Two engines, two hulls, and two of almost every water and fuel component: a catamaran doubles the pleasure in summer and doubles the winter to-do list. Leave any part of it to chance and you will meet the consequences in spring, usually in the shape of a cracked pump housing, a split length of pipe or an engine that refuses to turn over. An unhurried couple of days in the autumn, before the first proper frost, is all it takes to avoid that.

Service both engines before the cold sets in

Do the engine work while the boat is still afloat if you can. Run each engine up to temperature, then stop it and drain the sump straight away, while the oil is thin and still carrying the contaminants with it. On a catamaran that means doing everything twice, on both sides of the boat, so resist the temptation to rush the second engine.

• Replace the oil filter and refill with the grade your engine specifies.
• Change the primary and secondary fuel filters and drain any water from the separator bowls. Water left sitting in a separator is the classic cause of a housing cracked by frost.
• Remove the raw water pump impeller. Keep a new one for spring, because an impeller left compressed in one position for five months will take a set.
• Drain and refill the saildrive or gearbox oil, and inspect the anode on each leg. An anode half-eaten in October will be gone by March.

Check the coolant with a refractometer rather than by eye. A 50/50 mix of coolant and water protects to roughly minus 37C, far beyond anything a British winter will throw at you, but a system topped up with neat water through the summer may be weaker than you assume.

Drain the freshwater system properly

A full tank is not a safe tank. Water expands as it freezes, and pumps, pressure switches, plastic fittings and shore-side plumbing are usually the first casualties. Drain both tanks — on many catamarans there is one in each hull — then run the pump briefly to clear the lines and drain again.

• Open every tap, shower and deck-wash outlet, and leave them open.
• Remove the filter housing from the pump and empty it.
• Disconnect the lowest push-fit joint you can reach and let the pipework drain to that point.
• Empty the transom shower, the heads basin and any cockpit wash-down tap, which are easily forgotten.

If you have a water heater or calorifier, isolate it from the freshwater side, drain it at its own drain cock and leave the immersion heater switched off at the breaker.

Anti-freeze: use it, but use the right sort

There are two separate circuits on a catamaran and they need different treatment. The freshwater system is best simply drained and left dry, because any antifreeze you add must be flushed out thoroughly before you use the taps again. Where draining is impractical, use a propylene glycol anti-freeze sold as food-safe or potable, never automotive ethylene glycol, which is toxic.

The raw water side is different. After flushing with fresh water, pour anti-freeze through the seawater strainer while turning the engine over briefly on the starter with the stop lever pulled, so it circulates through the heat exchanger, exhaust elbow and silencer. On a catamaran, remember that each engine has its own intake, strainer and exhaust, and both need doing.

Fuel, batteries and a little peace of mind

Fill the fuel tanks to the top. A full tank leaves little room for condensation, which is what causes diesel bug and rusty tanks over winter. Add a fuel stabiliser and run each engine long enough to draw treated fuel through the system.

Batteries dislike being left partially charged far more than they dislike the cold. Charge them fully, then either remove them to a cool dry place and top them up monthly, or leave them aboard with a smart charger maintaining them. Label any leads you disconnect. Check the bilge pumps one last time, clear the cockpit drains of leaves, and leave a couple of moisture absorbers in the cabins with a little ventilation rather than sealing the boat up tight.

Toilets, holding tanks and the final checks

Pump out the holding tank, then flush the heads through with fresh water and add a little propylene glycol to the bowl and the pipework so the seals stay supple and nothing splits. Leaving sea water in a toilet pump is a reliable way to create a spring repair bill.

If you are staying afloat, close all seacocks and blank off the exhaust outlets to keep rain and snow-melt out. If you are ashore, support the keels properly, check the hull and anodes, and remove the outboard or saildrive leg if that is your habit. Whichever you choose, walk the boat one final time with a torch, look in every locker and under every berth, and satisfy yourself that nothing is holding water. Doing that now, in the quiet of the autumn, is what makes the first sail of spring a pleasure rather than a repair.