Winterising your boat

Why winterise your boat?

Cold weather, damp conditions and inactivity can wreak havoc on a boat. Systems like the engine, freshwater supply and electronics are all vulnerable to the elements and lack of use. Damp air trapped inside can cause mould, mildew, and corrosion, while freezing temperatures can damage plumbing, engines, and other systems.

The goal of winterising is to mitigate these risks, protect your investment, and ensure that when it’s time to hit the water again your boat is in top shape.

Your winterisation checklist

Below we've shared our steps for winterisation, but be sure to keep a detailed checklist of what you've done so you don't forget essential steps (and it's easier to reverse the process in the spring). 

Document everything you do, from draining water systems to disconnecting gas bottles. Leave reminders or signs on any systems that have been winterised so that nobody accidentally operates them before they’re ready

1) Remove and store boat items

Start by removing as many items as possible. Soft furnishings are especially prone to damp and mould if left on the boat. Valuables such as chart plotters and handheld VHFs, plus sails lifejackets and safety gear are better removed and store in a dry place. Not only will this protect your belongings, it also makes it easier to carry out any servicing or safety checks on these items throughout the winter months.

2) Ventilation and dehumidification

Boats are prone to damp and mould when sealed up for long periods of time. To prevent this, it's essential to ensure good ventilation.

If you’re leaving the boat on a mooring or in a yard without access 
to power, leave hatches or portholes slightly open to allow airflow, taking care to ensure they are still weatherproof. If your boat is in a secure marina and you have access to power, consider using 
a dehumidifier set to continuous drain mode (with a hose running into the sink to avoid the need to empty it regularly).

3) Draining water systems

Water left in pipes, tanks or bilges can freeze, expand and cause damage, so begin by emptying bilges and ensuring they are dry. Next, drain  freshwater tanks, removing remaining water from the pipes by opening all taps, and be sure to empty the heads (toilets) as well as deck showers.

For systems that can’t be completely drained, like water heaters or calorifiers we suggest flushing with antifreeze (safe for drinking water systems) as this will protect pipes and pumps from freezing.
If your boat remains in the water over the winter, ensure all seacocks are closed tightly. Boats that are hauled out for the winter should have their seacocks left open to allow for drainage.

4) Protect the exterior

To protect your boat from the elements remove canvas items like sprayhoods, dodgers, and sail covers, as they can become dirty and mouldy when left exposed for long periods. 

If you leave sails on the boat, particularly a furling headsail, ensure they are properly secured to prevent them from becoming unfurled in high winds.

A well-fitted cover over the cockpit can provide extra protection, 
especially if your boat is staying on a mooring. Double up on 
mooring lines, adding extra lines as a backup in case one fails, and check for any signs of leaks or damage to the hull.

5) Engine winterisation

Preparing the engine is one of the most important tasks when it comes to winterisation. Start by changing the oil and replacing the filters as old oil contains contaminants that can corrode the engine if left sitting for months. 

After this, flush the cooling system to remove any saltwater which can crystalise and cause blockages. If your engine is raw-water cooled, flush the system with antifreeze. Closed circuit cooling systems should also be topped up with antifreeze. In both cases, running the engine for a short period will help circulate the antifreeze through the system.

Fill your fuel tank to the maximum to prevent condensation from forming, which can lead to water contamination and bacterial growth (commonly known as diesel bug). There is some debate about whether it is better to leave tanks as low as possible due to the bio-content of diesel but our experience is that removing as much air as possible is the best way to prevent moisture from entering the tank. Adding a fuel stabiliser or anti-bug additive will also help keep the fuel clean over winter.

Additional tips for engine protection include smearing Vaseline on the fuel filler cap to prevent water ingress, spraying the engine with an anti-corrosion spray, and removing the saltwater impeller. If you’re not confident performing these tasks yourself, it’s worth having a professional service your engine during the quieter winter months

6) Batteries and electrical systems

Batteries discharge slowly over time, so it’s essential to keep them charged throughout the winter. If your boat has shore power, you can leave a smart battery charger connected to maintain the charge. For boats stored ashore without access to power, solar panels provide a simple and cost-effective solution.

 Small solar panels, rated at less than 10% of the battery’s amp-hour capacity, can be left permanently connected without a charge controller. If possible, remove batteries from the boat and store them in a warmer environment. If they must remain on board, ensure they’re fully charged and check them periodically throughout the winter. 

In addition to battery maintenance, take time to inspect and service other electrical systems, such as navigation lights, electronics, and wiring. Disconnect and store any removable electrical items like lights, as damp conditions can cause corrosion in connections

7) Regular winter inspections

Even after your boat is winterised, it’s important to make regular visits to check for any issues that may arise. Inspect mooring lines for wear and adjust them as necessary to prevent chafing.

If your boat is ashore, check the cover is secure, that no leaks have developed, and there are no signs of unwanted visitors like rodents. If your boat is in the water, monitor the bilges regularly and ensure the bilge pump is operational. Extra precautions like doubling up on mooring lines and ensuring fenders are well-placed can prevent damage during storms or high winds. 

If you're berthed at a boatfolk marina, the marina crew will carry out line and fender checks, particularly when bad weather is forecast. If you want your boat to receive an extra level of care but can't make it down yourself throughout the winter, don't hesitate to give your local boatcare team a call to see what they can do to help.