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Through France to the Mediterranean

The Gironde Estuary

Will Thomson

The Gironde Estuary, a majestic waterway in southwest France, holds both challenges and marvels for sailors.

The Gironde Estuary, a majestic waterway in southwest France, holds both challenges and marvels for sailors. In the first of this two-part series Imray Commissioning Editor William Thomson shares how he found his way with Imray through this gateway to the iconic Canal du Deux Mers that connects the Atlantic with the Mediterranean.

We moored alongside the visitor’s pontoon in Royan and I opened the engine compartment, checking my makeshift repair on the leaky fuel filter. A routine check earlier in the day, just off Ile d’Oleron, had revealed an alarming high-pressure leak streaming out from where the mechanic in Belle Isle had re-threaded the bleeder bolt. This was not the place to lose engine power; there was a big swell rolling in, the wind had just dropped and we were heading for the notorious entrance of the Gironde Estuary – famous as the launching spot of Blondie Haslers’ WWII Cockleshell expedition to disrupt shipping in Bordeaux – which is not somewhere you want to be when the swell collides with a spring ebb tide. 

The rapid tidal streams wrapping around Ile d’Oleron made it futile trying to turn back, so I turned off the engine and raised the spinnaker, trying to hit the minimum 5 knots we needed to catch the flood which would then push us up to Royan. But the wind vanished and we barely made 3 knots; at that rate we’d arrive at the very worst time, on the ebb in the middle of the night. With two young children onboard that would have been incredibly risky – nearly everyone I later met in Royan told me a story of someone they knew who died at the mouth of the estuary. 

Navigating this waterway requires utmost caution, as emphasized in the Atlantic France pilot book by Nick Chavasse; “Overfalls are severe and dangerous (5m). Do not attempt to enter the estuary in strong winds from the SW through W to N if there is any swell or on the ebb tide. If in doubt, stand off. Particular care is needed between Nos. 2A, 3, 4 and 5 entrance buoys where the channel is narrow and shoals quickly on either side. The tidal streams are very strong and do not always follow the line of the estuary in the mouth; constant checks are required to avoid being set off the intended track.”

As we bobbed in the long-period swell I tried a last resort on the engine and pumped half a cylinder of SikaFlex around the bolt. It worked! With the engine back on and a rise in the wind our speed shot up and we made up for lost time, arriving at the Safe Water Mark bang on time for the beginning of the flood. With massive breakers crashing in a cacophony of whitewater right on the edge of the channel, we obediently followed the lateral markers as the water turned from a deep Atlantic blue to the muddy brown of the Gironde Estuary. By now it was gusting 20 knots and we were absolutely flying.  Our SOG maxed out at 12 knots, most of it the powerful tide pushing us inland and we covered the 20M passage upriver in less than 2 hours, a record for our 31-foot Prout Quest.  

Safely moored alongside in Royan, I took stock of our situation. We had two choices; head around Biscay in October/November and brave Orca Alley, or continue up to Bordeaux and take the Canal de Deux-Mers into the Med. I called my predecessor, Imray’s Commissioning Editor Jane Russell (who I had worked with on my Explorer Guides) and asked her advice. Her reply was typically Jane, clear-headed and concise; “You’re in a small boat with two young kids and an unreliable engine. It’s very late in the season and soon the massive swells will be closing off Biscay ports for weeks on end. You’re there to have fun – take the Canals!”.

Passage planning

In the 1850s, ingenious French engineers completed an inland waterway connecting the Atlantic with the Mediterranean and they appropriately called it the ‘Canal de Deux-Mers’. (Deux = Two/ Mers = Seas). Technically, it’s made of two very different canals that meet halfway in Toulouse; the rustic Canal du Garonne, with 53 locks, connecting Toulouse with the Atlantic, and the Canal du Midi (a UNESO World Heritage Site) with 65 locks connecting Toulouse with the Mediterranean. While boats up to 98 feet can navigate the waterway, you need a beam less than 5.45m and a draught ideally less than 1.5m. While most catamarans are too wide, ours is an old-school 70’s design that measures in at just 4.3m wide, so just about fits in the locks. 

Maximum dimensions for boats in the Canal du Midi
Max. draught: 1.5m
Max. beam: 5.45m

With my mind at ease after committing to our autumnal canal cruise to the Med, I sat down and studied Nick Chavasse’s Atlantic France Pilot Book. By chance we had moored alongside Nick in Ile d’Oleron and I’m a massive fan of his book – he gets the tone just right, highlighting the dangers (of which there are many) but making it feel achievable by sharing simple solutions to overcome them. If you haven’t got it already, treat yourself to a copy! In Nick’s reassuring tone he sets out everything you need to sail up to Bordeaux and with his guidance I broke down the 150km journey into three legs to make sure we always had the flood pushing us along;

1)     Royan to Pauillac, where we would take down the mast. (approx. 55km)
2)     Pauliic to Bordeaux. (approc. 45km)
3)    Bordeaux to Castets-en-Dorthe, the first lock. (approx. 50km)

“As we were travelling inland, the idea was to leave each place at the beginning of the flood.”

We chose Pauillac as a stopping point because it’s the last place you can take down the mast before Bordeaux. As recommended in the pilot book, we called up the capitaine (Harbourmaster) in advance and got the guidance that we should arrive within 5 minutes of High Water. This was taking tide gates to a new level of precision and he explained why timing was critical; “the walls of our harbour don’t go to the seabed, so the current streams through. In a small boat, if you’re half an hour early or late you won’t be able to make headway against the current.” After experiencing our record-breaking SOG approaching Royan, which was mostly thanks to the flood, I believed him. Tidal streams in the Gironde are supercharged, even at neaps.

We left Royan with the flood and rode the tide up to Pauillac, carefully monitoring speed to arrive bang on time. If there was any doubt we were in wine country it was cleared up at the harbour entrance; instead of a red can marking the entrance, there was a vast bottle of Bordeaux red, several feet high. The vineyard vibes were further reinforced during my morning trip to the boulangerie, queuing up with a busload of seasonal workers picking grapes. 

We booked a slot to take the mast down and the capitaine’s assistants strolled over after their long lunch, the scent of red wine on their breath and baguette crumbs in the creases of their shirts. With a mix of my GCSE-French, their Pidgin English and our combined hand signals, we got the rigging loose, electrics disconnected, a strap around the mast connected to a crane and voila! The mast was suspended in the air, then it was lashed on the cabin roof and we were ready for the next leg. 

The Pauillac capitaine called up his colleague in Bordeaux and booked us in on the Pont d’Honneur, bang in the middle of the city. Saying his goodbyes, he gave me one more word of caution; “Don’t go anywhere near the bridge next to the pontoon when the current is flowing, it makes terrible whirlpools.” We may have chosen the relaxed route in talking the canals, but the adventure was still far from over. 

I thanked him for the tip and we fired up the engine, leaving with the LW Slack to maximise the time we had the flood pushing us up to Bordeaux. Looking up from the wheel, it felt strange not to see Luna’s mast rising proudly up to the sky, the myriad of stainless-steel rigging glistening gloriously in the sunshine. Instead, it was all lashed in an undignified bundle beside me, protruding off the bow with an ignominious yellow bucket on the end the protect it in case we hit anything. 

True to form, the tide catapulted us towards Bordeaux and we arrived long before the ebb, staying well away from the bridge as directed. What a spot! Ponton d’Honneur is a gated pontoon right in the centre of Bordeaux, giving you peace and quiet from the crowds while allowing immediate access to the heart of the city. The children ran around a beautifully landscaped square with a thin layer of water designed to reflect the stunning architecture, then we wandered around the maze of streets busting with character. Our cruise down the French coast so far had taken us to the chilled-out offshore islands of Belle Isle, Ile d’Houat and Ile de Re, so it was refreshing to soak up the metropolitan buzz of Bordeaux. Even if you’re not planning a cruise through the canals, I’d highly recommend visiting the city by sailing boat just for the experience. 

“This is one of the things I love about exploring by boat; quite often the pontoons are in the best locations, right in the thick of the action beside the prime real estate.”

The following morning was D-Day for our final push up to the canal entrance at Castets-en-Dorthe. Slack Water was expected for 10am, but a local boatman moored alongside us told me that the river follows its own rhythm; “It depends on so many factors, like how much rain there has been in the countryside – the only thing you can do is wait for the ebb to stop then go!”. I followed his advice and checked the bridge every 15 minutes, gazing down at the monstrous muddy whirlpools, sucking down the occasional tree-trunk that was floating downstream. Luna wouldn’t stand a chance punching through the current. 

But every time I checked the bridge the whirlpools became ever so slightly smaller. Finally, an hour and a half after when Slack was expected, the last vortices dissipated and I ran back to Luna, firing up the engine and unslipping the mooring lines; “We’re off!”. We had six hours to get to the lock at Castets-en-Dorthe, with no safe harbours between us and there. To add to the drama, the river experiences a fortnightly tidal bore locally known as the ‘Mascaret’ that causes a wake of destruction in its path, so we had to make it to Castets-en-Dorthe in one push or the ebb would send us back to Bordeaux with our tail between our legs.  


Many French rivers experience Tidal Bores, rare waves that rumble upstream around Spring Tides. The main ingredients are a tidal range over 6m in a wide estuary that tapers into a shallow and slow moving river. 

I settled the engine into a pitch she seemed happy with an we sat at 3 knots. At that rate we wouldn’t make it to Castets-en-Dorthe in time, but I was accounting for the building flood to give us a boost, which it did with rapidly increasing strength; our speed rose to 4 knots, 5 knots, 6 knots as we raced past vineyards, chateaus and rickety fisherman’s shacks built on stilts over the muddy water. The children poked their heads out the cabin skylights and took turns on watch, keeping an eye out for dark patches in the river - treetrunks – that needed to be given a wide berth.

Three hours in, our speed started to fall. We had reached the peak of the flood and it was now slowing; the SOG dropped to 5.5 knots, 5 knots, 4.5 knots. As long as we didn’t hit the ebb, we’d be fine – but it would be close. I looked around for clues to gauge the river flow; when currents hit an obstruction like a post or buoy it creates a bow wave upstream and turbulence downstream. At first these had been pronounced, but they were gradually becoming weaker. Finally, there was no pattern at all; it was Slack Water and the ebb was about to start. I gave the throttle a slight push – it was a delicate balance between not straining the engine and making sure we got there before the ebb became too strong to motor against. 

Tip for spotting the current

When currents hit an obstruction like a post or buoy it creates a bow wave upstream and turbulence downstream.

Finally, we rounded a corner and the vast lock appeared straight ahead. It looked like a dry dock or submarine pen, dark and cavernous and almost too narrow to fit into with walls that seemed to close in on you, towering high up so you had to tilt your head to see the top. It was my first experience of a lock, but a mix of reading the Inland Waterways Guide and watching YouTube put me in good stead; we got out the fender board (a plank that goes between your fenders and the wall) and got out some old rope to secure Luna to the slimy posts that run up the lock.

The lockkeeper gazed down at us, reminding me of a funeral when you look down at the coffin in the grave. He waved and I gave him the thumbs up. The huge metal doors behind us closed with a groan and a torrent of whitewater flooded through the hinges of the door in front. Luna surged against the mooring lines and gradually the old rope shuffled up the slippery poles until we were standing at the same height as the lockkeeper and the river was far down beneath us. The gate ahead opened with a clunk and we quietly motored into a brand-new environment for Luna; the tranquil Canal de Deux-Mers.