There is a reason the locals on the French Atlantic coast sail shoal-draught boats, and you understand it about an hour after you arrive. This is a coast of estuaries, sandbanks, shifting passes and a tidal range that can swing four metres or more on a big spring. If your keel is short, the coast opens up. If it is deep, the coast keeps half its secrets to itself.
I cruised two seasons here, the first in a 1.9 m fin-keeler and the second in a lifting-keel boat that came up to 0.9 m with the board raised. Same coast, completely different holiday.
What "shoal draught" buys you here
Start with the tide, because everything else follows from it. On the Pertuis Charentais, the waters between La Rochelle, the Ile de Re and the Ile d'Oleron, the range on a big spring approaches 6 m, and vast areas dry at low water. A boat drawing 1 m can carry on through stretches where a 2 m keel is sitting on the putty waiting for the flood. That single fact governs how far you get, where you sleep, and whether you spend the afternoon aground or ashore.
The Bassin d'Arcachon is the extreme version. The entry passes shift season to season, the lagoon dries over enormous flats, and the prized anchorage behind the Banc d'Arguin is a thin-water spot that punishes a deep keel. A shoal-draught boat reaches the back of the basin and stays afloat longer on each side of low water. The full lowdown on getting in and finding water is in the Arcachon basin sailing guide, and Arcachon is the single best argument for less keel on the whole coast.
The rivers and the drying harbours
The other prize is the river. The Gironde estuary runs inland to Bordeaux, and the upper reaches and the side creeks favour a boat that can take the ground or carry on over the shallows. The estuary itself is huge and the channel deep, but the interesting bits, the pontoons up the tributaries and the quiet anchorages off the main stream, reward a shoal draught. I have set out the run up to the city in the Gironde estuary to Bordeaux piece, and a fin-keeler does it too, but the shoal boat has more options at each stop.
Then there are the drying harbours. Plenty of small Atlantic ports dry completely at low water, leaving boats sitting on the mud or sand against a quay. A bilge-keeler or a lifting-keel boat with legs settles upright and you walk ashore at low water. This is exactly the same skill the Brittany crowd live by, and the bilge keel France drying-harbours guide covers how to dry on clean ground without bending anything. On the Atlantic the ground is more often sand than the rock you get further north, which makes drying out here forgiving and pleasant.
Crossing the sandbars
Some of the best places on this coast sit behind a bar, and the bar is the gatekeeper. A river or lagoon entrance with a shoal across it breaks heavily when wind opposes the ebb, and the safe window is a band around high water with the right swell and the right light. A shoal-draught boat has a wider window, because it floats over the bar earlier on the flood and later on the ebb than a deep boat does, but shoal draught is not a licence to ignore the swell. Time it for the flood, in daylight, with a settled forecast, and never with a big Atlantic swell running onto a falling tide. Get the timing wrong and a metre of keel will not save you any more than two will.
Where depth still beats you
Honesty matters, so here is where the shoal boat loses. Offshore, none of this counts. The Bay of Biscay does not care how much keel you have, and a light, shoal hull can be more tiring in a seaway than a deep, heavy one. If your season includes the Biscay crossing or long offshore legs, read the crossing Bay of Biscay small boat account first, because the qualities that make a boat good in the shallows are not the qualities that make it good in a Biscay gale.
The lifting-keel and bilge-keel boats also give something up to windward. A deep fin points higher and stands up to its sail better, so on a long beat in open water the deep boat is quicker and drier. On this coast you accept that trade because the inshore gains are so big, but it is a trade, not a free lunch.
And a few places simply have enough water that draught stops mattering. The big all-tide marinas at La Rochelle and Les Sables-d'Olonne float you at any state of tide whatever your keel, so for a boat that mainly marina-hops the shoal advantage shrinks. The visitor's-eye view of the biggest of them is in the La Rochelle visitor guide, and it floats a 2 m keel as happily as a 1 m one.
The numbers worth carrying in your head
A few figures frame every decision on this coast:
- Spring range in the Pertuis Charentais approaches 6 m, and 4 to 5 m is routine.
- A typical cruising fin-keeler draws 1.9 to 2.1 m; a lifting-keel boat can come up to under 1 m.
- The Arcachon entry passes move season to season, so last year's track is not this year's.
- Bars break hardest when wind and a big swell oppose the ebb, so plan crossings for the flood in daylight.
- The all-tide marinas float you at any tide, but the drying ports and back-bay anchorages do not.
Reading the chart for a shoal boat
Cruising shoal-draught on this coast is as much about reading the chart as reading the tide, and the two skills lock together. The figures on a French chart are drying heights and depths reduced to chart datum, the level of the lowest astronomical tide, so a sandbank marked as drying 2.3 m is 2.3 m above that datum and uncovers when the tide falls below it. To know whether you float over it, you add the height of tide for the moment you arrive to the charted depth, or subtract the drying height. Get that arithmetic into your bones and the whole coast opens up, because you stop seeing a bank as a no-go and start seeing it as a place you can cross for three hours either side of high water.
The shoal boat lives in that band. Where a deep keeler needs a deep channel that stays open all tide, you can plan a route that uses the flats while they have water on them and is tucked safely in a pool by the time they dry. That is a different way of cruising, planned around the rise and fall rather than around fixed depths, and it is the way the locals do it. The reward is reaching anchorages and creeks that simply are not available to a boat that has to stay in deep water the whole time.
Carry a sounder you trust, keep a lead line or at least a marked boathook as backup, and on the shifting passes such as Arcachon treat the chart as a guide and your eyes and depth gauge as the authority. Sand moves; the chart cannot keep up.
Making the most of less keel
If you already own the shoal boat, this is your coast and you should milk it. Carry the local tide tables, because the range is too big to eyeball, and read the Atlantic tides crash course if you have come from the tideless Med, because the rhythm of the day here is dictated by the water, not the clock. Pick your bar crossings, dry out on sand for the fun of it, and use the draught to reach the places the bareboat charterers in their deep production boats sail straight past.
If you are still choosing a boat for an Atlantic season, the lesson is simple. Every centimetre of keel you take off widens the map. You give up a little upwind speed and a little offshore stiffness, and in return you get the sandbanks, the rivers, the drying ports and the back of the basin. On this particular coast, that is a trade I would make again without thinking twice.
