The first winter I left our boat in France I did half the job. Engine flushed, water tank drained, job done, or so I thought. In March I found a split heat exchanger and a header tank that had cracked along a seam. The repair cost more than three seasons of doing it properly. So this is the list I now work through every October, system by system, written for someone leaving a foreign-flagged boat on the French coast rather than a yard apprentice who does forty boats a week.
Where you lay up changes how hard you have to work. A boat on the Atlantic at Brest or in the Morbihan can see hard frost in January, while a hull at Hyeres or Antibes rarely freezes at all. That difference decides whether you are protecting against burst pipes or simply preventing things from going stale. Be honest about your latitude before you decide how far to take this.
Start with the engine
The engine is where the money is, so it goes first. Run it up to temperature on the day you lay up, then change the oil while it is warm, because warm oil carries the acids and soot out with it instead of leaving them to sit on bearing surfaces all winter. Change the filter at the same time.
For a raw-water cooled or heat-exchanger engine, the real job is getting antifreeze through the cooling circuit. Mix propylene glycol, the non-toxic odourless type, to the right strength and draw it through the raw-water intake until it runs pink from the exhaust. Here is the trap most people fall into: a bottle marked minus 50 does not stay liquid to minus 50. The slush point, where ice crystals first appear, sits around minus 11 Celsius, well above the nominal rating. So aim for a genuine concentration around 60 to 70 percent glycol, which is the sweet spot. Go beyond 70 percent and protection actually gets worse, because near-pure glycol has a higher freezing point than a proper mix.
Pull the impeller out and bag it with a label. Rubber takes a set if it sits compressed against the pump housing for five months, and a relaxed impeller pumps better in spring. While you are there, slacken the alternator belt a turn so it does not hold a memory in one spot.
Fresh water, then the heads
Drain the fresh-water system completely. Open every tap, hot and cold, run the pump until it sucks air, then drain the calorifier and the hot-water tank. A calorifier holds litres of water against a cold steel hull and is a classic spring surprise.
For the parts you cannot fully drain, the pump body, the shower sump, the U-bends, push non-toxic propylene glycol through until it shows at each outlet. Use the propylene type here for certain, never the ethylene car coolant, because this is the system you will drink from in April.
The heads need the same treatment and people forget the pump body and the joker valve. Pump antifreeze through the bowl and out through the discharge until it runs clear pink. A holding tank should be pumped out, rinsed and left with a slug of antifreeze sloshing in the bottom. If you want the full picture on tank fitting and pump-out logistics, the related guide on hauling out winter when to book covers the yard side of timing this work.
Gas, batteries and the soft kit
Turn the gas off at the bottle and, if you are leaving the boat unattended for months, take the bottle ashore or to a locker. French exchange bottles run on a different thread to UK Calor, so if you are still carrying British gas, read the dedicated piece on gas bottles france boat before you assume you can top up locally.
Batteries hate two things over winter: being left flat, and being left to self-discharge with nothing watching them. A lead-acid bank left at half charge can sulphate badly in a single cold winter. Either leave them on a smart charger that the marina shore power supports, or take them ashore fully charged and give them a top-up every couple of months. Lithium banks want storing around 50 to 60 percent state of charge, not full.
Soft furnishings, cushions, charts, anything that can grow mould, comes off the boat or gets stood on edge with air around it. The single biggest cause of a horrible spring is not frost, it is damp, and that is a whole subject of its own. The companion article on boat damp mould winter goes into ventilation and dehumidifiers properly.
Afloat or ashore changes the list
If you are keeping the boat in the water rather than on the hard, the engine and water jobs are identical but you add seacocks, bilge pumps and the worry of a frozen log impeller. The overview on whether to keep your boat afloat winter france weighs that choice against lifting out, and the costs piece on wintering ashore france yards costs gives the hard-standing numbers. Many French yards charge by metre of length per month for hard standing, and a lift, pressure-wash and scrub will typically be quoted separately, so ask for an itemised price before you commit.
A reasonable budget marker: a small French 13kg propane exchange bottle and refill runs in the region of 35 euros deposit plus around 45 euros for gas, useful to know if you decide to switch off UK bottles entirely while laid up.
The checklist I actually use
Walk the boat once with a notebook before you leave and write down what state you left each thing in. Mine reads: engine oil and filter changed, cooling antifreezed, impeller out and bagged, belt slackened. Fresh water drained and antifreezed, calorifier empty. Heads and holding tank done. Gas off and bottle ashore. Batteries on charger or ashore. Fuel tank brimmed to keep condensation out of the diesel and a dose of biocide added against diesel bug, which thrives at the water-fuel interface in a half-empty tank.
Seacocks, rigging and the deck
If the boat stays afloat, work every seacock closed and open a few times before you leave so they do not seize over winter, and grease the ones you can reach. A seized seacock discovered in spring, on the wrong side of a launch, is a horrible thing. Leave the engine seacock closed, the bilge-pump float free, and the log impeller either removed and bagged or its blanking plug fitted. For a boat on the hard, the seacocks should be left open so any trapped water drains rather than freezing in the valve body.
Standing rigging gets ignored over winter and it should not. A quick walk of the deck with the boat laid up is the cheapest rig inspection you will ever do: run your eye and a finger along each swage for hairline cracks and rust weep, check the split pins, and look at the spreader tips. None of this is the full survey that the article on rig inspection covers, but it catches the obvious before five months of weather works on it. Slacken the halyards off so they are not loaded in one position all winter, and tie them away from the mast so they do not slat and chafe in every gale, which also spares your neighbours the maddening ping of a halyard against an alloy mast through the small hours.
Cover what you can. A boom tent or a proper fitted cover keeps UV off the brightwork and rain off the deck fittings, and it dramatically reduces the amount of water finding its way below through tired seals. The Mediterranean sun is as hard on a laid-up boat in winter as the Atlantic rain, just in a different way.
Diesel, fuel bug and the tank
Brim the fuel tank before you leave. A full tank has no air space for moisture to condense in, and it is the water sitting at the fuel-water interface that feeds diesel bug, the microbial growth that clogs filters and corrodes tanks. A dose of biocide added when you fill is cheap insurance, and if you suspect the tank already has water in it, drain a sample from the bottom and check before you walk away rather than discovering a blocked filter on your first passage in spring.
Last, leave a single sheet aboard listing everything you did and the date. When you come back in spring, jet-lagged and keen to launch, that sheet stops you putting to sea with an impeller still sitting in a sandwich bag in the chart table. I have nearly done exactly that, and the only reason I did not was the note I had left myself five months earlier.
