South Brittany taught me to respect fishing boats more than any other class of vessel I share the water with. The grounds off Lorient, the Glenan and the approaches to Concarneau are working seas, and at dawn the horizon fills with trawlers that do not behave like anything you learned to predict on a yachting course. They turn without warning, they tow gear you cannot see, and the man on the bridge is watching his net and his sounder, not you. Learning to read them is a survival skill in these waters, and most of it comes down to understanding why they move the way they do.
A trawler is dragging, not steering
The fundamental thing to grasp is that a trawling boat is not free to manoeuvre like a ship under way. It is towing a net through the water, sometimes a heavy bottom trawl, and that net dictates its course and speed. The skipper follows the fish and the seabed, which means the boat may suddenly alter course as it works a shoal, or turn at the end of a tow to shoot the gear back the other way. From a yacht half a mile off, that looks like erratic, unpredictable steering. From the trawler's point of view it is perfectly logical and entirely about the fishing.
You cannot anticipate the turns. What you can do is give a working trawler a wide and obvious berth, well clear astern where the gear is, and never assume it will hold a steady course while you cross close ahead.
The day shapes, and what they tell you
The rules give fishing boats a way of telling you what they are doing, and learning to read it transforms how you see a fishing ground. A vessel engaged in trawling shows two cones with their points together, one above the other, in a vertical line. On a boat of 20 metres or more the cones are at least 1.5 metres apart vertically; on smaller boats the shapes are scaled down but the meaning is identical. That double-cone is your signal that the boat is towing and that its movements will follow the net, not the rules of the road you would expect from other traffic.
At night the same boat shows the fishing lights instead of the shapes, and you read those rather than guess. But by day, the two cones apex-to-apex are the single most useful thing to spot, because they tell you to stay well clear and to watch for the unexpected turn.
A boat fishing other than by trawling, with nets or lines out, shows a different signal and may have gear streaming a long way to one side, which is its own hazard. The principle holds throughout: a fishing boat with gear out is constrained by that gear, and you keep clear of it.
Pair trawling, the one that catches people out
The behaviour that genuinely surprised me the first time was pair trawling. Two boats tow a single net stretched between them, working as a pair, and the lethal detail is the invisible warp running through the water between the two hulls. To a yacht approaching, it looks like two separate boats with a clear gap between them, an inviting gap to sail through. Sail through it and you foul your keel or rudder on the towing gear, and you have created an emergency for yourself and a furious skipper for company.
Fishing vessels of 20 metres or more engaged in pair trawling in close proximity to others show additional signals to mark this, but you should treat any two trawlers working a parallel course at the same speed as a pair until proven otherwise. Never sail between two boats that look like they are working together. Go round the outside of both.
Who keeps clear of whom
The rules give fishing boats a degree of privilege, and it is worth understanding precisely because it is easy to overstate. A power-driven vessel and a sailing vessel are both required to keep out of the way of a vessel engaged in fishing. So in the ordinary case, you keep clear of the working trawler, not the other way around. But the privilege has limits: a fishing boat is only required to keep clear of vessels restricted in their ability to manoeuvre, and only so far as possible, so do not expect a trawler to dodge a yacht in a narrow channel.
The practical reading is simple. In open water, you give way to the boat that is fishing. You do this early and obviously, altering course in good time so the skipper sees your intention, and you pass astern and well clear of the gear. Do not stand on your rights against a working boat. You will lose, expensively.
Where the fleets concentrate
The fishing effort off south Brittany clusters around the home ports and the productive grounds. Expect concentrations off Lorient and Le Guilvinec, around the Glenan archipelago, and across the wider approaches as boats steam to and from the grounds at dawn and dusk. If you are cruising these waters, the same care applies whether you are crossing open sea or threading a buoyed channel near a port, and my notes on cruising south Brittany flag the busy stretches.
Fishing gear is not confined to the boats, either. The same grounds are dotted with floating pot and creel markers that can foul your propeller, and that is a hazard worth understanding in its own right; I have set it out in pot markers and creels inshore. Between the trawlers and the pots, an inshore Breton passage demands a lookout that never relaxes.
Reading the fleet by time of day
Fishing grounds have a rhythm, and once you learn it you can anticipate where the boats will be. The day boats steam out before dawn, so the busiest moment on the water is often the grey hour after first light, when the fleet is converging on the grounds and crossing your track at speed with their gear not yet shot. Through the middle of the day they are spread across the grounds, towing, turning, working their sectors. Towards dusk they steam home, and again you get a pulse of boats moving fast on fixed lines back to port.
The implication for passage planning is simple. If you are leaving a port like Lorient or Concarneau at dawn, expect to meet the outbound fleet head on in the approaches, and give yourself room and time to let them pass. A yacht trying to motor out through an inbound or outbound fishing fleet in poor light at the change of day is asking for a close-quarters situation. I would rather time a departure for an hour when the grounds are quieter, or accept that the first half hour demands a sharp lookout and a readiness to alter course repeatedly.
There is a seasonal pattern too. Certain fisheries peak at certain times, the sardine and tuna seasons bring extra boats, and the grounds get crowded in a way the charts cannot show you. Local knowledge from the capitainerie or a neighbouring boat is worth asking for if you are new to a stretch.
Lights at night, and why you slow down
By night the day shapes are useless and you read the boat by its lights instead. A trawler shows particular lights that mark it as fishing, and they can be confusing among the working lights, deck floods and the loom of a port behind. The honest truth is that a brightly lit fishing boat working at night, with floodlights blazing over the deck, can be very hard to interpret from a yacht, because the work lights drown the navigation lights that would tell you its aspect. The answer is the same as in fog: slow down, keep clear by a generous margin, and do not try to thread between boats whose intentions you cannot read. If you cannot work out what a fishing boat is doing at night, treat it as unpredictable and give it the widest berth the water allows.
If you do foul gear
It happens, even to careful crews, and it is usually the propeller that catches a warp or a net. The first move is to take the engine out of gear immediately, because a turning prop winds the line on tight and can damage the gland and the shaft. From there you are into a problem that may need a dive to clear, in cold water, possibly in a tide. If you cannot free yourself and you are drifting into danger, it becomes a call for help, and knowing the French distress and safety call procedure means you raise CROSS calmly rather than in a panic.
The trawlers off Brittany are not out to ruin your day. They are working hard in difficult water, watching their gear and their catch. Read their shapes, give them room, never cut between a pair, and keep clear early. Do that and you will share the grounds with them happily for a whole season.
