How To Winterize a Boat

Rate this post

How To Winterize a Boat

Prepping for hibernation can’t be ignored—here’s are all the details on winterizing your boat.

  • If you live in a region that enjoys all four seasons, you’ll likely need a checklist for winterizing your boat. You may also be wondering the steps to winterize your outboard motor. Our experts at are here to help with our all-encompassing winterization guide.
  • Start with the basics: winter boat storage, boat covers, fuel treatments, engine winterization (for both outboards and inboards), battery care, and winterizing your water systems and sanitation.

It’s time to winterize your boat? Shorter days, cooler temperatures, and colorful changes in the trees are all signs that winter is coming and the end of the boating season is near—yes, we know it’s sort of depressing… but at least we can help you winterize your boat in the best way possible. Ready to get started?

When it comes to winterization of your boat, here’s the main factors to consider:

  • Whether or not to pull your boat
  • How to best cover your boat
  • Winterizing plumbing, air conditioning, and sanitation systems
  • How to winterize an outboard engine
  • How to winterize an inboard or stern-drive
  • Taking care of fuel and fuel systems
  • Taking care of batteries
  • Other minor issues that come up when you winterize a boat

winterize a boat

When it’s time to winterize your boat, doing the process properly will ensure a safe, worry-free winter, as well as an enjoyable, trouble-free boating season next year.

Winterization procedures protect boat systems and gear from freeze damage. Winterizing also guards items such as batteries, inboard and outboard engines, and lower units and sterndrives from damage and wear that lying idle can cause. Luckily for you, a concentrated weekend effort is all that’s needed to ensure your boat is protected during the brutal winter months. Though just as with anything else on your boat, if you run into a system or procedure that’s beyond your skill set, ask an expert.

Whether you store your boat in or out of the water this winter is entirely up to you, but boats stored in the water over winter require special care.

Whether you store your boat in or out of the water this winter is entirely up to you, but boats stored in the water over the winter require special care.

Should you take your boat out of the water for winter?

The first thing you’ll want to do is decide whether to store your boat in or out of the water over the winter. For trailer boaters the choice is easy. But for those with the fortunate problem of owning a larger boat, the decision of whether to haul out or tough it out at the dock might be a tough one, depending on your location. Each method has costs associated with it, which will vary depending on the type and size of your boat, as well as the boatyard you deal with.

Storing a boat in the water over the winter presents some unique challenges, including:

  • Preventing ice formation around the boat
  • Keeping corrosion at bay
  • Maintaining a heat source inside the boat, when appropriate
  • Winterizing freshwater systems and holding tanks

You can learn more about dealing with each of these issues by reading In the Water Winter Boat Storage. But no matter how much preparation you do, note that storing a boat in the water still requires regular visits to check on the systems and ensure nothing is awry.

What’s the worst part about storing a boat in the water over winter? Get it wrong and there’s a very real possibility that you could find your boat at the bottom of the creek instead of floating happily in its slip. That’s why so many owners choose on-land storage for the off-season.

The Best Way to Cover Your Boat

In or out of the water, you’ll need to decide how to cover your boat. The idea is to protect from snow, ice, and UV rays all winter long. If you do the job on your own you have three basic cover types to choose from.

  1. Plastic Tarps – These are the least expensive option. But they only last a season or two, they tend to flap in the wind, and they rarely fit properly.
  2. Canvas Tarps – They’re more expensive than plastic but since they’re heavier, they flap around less in the breeze. They also last a lot longer, and may be good for four or even five seasons. But the additional weight means you’ll need to construct a solid frame to support it.
  3. Fitted Covers – For many popular models, you can find pre-fitted covers that are an exact match for the boat. These are even more expensive, but as you might expect, they also fit the best and tend to last the longest.

Our article How to Cover a Boat has a more detailed explanation of some of the other plusses and minuses of each DIY option—as well as some advice on general boat covering issues.

If you don’t want to cover the boat yourself, there are two options that involve hiring professionals to help. The first is to find a canvas company that will design and build a custom-fitted cover. This is an expensive option, but it will also provide the best protection for your boat and will be reusable year after year.

The other professional option is, of course, to hire a shrink-wrap pro. Shrink wrap is a polyethylene with UV inhibitors, and is formulated to shrink when heated, which creates a much tighter seal than anything you or I could make with a tarp and ropes. That seal not only keeps the weather out of your boat, it also prevents the stretching and tearing that tarps commonly display after a few months in the elements.

If you’re having a tough time deciding whether to handle the covering job on your own or call in a pro, check out Should You Shrink Wrap Your Boat?. It’ll make the pros and cons of each method clear and help you make the best call.

Winterizing Water Systems

Pressure-water plumbing is just one system that must have potable antifreeze run through it, to prevent freeze damage.

Pressure-water plumbing is just one system that must have potable antifreeze run through it, to prevent freeze damage.

If you’ve got a faucet, showerhead, washdown nozzle, or any other fixtures onboard that provides water—raw or fresh—the system will need to be prepped with antifreeze. Otherwise pumps, hoses, and fixtures can break because of expanding ice inside.

Before you start, make sure to get the proper antifreeze. Look in your local marine supply or RV shop for what many folks call “the pink stuff.” You’ll likely find cases of it stacked to the ceiling at this time of year. This is the antifreeze that’s safe for drinking water systems. Antifreeze made with propylene glycol is what you’re looking for. Do not use automotive or engine antifreeze made with ethylene glycol, which is highly toxic.

For freshwater systems, first drain as much water as possible from the tank and lines, by opening one or more fixtures. Then remove the primary feed hose from the freshwater tank and place it into a five-gallon bucket filled with antifreeze. All that’s left to do is open each and every single fixture (hot and cold) until antifreeze comes flowing out. When you’re finished, don’t forget to reattach your freshwater tank feed hose. Hint: lots of folks forget about freshwater showers found near the swim platform on many boats.

For raw-water systems such as wash-downs and livewells, remove the raw-water hose for each pump from its closed supply seacock and submerge the hose end in a jug or five-gallon bucket full of antifreeze. Run each pump until until pink antifreeze comes flowing out of each fixture.

Sanitation and Air Conditioning Systems

Pay special attention to your head compartment and its sanitation system components at winterization time.

Pay special attention to your head compartment and its sanitation system components at winterization time.

Whether you’ve got a single portable MSD aboard or multiple electric-flush heads attached to a big holding tank, marine sanitation systems need to be carefully winterized to survive cold temperatures. An important first step is running lots of fresh water through all of your heads to rid the system of smelly residue. Next, empty your holding tank of its contents at a pumpout facility, flushing it with fresh water once or twice before hanging up the pumpout hose.

Using the same propylene glycol antifreeze you purchased for your freshwater system, remove the raw-water inlet hose for each head from its seacock (be sure to close the seacock first) and then submerge it in a jug or five-gallon bucket full of antifreeze. Pump each head until you are sure the antifreeze has run through it and all of its lines, all the way to the holding tank.

If you have a LectraSan or other waste treatment device, there may be some special steps you need to take. In this case, winterize it according to the manufacturer’s recommendations.

Make sure you use propylene glycol antifreeze when winterizing your boat's systems. Antifreeze made with ethylene glycol is highly toxic.

Make sure you use propylene glycol antifreeze when winterizing your boat’s systems. Antifreeze made with ethylene glycol is highly toxic.

Air-conditioning is another system that may come with special winterizing recommendations from the manufacturer. Even when they don’t, there are some different trains of thought regarding the best way to winterize an air conditioning system.

Our systems expert Ed Sherman, a noted authority in the field, prefers pumping potable antifreeze though the entire system. Simply close the air-conditioning intake seacock, remove the supply hose, dip it in a bucket of antifreeze, and then run the system until you see pink coming out of the overboard discharge. Make sure you reattach the hose when you’re done with the procedure. Wash, rinse, and repeat if your boat has more than one air conditioning unit.

How to Winterize an Outboard Engine

Outboards, inboards, and stern drives all need a little winter loving—but how you go about winterizing them is very different. Since outboards are the easiest to deal with, let’s tackle them first.

  • In any outboard—two-stroke or four—the most important task you should perform for winter layup is changing the lower-unit oil. Otherwise, if there’s any residual water suspended in the gear lube, freezing temps could cause catastrophic damage. Watch our How to Change Lower Unit Oil video to see how it’s done.
  • Another maintenance task that applies to both two- and four-stroke outboards is thoroughly flushing the cooling system with fresh water, with the engine in the tilted-down position. But you don’t need to run antifreeze through the system afterwards. Outboards are designed to drain completely when tilted all the way down, so no water should remain behind.
  • For four-stroke outboard engines changing the engine oil and filter is a must, as well as performing any other services that are factory-recommended prior to layup, such as changing fuel or air filters. Watch our How to Change Engine Oil on a Four Stroke Outboard Engine video to see how it’s done. Then, watch our How to Winterize a Four Stroke Outboard video for some other tips on storing four-strokes, in particular, through the winter months.
  • If your outboard is going to sit for months on end, you’ll want to fog the engine with fogging oil. If you plan to use (or at least start and run) your engine every few weeks, however, skip this step. Fogging oil usually fouls the spark plugs upon start-up and if you don’t let the engine sit for more than a few weeks between starts, fogging isn’t necessary in the first place.
  • If you’re in doubt, always enlist a service pro at your engine shop for help. Goofing up something you’re not familiar with can result in an expensive repair bill later.

How to Winterize Inboard Engines and Stern Drives

Changing the engine oil and running antifreeze through your engine block are only a couple of tasks you'll need to complete to prepare your inboard engine for winter.

Changing the engine oil and running antifreeze through your engine block are only a couple of tasks you’ll need to complete to prepare your inboard engine for winter.

The biggest threat to inboard boat engines in winter is damage caused by water that freezes inside the engine’s cooling passages. Leave an engine for the winter without protecting it and you can guarantee an expensive repair bill come spring.

Winterizing any sort of inboard engine involves removing the raw-water intake hose from its closed supply seacock, placing it in a five-gallon bucket full of antifreeze, and then running the engine until antifreeze is flowing copiously from the exhaust outlet. This guarantees that the antifreeze has run all the way through the engine’s internal cooling passages, as well as the exhaust components.

That antifreeze should be made with propylene glycol, like the pink stuff you used in your water and sanitation systems, but it should be rated for engine use. The difference is that it has corrosion inhibitors to protect the inside of your engine.

Changing the engine oil and filter is also an essential inboard winterizing habit you should get into. Leaving a batch of old oil in the engine can cause corrosion, residual water damage, or worse. And gasoline inboards that will sit for an extended period should be fogged, as well.

Boats with sterndrives have one other need: In addition to the aforementioned raw-water cooling and oil change procedures, you’ll want to change the gear lube in the stern drive’s lower unit.

If you own a stern drive and plan to do the winterizing on your own, now’s the time to watch our How to Winterize Your Stern Drive and Pressure Water System video.

Fuel Systems

Water is the enemy when it comes to fuel supply and storage systems on boats. That’s especially true if yours is a gasoline-powered boat with ethanol-blended fuel in the tank. Diesel fuel comes with its own set of challenges. Add in wide ranges of winter temperatures and condensation becomes a problem.

Traditionally, the pros have always recommended you store your boat with fuel filling the tanks—diesel or gasoline—at least 95 percent. This limits the amount of air in the tank that can introduce moisture into the fuel through condensation. Due to the nature of ethanol, however, these days some manufacturers offer different advice when it comes to gasoline-filled tanks. As Ed Sherman makes clear in Winterizing Your Boat’s Fuel Tank, when your boat will sit for more than two months leaving it filled to the brim may do more harm than good. Instead, you may want to run it down as low as possible, treat what’s left in the tank, and fill up with the fresh stuff come next spring.

Regardless of fuel type, always—and we mean always—add an appropriate fuel stabilizer. While diesel can be more forgiving, forgetting to add stabilizer to ethanol-blended fuel will always result in heartbreak.

Now is a good time to change fuel filters as well, especially if you have a stand-alone water/fuel separator filter. Check your manufacturer’s recommended service intervals for onboard fuel filters on your inboard and/or outboard engines.


If possible, batteries should be removed from your boat and stored at home where they can take on a trickle charge all winter long.

If possible, batteries should be removed from your boat and stored at home where they can take a trickle charge all winter long.

Probably the worst thing you can do to your batteries is leave them unattended and ignored in your boat all winter long. They should be on a trickle charge during this down-time, and if you don’t have a solar charger or a plug at the boatyard and your boat isn’t stored in the water the best place for your batteries is at home—either in the garage or basement—hooked up to a trickle charger. And don’t worry; Dr. Diehard says it’s perfectly fine to store today’s batteries on concrete.

Keep in mind that different battery types have different charging needs. For example, a conventional lead-acid battery has a much higher charging voltage tolerance than an absorbed glass matt (AGM) battery. Find out what’s best for your particular battery type and be sure to keep an appropriate trickle charger going on your batteries all winter.

If you need a more comprehensive explanation of battery maintenance needs—for all seasons and conditions—be sure to watch this Basic Boat Battery Check Up and Maintenance video.

The Final Count-Down

After going through all these systems and processes, are we finally ready to put Mom’s Mink to bed for the winter? We’re close. Here are a few final winterizing tips to finish the job:

  • Give it a scrub from top to bottom, inside and out. Why, you may ask? Leaving filth and grime to sit all winter long can cause permanent damage to your boat’s finishes, inside and out.
  • Organize and clean stowage compartments, lockers, and other areas that may have gotten dirty over the boating season. Not only will a clean boat greet you come spring, this will also increase the chances you’ll spot items that could cause a mess by leaking or freezing and bursting over the winter. Suntan lotion, bug repellent, or a stray can of soda are just a few of the items that you will regret leaving onboard.
  • Don’t forget the bilge or mechanical spaces, either. These areas should be nice and clean as well as free from any standing water, which can freeze over the winter and cause damage in tight areas.
  • Take off any gear that will fare better shoreside. Fishing rods and reels, safety equipment, electronics that are removable, clothing, and other gear will live a longer life if it isn’t exposed to the freeze-thaw cycle.

Yep, this is a long list of things to do, but each step is necessary to ensure boating bliss next season. Just remember—Memorial Day weekend will be here before you know it.

Editor’s Note: This article was originally published in September 2015 and was last updated in November, 2021.

You are viewing this post: How To Winterize a Boat. Information curated and compiled by along with other related topics.


Please enter your comment!
Please enter your name here