Essential Guide to Winterising Your Boat: Protect Your Investment for the Cold Season

Winterising your boat is a crucial task to ensure its longevity and performance. Boats are exposed to harsh elements throughout the year, but winter can be particularly unforgiving. Proper winterisation prevents damage caused by freezing temperatures, moisture, and corrosion. In this guide, we’ll walk you through the steps needed to winterise your boat, explaining why each is necessary to protect your boat during the off-season. 

Why Winterise Your Boat? 

Boats that are not properly winterised face serious risks. Freezing water can cause engine blocks to crack, fuel systems can become clogged and interior components can grow mould or degrade. The cost of repairing a boat that’s been exposed to winter’s harshness can be steep, making prevention through proper winterisation much more cost-effective. 

Key reasons for winterising your boat include: 

• Preventing freezing damage: Water left in the engine, plumbing or cooling systems can freeze and expand, causing cracks and breaks. 

• Avoiding fuel degradation: Unprotected fuel can deteriorate, leading to clogs, corrosion and engine issues. 

• Protecting the interior: Moisture buildup can cause mildew, mould and rot inside the cabin or below deck. 

While winterising your engine, many boat owners take the chance to give it a full service. This way, it doesn’t sit all winter with old oil and fluids, and you avoid the scramble for parts or engineers when the new season starts! 

What tools and supplies are needed? 

Before you start, make sure you have the necessary tools and supplies.  Ensure that you have all the necessary parts and tools prior to starting you winterisation process. 

• Fuel stabilizer 

• Antifreeze (non-toxic, for marine use) 

• Oil and oil filter 

• Gear lube 

• Grease for fittings and hinges 

• Cleaning supplies 

• Dehumidifiers or moisture absorbers 

• Boat cover (preferably custom-fit) 

Winterise The Engine 

Your boat’s engine is the most vulnerable component during the winter. It needs to be carefully prepped and protected from the cold. 

Step 1: Flush the engine 

First, flush the engine with fresh water. This removes salt, dirt and debris that could corrode engine parts. If you have an outboard engine, use a set of “muffs” to attach a hose to the engine's water intake. For and inboard this can be done directly through the raw water intake or strainer. It is often advisable, once the engine is flushed through, to run antifreeze through the saltwater system, so that any areas of standing water are replaced with antifreeze.  Do this until you see blue antifreeze come out through the exhaust. 

Step 2: Change the oil 

Water and acids can build up in the oil over time, leading to corrosion. Change both the oil and the oil filter to remove any contaminants before storing the boat. Running the engine briefly before the oil change helps warm the oil, making it easier to drain. 

Step 3: Drain the cooling system 

Most boat engines are water-cooled, meaning water flows through the engine to keep it from overheating. Drain all the water from the cooling system to prevent freezing. If your engine has a raw-water cooling system, it’s essential to replace the water with marine-grade antifreeze, which will prevent freezing and protect the engine’s internals. 

Stabilize The Fuel System 

Fuel left in the system over winter can deteriorate, leading to clogged fuel lines and engine problems. To avoid this: 

Step 1: Fill the tank 

Filling the fuel tank prevents moisture from building up and reduces the chance of condensation. Condensation in the fuel tank can lead to corrosion or microbial growth, especially with ethanol-blended fuel. 

Step 2: Add fuel stabiliser 

Once the tank is full, add a fuel stabilizer to prevent the fuel from breaking down. Stabilisers help keep the fuel fresh for several months and prevent gum and varnish from forming in the engine. 

Step 3: Run the Engine 

Run the engine for a few minutes to circulate the stabilised fuel throughout the system. This ensures that all parts of the fuel system, from the tank to the injectors are protected. 

Take Care Of The Batteries 

Boat batteries are vulnerable to cold temperatures and can lose their charge if not properly maintained. 

Step 1: Disconnect the battery 

Remove the batteries from the boat and store them in a cool, dry place where they won’t freeze. Leaving the batteries in freezing conditions can cause them to crack or lose their ability to hold a charge. 

Step 2: Charge and maintain 

Fully charge the batteries before storage. You can also connect them to a trickle charger or battery maintainer to ensure they stay charged throughout the winter. 

Winterise The Plumbing 

If your boat has a water system, such as a galley or head, it needs to be winterised to avoid damage from freezing water. 

Step 1: Drain the water system 

Completely drain all water from the freshwater tanks, pipes and pumps. Any water left in the system can freeze, causing pipes to burst. 

Step 2: Add antifreeze 

Run non-toxic, marine-grade antifreeze through the entire water system, including sinks, showers, and toilets. This prevents any remaining water from freezing and protects the plumbing. 

Step 3: Winterise the bilge pump 

Make sure the bilge pump is clean and free of water. Add a small amount of antifreeze to the bilge to prevent any water from freezing and cracking the pump or its hoses. 

Clean And Protect The Exterior 

Saltwater, dirt, and grime left on your boat’s exterior can cause corrosion and damage if not properly cleaned before winter storage. 

Step 1: Wash and wax the hull 

Give the hull a thorough wash with soap and fresh water. Waxing the hull after cleaning provides an extra layer of protection from moisture and dirt during the winter months. 

Step 2: Inspect and lubricate moving parts 

Inspect the boat’s exterior hardware such as cleats, hinges and hatches, for any signs of wear or damage. Apply grease or lubricant to any moving parts to prevent rusting and ensure they operate smoothly in the spring. 

Step 3: Check the propeller 

Check the propeller for damage. As the boat is out the water, look for chips and dings on the blades themselves and check the colour.  Sounds silly, but if you see a reddish or pink hue on a bronze propellers there are problems ahead.  This discolouration is due to dezincification, where the remaining copper is visible after the zinc has corroded away.  This will cause the propeller to become brittle and porous and ultimately weakens it, leading to failure.   

For outboards, inspect the propeller and shaft. Lubricate it before reattaching the propeller. This prevents corrosion and makes it easier to reassemble when you’re ready to use the boat again. 

Protect the Interior 

Moisture can accumulate inside the boat during winter, leading to mould, mildew and odours. 

Step 1: Clean the interior 

Clean all surfaces, including upholstery, carpets and storage areas to remove dirt and moisture. Mould thrives in damp, dirty environments, so ensure everything is dry before sealing the boat for the winter. 

Step 2: Use dehumidifiers 

Place dehumidifiers or moisture absorbers throughout the cabin to reduce humidity levels and prevent mould and mildew from forming. You can use electric dehumidifiers if the boat is stored in an area with access to power or passive absorbers for drier environments. 

Cover the Boat 

A good-quality cover is essential for protecting your boat from the elements during winter storage. 

Step 1: Choose the right cover 

Invest in a cover specifically designed for your boat’s make and model, as it will provide the best fit and protection. Custom-fit covers offer superior protection against snow, ice and UV damage. 

Step 2: Support the cover 

Use support poles or a frame to ensure that the cover doesn’t sag under the weight of snow or rain. Any pooling water can damage the cover and increase the likelihood of leaks. 

Step 3: Secure the cover 

Make sure the cover is tightly secured, with no gaps or loose sections that could allow water or debris inside. If the boat is stored outside, consider using additional straps or weights to keep the cover in place during high winds. 

Check the Boat Periodically 

Even if your boat is properly winterised, it’s a good idea to check on it periodically throughout the winter. Look for signs of water intrusion, damage to the cover, or pest infestations. Catching problems early can save you a lot of trouble in the spring. 

Winterising your boat may take some time and effort, but the steps outlined here are essential for preventing costly damage. By protecting the engine, fuel system, plumbing and exterior, you’ll ensure that your boat is ready to hit the water when spring arrives. Investing in proper winterisation will not only extend the life of your boat but also give you peace of mind during the off-season.