When should you winterize a boat, and what does it involve

Why warm states file the most freeze claims

It is tempting to think winterizing is a northern chore. The insurance numbers say otherwise. BoatUS Magazine, looking at ten years of GEICO | BoatUS Marine Insurance claims, found that Texas leads the country in freeze-damage claims, with more than seven times as many as Minnesota, and that even Florida files more than Minnesota does. More than half of the ten states with the most claims would be called warm-weather states, and only Hawaii routinely has none.

The explanation BoatUS gives is behavioral. Boaters in the far north know they have to winterize, so their claims usually come from something that was missed or done too late. In the South, the files are full of boats that were never winterized at all, or that relied on a heater to keep the engine warm until the power went out. A single hard night is enough, and nobody can predict which winter will bring it; the worst year in that decade, 2018, brought snow to Las Vegas and record cold to Los Angeles.

That is why BoatUS recommends winterizing the engine if the boat will be laid up for even a few weeks anywhere it could possibly freeze. Its exceptions are short: Hawaii, and in one article the Florida Keys.

Set the date by your first freeze, not the calendar

There is no national winterizing date. The work has to be finished before the temperature where the boat sits drops below freezing, which comes early on a northern lake and late, sometimes as a single cold snap, farther south. The date is local, and you are the one who knows it. If a yard is doing the work, BoatUS suggests a written contract with a firm time frame that starts well before the first typical hard freeze in your area, not on the day the forecast turns.

The job itself is shorter than most owners fear. BoatUS puts winterizing most boats at somewhere between an hour and a day. The risk is not the time it takes but the habit of putting it off, or of assuming the marina will remember a request made years ago. BoatUS says plainly that winter can sneak up on you and that the yard may not recall standing instructions.

What winterizing does to the engine

At its core, winterizing means getting every bit of water out of anything that holds water, or replacing it with enough of the right antifreeze. Fresh water expands by about 9 percent when it freezes, according to BoatUS, and pushes outward with enough force to crack an engine block, split hoses, or ruin a refrigeration system overnight. In the BoatUS analysis of ten years of freeze claims, more than three quarters involved cracked engine blocks or exhaust manifolds where water stayed in the engine or cooling system.

How that is done depends on the engine. On freshwater-cooled inboards there are two circuits: the closed freshwater side, which only needs year-round coolant mixed to the maker's recommendation, often 50/50 with water, and the raw-water side, where BoatUS prefers circulating winterizing antifreeze through the whole system with the engine running long enough to reach every part. Sterndrives vary; some draw cooling water through a thru-hull and are protected when the engine is, while others need muffs to flush and then run antifreeze through the drive. Either way, BoatUS says to store outdrives in the down position so water cannot collect in the exhaust hub and freeze.

Outboards are simpler but not identical from brand to brand. BoatUS advises following the owner's or service manual closely, because modern four-strokes and direct-injected two-strokes may have their own winterizing and flushing steps, and many newer engines flush through a garden hose fitting without running at all. Yamaha adds a storage tip for outboards kept outside: trim the engine fully in, or bag the dry lower unit, so moisture cannot collect there, freeze, and crack it.

Antifreeze is not all the same

Winterizing antifreeze is a different product from the coolant in the engine's heat exchanger. Engine coolant is ethylene glycol, which BoatUS describes as highly toxic; it should never go into a freshwater system because it cannot be reliably purged in spring. For raw-water and drinking-water systems BoatUS recommends a propylene glycol antifreeze with rust inhibitors.

Read the freeze rating carefully. BoatUS notes that a typical antifreeze labeled for minus 50 degrees Fahrenheit only protects PVC pipes from bursting down to about minus 10, and starts to freeze at about 15 degrees. Most winterizing antifreeze is meant to be used full strength. When you pump it through the engine or plumbing, keep going after it first appears at the exhaust or faucet, because it has to push out all the water already in the system before it protects anything.

Fuel, oil, fogging, battery, and trailer

Yamaha's storage checklist for outboards starts with an inspection from the top of the cowling down to the skeg, then an oil and filter change, so used oil carrying debris and corrosives does not sit in the engine all winter. It also calls for changing the onboard fuel filter, since any water in the canister can freeze. Fogging oil coats the cylinders and valves against rust during the months the engine sits.

For fuel, Yamaha says to run a stabilizer through the entire system before shutting down and to store the tank about seven eighths full to limit condensation, without ever plugging or capping the tank vent. Batteries should be fully charged, checked monthly, and brought indoors if the boat is stored outside in a cold climate. The trailer gets its turn too: inspect the wheel bearings for water intrusion and grease them, and look for loose or rotted bunks and rollers.

Some of these steps have the engine running. The U.S. Coast Guard warns that you cannot see, smell, or taste carbon monoxide and that it can make you sick in seconds, so run engine-on steps in open air with people clear of the exhaust, never in a closed garage or shed.

Common winterizing mistakes

Using a heater instead. BoatUS sees fires every winter from heaters, connections, and cords left running on unattended boats, and a heater fails exactly when it is needed most, in a storm when the power goes out.

Letting a friend do it. Many freeze claims begin with an owner saying a buddy handled the winterizing. If you hire a professional instead, get the work in writing: BoatUS points out that "winterizing" has no universal meaning, so list every job, including seacocks and the head, and add that the boat is not to be dewinterized until you say so.

Forgetting drains, covers, and stands. Plugged drain holes trap water that expands as it freezes. Tarps lashed together tend to shred and dump snow into the boat; BoatUS recommends a fitted cover or professional shrinkwrap with plenty of ventilation. Boats on the hard need properly set jackstands, at least three per side for boats over 26 feet, and boats left in the water need snow and ice cleared after every storm. Owners who visit the boat every few weeks, BoatUS says, are far less likely to find problems in spring.

Not writing it down. Winterizing is once a year, so it is easy to lose track of what was done and when. In HullLedger you set a winterizing window for each boat, a card shows whether this year is done when the window opens, and each winterizing you log is listed by season in the maintenance PDF you can later hand to a buyer.

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