By mid-July my speed over ground had quietly dropped half a knot, the engine was working harder to hold cruising revs, and a dive mask over the side showed me why: a green beard hanging off the waterline and a colony of barnacles starting up around the prop. The antifoul I had put on in April was already losing the fight, which on a Med berth in high summer is entirely normal. The question was not whether to clean the hull, but how.
That is the choice this piece is about. A mid-season hull clean in the water, done by a diver, against the alternative of dragging the boat out for a wash. In France the answer is shaped as much by environmental rules as by cost.
Why fouling outruns antifoul in French waters
Antifoul buys you a season, not immunity, and the warm Mediterranean eats it faster than the cool Atlantic. Growth in the Med is aggressive and slime-heavy, so even a strong copper-based paint slimes up by midsummer and most owners accept a scrub partway through the year. The Atlantic fouls hard too, with weed and barnacle pressure high in summer, but the cooler water and the shorter season mean a self-polishing paint on a boat that actually sails can often last the year on its own.
The single biggest variable is whether the boat moves. A hull that sits in a marina berth fouls far worse than one that scours itself at speed, because a moving boat keeps slime off the way a wiped self-polishing antifoul is designed to. If you leave the boat on a berth for weeks while you fly home, expect to need a diver, whichever coast you are on. The paint choice that suits each sea is set out in the antifouling and survey while based in France guide, and it directly decides how often you call a diver.
What a diver costs and what you get
An in-water hull clean is the cheap, fast alternative to a lift, and for a mid-season tidy it usually wins outright.
A diver will scrub the hull, props and running gear, clear the through-hulls, and check the anodes while down there, all without the boat leaving its berth. The price depends on hull length, how bad the fouling is and the port, but it is a fraction of a haul-out: a scrub costs you a tradesman's visit, not a travel-hoist booking, a wash bay and a relaunch. Get a quote by length before they get in the water, because a hull that has not been touched all season takes far longer than one cleaned routinely, and time is what you are paying for.
Two warnings. First, a diver dragging a hard pad over soft antifoul removes paint along with the slime, so brief them to use the right pad for your coating, or you pay to take off the protection you paid to put on. Second, the anode check is worth more than it sounds. A diver who tells you the shaft anode is half gone in July has just saved you a corrosion problem and a separate trip, which is exactly the kind of small intervention that keeps the bigger bills away.
It pays to find a diver before you need one. The good ones around the busy Med ports book up in high summer, exactly when every fouled boat wants them at once, so the owner who has a number saved and a relationship going gets seen in a day while the stranger waits a week. Ask at the capitainerie or on the visitor pontoon, because the local cruising grapevine knows who turns up, who uses the right kit, and who quietly takes your paint off with a wire brush. A diver who works your marina regularly also knows which berths the harbourmaster watches and which cleaning methods the port will tolerate, and that local knowledge is worth as much as the scrub itself.
Keep a note of what the diver finds, too. If the same patch of hull fouls heavily every clean while the rest stays fair, that tells you the antifoul went on thin there, or the boat sits with that side in the sun, and it feeds straight into how you paint next spring. A diver clean is not just a tidy-up, it is a free inspection of the bit of the boat you never otherwise see.
The rules that complicate it in France
This is where France differs from a quiet UK mooring. In-water cleaning sheds antifoul and fouling straight into the harbour, and French ports take that seriously.
Many marinas now restrict or ban scrubbing that releases biocide-laden paint into the basin, the same environmental thinking that has French yards collecting paint dust, washings and spent antifoul ashore under serious rules. Some ports require in-water cleaning to be done with a capture system, a skirt or a vacuum that catches the debris, rather than a brush and a cloud of paint. Others restrict it to nominated contractors who hold the right kit. Always ask the capitainerie before you book a diver, because turning up with your own man and cleaning into a basin that forbids it is the sort of thing that strains a foreign boat's welcome.
The fine print here echoes the wider compliance picture for visiting boats, from waste handling to discharge, that runs through the marina logistics, laundry, bins and pump-out in France guide. France is generally relaxed about visiting cruisers right up until you put something in the water that should not be there.
In-water clean or haul-out: choosing
The decision turns on what you actually need doing, and divers cannot do everything.
A diver is the right call for a mid-season scrub, a prop clean, a quick anode check, a lost line round the shaft, or a fast look at the rudder bearings. It is not the right call when the antifoul has genuinely failed and needs renewing, when you suspect osmosis and need a moisture meter on dry gelcoat, or when the seacocks want servicing. Those jobs need the boat ashore, and once it is ashore you may as well stack them, which is the whole logic of the antifouling and survey while based in France routine.
My own rule on a Med berth is one diver clean in high summer to carry the antifoul to the autumn haul-out, and that is usually enough. On the Atlantic, if the boat is sailing regularly, I often skip the diver entirely and let a self-polishing coat do its job until the boat comes out.
There is a middle option worth knowing about, too: doing it yourself. On a calm day in clear water, a mask, a fin set and a soft pad will get the worst of the slime off the waterline and the leading edges where fouling bites hardest, and that alone can claw back most of the lost speed. I keep a cheap scrubbing mitt aboard for exactly this. It is no substitute for a proper diver clean of the prop and the deep hull, but for a quick mid-passage tidy in a sheltered anchorage it is free and it works. The same port rules apply, though: if the basin forbids in-water cleaning, that includes you in your swimming shorts, not just the contractor with the vacuum rig. Do the DIY scrub at anchor in open water, not on the marina berth where the paint flakes settle on the bottom for the harbourmaster to find.
Folding it into the year
A diver visit is a small, predictable line in the budget, and the mistake is treating it as a surprise rather than a fixture.
If your boat lives on a Med berth and you sail it lightly, pencil in at least one in-water clean a summer and treat a second as likely in a hot year. If it lives on the Atlantic and you sail it hard, you may get away without one. Either way it belongs in the same annual sum as the antifoul, the anodes and the engine service, the full picture the annual running costs of a boat in France guide pulls together.
The half-knot I lost in July came back the afternoon the diver surfaced and gave me a thumbs up. Half a knot does not sound like much until you are punching into a Gulf of Lion chop trying to make a port before dark, and then it is everything. A clean hull is free speed, free fuel and a happier engine, and in French waters the trick is simply doing it the way the port allows.
