Why Winterising Matters More Than You Think

British winters are not a single event you can plan around. They are a long, damp, salt-laden slog of frosts, gales and weeks of drizzle, and a high-performance powerboat left alone through all of it will quietly suffer. Water trapped in a cooling system splits a block. A flat battery sulphates beyond saving. Damp air under a cheap tarpaulin grows mould in the upholstery and corrodes every alloy fitting it touches.

The good news is that a proper winterising routine takes a weekend, costs relatively little, and pays you back with a boat that fires first time in April. If you are on a mooring in the Solent, a berth on the Clyde, or a trailer in a farmyard in Norfolk, the principles are the same — only the sequence changes. Work through this list methodically, from the engine outwards.

Engine and Fuel System

Start with the engine while it is still warm from a final run, ideally on a fresh-water flush if you have one.

• Flush the cooling system thoroughly with fresh water, then drain it completely. On raw-water cooled engines, remove the drain plugs and open the block drains so no water sits in the jacket.
• Change the engine oil and filter before lay-up rather than in spring. Old oil carries acids and moisture that eat bearings over winter.
• Fog the cylinders with storage oil through the plug holes or intake, then turn the engine over briefly by hand to coat the bores.
• Fill the fuel tank to roughly 95 per cent. A full tank leaves little room for condensation, which is the real enemy of ethanol-blended petrol. Add a marine fuel stabiliser and run the engine long enough for treated fuel to reach the injectors or carburettors.
• Service the gearbox or sterndrive leg: drain and refill the leg oil, check for milky contamination that signals a failed seal, and grease the universal joints and splines.
• Replace anodes now so they are not forgotten, and check the impeller — a winter is a long time for a tired one.
• Spray the whole powerhead with a protective corrosion inhibitor, and wipe down terminals with dielectric grease.

Water Systems, Heads and Seacocks

Anywhere water can sit and freeze is a risk, and that includes systems you rarely think about.

• Drain fresh-water tanks, calorifiers and pipework. Open every tap and let the system run dry, then blow through with compressed air if you can. Leave taps open.
• Antifreeze the engine's raw-water side if the manufacturer allows it — use propylene glycol, not automotive ethylene glycol, and follow the manual.
• Empty and rinse the holding tank, then add a little antifreeze to the bowl and pump through to protect the seals.
• Close all seacocks and label them, and check hose clips while you are down there. This is the ideal moment to spot a perished hose.
• Clear deck drains and scuppers so rain cannot pool on deck or in the bilge over the coming months.

Batteries and Electrics

Batteries hate cold and they hate being left discharged even more. A battery left at 50 per cent charge in a frosty shed will often be scrap by spring.

• Remove batteries if you can and store them somewhere frost-free, ideally above freezing but cool.
• Charge them fully to around 12.6 to 12.8 volts for a standard lead-acid battery, then recharge every six to eight weeks. A smart maintenance charger left connected is the easiest answer if the boat has power.
• Clean and grease terminals, and check the electrolyte level on serviceable cells before storing.
• Switch off everything at the isolator and check for parasitic drains — a bilge pump float switch or an alarm can quietly flatten a battery in weeks.
• Inspect wiring for chafe, and spray exposed connectors with a water-displacing protectant.

Covers, Ventilation and Hull Care

The golden rule of winter covers is that airflow matters more than waterproofing. A sealed, non-breathing cover traps moisture against gelcoat, teak and upholstery, and mould follows within weeks.

• Use a breathable, fitted cover on a frame that sheds water and lets air circulate. If you use a tarpaulin, tent it so it never touches the boat and leave the ends open.
• Remove or prop cushions so air can move underneath, and leave locker lids and cabin doors ajar where it is safe to do so.
• Clean and wax the hull before covering. Dirt holds moisture, and a good coat of wax protects gelcoat through the frosts.
• Support the hull properly on a trailer or cradle with the weight on the keel, not the strakes, and slacken the winch strap slightly.
• Check the trailer if you are storing ashore: repack wheel bearings, inspect tyres for cracking and store them off damp ground, and free off the brakes.

Throughout the Winter and Into Spring

Winterising is not a single job you tick off and forget. Check the boat every few weeks, particularly after a named storm. Look for chafed mooring lines, a slack cover, water in the bilge or a battery that has dropped below 12.4 volts. Ten minutes with a torch saves a lot of money.

Come March, reverse the process carefully: refit and charge the batteries, reconnect the fuel line, run the engine on a flush muff, check all seacocks and hoses, and give everything a thorough inspection before you head out. Book your lift-in or launch slot early, because every yard on the coast is doing exactly the same thing on the same weekend. Look after the boat properly through the dark months and she will reward you with a summer of trouble-free running — which, after all, is the whole point.