenly pops up on AIS… behind us ! Still believe he saw another sailboat, but don’t understand why the AIS target took so long. I will check our cable, thanks for the advice, more because we regularly found AIS targets that we knew were nearby, but not show up for extended periods of time, then suddenly appear.

Marek Nowicki

I think I renew few weeks ago. Could you check your records and let me know?





Interesting as always.

I am struggling with an unreliable AIS :

It is a weatherdock transmitter TRX in a Raymarine network.

I get a message ” No GPS signal since 30 minutes” with alarm on the Raymarine cw 120.

So we changed the original GPS antenna for a Garmin that has a good reputation I guess with a new cable. And still get the same message…

I suspect a connection problem since some times it works and some times not.

When all seems to work I can get a signal from commercial boats up to 70 nm.

From yachts it is usually between 1nm and around 10 nm.

Our AIS antenna and Gps receiver is on a radar pole 4m above water.

Any advice is welcome sonce AIS is a major improvement on security… when it works.

Thank s

S/Y Hibernia II HR46

Patrick Genovese

Having a vhf antenna mounted on a pole is a good idea as a backup vhf antenna but you need to be aware of the fact that the lower the antenna the shorter the “radio horizon” aka line of sight distance. Personally I use a splitter so that the AIS share the main vhf antenna at the mast head, although I also intend to add a pole mounted vhf antenna as backup antenna.

Also check for sources of interference to your VHF radio. A very common source of interference are LED replacement bulbs some of them emit a substantial amount of RF noise. Other sources of RF noise are equipment like laptops, tablets etc. Using the masthead antenna tends the help by putting some distance between the noise sources and the antenna. The signal strength of an RF source follows the inverse square rule so doubling the distance from an interference source quarters the signal strength.

It is also very important that the antenna and cable installation are up to scratch it is very easy to mess up an installation by for example kinking or bending the coaxial cable too tightly resulting in a substantial increase in losses in the antenna system.

You can test for likely sources of RF noise by “sweeping” with a handheld vhf with its squelch set to minimum. If your radio supports it listen on CH 84 to 88 that listen on frequencies pretty close to the AIS frequencies or else use a scanner on 161.975MHz and 162.025Mhz. If you detect a lot of radio noise try switching off equipment to identify the source. What you do if you identify a local interference source will depend on what it is. You may be able to shield it or its supply cables or simply relocate the equipment.

With respect to the GPS antenna line of sight is not an issue because the GPS satellites are in orbit at an altitude of approx 20,000km. You mentioned that the GPS antenna is sited close to the radar, is it in the radar beam’s path ? It could be that your radar is swamping the GPS receiver with RF energy and that is why you could be losing your fix. An easy way to check this out is to turn off the radar and see if you have GPS issues. Is there something that is creating an RF shadow and shielding part of the sky e.g. a solar panel sited above the GPS antenna.

Also check your plotter diagnostic pages to see if you have errors on your NMEA network bus. A high error rate could be an indication of a wiring fault.

Hope this helps…



Hi Foster
From your description it sounds like you are relying on your plotter’s GPS antenna for your AIS. AIS transponders are required to have their own GPS receiver and antenna. If you did not connect an antenna directly to your AIS transponder than it is no wonder it complains about poor signal.

Patrick Genovese

Having been an very active and very hands on ham radio operator for about 15yrs where my main focus was the vhf, uhf and microwave bands I have a fair amount of hands on experience with antenna systems, coaxial cables and minimizing system losses.

Back to boats… & Antennas.

I have registered a significant improvement in my vhf performance by switching my vhf antenna cable from RG58 to Airborne-5 which is much more efficient than the typical RG58C/U that is typical of most VHF antenna installations on boats. The nice thing about Airborne-5 is that it is the same thickness as RG58 so the “mechanical” side of the installation does not pose additional problems.

There are other alternatives such as HYPERFLEX 5 and ULTRAFLEX 7 that provide even better performance yet keep the cable size reasonable. The only down side as usual is cost. My decision to go with Airborne-5 and not something even better was mainly down to availability at a reasonable cost. (I would have had to import Ultraflex/Hyperflex directly and the Minimum order qty was 100m)

RG58C/U: 22.10dB/100m 6.73dB/100ft
AIRBORNE 5: 12.85dB/100m 3.92dB/100ft
HYPERFLEX 5: 11.44dB/100m 3.49dB/100ft
ULTRAFLEX 7: 8.20dB/100m 2.50dB/100ft

The attenuation figures above are quoted @200MHZ so the actual attenuation at Marine VHF frequencies will be a little lower (better). CH 16 is at 156.800 MHz, AIS1 CH87B 161.975 MHz & AIS2 CH88B 162.025MHz

Note that a 3db increase/decrease in attenuation will result in a 50% loss/gain in power reaching the antenna when transmitting or reaching the receiver when receiving.

I have observed a marked improvement in the VHF radio performance mainly being able to pick up weaker stations further away that would have been out of reach previously. In so far as AIS i will pick up Class B consistently within approx a 20NM mile radius and Class A targets up to about 30 to 60NM.

Note that range will mostly depend on antenna height which will significantly impact the “radio horizon”. 20NM is about the upper limit for 2 sailboats with an antenna height of about 45ft above sea level. You can sometimes exceed the typical line of sight limit by getting a helping hand from atmospheric conditions that bend (“refract”) the radio signal over the horizon this effect will typically be more pronounced in summer where ionization levels in the atmosphere are higher.

I tested the DC resistance of the old RG58 as well as its attenuation using a calibrated RF power meter and it was close enough to spec to put down differences to measurement errors, basically its performance had not deteriorated significantly in about 5 years. The installation was a very good one with everything properly sealed and protected from corrosion etc.

One key factor in the installation is to avoid introducing unnecessary losses by:
a) using the absolute minimum number of connectors (avoid having a connector at the mast base if possible).
b) use high quality connectors of the correct type/size for the cable you are using.
c) don’t coil up excess lengths of cable
d) respect minimum bend radius
e) Protect exposed connectors (at the antenna) with anti corrosion gel and self amalgamating tape. Also make sure that exposed lengths of cable are properly supported and protected to avoid fatigue and chafe.
f) don’t be tempted to install a high gain vhf antenna as the radiation pattern would flatten out (like a squashed donut) which means that when heeled most of the radio energy is either beamed up into space or aimed at the water. A 3dbi gain antenna is probably the best choice for a sailboat.

Hope this helps..


Marc Dacey

This is great information. Thanks for your data points.

Matt Marsh

Agreed on all points, Patrick.

People often seem to think that cables and connectors are either lossless, or have some nominal but low loss. It’s just not true. Sure, that connector may be rated to lose only 0.2 dB when it’s working perfectly…. but once there’s a bit of saltwater in it, or the contact springs weaken, it might lose 2 dB. Or more.

I have spent more time troubleshooting connector and cable faults (impedance mismatches, flaky connections, mysterious high losses) than *all other problems combined* in RF systems.

Other industries that rely on RF are, increasingly, moving to designs where the RF stage is embedded within the antenna assembly and the long-distance wiring is digital. Marine VHF and AIS aren’t there yet, but it might be coming.


I asked a Croos-Channel ferry captain about the visibility of yachts at night-time.

He would like to see them with a masthead strobe light.

The important thing for him was that we be seen.

This was however many years ago.


A couple of years ago I had a goblin on board.
During the night, my AIS reduce its performance significantly, as well as my VHF transmision and reception.
As I use the same antenna for both equipments, I supposed a problem should be affecting the splitter. I check it, everything was OK. The goblin was still with us. I replace the splitter, and this magic passenger was still happy. Maybe some kind of night effect? It seems strange.
At last, after some time, I could get rid of him. The solution was to change the led bulbs of the tricolor and anchor lights on the top of the mast. Maybe its electronic circuits affected the antenna or/and the cable, who knows.
As this story comprise both issues, I found this could be interesting and useful, and maybe someone knows the reason.
Thank you very much for your site.

Matt Marsh

RF interference from “drop-in replacement” LED bulbs is surprisingly common. I’ve had some success in mitigating it with clip-on ferrite chokes on the power wires to the LED unit, as close as possible to the bulb.
The better solution, though, would be for LED bulb makers to comply with FCC and other regulations regarding interference on radio frequencies. It’s not an inherent flaw in LED technology, it’s just sloppy implementation of the driver circuits.

Johan Skylstad

One thing to be aware of when replacing conventional bulbs with white LED is that the white is made up by mixing different fluorescent on a UV LED. These only give a “virtual” white and work very poorly when put behind red or green glass in a nav light. The green component does not quite match the green in the glass and hardly any light slips through. On white NAV lights this is not a problem. I changed my bow BiColor to a real LED after a frightening epsiode a few years ago.

Charles L Starke

Hi Johan,
Do you mean real incandescent?
My mast is coming out next winter; does anyone have a recommendation for red over green lights, model and make, LED etc.? Those recommendations for this make real sense!
Thanks and best wishes
Charles Starke
s/v Dawnpiper

Johan Skylstad

Originally i had put a white LED bulb in my old BiCol but changed the whole assembly to a LED navlight after this episode. Retrofitting a LED bulb in a assembly designed for incandescent is what does not work when it comes to the RED and GREEN. White is not to bad.

Francisco Moreno

To the list of potential analog problems John lists, i.e., antenna, antenna cable, etc., I should add a curious one that is a digital (computer) issue.

We run two separate chart plotters at the helm station. A B&G Zeus 12 (2013) and a B&G Zeus2 7 (2015), both with the latest software available for each. While 99% of the time both plotters will show the exact same targets… there is the 1% when the Zeus2 will show additional targets not shown on the Zeus.

I have seen this rare event even with large cargo boats that were as close as a couple of miles away. I double-tested by zooming in, out, setting same scale on both plotters, and by going to the “list of targets” screen (i.e, a text screen, not a chart with icons). Present on one plotter, absent on the other.

Both plotters are getting the same data from the same NMEA 2000 net from one single B&G AIS on a dedicated cable run to a dedicated AIS-only antenna. It stands to reason that for some rare cases, one plotter filters out certain data that the other does not. I think this is some sort of software error. Could this happen on other brands and models? Possibly.

Bottom line, as John says, these are recreational-grade products. Do not blindly trust them. Keep your eyes open.


What is worse, coming to rely upon an AIS that is only telling you half the story or having none on board and being very scared in high traffic situations? Kind of the definition of being between a rock and a hard place!

Coming upon a panga longliner with only a lit cigarette for lighting 15 miles off the Mexican coast in the middle of the night is no fun either. Or a tug with a tow a half mile behind that is lost in shore lighting—. If you see a strobe while off the coast of Oregon or Washington you can be sure its just a crabber or fishboat catching some shut-eye—-. Thats the way it works in the real world. And why I feel safer the farther away from land I get.

Jay Peters

Thanks for raising these important points. I learned a valuable (if scary) lesson a couple of years ago about the lag time to refresh of my Class B AIS. A dredge boat which had been stationary for about an hour suddenly turned and headed at 11 knots for the shore to dump his load of sand. We talked on the radio and he said he was going to pass well ahead of me. As he got closer I was looking directly at BOTH his red and green lights. I called again, stated my (growing) concern and was again reassured he was passing well ahead. I then lit my sails with one of those gazillion watt spot lights and was amazed by how quickly a 300′ dredge boat could do a U-Turn. We talked again and he admitted he was looking at the AIS and not my clearly visible lights — and my AIS position was from nine minutes ago! So for close in maneuvering, John is right, make sure they have you visually! Jay

Dick Stevenson

Hi John,
I suspect an important reason for dim, hard to see nav lights is a hazing/crazing of the plastic lenses from UV. A stroll around any marina will reveal a significant percentage of boats that would be hard to see at night. The few I have mentioned this to have said they rarely/never run at night (the same answer is given by those who pull their inflatable up their stern obscuring their stern nav light). But, in my opinion, a boat should always be ready to safely run at night
It is my experience that 10 years is about the limit for these plastic lenses, less if in the tropics and more if in the higher lats. Some companies allow lenses to be replaced without replacing the whole fixture.
My best, Dick Stevenson, s/v Alchemy

Maurice Hollingsworth

Earlier this year we were crossing from Great Sale Cay, Bahamas to Cape Canaveral, Florida. About half-way across the Gulf Stream, a ship we had seen earlier in the night appeared again on our AIS. Initially it stayed quite distant. However, suddenly it appeared close – within a nautical mile. We were on a collision course with little time for correction. The ship had sought a pilot boat earlier so we were quite confident the ship was elsewhere than shown on the AIS. There were no nav lights to be seen. However, we knew this was no time to make incorrect assumptions. We turned 90 degrees to port. Unfortunately, I had not yet read John’s suggestions about rigging the preventer so it was not as incidental a tack as one would hope. (Thanks, John. I appreciate all the guidance.). The “ghost ship” on AIS stayed in place as we continued to move.

We use Vesper’s AIS in combination with a couple of iPads (one for backup). We have used it for three years without incident. It has worked very well. This incident came as a big surprise. I rebooted the iPad once we were clear of the ghost and tried a few other strategies before it finally disappeared.

Have others experienced similar “ghosts?” Any thoughts on possible sources of such a problem? Thank you, Maurice.

Maurice Hollingsworth

Hi John,
Thank you for the feedback. I purchased a Vesper XB-8000 which does not have its own screen. It uses a wifi signal transmitted to the ipad where iNavx does the interpretation. To follow-up, I will double-check the wifi signal and look more closely at the software consideration.

I appreciate the comments regarding COLREGS and have given close thought to our circumstances. I was incorrect in saying we “tacked” to port. Actually we turned to port which moved us away from the ship and the ship’s course. We resumed course later when the ship disappeared from our screen and we were further certain it was an AIS problem. The navigational description is best shown in the following diagram (pardon the rather scratchy drawing):

I welcome further thoughts on this navigational strategy, which I am thinking is within directive and spirit of COLREGS. Thanks again.

Dick Stevenson

Hi John,
One thing that I have always appreciated about you and the AAC site is the willingness to be realistic and the willingness to share thinking processes.
Your answers to Maurice is a case in point. Many an “expert” would have made a diagnosis according to Colregs, given a prescription of what to do and left it at that (and also would have left some vague implication that the choices were obvious).
I agree with your advice to Maurice. Sometimes it is possible to just slow down for a bit letting the ship get ahead rather than the work of a jibe (I have not seen the diagram).
Speaking of jibes, it has been my observation over the years: that most cruising boats are not well set up to jibe safely and easily. It then becomes something that we are un-willing to do and that leads to (sometimes) to waiting too long (similarly reefing should be easy) and problems.
My best, Dick Stevenson, s/v Alchemy

Terry Thatcher

On John’s recommendation, we purchased an ICOM stand-alone AIS before we went offshore bin October, 2016. Used a splitter and a new masthead antennae tuned for VHF and AIS. After 10,,000 miles around the Eastern Pacific, I can report that both transmission and receipt of AIS signals was very good. I can also say that whenever I called a commercial vessel and announced that I was under sail, they uniformly changed course if I asked—for instance, when we were sailing fast wing and wing and did not want to jibe. In addition, my wife and daughter tracked us all around the Pacific using one of the tracking sites. The $1,000 for that small AIS was a great investment.

Christopher Columbus

Hey everyone,

I’m a Merchant Mariner and just wanted to say that from the perspective of a bridge of a large commercial ship, AIS is far more useful when trying to acquire small recreational craft (ESPECIALLY at night), regardless of whether a radar reflector is being used or not. It’s commonplace for us to pick up an AIS target well in advance of a radar target (if we even can get a radar target). So for what it’s worth, the first piece of electronic equipment I’m adding to my new boat is an AIS transceiver.

Hope this adds some useful perspective.


Dick Stevenson

Hi Chris,
Thanks for your perspective. It has always been my thought that discerning much data from a bobbing and weaving masthead tricolor from a few miles away would be challenging. I have spent time going through large offshore windmill farms, often at night, and their myriad of support vehicles scooting around in unpredictable patterns. I noticed, after getting a transmitting AIS that, 4-6 miles out, many of these vehicles would make often subtle course changes, as they knew what my course was and that I was likely to maintain course and speed. It was a really appreciated relief not to be doing “the dance” and I found I needed to hale an approaching vessel far less often.
My best, Dick Stevenson, s/v Alchemy