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A Guide for Winterizing your Boat for the Off-Season

By The Ahoy! Crew
Published November 1, 2022

For boaters, especially in a La Niña year, as this one is threatening to be, winter weather and winter preparations often precede the true start to winter on December 21st.  In many parts of the United States freezing winter temperatures can mean that the best place for a boat to be is out of the water.  Hauling out of the water for an extended period of time and preparing one’s boat for winter can be a great way to check through all the boats’ systems and holds.  Further, much like many people get wood in the spring and summer for their winter wood stove, in a sense winterizing one’s boat can be thought of as the best way to prepare the boat for the spring boating season.

Winterizing a boat helps boat owners to stay on top of their boat’s best maintenance regime so come the next launch the boat is in tip-top shape. Follow the checklist below for a complete boat winterization program.

Boat Trailer

Starting at the final haul out, pay extra attention to the boat trailer.  While it is always important to maintain the boat trailer wheels and bearings, this is of prime importance at the final haul out before any extended storage period.  Thinking ahead to the next launch, a flat tire is not what you want to see…not if you could have prevented it.  

Boat Storage

  1. Storing a boat through the winter requires space to protect the boat from winter weather events.  Ideally, park the boat out of the weather, either inside a building or beneath a stable roof.  Alternatively, the boat may be stored in an open yard.  If so, consider covering the boat with a well fitting boat cover or complete shrink wrap.  A well fitting cover can protect your boat from water and debris settling on your topsides AND it is reusable.  Having said that, boat covers are neither entirely weather tight nor completely stormproof.  The cover can get weighted down or blown askew, puddle or catch debris in unexpected places.  Be prepared to visit the boat yourself or by proxy before and after weather events to check the boat and cover.  One may need to clear it and/or adjust tie-downs to make sure the cover is taut and secure.  Alternatively, boats in the open can be shrink-wrapped.  Shrink wrap takes quite a bit of skill to install well and is a total topside protection.  However, while shrink wrap is a more superior topside protection than even a well-fitting boat cover, it is a non-reusable, annual cost that produces a lot of waste.  Regardless of the cover you chose, storing your boat as close and conveniently as possible will save on time and gas if and when you go to check on her. 
  2. In some of our countries' more moist environments, many boat owners will plumb a dehumidifier during the off-season.  While this keeps moisture at bay, it requires a bit more vigilance on the boat owner's behalf so that water pulled from the air makes its way out of the boat without causing problems. 

Engine Winterization 

There are professionals that can winterize boat engines.  They will likely make efficient and effective work of this multi-step process.  Alternatively, some boaters may opt to winterize their engine on their own. Important steps are as follows:

  1. Change engine oil and filter on four-stroke outboards and all inboard engines.  It’s good practice not to leave old oil in an engine over winter because harmful chemicals and moisture can damage the engine over extended periods of time.
  2. Fresh water flush out saltwater from the raw water side of your cooling system.  Letting the freshwater run for a while rinses the salt out of the cooling system and circulates the new oil from the oil change recommended above throughout the engine.  
  3. When winterizing one is wise to winterize for the worst of winter weather.  You don’t want to risk freezing and cracking your engine block or any part of your engine.  Remove all water from your cooling system
  4. Replace fresh water in raw water with antifreeze.  Replace impeller with a liberal coat of silicone grease.
  5. Fog the engine with a quality fogging agent to lubricate and coat the inside of cylinder heads.  Consult your owner's manual for engine specific recommendations.  In general you will pull the spark plugs out and spray fogging spray into the cylinder head through spark plug holes.  This leaves a nice oil film on the cylinder interior walls that protects them from corrosion while the engine is not in use.
  6. Any engine with a fuel filter in their system will benefit from a fuel filter change at this time. 
  7. Boats with internal fuel tanks should be topped up to reduce the risk of condensation forming over the winter.  Put fuel stabilizer in fuel tanks.
  8. Run fuel out of outboard gas engines.  
  9. Clean up the engine compartment, engine room and-or engine cowling-s well after winter work is done.  Wipe any oil, dirt, and residue.  Apply corrosive protectant where you can.  When you leave the engine room clean before you put the boat away it will be that way when you come back in the spring. 

Examine the Propeller

  1. Propellers can take lots of abuse that is unchecked and unseen until the boat is out of the water.  Look for dents or leaks.  Check seals and zincs.  Change or replace as needed. 
  2. Consider removing the propeller for the off-season for safer secure storage.  Expensive propellers have been known to disappear over the winter.  


Electronic components that can be unplugged and taken down below or off the boat for storage should be. 


  1. Batteries should be turned off and ideally disconnected.
  2. Plug in a trickle charger to 110 or set up a solar panel.  Connect trickle charger to the battery for storage.  An even better option is, if batteries are small enough and light enough, to remove them from the boat and set them on a trickle charger through the off-season at home.  

Boat Clean Up

  1. Remove any and all fresh or open food products.  These can mold and/or attract unwanted critters.  Some people store canned/pre-packaged goods, spices, and oils in snap-lock, watertight containers while others prefer to take everything food related off the vessel.  Other items that can mold, mildew, or deteriorate when left unattended in the elements should be washed with freshwater and dried completely then either removed to a dry, climate-controlled environment or stored down below.  Cleaning, drying and storing these items should prevent them from absorbing water from the air around them or never fully drying.  These items include cushions, life jackets, cockpit carpets/mats, towels, and/or lines that may have dirt or salt embedded in them.  
  2. Sweep and vacuum all nooks and crannies.  Wipe down all interior surfaces from top to bottom, and stem to stern: anything and everything that can mold, mildew, or deteriorate over time.  Products are abundant for this task.  I prefer a simple microfiber cloth and an ‘almost all purpose’ solution of 7 parts water, 3 parts vinegar, plus a few drops of tea tree oil.  For wood surfaces I like a mostly water solution with a few drops of Murphy oil soap and a drop of tea tree oil.  
  3. Close all port lights, and hatches securely.
  4. Wash the topside surfaces with a mild soapy scrub and a hearty freshwater rinse.  Stainless can be washed with a stainless cleaner like, Barkeepers Friend, dried, and lightly coated with wd-40 to protect it through the winter.
  5. If applicable, wash and dry exterior canvas, wash and polish isinglass.  Further, if the boat is to be stored outside consider removing canvas and isinglass to protect their surfaces from wind driven ice or debris that could scratch, dent or damage them.
  6. After all freshwater washing is done make sure seacocks are drained then closed.  Some seacocks have a drain nut to ensure total drainage.  Leave no water behind.
  7. Fiberglass boat owners will do their boat well by washing and waxing the hull before storing their boat for the winter.  The wax helps protect the gel coat through the winter and makes for easy spring cleaning. 

Water System Winterization

Preventing cracked plumbing from holds to hoses is key when winterizing.  It only takes one cold snap with freezing conditions to sweep past a boat and freeze liquids very quickly.  Drain fresh water from tanks.  Replace water in the hoses with rv/marine water system antifreeze.

All in all, problems are exactly what systematic boat winterizing aims to avoid.  Winter care and maintenance aim to improve your upcoming boating experience and keep your boat at its best.  Maybe fuel efficiency or engine performance will be improved from the end of one season to the beginning of the next. 

After all this hard work, ideally, the winter will pass and your boat will be turnkey ready and waiting for an excellent boating season.  Unfortunately, this is not always how winter passes.  Unexpected events or circumstances beyond one’s control can get in the way, cause damage or total loss.  Ahoy! offers insurance to protect your boat when you otherwise cannot. 

Get a quote today!


Anti Freezebatteriesboat storageboatingelectronicsEnginefresh water systemguideoff seasonpropellertrailerwinterwinterizing

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