We were three miles off Roscoff when the fog came down like a dropped curtain. One minute I could see the Ile de Batz light, the next I could not see the bow. The tide was running, there were rocks to leeward and a ferry due, and I remember thinking, with sudden clarity, that I was very glad of the small dome on the radar arch. That day made a radar convert of me. Whether it should make one of you depends entirely on where and how you cruise, so let me lay out the honest case rather than just selling you a box.
The north Brittany fog problem
This is not the Mediterranean. The north coast of Brittany and the western Channel are among the foggiest waters in Europe, and the fog here is the bad kind: thick advection fog that rolls in off a warm sea, sits for hours, and reduces visibility to a boat length. It does not burn off by mid morning the way a coastal mist does.
Combine that with the other hazards of this coast, big tides, rock fields you navigate by transit, and a steady stream of commercial traffic, and you have the one stretch of French water where radar genuinely changes your safety margin. Before you cruise it, understand the conditions, because the way fog on the French Atlantic coast behaves dictates everything about how you plan a passage here. The kit follows the conditions, not the other way round.
What radar actually gives you that AIS does not
The clever objection is this: AIS already shows me the ships, so why pay for radar? It is a fair point and it deserves a straight answer.
AIS shows you vessels that transmit AIS. That is most commercial ships and a growing number of yachts. Understanding how to use AIS in French coastal traffic is genuinely the cheapest collision avoidance upgrade you can make, and for open water shipping it is often enough.
Radar shows you everything. The fishing boat with its AIS switched off, the unlit yacht with a flat battery, the moored buoy, the rock, the squall line, the coastline itself when you are feeling your way into an anchorage blind. In Brittany the things most likely to ruin your day, an open boat lobster fishing on the edge of a rock field in fog, do not appear on AIS at all. Radar and AIS are not competitors. They answer different questions, and in fog you want both. The radar tells you what is there; the AIS tells you who it is and where it is going.
The cost and the power, honestly
Modern solid state radar is a different animal from the old magnetron domes. A current solid state dome such as a Raymarine Quantum is an 18 inch radome with pulse compression that gives clean short range detail down to about 6 metres, which is exactly what you want when feeling into a harbour. It is also far kinder on power, drawing a fraction of what the old units pulled, which matters on a sailing boat at anchor or on battery.
The money is real, though. A solid state radar dome on its own typically starts around 1,200 euros and rises from there, and that assumes you already have a multifunction display to plug it into. If you do not, you are also buying a radar capable plotter, which is why I always say to choose a chartplotter for French waters that can grow into radar even if you fit the dome a season later. Add a mounting on the backstay or an arch, cabling and installation, and a realistic all in figure for retrofitting radar to a boat that has a suitable plotter is 1,500 to 2,500 euros.
That is not nothing. It is roughly a season of marina fees, so the decision deserves thought rather than a reflex yes.
When you genuinely need it, and when you do not
Here is my honest cut.
You should seriously consider radar if you cruise north Brittany, the Channel Islands approaches or the western Channel regularly, if you make passages that cannot always wait for perfect visibility, or if you sail short handed and want another set of eyes when you are tired. On this coast, on a boat that goes out in marginal conditions, radar moves from luxury to sensible safety kit.
You can probably manage without it if your cruising is Mediterranean, where fog is rare, if you only ever sail in good visibility and are happy to sit in harbour when it is poor, or if your budget is better spent first on AIS, good charts and a reliable plotter. For a fair weather Med sailor, radar is the wrong place to spend the next 2,000 euros.
The honest middle path, and the one most thoughtful Brittany cruisers take, is to buy a radar capable plotter now and a dome when the budget allows, having first nailed AIS. That sequence gives you the biggest safety gain per euro and leaves the door open.
If you fit it, learn to read it
A radar you cannot interpret is worse than none, because it breeds false confidence. The screen in fog is a confusing mess of returns, sea clutter, side echoes off your own rigging, and real targets, and telling them apart takes practice. Switch the radar on in good visibility, on a clear day with traffic about, and learn what each thing on the screen corresponds to outside. Practise the EBL and VRM, the bearing line and range ring, until plotting whether a target is closing is second nature. Set up a guard zone so the radar warns you of a target entering a ring around the boat while you concentrate on pilotage.
The day the fog drops three miles off Roscoff is not the day to learn what the buttons do. Do that work on a sunny afternoon, and the kit will repay you the first time the curtain comes down.
The cheaper kit that comes first
Before you spend four figures on transmitting radar, there are two cheap pieces of fog kit that every boat on this coast should carry, and they cost a fraction of a dome.
The first is a good radar reflector or, better, an active radar target enhancer. A passive reflector improves the echo a ship's radar gets off your hull, which on a small fibreglass yacht is otherwise feeble. An active RTE, which listens for a radar pulse and answers it, makes you far more visible and costs a few hundred euros rather than a few thousand. It does nothing for what you can see, but it helps the ferry see you, and in fog that is half the battle.
The second is a proper fog signal and the discipline to use it. A foghorn, the right sound signals for your situation, navigation lights on in daylight murk, and a crew posted forward to listen as well as look. None of that is glamorous, but on this coast the boats that come to grief in fog are usually the ones that stopped doing the basics, not the ones that lacked a five thousand euro electronics suite.
If you are on a tight budget and cruising Brittany, spend in this order: a good reflector or active target enhancer, AIS, then radar when funds allow. That sequence keeps you visible and aware long before you can afford to be all seeing.
The verdict
Do you need radar for fog on the French coast? In the Med, almost certainly not. Cruising north Brittany and the western Channel with any ambition, yes, or at least buy toward it. Fit AIS first because it is cheaper and shows you the big traffic, then add a solid state dome when you can, and spend an afternoon learning to read it before you ever need it in anger. On the foggiest coast in France, that small spinning dome is the difference between navigating blind and navigating with your eyes open.
