The Offshore Voyaging Reference Site

Navigating in Fog, Part 1, The Tools


Hands up all those who like sailing in fog. What…no takers? I think I can honestly say that I’ve yet to meet anyone who actually looks forward to passagemaking in fog, although I’m sure there must be one or two confirmed masochists out there who do.

Newcomers to cruising have every right to be concerned about their first forays into seriously reduced visibility, but even at the other end of the spectrum I’m well aware that there are seriously experienced cruisers who blanch at the thought of fog, and I can understand why.

But with thought and preparation, dealing with fog can become just another aspect of cruising to be safely negotiated, like any other of the challenging parts.

Now by fog, I mean the real stuff, not just mist, the sort of reduced visibility that anyone should be able to cope with.

In the early years of my sailing career my friends and I used to head off many Friday evenings to cross the English Channel, where there was always a high likelihood of fog, especially north of the Channel Islands.

Somewhere in my photo archive from those days I have a pic I took from the cockpit where one of the crew is only just discernable standing in the bow…in a 27-ft boat. That’s fog! In those days we couldn’t afford such luxuries as radar, which made life perilous indeed when we happened to be caught in the middle of the shipping lanes amidst an array of bleating fog horns—it still retains the capacity to make me shudder.

But today, with the amazing array of technical equipment we can call upon to assist us—radar, AIS, plotters—the odds have swung substantially in our favour.

So, imagining that you’re planning a cruise to somewhere where fog is an ever-present challenge, here are some points to consider:

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Conor Smith


Nice article! Could you please clarify the life of the magnetron and how switching it on/off often, can lessen its life? Do you mean, turning on the radar ofen and leaving it on standby, without transmitting, is bad for it? Or simply switching often between standby and transmit is bad for it?
thanks conor

Colin Speedie

Hi Conor

as I understand it, the part that reduces the life is simply turning it on (i.e. activating the magnetron), even if the set is left on stand-by and not actually in use.
On many of the boats that I’ve sailed on, where a multi-function display (MFD) is used, the radar feature has been left enabled, so that as soon as the MFD is switched on the radar goes through its warm up cycle and then remains on stand-by. You can often hear the radome go through it’s routine, which gives this away. All you need to do is to go through the menu on the MFD and de-activate the automatic warm up and you should have no problem.
This is what we have done with our set. Then when we’re in an area like Nova Scotia where fog can be a regular feature we re-enable the automatic warm up, then the set is ready to go instantly if we need it.
Best wishes

Dick Stevenson

Hi Colin,
A really nice article. Thanks for the writing and for all the data collection you must have done.
As for the confluence of fog, helmsmanship, and incoming data, I almost wish for the days where I would just be on the helm and the only incoming data was from my senses. On Alchemy, we have moved toward the SOP of having both of us active in fog when in any sort of congested waters or near shore: one of us on the helm and helm alone (unusual in itself as we are usually on autopilot of some sort) so reactions can happen swiftly, and one of us on the instruments and calling out information. Alone, it is just too difficult to process and evaluate the incoming data from AIS and radar etc. and then to change focus to what is actually out there: what you can see, hear, smell etc. It takes just too long to transition.
Heavy fog is just hard work to do safely.
My best, Dick Stevenson, s/v Alchemy

Colin Speedie

Hi Dick
Your description of how you handle fog in busy areas and close to shore is exactly the same as our own. The helmsman does that and looks and listens. The other crew member looks at all of the electronic inputs and calls the shots. As you say, otherwise there’s too much information for one person to process.
There will be more on this in the next parts of this piece, so I’ll say no more, except that, yes, navigating in thick fog is hard work!
Thanks for the compliments – much appreciated.

Rob Gill

Hi Colin,
Excellent topic and intro thanks – especially as we are going through the Cat 1 certification process at the moment. Two comments and questions if I may:

Your comment that ship manoeuvres “tend to be relatively small (single digits), so a large one may signify an entry to a port” is both insightful and a moot one, particularly at night or in poor visibility. As a professional navigator (all be it 30 years ago), we were trained to make our changes of course or speed “POSITIVE” as required in Rule 8 (a) of the collision regs. In poor visibility or at night this was doubly emphasised, being important to be “large enough to be readily apparent to another vessel observing visually or on radar” as required by Rule 8(b). You will for sure have noticed ships making small alterations in good visibility at long range, especially in busy shipping lanes, where ships will often avoid large alterations of course being confined by the presence of chart boundaries and other vessels. But unless so constrained, my approach was ALWAYS to show the stand-on vessel (irrespective of size), a change of coloured nav light at night or equivalent aspect change by day, whatever the visibility.

Then a cautionary tale about radars and container ships, especially those with high deck stows. Some container stacks can cause “spurious” small echoes rather similar to those of a small craft. On one vessel I was on we would pick these echoes up at about 4nm, and they would remain on a steady relative bearing only to disappear at less than 0.5nm. I was warned about this by the Chief Officer as he handed over to me for my first watch leaving Le Havre, heading for the Channel in misty conditions. Sure enough, after about 10 minutes right on dusk (doing over 20 knots) about 30 small echoes popped up on our starboard bow at around three miles. Nothing visible through binoculars. Determining they were probably these “spurious” targets I stood on, but sheepishly asked my lookout to take the wheel of auto-pilot and keep an eye out. I remember his shake of the head and look of …”newbie”. Then, at about 0.5nm, a French racing fleet emerged out of the gloom like ghostly swans drifting with no wind or nav lights. Too late to avoid them, we zig zagged between with me running from bridge wing to bridge wing calling helm commands. I was looking vertically down into some cockpits we were so close at times – talk about radar “crying wolf”!

Then one question – the Echomax 180 you referenced has a reflective area equivalent to 8msq (in ideal conditions). The Cat 1 requirement is minimum 10msq for offshore. The larger EM230 exceeds this by double, but at a cost of some weight and significantly more windage up the rig. Like you I am sceptical as to their efficacy in a seaway and am sure you have considered all this carefully – what have you elected to use Colin and why?
Best regards,

Colin Speedie

Hi Rob
I absolutely agree that making a ‘positive’ course alteration (and early) is the best practice. In most cases this should be around 50 degrees or to show the other nav light if at night. And I’m glad t hear that this was your won training and practice too. But I’m not sure it’s the same today.
My guess from talking to ship’s officers both in person and on the VHF couple to my own observations of ships behaviour suggests that there is far more confidence in equipment (which may be misplaced) and so the tendency these days is to ‘cut it fine’. I have hardly ever seen a big ship make a major course alteration for a yacht in any case, no doubt for many of the reasons you state, but then I did an awful lot of sailing in the English Channel.
Out on the ocean I have watched ships bearing down on us, watched the radar and AIS and come to the conclusion that they are not going to alter course for us and picked up the VHF mic and even them a call, only to be told ‘ yes, we’ve got you there, don’t worry, we’ll pas 1/2 a mile around your stern’. Which seems to indicate to me that their radar is a lot better than mine….
Maybe it’s a bit like people who drive safe cars far more aggressively?
None of which, by the way, is meant to suggest that ship’s officers today are any less conscientious. I think that most ships officers are good, safe hands.
But they are human, with all the possibility for error that implies – see your own comment about ghost echoes and container ships, a salutary tale if ever there was one.
Finally, your question. We have a tube type reflector for insurance purposes, but I place no faith in it whatsoever. Your point about the maximum surface area required is correct and the simple point is that to achieve that figure would require a reflector so large it would be impractical for use aboard the size of craft we’re talking about here.
Instead we have radar, AIS, eyes and ears on watch as required and we’re encased in 15 Tonnes of angular aluminium in the ‘keep water out’ position – which paints up very nicely indeed on radar, as several friendly officers of the watch have told us!
Best wishes

Rob Gill

Hi Colin,
We are away cruising in our NZ summer hence the delay in replying.
Where we sail the shipping traffic volumes are so low that we just keep out of the road of any big ships whether we are the stand-on or give-way vessel. We are cruising they are working! I find your observations Quite disturbing. Let us hope in restricted visibility these “professionals” would make their course alterations more positive and observable on radar. We would have failed our radar endorsement for any less!

Dick Stevenson

Hi Rob & Colin,
I also have seen few commercial vessels make big course changes: the rare exception is I have hailed them on VHF and they may not have seen me or felt (like I did) that they were cutting it too close. I have felt, since getting AIS tx capability, that vessels will make minor adjustments to their course 4-6 miles out to clear us. I do know, that I need to communicate with others less frequently with AIS tx.
As to CPA distance, unless in congested waters, vessels will get a call from me generally if their CPA is less than a mile. Under a mile, there is just too little time for safe maneuvering or too much chance for mis-communication. I do not mind if they cut it closer after we have established a VHF comm.
BTW, as a method of establishing my seriousness when I think things are a little loosy goosy or a vessel is not responding to my hail, I may announce the names of the vessel I am attempting to communicate with and that I am talking on ch 16 high power (usually I am on low power ship to ship) and then state my concerns. I do this rarely and only when I want/need action, but saying I am on high power does flag that others may be monitoring what is occurring and listening to my concerns. Most times, early on, I will adjust my course if it does not undermine my obligation to maintain speed & course.
My best, Dick Stevenson, s/v Alchemy

Fred Vithen

We are in the progress to to change our old Simrad, probably from 2000.
Since we bought our alu Koopmans in NL 2014 (we are second owners) we haven’t had much use of a radar doing the Canals from NL to Black Sea and then basically only doing day sailing in the Med.
Next season though we are planning to cross over to Islas Canarias in September and then wait for the trade winds to establish. 2018 January we will most probably cross the pond via Cape Verde.
Means we need a functioning radar.
Our yacht is from 2001. A proper deck house boat (not a Nautical motor sailor) made of aluminium, 22 tons, 46 feet.
We installed an iMac in the protected deck house with Navionics running with a separat GPS and a AIS B transponder (digital yachts).
As 2nd backup we have a iPad Waterproof, Nude, protected.
Our radar is mounted at the aft on a foldable (on the old canals as you probably know you have to fold it sometimes due to very low bridge clearance) “mast”.
So far our idea was to, maybe, buy the WiFi Furuno and replace the old Simrad.
Means the radar display will be the iPad.
I’m not so happy about mixing my plotter with a radar display. I rather have them separate.
Do you have any experience or shared information about this radar.
Crossing the pond it will most probably just be used for spotting squalls.
We had some scary encounters with small wooden fishing boats not showing on the radar outside India (sailing on another yacht that time).
Will this radar cope with that, you think?
Thank you for sharing valuable information.
Best regards and a Happy New Sailing Year
Fred Vithen (Swedish), S/Y Sans Peur

John Harries

Hi Fred,

Much as I like Furuno, I would not trust any radar, or any mission critical device, that relies on WiFi.

You will find our radar recommendation here:

Colin Speedie

Hi Fred
I’m with John on this one and would never rely on WiFi for any mission critical device. I’ve seen far too many problems with WiFi and things that don’t matter to trust it yet. The last thing in the world you need is to be stuck in fog in the shipping lanes and the WiFi quits communicating.
Not that the Furuno is all bad news – low cost, simple installation etc. But there are downsides – apparently you can adjust the set for rain clutter but not sea state or gain – without which I wouldn’t want one. Early reports suggest that definition over 8 miles is weak, which seems strange as it’s a 4Kw radome, but that effectively rules it out (for me, at least) as serious tool for ocean sailing, where you use long distance far more for ship and squall spotting. And some features can’t be used on an iPhone, such as range and bearing. But let’s be fair – this is Mark I, Furuno make good radars and who knows but they’ll make this more effective over time.
What I’d recommend would be the stand-alone Furuno colour radar, such as the 1935 interfaced with AIS (which can be done with the correct cable), which is as good as it gets for serious use aboard an ocean going boat of your size. More costly, more to install, but this is a proper tool, fit for purpose.
Your comment about wooden trawlers chimed with me – we had similar problems off Africa and Brazil – even with a fairly good radar they are very hard to spot – but do read part III of this series where I go into some detail on ways to at least improve this tricky subject.
Best wishes

Marc Dacey

Excellent summation, Colin, and because I find it so agreeable, I’m going to assume we are on the right track, and, with our boat show coming up in a couple of weeks, some of those assumptions will be backed by purchases. In the above note, I also assume you meant “What I’d recommend would be the stand-alone Furuno colour radar, such as the 1835 interfaced with AIS (which can be done with the correct cable).” That’s the model you and John prefer, as you wrote in the article.

But you may have meant the 1935 after all, as (confusingly) that is also a Furuno model number from the same “family”.

Colin Speedie

Hi Marc
Off the top of my head I think the difference is actually the radome – I think the 1935 is an open array, while the 1835 has the conventional enclosed radome. A good set, which I like a lot.
Good luck at the Boat Show!
Best wishes


I use PC software Coastal Explorer as a plotter with which I am satisfied. It runs on a laptop hidden in the chart drawer which drives an external monitor at the nav station and a waterproof daylight viewable 1024*768 monitor mounted to the aft end of the cockpit table (large aft cockpit with dual wheels). Both monitors display the same screen and the cockpit monitor has resistive touch which works OK.
I use a Simrad 4G radar with a Simrad NSS7 at the nav station and a B&G Zeus 7 also mounted to the cockpit table.

My learnings and opinions on Radar, AIS and Radar reflectors, based mostly on my own experience and partly and what I read and heard, are as follows:

1. I can’t recommend the 4G radar because it is unreliable, its mid-range performance is deficient und its MARPA feature is useless.
The fact that it uses little power, turns on instantly and never needs a new magnetron are irrelevant if it doesn’t deliver on the core features of a radar, which should be the reason to have one in the first place. I can only guess why it has been so successful and my guess is that many owners don’t really use it, can’t tell good from bad or are not open about their disappointment.
In any case, if you want to judge a radar, don’t do it in port. The 4G will tell you if the slip next to yours is vacant or not but who needs a radar for that?

2. I no longer think radar overlay is important to have.
I no longer run my NSS7 or B&G Zeus 7 in that mode and I would venture the following bet: if 10 ramdomly picked readers of this would be forced to become professional mariners 5 days/week 10hrs/day for 6 months and they would have on their boats a magnificent 24” professional ECDIS system with 24kw 6 foot open array, I bet that by the end of the 6 months 8 out of 10 would have their screens set up as a split screen with chart on one side and radar on the other. The radar-side would also show AIS targets and waypoints but no chart.
For a while in 2013 and 2014, I helped test the reverse-engineered integration of the 4G radar in Open CPN but I turned back to Coastal Explorer and don’t miss overlay at all.
There is a good read here on this:
by Peter Hayden, owner of a Nordhavn 60.

3. The most critical use of radar is assessing passing situations (debatable, of course, but my learning).
I had a hair-raising experience off the African coast with a cruise ship that brought this point home to me. Even though I was the stand-on vessel, I desperately wanted take avoiding action but absolutely couldn’t tell if the cruise ship would pass ahead or astern.
A critical tool for this is ARPA with a *relative* motion vector (not true motion vector such as normal AIS display gives you). If you are on collision course with another vessel, then a relative motion vector of that vessel will point directly at you even if its course is 90° to your own. If it points slightly ahead or astern, that is where that vessel will pass you.
It’s the most basic feature, really, and every Furuno standalone radar, current or past model, has it but none of the MFD offerings of Furuno. Simrad/B&G have it but their vectors are so completely off that it makes no difference if it is set to true or relative. The other vendors I don’t know.
My advice is check for this feature.

4. MFDs are only a second-best solution.
In my opinion there are some valid reasons for having an MFD but really, they only fall in three groups:
– came with the boat
– space constraints
– budget constraints
These days, if anyone tells me of their super-duper new MFD, I lose interest. Closing in on 50 years of age, I realize I have spent an undue amount of the time I am alotted planning and debugging and generally thinking about fancy MFD installations and the latest features. If I were to build a new boat, I would design electronics following the principles:
– professional stuff
– rock solid standalone systems
– PC charting
– NMEA0813

5. Try for a dual-station installation.
I have avoided many a grounding with the chart displayed at the wheel and would not want to be without it. But when we were en route from the Azores to the Isles of Scilly, I never moved to the aft end of the cockpit for days on end. I was grateful to have chart display, radar, instruments and autopilot control at the nav station below deck. It’s where I lived. This will be less of a problem with a center cockpit layout and generally speaks for such boats. But with ours, my wife and me stayed below with the companionway closed much of the time and the heater running and only sticking our heads up for a look around every 15 minutes. And sure, I could appreciate a Boreal.

6. Don’t do self-leveling radar mounts.
Ours is a Scanstrut mounted to a radar pole sitting on the stern scoop 4 meters high. The 4G radome is of average weight and will be less than a typical 24” radome. Even with such a light radome, the Scanstrut was overpowered on ocean passages in 20 knots true. This resulted in the radar overswinging, negating the purpose of the self-leveling mount.

7. Look for AIS target trails
Colin recommends AIS ROT display. Coastal Explorer has a nice alternative: AIS target trails. A light grey line plots the course of the AIS targets so you can easily see course changes after only a minute or so. It’s how I noticed that the cruise ship of the Moroccan coast had finally altered course for us.

8. Radar reflector
I have an Echomax XS RTE (radar target enhancer, active). I can’t speak to its effectiveness but find it reassuring. It’s still working after 6 years with the boat in the water for 2 northern winters. I have used the alarm only on the relatively few ocean passages and then, I forgot to turn it back on after a ship had passed a few times. As a backup I have a smallish Tri-lens passive radar reflector which I selected for the fact that this design suffers much less from heel than the other models. It offers much less area than a larger Echomax but I have it as a backup only. If you get a Tri-lens, make sure you use a mount at the top as well as the bottom (not standard but an option).

Marc Dacey

Henning, I’m sure your observations will encourage a fruitful discussion. Thank you for your detail and your rationale for your choices.

Colin Speedie

Hi Henning
much good food for thought – a few comments:
1. I hope that 4G radar gets sorted out – I really appreciate closer rang target recognition (3M and below) as this is a real asset with fog filled entries to ports, wooden fishing vessels at night etc.
2. Overlaying radar – I’m not a fan either, and I’ll be covering why in the later parts of this post.
3. Overtaking vessels are always hard to call. Thanks of the tip on relative vectors, which I’ll definitely have a look at.
4.I can only agree.
5. If you can afford it – and I’m a little worried about adding anything more than necessary in the interest of maintaining simplicity and reliability. In my view, more = more trouble.
6. This tends to confirm the point I made in the post.
7. That’s an interesting feature, and I can see how it would be useful.
8. If you don’t have a boat that casts a strong reflection, it seems the XS RTE has some merit. Much more, in my view than any passive reflector.
Thanks for the very useful comment.

Marc Dacey

It’s been a few years now since a long-time radar technician of my acquaintance, when asked what the best radars, pulse or thee (then current) 3G radars were for passagemaking, answered “both: pulse for offshore and 3G for approaching the pilings in fog at 3 AM”. While I’ve seen some impressive stuff via Panbo, I’m not persuaded that “one radar to rule them all” quite exists yet.

I look forward to the “why not radar overlay/why not MFD” advice. It’s directly opposed to all the trends in marine electronics, and so likely has real-world merit!

John Harries

Hi Marc,

I think your radar technician friend had been reading too much marketing rubbish from the manufactures of digital radars, or perhaps he sells radars. There is really no need to have two radars since a properly tuned magnetron radar, such as our venerable Furuno 1832, will easily assist you in “approaching the pilings in fog at 3 AM” and the newer 1835 is even better.

AS I have said many times before, we regularly measure range and distance to mooring buoys at close ranges.

No question that digital radars have benefits (and drawbacks), but I don’t want to see our already expensive boats made even more so by a recommendation to have two radars, based on the incorrect assumption that magnetron radars are no good close in.

More here:

Sorry, I know that sounds both hash and contradictory, but I think it’s important to be careful not to adopt marketing hype as fact, particularly when doing so can cost people big money.

Dick Stevenson

Hi all,
It was my evaluation of the research, a decade ago by this time, that the active radar reflectors available were not reliably effective. All who owned one where I asked said variations on Henning’s comment, ” I can’t speak to its effectiveness but find it reassuring”. They sounded great, but were less so in the research I found. I have not seen reports of research to change this evaluation, but am far from in lots of information loops. Has this changed?
With the shaky research on active radar reflectors, I went passive as much simpler and less complicated and needing no power. I went (20 years ago now) w/ a Firdell Blipper on the mast. Research suggests I would choose a Tri-Lens were I to buy now. I also put up a Davis Echomaster (one of the take apart aluminum ones) in a “catch-rain” position to the spreader on passage or when things close down to increase echo making.
A few reports from ship’s bridges have had me easily seen (fg boat).
My best, Dick Stevenson, s/v Alchemy

Dick Stevenson

Hi Henning,
In re-reading my comment, I see that my quoting you could be taken as critical, and I did not mean it as such. In the light of good research and/or field reports, I also would find my choices re-assuring.
My best, Dick

Marc Dacey

Dick, our “S/V Alchemy” is steel. We are seen from space, evidently. The cambered deck also gets jealous looks from SSB operators. They haven’t seen the fluffy slippers we must wear to keep the off-watch happy.


Thank you for this informative article – I am currently in the process of considering my options to install a Radar on my 39′ steel cutter. I would prefer to fit the radome on the mast (more height but more angle when healing) but could fit at the stern on a pole of ‘goal’ posts (less height but less angle). There is lots of commentary so I may have missed it but is there an absolute view on which is better. Also – now we have installed, and put to good use, our two way AIS I question how much extra safety I may actually secure from a Radar for much of the time. I would grateful for views on this observation from those in this place clearly more experienced than myself.

Marc Dacey

I faced the same issue and decided to have our AIS whip off the first spreader and the radome just above the top of that. There’s no sign of them interfering with each other. I note that from Toronto, I can see AIS targets locking up the Welland Canal over 30 miles away, plus Class B boats 25 miles away on the U.S. side of the lake…which is what I wanted by way of early warning and which I expect will be sufficient for the open ocean.

The radar, a Furuno 1815, has worked very well and I am getting better at tuning the gain to see approaching weather, also at more or less 25-30 NM distance. I feel that the radar and AIS are complementary in terms of alerting you of other ships (or shorelines or, soon, AIS-equipped buoyage), and alerting other ships to your presence when even a steel boat (a good radar target) might otherwise be screened by waves or low land. Being able to ID a fast ship (or many fast ships) approaching harbours or TSS zones is a huge advantage.

John Harries

Hi Martin,

I much prefer pole mount to mast mount:

And I don’t believe that AIS, while very useful, is a substitute for radar. There are still plenty of boats out there that don’t transmit AIS, and some that don’t receive. Also radar has many uses other than collision avoidance.

John Harries

Hi again, Martin,

It just struck me that when answering your question I did so based on my own cruising grounds.

So I should add to the above that while we use and appreciate having radar wherever we sail, I think it’s perfectly rational, if cruising an area not given to fog, to not bother to install radar at all, particularly given, as you point out, the availability of AIS for collision avoidance.

Terence Thatcher

Does anyone use fog horns anymore? My radio is supposed to run a horn, but the function is not working. And I don’t want to have tom push a button each minute.. If I have a horn, it want it to be smart enough to blow regularly. Thanks.

John Harries