Time to Think about Winterizing - 11/04/2009

If you don’t know what you are doing winterizing can be quite expensive – either to pay someone else to do it, or to suffer the consequences next spring and pay to have things fixed. Happily, winterizing is not rocket science and even the Three Stooges could do it if properly instructed. Enter the professor: Paul Esterle, author of “Maintain and Improve Your Powerboat” which was just published by McGraw-Hill, and who has the website “thevirtualboatyard.com” has written some instructions for us.

Fram in Ice
Explorer Fridtjof Nansen was careful to winterize his vessel “Fram” and she survived 3 winters in the Arctic Ocean ice quite handily.

Old Man Winter’s Coming!

By Paul Esterle,


It’s not nice to rain on anyone’s parade, but the fact is winter is around the corner. Labor Day has passed and, while there is yet some great boating weather to be had, we need to start thinking about winterizing.

Most people think only of the engine and water systems when you mention winterizing. There are really five main areas of concern regarding winterization:

  1. Cleaning the boat
  2. Winterizing the engine and outdrive
  3. Winterizing the fresh and waste water systems
  4. Preparing the cabin
  5. Inspecting the trailer and/or winter cover

Cleaning the Boat

Lets face it, the more you do now, the less you have to do in the spring. This means you should spend the time now and thoroughly clean the boat. That way, the summer’s accumulation of dirt and debris won’t be fossilizing itself onto your boat during the winter.

Take the time to scrub the nonskid and get all the dirt out. Wash and wax the hull. Get a good bottom cleaner and clean the growth off the bottom now. You will thank yourself in the spring when it comes time to apply another coat of bottom paint.

Don’t forget the canvas. Clean any mold of mildew off and clean and polish the clear vinyl. Remove the canvas and take it home, if possible.

Winterizing the Engines and Outdrives (Inboard or I/Os)

This is the area most people think about when you mention winterizing. It can be done quickly if you have all the needed supplies ready.

Change Oil:

Start the process by warming up the engine or engines. This does two things; it warms up the oil and opens up the thermostat. Once the oil has warmed up, change both the oil and the oil filter. This will leave nice fresh oil sitting in your engine, without the summer’s build up of acid, water and gunk. It will also be one less thing to do in the spring. If you don’t change the oil, at least add some crankcase conditioner to the oil.

Top Off Fuel:

While you are at it, change the fuel/water filter and top up the gas or diesel tank. The transition from warm to cold air during the winter season will allow moist air to come in the tank and condense out as water. The less air in the tank, the less condensation. [Fill tank 95% full, leaving some room for expansion.]

Fuel Stabilizer:

Add an appropriate amount of fuel storage conditioner to the tank. [For those using E-10 fuel be advised that fuel stabilizer will not stop phase separation. The good news is it has not seemed to be an issue the last couple of years.]


The next task is to run antifreeze through the system. Non-toxic marine antifreeze should be used. Don’t use automotive type antifreeze, as it is toxic. It also tastes sweet to animals, which will die if they lick up any spills. [It also kills humans and is hard for detectives to discover, according to SCI.] Marine antifreeze comes in three different flavors, -50, -60 and –100. These temperatures are the temperature that the antifreeze will solidify. The -50 is fine for water systems.

Use a –60 or –100 for the engine, though. Any residual water in the cooling loop will dilute the antifreeze and impact the freeze protection of the engine. The –60 and –100 also have more corrosion inhibitors for use in engines.

The Outdrives: Most marine stores carry a winterizing kit that includes a plastic container for the antifreeze and a plastic hose used to connect to the flushing muff on the outdrive. Some I/Os and inboards will have separate cooling water intakes in the bottom of the boat. In these cases, remove the intake hose from the seacock and place it in a bucket of antifreeze.

Drain the outdrive oil. Check the oil for water (it will look like coffee) and metal chips. The water in the oil will indicate a leaking seal and the chips indicate mechanical problems.


With the engine warmed up, begin running the antifreeze through the engine and/or outdrive. As you reach the end of the antifreeze in the container, start spraying fogging oil in the carburetor. Smaller engines and outboards will probably die while larger engines will bog down. Shut off the engine, if it didn’t shut off itself, as the last of the antifreeze runs through. The fogging oil will give the cylinder walls a healthy coating of oil and corrosion blockers for the winter.


Clean the carburetor flame arrestor and lubricate any grease points spelled out in the owners manual. Check for loose or missing fasteners. Replace the zincs if they are more than 50% gone.


It’s also a good time to check the prop for damage. It wouldn’t hurt to pull the prop and grease the spines while you’re at it. If the prop is damaged, the winter season is the ideal time to have it refinished. No sense in waiting until the busy spring season to get it done.

Outboard Engines:

Outboards should be flushed with antifreeze, fogged, have the lower unit oil changed, greased and inspected. If you haven’t had the impeller checked or changed recently, have it done now. Four-cycle units need the crankcase oil changed. Store the engine upright on a rack of on the boat or in a shed.

Winterizing the Fresh and Waste Water Systems

This may sound simplistic but remember to have the holding tank pumped. Leaving that stuff sitting in the boat all winter isn’t good, even if there is antifreeze in it.

Freshwater System:

Pump out as much of the fresh water as you can. Next, add several gallons of special antifreeze made for water systems to the tank. Start with the faucet farthest from the pump and run it until the antifreeze comes out. Work your way back through the boat until antifreeze has appeared in all the faucets.


Flush your heads several times with fresh water. Add antifreeze to the head and pump it through to the holding tank (you did have the holding tank pumped, right?). Don’t scrimp on antifreeze; make sure it gets through all the head hoses to the holding tank.

AC System and Other Places:

Drain all water from your boat where at all possible. Don’t forget to put antifreeze in the AC cooling loop and hot water heater. Shower sumps and any sea strainers you have should be sucked dry. If you can’t do that, add antifreeze. If there is usually a little water in the bilge, add a little antifreeze there, too.

Remember, if there is any water in the boat it will freeze and usually break whatever it is in.

Preparing the Cabin

Go through the cabin and remove anything you can to a cool dry place in your house. Any food or drinks should be removed. Cushions, curtains, life preservers, towels and spare clothing should all be taken home. If possible, remove the electronics and take them home, too. Wipe down the refrigerator or icebox with a mildew cleaner of bleach solution.

Open all doors, drawers and compartment to minimize closed in spaces. Place dehumidifier tubs throughout the boat to absorb excess humidity. Don’t forget to check them once or twice during the winter, if possible.

Remove the batteries and store at home. They should be fully charged and stored in a cool dry place, not on a concrete floor out in the garage. Don’t forget to check the electrolyte levels and add distilled water if necessary. A trickle charge now and then won’t hurt, but leaving the battery charge hooked up all winter can inadvertently cook the batteries.

Inspecting the Storage Arrangements

Your Trailer:

If you keep your boat on a trailer, jack the wheels up off the ground to minimize sidewall cracking. Grease the wheel bearings now, which will protect them from snow and ice, and will be one less thing to do in the spring. Give the trailer ball socket on the trailer coupling a light coat of grease to prevent rusting. Make sure the boat sits bow up so any water that gets aboard will drain out the transom plugs.


A trailer boat is best protected with a properly sized cover. The cover should fit well and be firmly tied underneath the boat. Use support poles to eliminate any sagging areas of the cover that would trap water or snow. These can tear the cover or actually damage the boat if not emptied out.

Consider adding a tarp over the fitted cover. Tarps are cheap, covers aren’t and the tarp will keep a lot of the bird dropping, snow and rain off the cover.

Cradles: Many boats are stored on jackstands or cradles. The jackstands should be located near bulkheads for best support. The hulls of large boats will sag if there isn’t proper support. Sailboats should have most of their weight supported by keel blocks with the jackstands to stabilize the boat. The jackstands should be chained together under the boat to prevent them “walking” out from under the boat during a storm.

Likewise, covers and tarps should never be tied to jackstands. The wind could catch a tarp or cover and blow the jackstands out from under the boat. Tie the cover or tarp under the boat, going from side to side through the grommets. You could also attach gallon jugs filled with sand to the grommets to hold down the tarp.

Your Shrink:

If shrink-wrapped, make sure that there are no water-trapping sags in the wrap. There should also be ventilators in the shrink-wrap cover to allow the boat to breathe during the winter.

In-Water Storage:

If you store in the water, make sure you have all the seacocks closed. If you are using an ice eater or bubbler, check them regularly to make sure they are still operating. Some folks use electric heaters or light bulbs in some spaces to avoid having to winterize or to cut down on any mold or mildew forming. This practice is not recommended as prolonged power outages during winter storms can allow the boat to freeze. A heater, tipped over, can also start a fire.


It doesn’t sound like fun at all, but the more time you spend properly winterizing now, the better off your boat will be. In addition, the work done now will speed up the commissioning process in the spring, when we all want to get out on the water as soon as possible.

--Our thinks to Paul Esterle for this fine guide to boat winterizing. If you liked what you read, why not get Paul’s new boat “Maintain and Improve your Powerboat” published by McGraw-Hill. Also, visit his website: thevirtualboatyard.com.