Spring Commissioning: Your Complete Guide to De-Winterizing a Boat

The De-Winterization Checklist

As temperatures warm up and spring gives way to summer, it’s easy to get caught up in the excitement of a new boating season. But before you rush to hit the water, make sure you undo all the hard work you did last fall to protect your boat from cold weather. Proper de-winterization is key to making every system operational once again.

This comprehensive guide will help you get your boat’s engine, battery, and internal systems ready for that first launch. Making a little extra effort now to de-winterize your boat can prevent major headaches later that will make you spend more to keep it running smoothly.

Get started on this spring commissioning checklist to get your boat ready faster and with fewer missed details.

1. The Engine & Propulsion

The more care you took last fall to winterize your boat, the less boat spring prep you’ll need to do. Still, even the best-winterized engine needs a few touches to restore the cooling system and ensure that no fluids were lost over the winter.

Outboard engines are usually winterized the least, so they need the most attention in the spring. Look for damage to the rubber outdrive bellows and replace any cracked or stiff materials. Inspect the control cables and invest in a new set if there is any damage to their jackets. Top up any outboard or sterndrive engines with a little extra lower unit oil, since they tend to lose some of it over the winter.

Fluids Check

All boat engines need a top-up on fluids, including engine oil, gear lube, and power steering fluid. If you didn’t already change the oil and filter at the end of the last season, replace them now. Check the steering before starting the engine. If it seems unusually stiff, consider replacing the power steering fluid or power trim oil.

Antifreeze Flush

Remove all antifreeze from your cooling system by flushing it out before starting the boat again. Check all the hoses for cracks and leaks first. Run the engine on a flush system to clear out the antifreeze, then add a mix of 50/50 coolant and water. Collect the antifreeze and dispose of it at a marina or automotive shop.

Belts, Hoses & Clamps

Give the engine a quick once-over for obvious signs of wear on belts and hoses. Replace any belts and hoses that are cracked, kinked, or don’t want to stay in place. Tighten clamps on hoses to prevent leaks.

Propeller & Drivetrain

Inspect the propeller for nicks that indicate damage. Propellers that fail suddenly can leave you stranded, so replace damaged ones right away instead of waiting to see what happens. Check that the prop shaft wasn’t damaged or dirtied during winter storage. Cleaning the prop shaft to remove any dried residual oils or sticky grease provides better performance.

2. The Battery

You should have removed the battery before storing the boat for the winter. That means you’ll need to prepare it for reinstallation or invest in a new one if needed.

Inspection & Reinstallation

Clean the terminals if there is any corrosion or white residue lingering from the previous year of use. Look over the battery for any signs of damage like bulging, leaking, or cracks. Place the battery back into the holder on the engine, clamping it down or closing the hold-down as applicable. Reconnect the cables to the terminals, starting with the positive first and then the negative.

Charge & Test

It’s best to give the battery a full charge and test its health before putting it in the boat, to save time and effort if it turns out to be in poor condition.

Use a charger to bring the battery up to a full load, then try a load tester to see how it responds. If the tester reports anything but a good cranking condition, invest in a new battery to prevent surprise failures while on the water.

3. The Fuel System

One of the easiest parts of learning how to start a boat after winter is preparing the full system. You should have filled the tank before winter storage and prepared the fuel with stabilizer. As long as that’s the case, all you have to do is check the fuel lines for damage and inspect the fuel to make sure it’s not contaminated with water.

Fuel Lines & Filters

Locate the fuel tank and visually check the fuel lines connecting it to the engine. Look for cracks and other signs of damage, like kinking and fuel residues that hint at leaking. Replace the fuel filter, even if you didn’t put many hours on it before winterizing, since a winter of fuel exposure tends to wear them out.

Fuel Tank

Open the tank and use a bright light to visually inspect the fuel. If it’s milky or cloudy, it may contain water. Separated fuel will have distinct layers of light and darker colors. Don’t run the engine on suspect fuel. If you have any questions about the fuel's quality or stability, use a portable pump to remove it and start with fresh fuel to prevent damage.

4. The Electrical Systems

If you have any concerns about items from this part of the boat pre-launch checklist, you should get the help of a professional.

Wiring Check

Before starting the electrical system or bringing your electronic systems back on board, conduct a quick wiring check. Open the electrical panels and check connections running in and out of various points around the boat.

Rats or other pests that gained access to the boat can damage wiring in particular. Any frayed, corroded, or worn wiring needs replacement, since the combination of electricity and water makes for dangerous situations.

Electronics

Gather all the navigation systems, screens, entertainment accessories, and other electronics you removed for the winter. Reinstall them as needed and test all the lights, horns, bilge pumps, and other electrical systems. If anything fails to switch on, or seems to run more slowly or loudly than last season, have an electrician inspect the system before your first outing.

5. The Freshwater & Sanitation Systems

Wrap up your marine engine de-winterization efforts by bringing your fresh water and sanitation systems back on board. Then you’ll be ready to set sail.

Leak Check

Before rushing to flush, consider a leak test. Turn the water pump on for a few seconds, then check all the faucets, connections, and pumps. This lets you spot leaks while they’re still minor. This is even easier if the antifreeze is in the system, since it’s usually colored pink and easier to see.

If you don’t see any signs of leaks, you can move on to the flushing stage.

Flushing

Your freshwater system also needs a flush to clean out the antifreeze lingering in the tanks and lines. Run the freshwater pump with all faucets and showerheads open. This will flush the majority of the antifreeze out. When the pump runs dry, stop it and fill the tanks with a few gallons of fresh water. Start the pump and flush again. Keep repeating this process until the water comes out clear and no longer milky or pink-colored.

If there’s a lingering smell or taste, keep flushing. Then fill the tanks with fresh water and close up the faucets and other fixtures.

Sanitation

You’ll need to prepare the head as well before you can enjoy your day on the water. A non-working sanitation system quickly interrupts your enjoyment of your boat. Pump out what’s in the holding tank, expelling it into a waste accepting station as you would if the tank were full.

Run water through the system like you did with the freshwater system. It doesn’t have to get as clear as you would for drinking water, but you still don’t want a lot of antifreeze lingering in the hoses.