How to Keep Your Boat in the Water Over Winter (De-Icers, Covers and Checks)

Follow the full winterizing procedure for your engine: stabilize the fuel, change the oil and protect the cooling system. BoatUS notes that on a boat in the water you close the intake seacock first, then draw non-toxic antifreeze into the raw-water side from a bucket until it flows out of the exhaust. Drain or fill the sea strainer, seacock body and water-lift muffler too. See our sterndrive and diesel winterizing guides for step-by-step details, and check your engine manual for its drains and procedure.

Fresh water, the head, air conditioning, washdown and livewell pumps all hold water that can freeze. BoatUS's plumbing guide says that if the boat is in the water, you pour antifreeze into the sink drains and close their seacocks. It also warns that a raw-water strainer left full of water can crack and possibly sink the boat. Use only non-toxic propylene glycol in water systems, never automotive coolant.

Since below-waterline parts are the top cause of sinkings at the dock, inspect them now, before the boat is left alone for months:

• Exercise every seacock; a seized one cannot be closed in an emergency.
• Look for cracked, soft or swollen hoses, rusted clamps and weeping fittings. Replace anything doubtful.
• Close the seacocks you do not need while the boat sits.
• Keep cockpit drains and scuppers clear so rain and snowmelt can get out.

If a seacock or below-waterline hose needs replacing, that is a haul-out job for a pro.

BoatUS says you should not winterize the bilge pump on a boat staying afloat, but you must make sure it works. Clean the bilge, lift the float switch by hand to confirm the pump runs and water goes overboard, and check that nothing (debris, wiring, ice) can jam the float. Remember that the pump is a backup: if it runs often, find and fix the leak rather than counting on the pump to keep up all winter.

The bilge pump is only as good as the battery behind it, and a discharged battery can freeze and crack in hard cold.

• Charge every battery fully before you leave.
• If you keep the boat on shore power with a charger, use a marine charger in good condition, a shore power cord with no damage or burned ends, and a pedestal with ground-fault protection. See our shore power guide.
• Without shore power, check battery voltage on every visit and recharge as needed.
• Keep the bilge pump wired so it can run with the battery switch off, as most boats are; confirm yours is.

A winter cover or shrink wrap keeps snow and ice out of the cockpit, but it must be built to shed weight. BoatUS warns that rain and snow can make a cover sag, tear and even make the boat top-heavy, so rig it with a supported slope down and over the sides. Include vents to limit mildew and an access door so you can get aboard. Heavy snow can push a boat low enough to put above-waterline fittings, including exhaust outlets, under water, so plan to clear snow after big storms. See our shrink wrap guide.

A de-icer or bubbler does not heat the water. Kasco explains that its units push warmer water from below up to the surface, which keeps an opening in the ice around boats and docks. Water is densest at about 39°F, so the bottom of a lake or marina stays a little warmer than the surface. That only works if there is enough depth below the unit; check the maker's minimum depth for your model and location.

A de-icer protects against the slow squeeze and lift of ice forming against the hull and dock. It cannot stop every kind of ice damage: moving ice pushed by wind or current, or very shallow water that freezes to the bottom, can still cause trouble.

• Mount it with the maker's dock mount or suspension lines, at the depth and angle the instructions call for, so the open area covers the boat and dock.
• Keep it off the bottom so it does not stir up silt, and keep the propeller guard clear.
• Kasco's own rules of thumb, as a starting point: in most cases hang the unit about 4 to 6 feet below the surface and at least about a foot off the bottom; in water only about 3 feet deep or less, long-term de-icing gets hard, so place the unit as close to deeper water as you can and angle it toward the shallow spot. Hanging it straight down makes a round opening; tilting it makes a longer opening you can aim at the boat.
• Install in late fall, before ice forms. Kasco notes that installing through ice is harder and can be dangerous.
• Size it for your winter. Kasco suggests smaller units for mild climates and bigger ones for the northern states, and says that when in doubt, size up and run it less. Point the unit toward shore, not out into the lake, so it does not leave a hidden hole where other people walk or ride.
• Use a thermostat or timer controller if your unit offers one, so it runs only when it is cold enough to need it. Kasco sells controllers that switch on by temperature or time. Kasco puts typical winter power costs at roughly $40 to $50 a month per unit, depending on region and run time.
• Route the cord so it cannot be crushed, chafed or frozen into the ice, and avoid splices and household extension cords.
• Consider whether your marina already runs a de-icing system; adding your own may not be allowed or needed.

A de-icer is an AC appliance sitting in the water. Kasco recommends plugging its units into a GFCI-protected outlet or control box, and says no one should ever enter the water while a de-icer is running. The Electric Shock Drowning Prevention Association specifically includes aerators among the AC equipment around which swimming should be prohibited. BoatUS adds that ESD is far more likely in fresh water and advises staying out of the water within 150 feet of any electrical equipment.

• Press the GFCI test button when you visit to make sure it trips, then reset it.
• If the GFCI trips again on its own, do not keep resetting it. Unplug the de-icer and have it and the circuit checked.
• At a private dock, have a qualified marine electrician inspect the dock wiring every year and add ground-fault protection if it is missing.

Metal equipment in the water near your boat, plus shore power, can speed up corrosion of the hull fittings, drive and props. Before winter, check your boat's anodes and replace any that are half gone. Many de-icers have their own replaceable anode; check and replace it as the maker recommends. If your boat stays plugged in, a galvanic isolator helps protect the underwater metals. See our anodes guide.

The open water around a de-icer can be hidden by snow or a thin skin of new ice. Kasco recommends "Thin Ice" or "Open Water" signs, lighting, fencing or other measures your area requires. Many states and towns have their own rules, so check with your state natural resources agency. Tell your neighbors, ice anglers and snowmobilers nearby, and never walk on ice near a running de-icer.

Ice, snow load and changing water levels (reservoir drawdowns, storm surge) all change how the boat sits. Leave enough slack for the boat to move with the water, add chafe gear where lines touch chocks or ice-crusted docks, and keep fenders between the hull and dock. See our dock lines and fenders guide.

BoatUS recommends checking the boat every few weeks and especially after heavy storms or long cold spells. On each visit:

• Look at the waterline: a boat sitting lower or listing may be taking on water or carrying too much snow.
• Check that the bilge is dry, the pump works and the float moves freely.
• Read the battery voltage and confirm the charger is working.
• Make sure the de-icer is running, the GFCI has not tripped and there is open water around the hull.
• Clear snow from the cover and check that drains and scuppers are not blocked.
• Check lines, chafe gear and fenders.

If you cannot visit, arrange with a friend at the marina or pay for the marina's winter watch service.

Unplug and pull the de-icer, rinse it, check its anode and store it dry. Inspect the hull at the waterline for ice scrapes, check the anodes again and follow your normal de-winterizing steps before running the engine.