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Winterising 'checklist' for hardstanding where power is not available

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What is the issue?
When the boat is lifted out of the water for the winter there is a range of tasks that will help it come through the winter intact. If there is no electrical power to provide any warming the most important of all the preparations is to prevent frost damage to items that contain water.

Why address this?
Yachts have several hidden reserves of water such as in the water tank and it’s associated water lines, engine raw water feed and coolant, batteries, marine calorifier tank, bilge, shower sumps, toilets etc. If any of these were to freeze serious damage will occur. If there is no source of power to deliver heat and there is any possibility the vessel will be subjected to freezing temperatures it is vital that additional measures be taken to the standard winter layup to prevent frost damage. The boat will also need additional ventilation to keep it free from damp and mildew.

How to address this?
If you have to lay up your boat without power you must remove all fluids from the boat, or protect them from freezing by the addition of anti-freeze. Extra ventilation will also be required in order to prevent mould and mildew.


Before we start we should touch briefly upon antifreeze. Please avoid the highly toxic ethylene glycol (EG) type made for vehicles as it is poisonous and deadly to wildlife, and when used for winterising can end up in the waters around your vessel. Select a propylene glycol (PG) antifreeze intended for marine/RV use that is slightly more expensive to produce, is odourless, tasteless, biodegradable, and nontoxic. Some cost efficiencies can be had by using a propylene glycol/alcohol blend. This is fine for the drinking water and sanitation systems, but is not recommended for winter engine storage, since some of the alcohol can evaporate resulting in reduced protection towards the end of winter layup.

Given the choice opt for the lowest temperature available to make allowances for any residual waters in the system that will dilute the concentration of the antifreeze leaving you with a higher freezing point of protection than indicated on the bottle. Propylene glycol antifreeze for boats or caravans freshwater systems are readily available down to -15°C (5°F).

First off attend to the standard lay-up as appropriate in the winterising 'checklist' for hardstanding where power is available Experience. The only significant interleaving exception to this list is to antifreeze the engine. If this additional step is not carried out water in the cooling chambers can freeze, expand and crack the engine block and manifolds. This can be handled by:

  • ☐ Preparing a jug or bucket of anti-freeze.

  • ☐ Close off the raw water intake seacock and disconnect the hose from the head of the stopcock.

  • ☐ Put the end of the hose in the bucket or jug of antifreeze mixture.

  • ☐ Start the engine and run it until the anti-freeze is seen discharged from the exhaust.

  • ☐ Turn off the engine and reconnect the hose to the seacock but keep the valve closed.

  • ☐ Seal off the exhaust outlet - simply slice off the bottom of an appropriately sized plastic bottle and duct tape it in place.

The following additional further additional general measures are also advisable:

  • ☐ A poorly charged battery may burst as a result of freezing so it is advisable to remove the batteries from the boat. Store in a warm dry place charging them every 30 to 60 days. Alternatively add a trickle charge device such as a wind vein or solar panel that can keep them topped up through the winter, or come down and attach a battery charger every month if possible.

  • ☐ Check the engine coolant has antifreeze properties. Some engine coolant systems only offer anti-corrosion mixtures and offer no protection against freezing. If this is the case then the system must be drained. Otherwise, top up if required.

  • ☐ Drain the fresh water cooling and heat exchanger system and replace the coolant with 50:50 completely non-toxic antifreeze (make certain that it has no harsh chemicals) to water. Check all the fresh water from the hoses and pumps have cleared. This may require you to disconnect hoses at both ends.

  • ☐ Alternatively, or if all the water cannot be removed, add non-toxic anti-freeze into the main holding tank. Turn on the pump and close all the taps save the one farthest away from the pump. Run it until you see the antifreeze come out and close it off. Repeat with all the taps, hot and cold including showerheads, working back towards the pump.

  • ☐ Remove the hose from the head(s) intake seacock and sit in a bucket of 50-50 antifreeze and water. Pump the head until the antifreeze has flushed thtrough the system. Replace the hose on the seacock.

  • ☐ Make sure that all raw water strainers are purged and filled with antifreeze.

  • ☐ Pour some antifreeze into the bilge to prevent any residual water that cannot be removed from freezing.

Before closing it is worth checking your insurance policy regarding damage related to freezing and winterisation maintenance. Many boat insurance policies don’t cover ice and freezing-related damage.


Without a dehumidifier, an enclosed vessel is vulnerable to mould damage and it is likely to develop a stale and unpleasant smell that is hard to entirely remove with a spring clean. Likewise, and although the rigours of winter can best be kept at bay by placing a cover over the boat Experience, this only adds to the problem. Any added canopy will dramatically reduce airflow and the lack of ventilation can make the boat go very stale below decks.

Washboards with an integrated vent aids ventilation
Photo: CC0

The answer to mould and mildew is to add as much ventilation as possible. If it is possible to do so without letting in the debris, rain and snow, leave some hatches and maybe a window slightly open. If this is not possible create or install a few weatherproof secure vents that let the fresh air in. If you don’t have all-weather vents on hatches, fitting them will make all the difference.

Replace washboards with vented cover board for winter
Image: Tony Gibson

Above and below are approaches to add extra ventilation by replacing the main companionway washboards for the winter with a single made-to-measure board either with water protection, above, or without, below, where it is used under a tarpaulin.

Replace washboards with vented board under boat cover
Image: Tony Gibson

The same approach can be applied to hatches using a securing bolt and rod that may only be undone from the inside. Add a wire mesh to the boards if you have any concern about rodents being in the area.

Winter ventilation by adding port hole covers
Photo: Tony Gibson

With some of the above measures in place and all interior doors opened from the head door to the storage and galley lockers, and the drawers slightly ajar for increased ventilation you should not have a problem. If you still have issues it is possible to use a chemical dehumidifier and a chlorine dioxide mould-odour eliminator, such as Aqua-Tab, that is widely regarded as an effective odour reduction compound.

With thanks to:
Michael Harpur, Yacht Whistler.
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