Winterising top tips 

Things to consider to protect your boat through winter

“When putting your boat to bed for the winter there are a few things to consider to protect it through the winter months”, explains RYA Chief Instructor, Motor Cruising and Power, Rachel Andrews.  “This list is by no means exhaustive but it will give you a few top tips”.   


Use it.  The best way to winterise a boat is to use it as it’s designed to move.  A boat contains a multitude of systems that hate inactivity – particularly the engine.  

There are plenty of other items that would benefit from winterisation but if you only do one thing, do it on the engine.  

1.    First on the list - general engine cleaning and observation. Shine plenty of light, use a mirror on a stick or a digital camera to see under and behind things. Dry the bilges to prevent corrosion and if necessary, paint them white to highlight any leaks and drips in the future.  

2.    Whether your boat is being hauled out for the winter or not, fill your fuel tank to prevent condensation, which in turn prevents the growth of diesel bug.    

3.    Change the engine oil and replace the oil filter before leaving your boat for the winter. Leaving the old oil contaminated with the acidic by-products of combustion inside the engine block will shorten the engine’s life and a neglected oil system will cause expensive damage. Also consider using flushing oil or a flushing additive during the oil change which helps to remove more of the contaminants.  

4.    Check the gearbox or outdrive oil and replace if it looks cloudy or milky.    

5.    Most diesel engines use either raw water or keel cooling – both of which need attention when winterising. Raw water systems require draining before  leaving for the winter, by closing the water inlet valve, or sea cock, disconnecting a hose from the circulating pump, (unless there is a dedicated tap or plug), then refilling with a strong solution of fresh antifreeze. Run the engine to fully circulate the new solution. Simply draining the system is unlikely to remove all the water inside, which may then freeze and cause damage over the winter.  

6.    Check the water pump impeller and consider replacing it when de-winterising in case the blades have deformed over the winter.  Keel cooling systems can be left alone providing they contain the correct water/antifreeze mixture. This can be checked using a strength tester available from marinas and good car spares outlets. Note that antifreeze has a limited life and if it has to be replaced then it is a good time to replace any suspect hoses. Keep the old hoses as emergency replacements.

7.    Remove the air intake filter and block the intake with an oily rag to prevent rust inside, do the same for the exhaust. Squirt a little oil into the intake and turn over the engine, (without starting), to distribute it over the cylinder walls. Be sure to place a warning about the blocked intake on the engine control panel to prevent anyone turning the engine over.  

8.    Where possible, remove the batteries and keep them warm and dry over the winter, fully charged or topped up at least every four to six weeks. Batteries left uncharged for long periods may need to be replaced completely.   If you’re unable to remove batteries or if the boat is staying on its mooring, leave them fully topped up and regularly recharged, as full batteries are less likely to freeze in sub-zero temperatures.  

9.    Relax or remove all belts and protect the drive wheels. Rust on these can chew up a belt very quickly in the new season.  

10. If you’re taking the boat out of the water make sure it is angled bow upwards slightly to enable rain water to run off immediately from covers, decks and cockpit.    

11. Covers should keep water out but allow air to circulate. Proper through-draught will prevent condensation which leads to dry rot, mould and corrosion (especially if left for more than a single season).  

12. The internal freshwater supply system also requires attention. Drain the entire system including tank, pump, calorifier, water filters and all taps especially shower mixers. Look for any areas where water could still be trapped in pipes. Plastic piping is less vulnerable than copper piping but rigid unions can still be damaged by freezing.

13. If you have a water-based central heating system using antifreeze then the same checks carried out to the keel cooled engine system should be applied. If the system doesn’t use antifreeze then it should be drained as for the freshwater supply.

14. Remove any foodstuffs which may be damaged by the frost or attract unwanted visitors such as mice and rats.

15. Store all linen, clothing, blankets, curtains etc. ashore – washed and dry.  Prop the fridge door open – mould will form in less than a week if left closed. Ensure through-ventilation. Leave cupboards and drawers open; prop up bunk cushions, leave under-berth locker lids open. Get circulation into every possible conceivable nook and cranny.  

16. Ensure tight-fitting covers for deck-installed electronics and consider spraying behind electronics with water-repellent silicone.  Check your navigation lights are still serviceable.    

17. If leaving the boat afloat, check all through hull fittings for leaks and corrosion.  Don’t forget to check your stern glands and repack with grease if appropriate.  

18. Make a list of what you have done to winterise the boat so you remember what to reverse in the spring and leave signs all around the boat so no-one accidentally operates a winterised system.