How to Winterize a Boat: Steps, Checklist and Costs

As summer draws to a close many boat owners will be asking themselves: do I need to winterize my boat? This is an important question to be asking, because freeze-damage can cause extensive and even catastrophic problems. It can burst pipes in plumbing systems, crack engine parts, and split apart fiberglass. Fortunately, you’ve come to the right place — we’ll lay out the procedures you need to follow and run through a comprehensive winterize boat checklist, so you can rest easy after storing your boat for the season.

Do I Need to Winterize My Boat?

If you live in an area where temperatures may drop below freezing the answer is yes. It’s critical you winterize a boat even if you live in an area with mild winters where sub-freezing temperatures are the exception rather than the norm. That said, a lot depends on the nature of your boat. For small boats that are very simple and have few systems, winterizing it can mean putting on a cover and taking care of the motor. For big luxury center console boats over 40 feet, on the other hand, you’ll have a large number of tanks, pumps, and pipes to deal with. So recognize that while all boat owners need to winterize a boat if they live in a climate that’s not tropical, just what it means to do so can be very different from one boat to another.

Some boaters wait until the last minute to winterize – and some wait just a bit too long.

When Should I Winterize My Boat?

Most boaters winterize their boat when they believe the last trip of the season is behind them. However, some people who live in areas with a mild climate will wait to see if and when freezing weather comes along, so they can get in another adventure or two should the weather remain nicer than expected. Either way, the important thing is to pay attention to the forecast and if there’s a freeze being predicted, have the boat winterized before it happens.

Steps to Winterize a Boat

Remember, every boat is different and the winterization process can vary quite a bit from one to another. That said, here are the critical steps:

• Winterize the engine(s)

• Winterize the plumbing systems

• Winterize any pumps or compartments that may hold water

• Remove the batteries

• Treat the fuel

• Cover the boat

Winterize the engine(s)

This process is a bit different depending on what type of power system your boat has. It can also differ depending on the engine’s manufacturer and model. It’s important enough that we’ve dedicated an entire section to this process, so see How to Winterize a Boat Motor, below. Also check out How to Winterize a Boat Motor a Step By Step Guide.

Winterize the plumbing systems

Winterizing the plumbing system in a boat is similar to winterizing one in a summer home. You’ll need to drain the water out of the system, then add non-toxic antifreeze. Start by opening the faucet farthest from the water tank and let it run until completely drained. Then open each in turn working your way back towards the tank. When the system has run dry, add antifreeze to the tank and run it through the system, shutting off the faucets only after antifreeze has begun coming out. If your boat has a hot water heater, be sure to turn it off before draining the tanks down.

You’ll also need to pump out the boat’s holding tank, then add some antifreeze to be sure any liquid left in the bottom doesn’t freeze. Then be sure to flush the head until antifreeze runs through the lines. If your boat has a self-contained head (a portable marine sanitation device, or MSD), remove it from the boat and properly dispose of any waste in its holding tank, then drain the freshwater reservoir. 

Winterize pumps or compartments that may hold water

Livewell pumps, washdown pumps, fishbox macerators, and any other accessories that may have water in their lines or in the pump itself need to be drained and given a dose of antifreeze. In cases where a raw water intake feeds the system, you can remove the intake line at the seacock, submerge it into a five-gallon bucket full of antifreeze, and activate the pump to get the liquid running through. If the pump can’t pull a prime, hold the end of the intake up higher than the pump and pour in some antifreeze to get it started.

Drains should also be checked, as some of their lines could be holding water. These can be blown out with compressed air, then you can pour antifreeze directly into the drain.

Compartments that hold water, like livewells, must be fully drained and the pumps and lines given a dose of antifreeze.

Remove the batteries

Batteries should be disconnected and removed from the boat. Put them on a trickle-charger or battery maintainer for the off-season. This is also a good time to clean up any dirty or corroded connections.

Treat the fuel

Fill the boat’s fuel tanks to about 90 percent, to prevent the condensation from forming while allowing enough room for expansion without fuel coming out through the vent. Since the boat will likely be sitting for an extended period of time, you’ll also want to add fuel stabilizer to the tank. This is especially important if your boat is gas-powered and there’s ethanol in the fuel. Note: do this before winterizing the engines, so the stabilized fuel is run through the entire fuel system as well as being in the tank itself.

Cover the boat

Your main mission here is to keep out water, so it doesn’t creep into compartments, cracks, and crevices where it can cause freeze damage. A good cover will also keep out the dirt and leaves. But you need to make sure it can vent properly or mold and mildew will form. Standard hardware-store tarps are terrible for this use — it’s best to have a custom canvass cover made for your boat, or have the boat shrink-wrapped by a professional who knows where to add vents and how many to use. 

Covers should fit tightly and be secured to prevent flapping in the wind.

How Much Does it Cost to Winterize a Boat

There is no one-size-fits-all answer to this question. Obviously, size matters. But it also depends on the complexity of your boat’s systems and whether you pay a professional to do the job or you spend your own time on it. We can, however, offer a few case-studies to help you get some idea of the burden to bear in case you’re scratching your head, asking yourself “how much does it cost to winterize a boat?”

With a small skiff with no additional systems other than an outboard motor, you need only pay for motor oil, filters, and a cover. Figure on spending a few hundred dollars, maybe a bit more if you buy a custom cover (but then you won’t have to pay for shrink-wrapping in the future). On a midsized boat like a 28-foot pocket cruiser, you’re likely to spend $1,000 or so between supplies and a shrink-wrap job, and custom covers can cost several thousand dollars. Pay to have it done by a pro, and cost will climb by 50 or so percent. On larger boats and yachts the job is generally left to professionals and will run into the thousands of dollars.

How Long Does it Take to Winterize a Boat

Again, this all depends on the size and nature of the vessel. That little skiff won’t take more than a few hours, but the midsized boat will require a full day’s work. And the bigger the boat is the more work that’s involved, so in some cases the process can take several days.

How to Winterize a Boat Motor

This part of the job is so important that if there are any doubts in your mind as to whether you can handle it or not, you should have a professional do the job. That said, there’s a huge difference in complexity between outboard motors and inboards. 

How to winterize an outboard motor

Start the process by giving the engine a thorough freshwater flush. Outboard motors are designed to drain completely when tilted down, so you don’t have to worry about the cooling system nor antifreeze. Changing the oil and oil filter, however, is critical. Oil builds up acids over time and you don’t want used oil sitting in the lower unit or the powerhead for months on end. Note: before changing the powerhead oil be sure to run the engine up to operating temperature.

The oil changing process will differ a bit from one outboard to the next so refer to your owner’s manual to get the specifics. That said, whenever you perform an oil change in an outboard be sure to visually inspect the old oil and look for a milky white color. If you see it that means there’s water in the oil, and you have an issue that needs professional attention.

If your outboard will sit for more than a month without use, it also needs to be fogged. The process differs depending on your fuel delivery system, and may include spraying fogging fluid into the carburetor as the engine runs, or may require adding fluid to a remote fuel tank then running it through the EFI system. This is another stage where it’s important to check your owner’s manual and follow the manufacturer’s instructions for your specific make and model.

Also remember to leave the engine in the tilted-down position, and cover it to prevent weathering. Be sure to use a cover that breathes, and make sure it’s secure and doesn’t flap in the wind or it could wear away that pretty finish.

How to winterize an inboard motor

With inboards you still need to do an oil change, but you also have a cooling system that needs to be winterized. This process involves finding drain plugs, adding antifreeze, and running it through the system, and will vary quite a bit from one motor to the next. Again, you’ll need to refer to your owner’s manual and if you find anything doubtful or confusing, farm this job out to a pro.

When the snow starts falling, boats that are properly winterized will be fine but those that aren’t may suffer from all sorts of damage.

Winterize a Boat Checklist

Okay: we’ve covered all the bases for how to winterize a boat. You’ve asked how long does it take to winterize a boat, considered the cost to winterize a boat, and thought about when to winterize your boat. Now, let’s boil the process down to a handy winterize a boat checklist.

Motors

• Winterize the engine(s), using the owner’s manual as a reference or paying a professional who’s familiar with your specific power system and its needs.
• Oil and filters have been changed
• Old oil has been visually inspected
• Outboards are tilted down and covered
• Inboard cooling system(s) have been winterized
• Engine has been fogged as per manufacturer’s instructions

Plumbing System

• Freshwater systems including tanks and lines have been drained
• Freshwater systems including tanks and lines have received antifreeze
• Portable heads have been removed and drained
• The head and/or waste tank has been drained
• The head and/or waste tank has received antifreeze

Pumps or Compartments 

• Any and all pumps and their lines have been drained
• Any and all pumps have and received antifreeze
• Any compartments with drains have been blown out and received antifreeze

Batteries

• Remove them from the boat
• Put the batteries on a trickle charger
• Clean any dirty or corroded terminals

Fuel

• Fuel tanks have been filled to approximately 90 percent
• Fuel tank has been treated with a fuel stabilizer
• Treated fuel has been run through the system

Covers

• The boat has been covered or shrink-wrapped
• Proper ventilation has been ensured
• The cover is secure and won’t flap or saw back and forth in the wind

Fail to assure proper ventilation, and mold and mildew will set in. This leaning post cushion was ruined, as a result.

Winterizing a boat may seem like a complex process, but in truth it’s only as complex — or as simple — as the boat and its systems are. But we do have one final word of advice: regardless of what size or type of boat you’re winterizing it’s wise to take the time to give it a thorough cleaning and a thick coat of protective paste wax before you put it away for the winter (see 3 Simple Ways to Keep Your Boat Looking Good as New). That way, not only will your boat be ready for action as soon as spring returns, it will look sharp, too.