The Ultimate Boat Winterisation Guide

Boat winterisation protects more than the engine. Water trapped in a shower mixer can split a fitting, a small leak can soak the interior, and a flat battery can leave the bilge pump unable to remove water collecting inside the hull. The right preparation deals with the whole boat, whether it is coming ashore, staying on a mooring or being used through winter.

This guide explains what to check, what to drain or protect, which supplies to gather and what to record for spring. It covers sailing boats, motorboats and smaller powered craft in UK conditions, with clear distinctions where the correct procedure depends on your equipment.

Start with your manuals. The boat builder's instructions and the manuals for your exact engine, drive, batteries, pumps and appliances take priority over general advice. Winterisation is a plan for your boat, rather than one procedure that suits every installation.

Boat winterisation: the quick-start checklist

1. Confirm the storage plan. Check your insurance conditions, berth or yard arrangements and who will inspect the boat.
2. Book work early. Arrange lifting, engine servicing, rig inspections and safety-equipment servicing before autumn bookings fill up.
3. Identify every water-filled system. Include engine cooling, freshwater, toilets, showers, pumps, heaters and any less obvious accessories.
4. Service and protect the engine. Follow the storage procedure for the exact model and cooling system; prepare the fuel as instructed.
5. Drain or winter-protect domestic plumbing. Include the hot-water tank, often called a calorifier, pump head, filters and outside shower.
6. Make a battery plan. Preserve essential pumps and alarms afloat, with charging suitable for the battery chemistry.
7. Clean, dry and secure the boat. Remove vulnerable soft furnishings and sails where appropriate; check covers, drainage and moorings.
8. Label and record everything. Leave clear warnings on winterised systems and make a checklist of changes to reverse before use.

If frost is forecast before everything is finished: prioritise protecting the engine's vulnerable water circuits and draining exposed freshwater equipment. If you cannot confidently complete the correct procedure, arrange professional help. An unfinished service list can wait; trapped water may not.

1. When should you start winterising a boat?

Start planning before your final regular outing, then complete frost protection before freezing conditions reach the boat. There is no reliable UK-wide date: an exposed inland yard, a sheltered coastal marina and an unheated storage building present different conditions. Coastal water may moderate temperatures, but it does not protect deck showers, above-water pipework or a boat ashore.

Winterisation addresses five connected problems: frost can damage water-filled equipment; corrosion attacks metals and connections; moisture encourages mould and damages interiors; stored fuel can deteriorate or become contaminated; and batteries can discharge while the boat is idle. A cover alone addresses only part of the job. Further guidance: RYA winterising tips.

Choose a realistic storage and inspection plan

Ashore gives access to the hull and underwater fittings, but the boat still needs secure support, drainage and frost protection. Afloat avoids a full lay-up if you are winter boating, but moorings, hull openings, pumping and battery charging need continuing attention.

Check your own insurance schedule for navigation limits, lay-up dates, unattended periods, security requirements and any conditions for winter moorings, heaters or shore power. Obtain agreement before changing arrangements that affect cover. Do not assume another owner's winter policy applies to you.

Equipment: manuals, maintenance log, camera or phone, labels, marker pen and a working supplies list.

1. Record engine and equipment model numbers, engine hours, existing faults and service dates.
2. Photograph the hull, propeller, anodes, accessible hose connections, battery wiring and normal valve positions. Take wider photographs as well as close-ups.
3. List every system containing water, including generators, raw-water air conditioning, deck wash pumps, livewells and ballast systems if fitted.
4. Divide the work into jobs before lifting, jobs ashore and jobs before leaving the boat. Pumping out the holding tank, for example, may be easier before haul-out.
5. Book contractors and agree exactly what their service includes. Engine servicing and complete frost protection are not necessarily the same booking.
6. Record the product, quantity, coolant specification, measured protection and any disconnected components as work is completed.

Avoid: relying on memory, leaving all jobs until lifting day or assuming that a paid engine service also covers the toilet and domestic plumbing.

What if you will use the boat throughout winter?

Keep a written departure and return checklist. Service the boat normally, protect unused branches such as the transom shower, and restore the agreed frost protection after every trip. Opening a water-inlet valve or refilling a drained system changes its winter status.

If frost protection depends on powered heating, consider what happens during a marina power cut. Approved heating needs suitable installation and monitoring; it should not become an unexamined substitute for draining equipment that will remain unused.

Which jobs are reasonable to do yourself?

Cleaning, drying, photographing, checking dates, inspecting accessible equipment and draining straightforward plumbing are often manageable owner tasks. Routine servicing can also be appropriate if the manual, tools and your competence support it.

Use a qualified marine professional for unfamiliar engine preservation, pressurised fuel-system work, suspect hull fittings, drive bellows, structural damage, mains electrical faults or battery-system changes. Use a competent rigger for work aloft and uncertain rig defects, and a suitably qualified marine LPG engineer for gas work. Ask for a written record of what has been done and what must happen before restarting.

Afloat versus ashore: how winter preparation changes

2. Clean and inspect the hull, underwater equipment and seacocks

Why it matters: growth and dirt conceal damage, while a worn fitting or leaking hose can become more serious during unattended storage.

Equipment: suitable boat cleaner, soft brushes, freshwater hose, gloves, torch, inspection mirror, camera and the correct tools for any authorised servicing.

Hull and underwater gear

1. Clean promptly after lifting. Use the yard's designated washdown area and waste arrangements. Keep concentrated pressure away from seals, bearings, vulnerable coatings and fittings.
2. Inspect the hull. Photograph new cracks, impact marks, blisters, coating failure and changes around the keel or transom. Have structural concerns assessed before covering or painting them.
3. Inspect propellers and shafts. Look for damaged blades, corrosion, fishing line and unusual movement. A cutless bearing is the water-lubricated bearing supporting a propeller shaft; excessive play needs assessment rather than guesswork.
4. Check rudders and drives. Look for looseness, damage, leaks and deteriorated seals. Review the service intervals for flexible drive seals, including the sterndrive bellows and saildrive diaphragms explained in the engine section.
5. Check shaft seals and stern glands. These seal the rotating shaft where it passes through the hull. Different designs require different attention; do not grease a seal simply because another boat's gland uses grease.

With outboards and sterndrives, fishing line behind the propeller can damage the shaft seal. If removing the propeller is within your competence, follow the manual for isolation, washers, grease, tightening torque and locking arrangements. Otherwise ask the engineer to include it. Source: Mercury Marine maintenance guidance.

Check sacrificial anodes

Sacrificial anodes are replaceable metal components that corrode to help protect other underwater metals. Check the hull, shaft, propeller, drive and any engine anodes specified in the manual.

Choose the correct anode alloy and pattern for the equipment and the water where the boat lives; zinc is not a universal choice. MG Duff advises renewal when its anodes are more than 50% wasted. Replace earlier if the remaining anode cannot protect the boat until its next inspection, and follow equipment-specific limits. Never paint the working surface. Unusually rapid loss, or corrosion despite apparently unused anodes, deserves investigation. Source: MG Duff anode inspection and selection guidance; MG Duff fitting guidance.

Skin fittings and seacocks: treat afloat and ashore differently

A skin fitting passes through the hull. A seacock is the valve used to control the attached water connection. Inspect accessible fittings, hoses, clamps and backing areas for leaks, cracks, corrosion and movement. Gently operate serviceable valves, but do not force a seized one.

Afloat: close seacocks serving unused systems where this is safe and appropriate. Identify cockpit drains, essential discharges and other openings that must remain operational. Before disconnecting any below-waterline hose, positively isolate its inlet; if isolation is uncertain, arrange a lift. Label closed engine and toilet inlets.

Ashore: include valves and connected hoses in frost protection. Water can remain trapped in valve bodies, so use the valve manufacturer's draining procedure and storage position. Simply turning every handle open or closed is not a complete plan. Source: BoatUS seacock maintenance guidance.

Avoid: dismantling suspect underwater fittings afloat, forcing valves or applying a universal lubrication treatment. Some composite valves require no lubrication at all. Source: TruDesign ball-valve guidance.

3. Winterise the engine, drive and fuel system

Why it matters: an engine can suffer frost damage in its water circuits, internal corrosion during storage and starting or running problems caused by deteriorated fuel. The correct procedure depends on both the engine and its installation.

Equipment: the exact engine and drive manuals, specified oils and filters, drain trays, waste containers, suitable hand tools, required replacement seals, and any manufacturer-approved flushing or preservation equipment. Buy antifreeze only after identifying the circuit it will protect.

Identify the cooling system before doing anything

Closed cooling does not mean the whole installation is frost-protected. Volvo Penta explains that raw water remains in parts of its closed-cooled installations and must still be drained as specified. Yanmar's JH manual separately instructs owners to drain seawater while retaining the engine coolant. These are examples of the distinction, not interchangeable instructions for all engines. Sources: Volvo Penta cooling-system explanation; Yanmar JH operation manual, long-term storage.

Service first, then complete storage protection

1. Deal with faults. Investigate overheating, coolant loss, fuel leaks, unusual noises and starting problems before storage.
2. Complete due servicing. Follow the schedule for oil, oil filter, fuel filters, belts, impeller and gearbox or drive lubricant. Where an oil change is due, doing it before lay-up avoids leaving used oil in the engine throughout storage.
3. Inspect drained lubricants. Milky gear lubricant can indicate water ingress. Have the cause checked; changing the lubricant alone does not repair a leaking seal.
4. Prepare the fuel. Complete any required circulation of treated fuel before the final cooling-system preservation stage.
5. Protect each cooling circuit. Follow every drain point, hose and component named in the manual. Confirm that drains actually flow; a blocked drain is not an empty circuit.
6. Finish preservation and label the controls. Record removed impellers, disconnected hoses, closed inlets, drain plugs and any intake or exhaust closures required by the manual.

Use the specified lubricant and coolant, including the correct chemistry and concentration. A matching colour does not establish compatibility. Check coolant age as well as frost protection, and use a tester appropriate to the fluid. Beta Marine's published oil and coolant requirements illustrate why a generic shopping list is insufficient. Source: Beta Marine general aftercare.

Inboard engines: protect the whole installation

Trace the raw-water route from the inlet and strainer through the pump, coolers and exhaust. Include components outside the engine itself. A generator needs its own procedure even if it shares the main engine's brand.

Some engines require draining; others specify an approved antifreeze preservation process, or draining followed by treatment. Do not replace this with an improvised bucket routine. Residual water can dilute the fluid, and thermostat-controlled passages may not receive protection just because coloured liquid appears at the exhaust.

Only run an engine with the cooling-water supply and flushing arrangement its manufacturer permits. Keep people clear of moving parts and exhaust, and ventilate petrol engine spaces as instructed before starting. If hoses need disconnecting afloat, isolate the sea inlet first. Unfamiliar raw-water and wet-exhaust arrangements are a sensible job for a marine engineer.

Outboards: flushing is not running the engine dry

Freshwater flushing helps remove salt and contamination, but the flushing connection determines whether the engine may run. Yamaha distinguishes lower-unit flushing adapters from integral freshwater flush connections: do not assume a hose connected anywhere provides a safe running supply. Follow the instructions for your exact engine and adapter, including propeller-removal precautions. Source: Yamaha outboard FAQs.

Do not start an outboard out of the water to clear it. Mercury warns that running without a proper water supply can damage the water-pump impeller, the flexible component that moves cooling water. Its outboards are designed to drain when fully lowered; follow your own manual for drainage, storage and transport positions. A small portable four-stroke may also have restrictions on which side it can lie. Source: Mercury Marine cooling and drainage guidance.

For an outboard left afloat, check the maker's cold-weather instructions and the actual installation. Tilting the leg clear of the water does not automatically remove all trapped water or complete winterisation. Check anode immersion requirements for any drive components left submerged.

Sterndrives and saildrives need additional attention

A sterndrive combines an inboard engine with an external drive. Winterising the engine does not service the drive. Include gear lubricant, anodes, cooling passages, seals and the bellows: flexible rubber sleeves around parts of the transom assembly. Ask an engineer to inspect inaccessible bellows, bearings and joints and check replacement intervals. Source: Mercury Marine drive inspection guidance.

Set the stored drive position according to its manual, with adequate ground clearance. A saildrive passes through the hull beneath the engine; its hull diaphragm is the flexible seal around that installation. Check its drive oil, anodes, propeller arrangements and diaphragm inspection or replacement schedule. Do not transfer sterndrive instructions to a saildrive.

Petrol fuel: use a storage plan for the actual system

Check the permitted fuel grade and ethanol content in the engine manual. If stabiliser is specified, add the correct dose to suitable fresh fuel and circulate it for the instructed period before storage. Stabiliser does not restore stale fuel or remove existing water contamination. Source: Yamaha fuel-system guidance.

Do not automatically fill every tank to the brim. The correct storage level depends on the tank, venting system, engine guidance and storage rules. Some manufacturers recommend a high level with expansion space; other arrangements require draining. Mercury, for example, discusses approximately 95% for older vented tanks, rather than an unrestricted brim-full instruction. Never block a required fuel vent. Source: Mercury outboard storage guidance; Yamaha extended-storage guidance.

A carburettor's small fuel reservoir may need draining, but disconnecting the fuel hose and running until the engine stops is not suitable for every petrol engine. Follow the specified procedure for carburettors, electronic fuel injection and direct-injection systems. Arrange safe removal of unwanted fuel; never discharge it into the bilge or drains.

Diesel fuel: control water and contamination

Inspect the filler-cap seal, accessible fuel lines and the water separator, which collects water before it reaches the engine. Drain collected water as instructed and investigate recurring contamination. Sludge, repeated blocked filters or suspected diesel bug, microbial contamination associated with water in fuel, call for diagnosis and possibly tank cleaning.

Choose the storage fuel level from the engine and tank guidance, allowing required expansion space. Do not assume petrol stabiliser treats diesel, or that a diesel additive removes an existing tankful of water. Use a compatible stabiliser or biocide, a treatment that kills microorganisms, only where appropriate, following its label and engine guidance. Yanmar's JH instructions allow different fuel-storage approaches, reinforcing the need to check the actual manual. Source: Yanmar JH long-term storage instructions.

When is fogging appropriate?

Fogging applies a protective oil coating to internal engine surfaces for storage. Some petrol engines specify it, but the product, application route and sequence vary. Mercury's guidance distinguishes conventional engines from certain direct-injection two-strokes, while Yamaha offers different preservation products for different petrol systems. Sources: Mercury fogging guidance; Yamaha extended-storage guidance.

Do not spray fogging oil into an unfamiliar intake, particularly on a diesel. Follow the exact engine preservation instructions; if none are available, ask the manufacturer or an authorised marine engineer. Avoid copying another engine's procedure, altering belt tension without instructions or restarting a fully winterised engine just to hear it run.

4. Choose the right antifreeze for each circuit

Why it matters: engine coolant and fluid approved for drinking-water plumbing are not interchangeable. The wrong chemistry can be unsafe or damage components, while excessive dilution can leave a correctly chosen product ineffective.

Equipment: equipment manuals, the product label and safety data sheet, suitable gloves, separate labelled containers and, where required, a tester calibrated for the correct glycol type.

• Closed engine cooling: use coolant meeting the engine manufacturer's exact specification, concentration and change interval. Retain it for storage unless the prescribed procedure says otherwise.
• Raw-water engine preservation: use only a product and method approved for that engine's storage procedure. A product approved for domestic plumbing is not automatically an approved engine coolant.
• Potable-water plumbing: potable means suitable for drinking. If antifreeze is permitted, use a winterisation fluid explicitly approved for potable-water systems and compatible with every component it will contact. These products are commonly propylene-glycol based. Never use automotive ethylene-glycol coolant in drinking-water plumbing.
• Toilets and pumps: obtain approval from their own manuals. Some specify draining and discourage antifreeze use.

Do not choose by colour or the word “marine” alone. Star brite's potable-water antifreeze, for example, has a defined formulation and ready-to-use instructions; that does not establish compatibility for every pump or heater. Source: Star brite product directions.

Check dilution and rating. Follow the label: some products are concentrates, while others must be used undiluted. Drain residual water as directed before treatment. Also distinguish freeze protection, when ice crystals start forming, from burst protection, protection against expansion damage under the stated conditions. A headline burst temperature is not necessarily the temperature at which the fluid stays liquid. Source: Star brite explanation of freeze and burst points.

Collect and dispose responsibly. Keep used coolant, antifreeze, oil and fuel in suitable labelled containers, separately. Do not pour them down drains or release them overboard. Ask the yard or local authority which facility accepts each waste stream; “non-toxic” does not mean approved for discharge. Sources: council coolant-disposal guidance; GOV.UK waste-segregation guidance.

5. Winterise freshwater tanks, pumps, pipes and calorifiers

Why it matters: an empty tank does not mean an empty system. Water can remain in pump chambers, filters, low pipe runs, mixer valves and shower heads.

Equipment: freshwater-system manuals, buckets, towels, basic hose tools, labels and any approved drain fittings, bypass kit or potable-water winterisation fluid.

Work through the system in a controlled order

1. Turn off water heating. Isolate the immersion heater, the electric element heating the tank, and any other heat source before draining. Let hot water cool, isolate incoming supplies and release pressure safely.
2. Drain the freshwater tank. Use the designed drain or the pump as its manual permits. Switch the pump off when appropriate; do not leave it running indefinitely.
3. Drain the calorifier separately. A calorifier stores domestic hot water, often heated by the engine through an internal coil. Use its specified drain and air-admission procedure. Opening a sink tap alone may not empty it.
4. Drain branches and fittings. Include hot and cold feeds, shower mixers, transom showers, deck outlets, filter housings and any connected appliances. Include accumulators, the small pressure vessels fitted to smooth water flow. Remove cartridges or disconnect components only as their instructions require.
5. Deal with the pump head and low points. Follow the pump's draining procedure. Run it dry only if that model allows it, and only for the stated period.
6. Apply any approved additional protection. If using a potable-water antifreeze process, protect every required branch and bypass a separately drained calorifier only where permitted. Do not improvise bypasses or use unrestricted compressed air.
7. Leave the system in its specified storage condition. Record disconnected hoses, drain valves and tap positions. Label the pump and heater so neither is operated accidentally.

Whale's pressure-pump instructions include specific draining steps and an exception for its Twist deck shower. This is why “leave all taps open” still needs checking against the fitted equipment. Surejust also specifically requires draining an unused calorifier where freezing is possible. Sources: Whale Watermaster instructions; Surejust calorifier guidance.

Keep the two calorifier circuits separate in your mind. Draining domestic water does not drain the engine-heating coil. Protect that coil according to what circulates through it: the engine coolant specification or the relevant raw-water draining procedure.

Avoid: leaving outside showers connected and full, assuming insulation prevents freezing, or switching an empty water heater back on. Before spring heating, refill and bleed the domestic system fully as the heater manual requires.

6. Clean toilets and holding tanks, then check bilges and drainage

Toilets and holding tanks

Why it matters: retained waste causes odours, while water trapped in pumps, valves and hoses can freeze even when the bowl looks empty.

Equipment: gloves, suitable toilet cleaner, pump-out access, hose tools, containers and the exact toilet and waste-system instructions.

1. Empty the holding tank at an approved pump-out facility and rinse as the tank manufacturer permits.
2. Clean and flush the toilet using products approved for its seals, hoses and treatment system.
3. Isolate the appropriate seacocks and electrical supply before dismantling anything. Trace both inlet and discharge routes, including remote pumps and low sections.
4. Follow the model's winterisation procedure for the toilet, pumps, tank and associated valves. Protect freshwater-flush and raw-water-flush installations according to their different layouts.
5. Maintain required tank ventilation and label disconnected plumbing and closed valves.

Do not assume antifreeze is always recommended. Jabsco's Deluxe Flush instructions specify complete draining and discourage antifreeze because complete penetration cannot be assured. Other Jabsco equipment has different procedures. Pouring fluid into the bowl alone does not protect the inlet hose or every pump. Source: Jabsco Deluxe Flush servicing and winterisation instructions.

Avoid: automotive coolant, incompatible toilet chemicals, sealing tank vents or assuming the macerator, which breaks up toilet waste, and shower-waste pump are protected because the main toilet is drained.

Bilges, pumps, float switches and drainage routes

Why it matters: a working pump cannot remove water if its intake is blocked, its discharge is frozen or its battery is flat.

Equipment: absorbent pads, approved bilge cleaner, bucket, torch and clean water for a controlled pump test.

Remove oil and fuel contamination using suitable collection methods before cleaning. Dispose of contaminated liquid ashore. Dry accessible bilges, then investigate recurring water rather than accepting it as inevitable.

Clean pump strainers and float switches, the devices that trigger automatic pumping as water rises. Test manual and automatic operation according to the pump's instructions, confirming actual discharge rather than just listening for a motor. On a boat staying afloat, verify the automatic circuit still works with the main battery switch in its intended winter position. Source: Canal & River Trust winter bilge-pump guidance.

Clear cockpit drains, scuppers, anchor-locker drains and accessible drainage channels between bilge compartments. Check hoses are secure and discharges unobstructed. Afloat, preserve essential drainage and pumping. Ashore, winterise pumps and trapped pipe sections as their manuals require; use a hull drain plug only where the boat's storage instructions permit, and record its removal for launch.

Avoid: treating a bilge pump as a repair for a leak, adding antifreeze to an active bilge without a designed procedure, or closing a valve that an essential drain or pump needs.

7. Look after batteries, electrics and shore power

Why it matters: self-discharge and small standby loads can flatten batteries during storage. Battery chemistry determines the correct charging, temperature and storage approach.

Equipment: battery and charger manuals, an appropriate charger, battery monitor or suitable meter, terminal protection and insulated tools where connections need attention.

Lead-acid batteries: flooded, AGM and gel

Flooded batteries contain liquid electrolyte, the fluid involved in storing and releasing energy. AGM batteries hold it in absorbent glass matting; gel batteries use a gelled electrolyte. Their charging requirements differ, even though all three are lead-acid designs.

Charge before storage, keep batteries clean and dry, secure them properly and maintain charge using a compatible charging regime. A partly discharged flooded lead-acid battery is more vulnerable to freezing. Monitor charge rather than assuming a battery will last until spring. Source: Trojan battery storage guidance.

Only check or top up electrolyte on batteries designed for it, following the maker's sequence and using the specified water. Do not open sealed AGM or gel batteries. Provide the required ventilation while charging, keep ignition sources away and protect terminals against short circuits.

Lithium batteries need their own plan

Most recreational marine lithium installations use lithium iron phosphate, or LiFePO4. Follow the battery manufacturer's storage charge level, temperature limits and inspection interval. Do not apply a universal “store at 50%” or “keep fully charged” rule.

The battery management system, or BMS, controls protection functions, but small loads can still create storage problems. Check for standby consumption and confirm how every charging source, including solar, responds to low battery temperature. Victron's Lithium Battery Smart guidance, for example, permits charging only from +5°C: other models have their own limits and may use approved heating arrangements. Source: Victron lithium operation and charging instructions.

Avoid: using lead-acid equalisation or desulphation modes on lithium, bypassing cold-charge protection, or treating a BMS low-voltage shutdown as an acceptable storage endpoint.

Should batteries be disconnected or removed?

Ashore, isolation or removal may be appropriate if no essential service needs the bank. Photograph and label wiring first, and follow the installed system's shutdown sequence, including solar controllers and chargers. Store removed batteries securely in the environment specified by their manufacturer, with protected terminals.

Afloat, identify which bank supplies automatic bilge pumps, alarms, monitoring and any essential equipment. Preserve those circuits with a reliable charging and inspection plan. Do not assume that either “all switches off” or “leave everything on” is safe for your installation.

Use shore power carefully

Inspect the lead, inlet and connectors for cuts, looseness, corrosion, heat damage and water ingress. Keep cables supported clear of the water and fully uncoiled. A residual current device, or RCD, cuts the supply when it detects certain electrical leakage faults. Follow the marina's rules and have damaged equipment or repeated RCD trips investigated by a marine electrician.

When connecting, attach the boat end first and the shore end second; when disconnecting, remove the shore end first. Use the supply switching arrangements as instructed. Never make improvised mains connections. Source: Boat Safety Scheme shore-power guidance.

8. Control damp, condensation and interior moisture

Why it matters: condensation forms when moist air meets colder surfaces. Persistent moisture encourages mould, corrosion and deterioration, especially inside closed lockers and beneath cushions.

Equipment: suitable cleaners, cloths, a humidity meter if useful, secure moisture absorbers for small spaces and, where appropriate, a low-temperature-capable dehumidifier.

1. Find leaks first. Check windows, hatches, deck fittings and plumbing. Water appearing after rain needs investigation; no moisture absorber repairs a leaking hatch.
2. Remove moisture-holding items. Take bedding, towels, spare clothing and removable upholstery ashore where practical. Clean and dry them before storage.
3. Dry the interior. Clean lockers and accessible surfaces. Support remaining cushions on edge and open internal locker doors where safe to encourage circulation.
4. Clean the galley. Remove perishables, defrost and dry the fridge, and secure its door slightly open while it is switched off.
5. Choose a workable moisture-control approach. Maintain weather-protected ventilation, or use a suitable dehumidifier under its operating instructions. Keep permanent safety ventilation unobstructed in either case.

Moisture absorbers can help in small enclosed spaces, but their capacity is limited. Secure liquid-collecting tubs upright and away from electrics, wood and metal surfaces that a spill could damage.

Using a dehumidifier aboard

Choose for the boat's actual winter temperature, not a warm-room extraction figure. Check the permitted temperature range, unattended-use instructions, automatic restart behaviour and drainage arrangement. Meaco highlights low-temperature performance and continuous drainage as important considerations for boats. Source: Meaco boat-humidity guidance.

Secure the unit upright, keep its air paths clear and route drainage so it cannot spill into the boat, freeze or depend on an isolated outlet. Check a proposed sink drain against the winter seacock plan. Limit unnecessary outside-air exchange only where safe and consistent with the boat's ventilation requirements.

Avoid: sealing the boat completely, blocking permanent vents or using a gas cooker or portable unflued gas heater to keep the interior warm. These can create serious carbon-monoxide and fire risks. Source: Boat Safety Scheme carbon-monoxide precautions.

9. Clean and store deck equipment, sails, rigging and canvas

Why it matters: salt, damp and winter movement accelerate wear. Unused sails and canvas also add windage, the area exposed to wind loading.

Equipment: freshwater hose, soft brush, material-approved cleaners, drying space, labels, storage bags and suitable messenger lines if removing halyards.

Sails and running rigging

For extended lay-up, remove sails, inspect stitching, chafe points and UV protection, and arrange repairs. Rinse or clean only as the sailmaker permits, then dry completely. Fold or roll according to the sail construction and store somewhere dry, away from rodents and heavy objects. Source: North Sails winter-storage guidance.

Running rigging means the ropes used to control sails, including halyards and sheets. Photograph their routes and label ends before removal. If replacing halyards with messenger lines, use a suitable method so a failed connection does not lose the route through the mast. Wash rope only with compatible products and dry before storage.

If winter sailing means sails stay aboard, inspect furling gear and secure sails against accidental deployment. Do not rely on a single cover tie or the furling line alone as your entire storm preparation.

Standing rigging and deck hardware

Standing rigging supports the mast. Check accessible wires or rods, terminals, rigging screws, attachment plates and retaining pins for corrosion, cracks, damage or movement. Broken wire strands need professional attention. Arrange a rigger's inspection where access or diagnosis is uncertain; an examination from deck level cannot establish the condition of the whole rig. Source: Seldén annual rig-maintenance guidance.

Clean blocks, tracks, clutches and winches and service them according to their manuals. Use only specified lubricants: more grease is not automatically better. If the mast remains stepped ashore, agree support and rig arrangements with the yard and rigger.

Clean and dry sprayhoods, dodgers, cockpit enclosures and covers with products suitable for the fabric and clear panels. Remove unnecessary canvas for long storage; support any cover that stays fitted and protect it from sharp edges.

Avoid: packing damp sails, harsh cleaning chemicals, unrecorded rope removal, unsupported covers or loosening standing rigging without an agreed plan.

10. Secure the boat against winter weather and theft

Why it matters: repeated movement causes chafe, while covers can collect rain or catch the wind. Small weaknesses become more significant during long unattended periods.

Equipment: suitable mooring lines, chafe guards, correctly sized fenders, supported covers, approved tie-downs and security devices appropriate to your insurance requirements.

For boats remaining afloat

Inspect lines over their full length, including beneath sleeves. Check cleats, fairleads, pontoon fittings and the lead of each rope. Add or renew lines as the berth requires, accounting for tide, surge and changing river levels. Simply tightening every rope can leave the boat unable to rise or fall safely.

Position chafe protection so it stays at the contact point. Use independent additional lines where appropriate, rather than loading every backup through the same damaged fairlead. Adjust fenders to protect likely contact areas and inspect their ropes too.

For help assessing diameter, material and line layout, see our mooring-rope sizing guide. Suitable mooring equipment and boat fenders should be chosen for the boat and berth.

For boats ashore and on trailers

Let the yard position and support the boat for its hull, rig and drainage requirements. Do not move props or adjust cradles yourself. If a support shifts or the boat appears unstable, keep clear and contact the yard.

Arrange covers with enough support to shed water and enough ventilation to limit trapped moisture. Secure straps without loading unsuitable fittings or obstructing drains. Remove loose deck gear and unnecessary wind-catching items.

For trailer boats, inspect tyres, bearings, winch gear, supports and tie-downs, following the trailer manufacturer's storage instructions. Lock the trailer and secure or remove portable outboards as required. Photograph serial numbers and remove valuable electronics where practical.

Avoid: making major mooring changes during a storm, leaving a sagging cover full of water or going aboard an unstable boat. Arrange inspections before forecast severe weather and as soon afterwards as access is safe.

11. Check safety equipment, gas and domestic systems

Why it matters: winter is an opportunity to service equipment without losing boating time, while heating, fuel and electrical systems still need to remain safe during visits.

Equipment: equipment records and manuals, a service-date list, suitable dry storage and replacement batteries or parts specified by the manufacturer.

• Lifejackets and liferafts: clean, dry and inspect as instructed. Check service dates and book authorised servicing where required. Keep suitable flotation available for visits to the boat.
• Flares, beacons and radios: check expiry dates, beacon battery and service dates, registration details and portable-radio battery care. Use approved disposal arrangements for expired pyrotechnics.
• Fire protection: check extinguishers, fire blankets, fixed suppression systems and access to shut-offs. Arrange the service specified for each item.
• Smoke and carbon-monoxide alarms: check their age and batteries, and test according to the instructions. Keep protection in service whenever anyone is aboard.
• LPG: shut cylinder valves when gas is not required. Check accessible hoses and locker condition without dismantling the installation; keep locker drains and permanent ventilation clear. Follow marina or yard rules for cylinders kept aboard or removed to suitable storage.
• Heating, refrigeration and air conditioning: follow each unit's storage instructions, including water circuits, condensate drains and any required shutdown cycle. Drain unused raw-water equipment separately.
• Watermakers, washing machines and specialist systems: obtain their own preservation instructions. A watermaker produces freshwater from seawater and may need its filtering membranes preserved rather than ordinary freshwater draining or antifreeze treatment.

Use a Gas Safe registered engineer with the relevant LPG boat competence for gas servicing and repairs. The RYA recommends checking manufacturer service intervals and using a boat-qualified engineer. Legal requirements vary with the boat's use, including residential and commercial operation; a BSS certificate is not a substitute for ongoing maintenance. Source: RYA gas installation and maintenance guidance.

Test alarms when boarding and regularly while aboard. Never use a portable generator in a cabin, enclosed cockpit or near openings through which exhaust can enter. Sources: Boat Safety Scheme fire-safety guidance; BSS carbon-monoxide precautions.

Avoid: removing all safety equipment while the boat is still used, obstructing gas-locker drains or making unqualified repairs to gas, mains electricity or fixed fire systems.

Practical tools and winterisation supplies checklist

Use this list after checking the manuals. Quantities depend on the actual installation; guessing antifreeze volume from boat length can leave individual circuits unprotected.

• ☐ Manuals, maintenance log, camera, waterproof labels and warning tags.
• ☐ Gloves, eye protection, torch, inspection mirror, buckets, towels and absorbent pads.
• ☐ Suitable spanners, sockets, screwdrivers and any specified torque wrench or service tools.
• ☐ Correct engine oil, filters, drive lubricant, seals and any due service parts.
• ☐ Approved flushing equipment, hoses and adapters for the particular engine.
• ☐ Correct closed-circuit coolant, separate approved winterisation fluid where needed, and a suitable tester.
• ☐ Compatible petrol or diesel treatment where specified, with a means of measuring the dose.
• ☐ Approved freshwater-system fittings, drain equipment and any permitted calorifier bypass kit.
• ☐ Material-compatible hull, bilge, toilet, sail and canvas cleaning products.
• ☐ Correct replacement anodes and specified fitting hardware.
• ☐ Chemistry-compatible battery charger and suitable charge-monitoring equipment.
• ☐ Moisture-control supplies, dry storage bags and appropriate cover supports.
• ☐ Sound mooring lines, chafe protection, fenders and required security devices.
• ☐ Separate labelled containers for used oil, coolant, fuel and contaminated liquids.

Our winter essentials range is a useful starting point for winterisation supplies. Check each product's specification against the system it will serve, especially antifreeze, fuel treatments and battery chargers.

Common boat winterisation mistakes and how to avoid them

A manageable winter inspection schedule

The following is a practical starting schedule, not a universal interval. Increase visits for exposed berths, boats depending on mains power, recurring leaks, severe weather or insurer and marina requirements. Arrange named cover if you cannot attend.

Record the date, bilge condition, battery readings, signs of leaks and work completed. Photographs taken from the same positions make changes easier to spot. Remote monitoring helps identify problems but does not replace someone able to inspect and respond.

Spring recommissioning: reverse the record before starting

Recommissioning means returning the boat and its systems to safe working order. Use the winterisation record as a job list, checking each change rather than simply reversing it without inspection.

1. Complete outstanding repairs. Resolve structural, cooling, fuel, electrical and underwater-fitting concerns before launch or use.
2. Restore engine systems. Follow the engine's return-to-service procedure. Account for drain plugs, hoses, impellers, belts and intake or exhaust closures; check fluids and establish the cooling-water supply before starting.
3. Check hull openings. Confirm seacocks, hoses, clamps, drain plugs, transducers and seals are correctly fitted. Inspect immediately after launching for water ingress.
4. Recommission freshwater and sanitation. Restore connections, flush winterisation fluid into suitable collection arrangements, and clean or sanitise as the system and product instructions require. Refill and bleed the water heater before energising it.
5. Restore electrical readiness. Check battery condition, charge, terminals, essential pumps, alarms, lights, navigation equipment and communications.
6. Refit and inspect sailing equipment. Restore rigging and sails under the appropriate instructions, and complete any required professional checks.
7. Check safety equipment and domestic systems. Restore serviced items and confirm gas, heating and fire protection are ready.
8. Test progressively. Conduct an attended first start with the proper cooling supply, checking leaks, alarms and operation. Follow with a controlled trial before a longer passage.

If the boat has been used during winter, apply the same checks to any system that remained winterised. Never assume the whole boat is ready because the engine has been running.

Final boat winterisation checklist

Tick each item when completed, or mark it not applicable. Write down any job still outstanding and who is responsible for it.

• ☐ Storage arrangements, insurance conditions and inspection responsibilities confirmed.
• ☐ Manuals, model numbers, service records and condition photographs saved.
• ☐ Hull, keel, rudder, propeller, shaft and drive inspected as access allows; concerns booked for repair.
• ☐ Anodes checked and renewed where necessary, with the correct alloy and fitting arrangements.
• ☐ Skin fittings, seacocks, hoses and clamps checked; winter valve positions recorded.
• ☐ Engine, drive and generator servicing and model-specific preservation completed.
• ☐ Closed coolant and separate raw-water protection checked and recorded.
• ☐ Petrol or diesel storage plan completed; required tank vents unobstructed.
• ☐ Freshwater tank, calorifier, pumps, filters, mixers and outside outlets drained or protected as approved.
• ☐ Toilets, holding tank, waste pumps and other water-filled equipment winterised individually.
• ☐ Bilges clean; drains clear; essential pumps and automatic switches tested.
• ☐ Battery storage, isolation, charging and low-temperature protection set for the installed chemistry.
• ☐ Essential power preserved afloat; shore-power equipment checked where used.
• ☐ Leaks addressed; bedding and vulnerable furnishings removed or dried; ventilation maintained.
• ☐ Sails, ropes and canvas cleaned, dried, inspected and stored or secured appropriately.
• ☐ Moorings, chafe protection, fenders, covers, supports and security checked.
• ☐ Gas and domestic systems left safe; safety-equipment servicing arranged.
• ☐ Waste collected for appropriate disposal.
• ☐ Controls labelled, spring reversal list complete and next inspection arranged.

Boat winterisation FAQs

Does a boat in a mild coastal marina still need winterising?

Yes, it needs an appropriate winter plan. Even where severe frost is less frequent, exposed plumbing can freeze and corrosion, damp, fuel deterioration and battery discharge still matter. Base protection on conditions at the boat and the equipment instructions, not the average regional temperature.

Can I leave winterisation until the boat is lifted out?

Only if vulnerable systems are protected until then. Frost can arrive before lifting day, and jobs such as pumping out waste or making an operational engine check may be easier beforehand. Coordinate the work with the yard rather than treating haul-out as the starting signal.

Is an insulated engine cover enough to stop frost damage?

Insulation slows heat loss; it does not provide heat indefinitely. It cannot replace the specified engine draining or preservation procedure. Any active heating plan needs suitable equipment, reliable power, monitoring and an agreed response if power fails.

Do I need antifreeze if I have drained the system?

That depends on the system. Some manufacturers specify complete draining; others require an approved antifreeze treatment as well. The important question is whether the prescribed procedure has protected every vulnerable component, including places that retain water.

Can I use the boat once it has been winterised?

Yes, after completing the necessary return-to-service checks for the systems you will use. Restore cooling and operating connections first, then repeat the required winter protection afterwards. Never start an engine while its winter warning labels still describe an unsafe operating condition.

What if I do not have shore power?

Build the plan around approved draining and preservation, weather-protected ventilation and scheduled battery maintenance. Afloat, ensure essential pumps have an adequate energy supply and inspection arrangement. Solar may contribute, but check winter output and battery cold-charging restrictions before relying on it.

How much antifreeze should I buy?

List the separate circuits, their capacities and the approved application method. Include hoses and accessories, then follow the product's instructions on displacement and dilution. Boat length alone cannot provide a reliable quantity. Bring system details when asking for help.

Can I tell whether the boat has suffered frost damage just by looking?

Not reliably. A split housing, leak or displaced fitting may be visible, but internal damage can remain hidden until refilling or operation. If protection was uncertain during a freeze, have vulnerable equipment checked before starting or pressurising it.

What information helps when buying winterisation supplies?

Have the engine, drive, pump and heater model numbers, battery chemistry, storage location and relevant manual specifications ready. For antifreeze, identify the exact circuit and required product approval; a photograph of the existing container can help, but does not replace the specification.

If you need help choosing suitable boat winterisation supplies, contact Pirates Cave Chandlery with your equipment details and storage plan. We can help you compare suitable options against your manuals and put together a practical supplies list.