How often should I winterise my boat, and what determines the timing?
I keep my boat afloat and sometimes use it into November, so I'm unsure when to winterise the engine and water systems. Should I do it on a fixed date each year, and what happens if I take the boat out again afterwards?
Answer
Winterise your boat once a year before its winter lay-up, completing frost protection before the first freezing weather reaches your mooring or storage yard. Timing depends on the local forecast, whether the boat is afloat or ashore, its engine and plumbing, and your plans to use it through winter.
Forecast and final trip
Start with the forecast for the boat's location and the date of your last planned outing. A calendar reminder helps with booking servicing, but cannot tell you when exposed pipework or trapped cooling water will freeze.
In Britain, September or October is a sensible time to arrange the work. The deadline varies considerably between a sheltered south-coast marina and an inland Scottish yard. Complete protection before a forecast frost. Do not wait for several freezing nights to confirm that winter has arrived.
- Boat ashore: cold air reaches the hull, engine space and fittings more readily, so arrange frost protection promptly around lift-out.
- Boat afloat: surrounding water moderates temperatures, but exposed pipes, cockpit showers and machinery can still freeze.
- Long unattended lay-up: prepare when regular use ends, even if freezing weather is several weeks away.
Winterisation also prevents deterioration during storage. Once your season has finished, waiting until the last frost-free day offers little benefit.
Protect both cooling circuits
For a conventional inboard diesel, minimum winter preparation means frost protection for the cooling system, an oil change and the appropriate filter service. Change the oil before storage: used oil contains soot and potentially corrosive contaminants.
Check the engine manual before choosing a procedure. A heat-exchanger-cooled engine has two separate circuits: the sealed coolant circuit and the raw-water circuit, which draws water through the seacock and strainer. Antifreeze in the sealed circuit does not protect water trapped in the raw-water pump, heat exchanger or exhaust system.
- Check the sealed coolant's frost protection with a tester suitable for that coolant.
- Drain or protect the raw-water circuit using the manufacturer's procedure and compatible winterising antifreeze.
- For directly cooled engines, follow the specified draining or antifreeze procedure. Their internal water passages need protection too.
- For outboards and petrol sterndrives, follow the exact model's storage instructions. Draining, flushing and fuel preparation differ.
Never run an engine without its required cooling-water supply. Collect discharged antifreeze for proper disposal.