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How to winterise your boat

4 November 2022

With the Autumnal nip now in the air, we don’t have long left until winter is upon us.

The UK’s unpredictable and sometimes extreme weather conditions during the winter months can wreak havoc on your craft if it is not properly prepared. So, if you’re going to leave your boat unattended for any length of time this winter, we recommend you winterise it so that you don’t have any unwelcomed surprises when you return in the spring. Storing your boat correctly over the winter can help prevent the effects of corrosion, among many other things, and the more effectively you winterise, the more easily she’ll relaunch next year.

We have selected some of the most helpful hints and tips for winterising your boat this year from our expert staff, knowledgeable customers and our years of boating experience.

Please be sure to check with a boat engineer if you have any questions or need some help. Our marina staff will be able to give you contact details of services local to you.


Draining fresh water

Open your taps and let the fresh water drain overboard. When water stops coming out, turn the water pump off at the switch panel. Leave all taps on (especially the hot taps if you have a calorifier). Don’t forget your shower too, making sure to place the shower head in the shower tray or bath.

Turning the stop cock off is not sufficient by itself.


Inboard raw water

Cooled engines should have the sea cock turned off, anti-freeze fed into the raw water feed and fed around the engine until it leaves the exhaust. Check that the sealed cooling, if present, also has the required level of anti-freeze in the system.


Anti-freeze levels

Engines should be checked for a coolant anti-freeze level of at least -20 degrees and ensure that the coolant levels are topped up.


Prevent diesel bugs

If your vessel is being lifted out for the winter, you need to prevent the growth of diesel bugs. Diesel bug is a microorganism that grows on fuels and feeds on the hydrocarbons, creating biomass, biofilms, and damaging by-products. These microorganisms thrive in even the smallest amounts of water, often from condensation and particularly at the interface of fuel and water. The easiest way to combat the threat of diesel bugs is to fill your fuel tank to the brim to prevent condensation forming. Just before refuelling is the perfect opportunity to use a fuel treatment to kill off any bugs that may already be present.


Battery levels

Batteries that are left uncharged for long periods may need to be replaced completely, so ongoing maintenance is essential. Full batteries are less likely to freeze in sub-zero temperatures and should be topped up and fully charged every four to six weeks.

Battery levels on all wet cells should be checked and topped up with distilled water unless these are of the ‘sealed for life’ type. Turn off battery isolators, and if you have an installed marine battery charger, this should be turned on to keep the batteries topped up.



In short, there should be moving air always circulating throughout your whole boat over the winter months. An unventilated boat will trap moisture, so ensuring there is ventilation over winter is essential to keep down damp. Creating a good through-draught circulating around your boat will help, so leave a couple of window hoppers open for air flow to stop mould and mildew growing.

Store all linens and clothing ashore, open all drawers and cupboards, and prop your fridge door open too as mould can grow within a matter of days if left shut.

Remember to avoid blocking any low-level vents around the vessel.


Instant water heaters

Instant water heaters should be drained using the drain plug, leave the plug out with a bowl under the outlet and leave the thermostat control on maximum.


Diesel heaters

If your boat has diesel heaters with a frost stat, you should ensure that you have a full tank of diesel and very good batteries. If you have access to electricity through a metered lead, and have a marine battery charger, connect to the shoreline so that batteries do not go flat.

Do not rely on mains electricity to keep your batteries topped up!


Electric heaters

Running a small heater with a thermostat can be very beneficial for your boat to keep the boat temperature from dropping below zero. Always ensure electrical supply can’t be interrupted, with suitable electric breakers to cope, and appliances are trustworthy.

The recommended heater is a greenhouse ‘tube’ heater, which are very low wattage and cannot cause fires. Do not use fan heaters, bar heaters, gas heaters, or any heater that has exposed elements. These heaters are the number one cause of fires on boats, and they may invalidate your insurance if they are found to be the cause of a fire.

Do not rely on mains electricity to keep your craft from freezing.

Electric heaters should always be used with caution.


Smoke & CO2 alarms

Smoke & CO2 alarms should have the batteries removed if you are not on the craft. During the winter months, it is prohibited for alarms to be going off onboard a vessel due to flat batteries in alarm systems.


Mooring lines & ropes

Mooring lines and ropes should be used correctly. Check all mooring lines for chafing or wear and if they are worn, they should be replaced. Please refrain from using the whole 10 metres of line on a mooring tee to secure your craft, as this will cause problems if we need to loosen your ropes due to water levels, wind, or snapped ropes.


Collapsing covers

Unless you are storing your boat indoors, you should always cover it. Sadly, no cover is immune to the effects of the battering wind and the weight of snow during winter, even if it’s the shrink-wrap kind. If the cover collapses your boat will be exposed to the winter weather. The only way to guard against this issue is to check the cover regularly. If you find the cover has failed, then you will have only days’ worth of damage to deal with rather than months if left unchecked.



Preparation is key! You should not leave these actions until last minute. Give yourself plenty of time to make your action list well before the cold weather arrives. To ensure that your boat is ready for hibernation you should prepare well in advance. Prevention is most definitely better than cure!

Please be aware that this list is not exhaustive and does not guarantee that frost damage may not occur.


General engine maintenance

General engine cleaning and monitoring should be high on your priority list, but is best done under the experienced responsibility of a boat engineer.

They will check all the way around and underneath all the workings, particularly all elements of the exhaust, change the oil filters and coolant and dry the bilges off completely to prevent corrosion.

If you need the details of your local services to help you with this, please contact your marina who will be happy to help.


Please contact your marina for help on anything in this article. They will be able to advise if any of the actions can be completed by the marina on your behalf before any winter damage is possibly caused and will also have extensive lists of boat services that can help you in your local area.

*This article is to simply advise, so please contact a boat engineer if you require further information regarding winterisation.

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