Winterisation is necessary to protect your engine, its controls and the electrics from damp, corrosion and damage from frost or the effects of petrol ‘varnish’.

For the domestic side of things, it is important to stop frost from getting at the plumbing, and the damp from creating nasty smelling, hard-to-remove mould marks from all the soft furnishings and headlining. Read on below for our full list of Boat Winterisation tips…

The Engine

It’s recommended that your annual service is completed in the autumn, at the same time as the engine is winterised.

Why do this now? Well over the summer season the engine will have been slowly contaminating its oil with the usual chemicals that turn it from a nice clear green or gold colour, into a muddy grey colour. Over the winter, the oil will sit for a long while, and any water and acids dissolved in it will sit under the oil wherever it lays in the engine. Over the winter, these acids start to eat their way into the various metal bearings and the sump metal. It might not be a problem over a winter or two, but it does contribute to premature engine wear over time.

A service will also highlight any issues with the engine that might then be solved over the winter months. For example, a service includes checking the gearbox oil. If water is found in the oil then there is a chance to cure the issue before it gets worse, or causes expensive gear corrosion whilst in storage.

Winterising the engine makes sure that there is no longer any threat from water left in the cooling system that might freeze and cause damage. Everything is drained and anti-freeze is run in to vulnerable places. We’ve seen new boats that have been freshly imported, and where the first frosts have fractured exhaust manifolds, so age is no protector.

Fogging oil fed into the engine air intake helps prevent corrosion in the engine’s airways, valves and exhaust. Although it does cause a fair amount of smoke when re-commissioned, this is nothing to cause concern.

Boat Control Systems

A big area of concern to do with winterisation will be the boat control systems. Engine and steering control systems will have been used throughout the year, and will be in need of their annual lubrication service. Carried out in the autumn, the damp of winter then has little to get hold of to cause problems in spring. Even if the boat has been little used, owing to the weather, the lack of exercise will have helped to exacerbate the stiffness of the cables and linkages, so servicing is still important.

To stop condensation in fuel tanks, they should be filled as high as practically possible. The fuel needs to be treated with a stabiliser to keep the fuel fresh and stop corrosion and gum forming.

Marine Batteries

Marine batteries are more expensive than the usual car batteries because of their capacity to be deep-discharged without sustaining damage. However, they are not immune to damage from incorrect storage. So it’s best to keep them charged to prevent them freezing or degenerating while not in use. One of the most common springtime issues we have to deal with is the wholesale replacement of boat batteries that have been left flat over the entire winter, and as a result have suffered internal damage to the point that they will no longer hold enough charge to start the engine.

Down Below

Here’s a great tip for keeping your interior furnishings protected from the cold and damp: If you can take it out and store it somewhere away from the damp and cold, then do so! Cushions, bedding, clothes, sponges, cloths and towels all attract damp that leads to mould. If you have somewhere for all the internal loose upholstery, that helps too. The only issue I have come across is that it feels like there’s about twice the quantity of gear coming off the boat than ever went on.

For larger boats, winterising should also include servicing and frost protection for the domestic systems, such as hot/cold water systems, generators, foul water systems and domestic electrics. And remember that bugs like nice warm places in the winter, so if you have any ventilators, leave them open to help stop condensation by all means, but put some form of netting over to stop the bugs getting in.


If power is available it’s well worth putting a small greenhouse style frost-preventing heater in the engine bay and cabin. These very low consumption heaters are no substitute for correct winterisation servicing, as unreliable marina power can leave engines vulnerable to frost. If you are going to leave your boat connected to shore power it is advisable to make sure it’s galvanically isolated from all the other boats on the same shore power circuit, otherwise they might start to use your anodes when theirs are exhausted. Such heaters are very effective at reducing damp and condensation, but do need to be carefully mounted to ensure they cannot be covered or otherwise make contact with flammable materials.

The Hull and Superstructure

It’s also a good time to consider weather protection for the boat. Is the cover you have up to the job of protecting the boat over the winter? If you’re considering a new cover for next season, then it might be better to have it made in the autumn to protect the boat over the winter months.

It might also seem a strange thing to do, but the topsides will benefit from a clean and polish too. Falling leaves make some very annoying brown marks as they rot. If they fall on a polished surface, the effect is much reduced. Mould and organic growth have less to get their roots into if the boat is clean and the crevices are free of anything for the moss to get its roots into. Roots expand the gaps and cause woodwork to split. Dust and dirt in cracks and crevices attract moisture which freezes, and expands the joints leading to leaks.

Keep checking your boat during Winter…

Don’t forget to visit the boat regularly over the winter to just make sure all is as it should be. Covers can move, for example, allowing rainwater in. Are the bilge pumps still working ok? The more that can be done to protect your boat, either by servicing or removing vulnerable equipment, then the longer everything will last and the easier it will be to get boating again in the spring.

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