The first time I took the Chenal du Four I had read so many warnings that I half expected breaking water from the moment I cleared Le Conquet. What I actually found was a wide, well-marked channel that behaves itself if you arrive at the right state of tide. The reputation is earned, but it belongs to the wind-against-tide days, not to a settled morning with the stream under you. This is the route I run now, written buoy by buoy rather than as general advice.
The channel runs roughly 20 nautical miles from the Pointe Saint-Mathieu near Le Conquet up to the Le Four lighthouse at the northern end, threading between the Finistere mainland and the offshore islands of Beniguet, Molene and Ushant. It is the shortest sea road from North Brittany down to the Iroise and the Bay of Biscay, and for a yacht doing 5 or 6 knots it is the only sensible inshore choice.
The leading lines that hold it together
What makes the Four manageable is that it is built around clear transits, not a single line of buoys you nervously hop between.
Coming from the south, the headline transit is the Kermorvan lighthouse in line with the Saint-Mathieu light and its direction light on a bearing of 158.5 degrees. Hold that astern going north, or ahead going south, and you are in the deep water. Kermorvan is France's westernmost mainland lighthouse, a square white tower that shows a steady white character and is visible for about 22 nautical miles, so you pick it up early. The Saint-Mathieu light sits beside the old abbey ruins on the cliff and is hard to mistake.
Further north the channel hands you on to other marks: Les Plâtresses, the Valbelle buoy, La Grande Vinotiere, and finally the Le Four tower itself standing on its reef at the northern gate. I keep the largest-scale SHOM chart open (chart 7122 covers the channel in detail) and tick the marks off as they come abeam rather than trusting the plotter alone.
Stream rates and why timing is the whole game
The Chenal du Four runs up to about 6 knots at the worst of a big spring, and even on an average tide you will see 4 to 5 knots through the narrows. A boat that makes 6 knots through the water has no useful margin against that, which is why you never fight it.
The tide turns to the south at roughly HW Brest minus 0030 in both the Four and the Raz de Sein further south, and that single fact is the key to linking the two gates in one day. Slack water in the Four falls near HW Brest plus 5 and again near HW Brest minus 1, but treat those as a starting point. Different pilots quote slightly different figures and the real water does what it likes, so I always cross-check the tidal stream atlas for my exact date.
If the coefficient idea is new to you, our guide to reading a French tidal coefficient is worth ten minutes before you go, because every marina office and weather bulletin in Brittany speaks in those numbers and the Four feels completely different at coefficient 45 than at 95. For the wider picture of how the regional gates interlock, tidal streams brittany gates lays out the timings side by side.
A southbound run, step by step
Here is how a typical southbound day shapes up for me.
I start from L'Aberwrac'h, which sits perfectly for staging the passage. If you have not been there, laberwrach first french port explains why it makes the ideal jumping-off point and a comfortable place to wait out a poor forecast. I time my departure so I enter the northern end of the Four to pick up the start of the south-going stream, which means leaving on the tide rather than at a fixed clock hour.
Down past Le Four lighthouse I get onto the Saint-Mathieu transit and let the stream carry me. La Grande Vinotiere and the Valbelle buoy come up in order, the channel stays a comfortable width, and the leading line keeps me clear of the reefs on either hand. The aim is to carry the last of the south-going stream right down to the Pointe Saint-Mathieu, then either turn into Le Conquet for the night or press on for the Raz de Sein, arriving there near its own slack.
If you are bound for the Raz the same day, build the day so you reach it close to slack and read the chenal du four raz de sein passage together, because the two gates are best planned as one continuous piece rather than two separate problems.
What actually goes wrong
The danger is never the tide on its own. It is wind against the stream. A fresh westerly or northwesterly over a strong south-going Four kicks up short, steep, breaking seas, and the same wind over the rougher patches near Le Four and around the islands turns an ordinary channel into a place you do not want a tired crew. My rule for a first passage or with nervous people aboard is a coefficient under about 70 and a forecast that genuinely holds, with no front sliding in early.
Fog is the other one. The channel is buoyed but it is no place to grope around blind, with Brittany Ferries entitled to use it under certain conditions and fishing boats working the edges. If the visibility is poor I simply do not start. Le Conquet and L'Aberwrac'h are pleasant places to lose a day.
Le Conquet as a bolthole
Le Conquet sits right at the southern end of the channel and makes a useful staging port, though it largely dries and the visitor moorings are exposed to the northwest. The Penn ar Bed ferries to Ushant and Molene run from here and from Brest, so expect traffic. I treat it as a tidal stopover rather than an all-weather marina, and if I want a proper berth I carry on round to Camaret in the Bay of Douarnenez.
Northbound is a different rhythm
Everything above describes the southbound run, which is how most visitors first meet the Four on their way down to Biscay. Northbound, the logic flips but the principle holds. You want to carry the north-going stream up the channel, which means timing your entry at the southern end near the Pointe Saint-Mathieu to pick up the new north-going flow, roughly six hours offset from the southbound window.
The transits are the same lines read the other way. The 158.5 Saint-Mathieu and Kermorvan lead is now ahead of you as you come up the channel rather than astern, and you tick off La Grande Vinotiere, the Valbelle buoy and Les Plâtresses in reverse order before the Le Four tower marks the northern exit. From there the route opens toward L'Aberwrac'h and the rest of the north coast. The one thing that changes is the sea state at the ends of the channel, which can be lumpier on the northbound exit if there is any northwest in the wind, so I still want a benign forecast and a sensible coefficient.
Sharing the channel
The Four is a working seaway, not a quiet backwater. Brittany Ferries is entitled to use it under certain conditions, the Penn ar Bed island ferries cross it, and fishing boats work the edges around the islands and reefs. None of that is a problem if you keep a proper lookout and stay in your part of the channel, but it does mean the Four is no place to be head-down at the chart table or distracted.
I keep to the side of the channel that suits my direction, much as I would on a road, and I give commercial traffic plenty of room because they have far less flexibility in the narrows than I do. A clear VHF watch and an eye on AIS for the larger vessels rounds out a relaxed transit. The combination of strong tide and commercial traffic is exactly why visibility matters so much here, and why fog turns a manageable channel into one I will not enter.
A short pre-departure list
Before I slip the lines for the Four I check five things, and they have not let me down yet.
- The HW Brest time for the day and the slack windows built off it.
- Today's coefficient, and whether it puts me in benign or serious territory.
- The wind direction and strength against the stream I will be carrying.
- The visibility, honestly assessed, with fog a hard no.
- The largest-scale chart on the table with the 158.5 transit marked.
Get those right and the Chenal du Four is exactly what it should be, a satisfying, well-paced piece of pilotage that opens the door to the whole of South Brittany. Force it on the wrong day and it will remind you why the pilot books shout. The choice, almost always, is yours to make from the comfort of a harbour the day before.
