Winterize Now

Unfortunately, the boating season is either winding down or over for most of you.

By now you have probably performed certain maintenance to protect your valuable asset.  The time and effort you spend on vessel winterization now will have a definite effect on your boat's performance (or lack of it) and can certainly save you time, effort, and money in the spring.  You should also remember that your insurance policy may not cover damage done by lack of maintenance or neglect.

The following is a checklist of items we at S3 Maritime have prepared that should be accomplished for vessel winterization.

Check the owner’s manual for your boat and systems for manufacturer's recommendations.

Fuel Systems:

  • Fill your fuel tank(s) to avoid condensation over the winter months.
  • Add a fuel stabilizer by following the instructions on the product and the engine manufacturer’s recommendation.
  • Change the fuel filter(s) and water separator(s).

Engines, Generators, and Transmissions:

  • Change the oil and filters to avoid exposing the internal bearings and engine parts to the acids and moisture in the oil that can cause corrosion of the vital engine parts.
  • Check the fresh water cooling (anti-freeze) for pH and adjust or replace as necessary.
  • If you are not using the boat during the winter, drain the water from the raw water cooling system and shut off the water intake valve.  Be sure to label this somewhere to remind you of its status.
  • Gasoline engines and outboards with carburetors need to have the engine run to warm up the oil before you change it.  Shut off the fuel and let the engine run until it stops.  It is important that all fuel is drained from the carburetors to prevent deposits of evaporated fuel.
  • Remove the spark plugs and spray fogging oil in the cylinders to lubricate the cylinder walls and pistons.
    Change transmission oil and or lower unit oil.


  • Check all battery levels to make sure they are topped off and connections are tight.
  • Check output voltage of battery chargers for appropriate settings.

Water Tanks:

  • Open both hot and cold spigots to run tanks dry.
  • Turn off fresh water pumps.
  • Pour a few gallons of non-toxic anti-freeze into the water tank.
  • Turn on the pump and open both hot and cold spigots on each faucet starting with the furthest one and moving closer to the pump.
  • When all faucets have anti-freeze coming out of them, the system is winterized.
  • Shut off sink drain thru-holes and pour non-toxic anti-freeze down them.
  • Be sure to tag all breakers and thru-hulls that have been turned off and closed.
  • Leave water in tanks if your watermaker is equipped with an automatic fresh water flush feature.

Holding Tanks:

  • Pump out the holding tank at an approved facility. While pumping, add freshwater to the bowl and flush several times.
  • Run deodorant through the system and into the tank.
  • Shut off the thru-hull.  Pour non-toxic antifreeze into the toilet and pump it throughout the system and into the holding tank.
  • Be sure to label your thru-hull “closed”.

Air Conditioning:

  • Shut off thru-hulls to air conditioning systems.
  • Open the system and drain all the water out.
  • Run non-toxic antifreeze through the system by removing the input hose from the pump and sticking it in the antifreeze.  Run the pump flushing the antifreeze through the system until it exits.
  • Turn off the pump and reconnect the input hose.
  • Vacuum intake filters.

Diesel Furnace:

  • If you plan on using your diesel furnace through the winter season we recommend having a service technician inspect the unit. We do recommend that your unit is serviced annually.


  • Consult with owner’s manual.  Be sure that the system is either stored with pickling solution or is set to fresh water flush approximately every fourteen days (unless you have drained your fresh water tanks). If you have questions regarding service for winterization for your Watermaker please contact us and we will happily advise you.


  • Check operation of bilge pumps and float switches along with any electrical connections that may be subjected to bilge water submersion.
  • Make sure the bilges are clean and dry.  This way you will be able to detect any leaks that may occur.


  • Lubricate and exercise all thru-hulls to be assured of proper operation.
  • Close and tag all thru-hulls that are not associated with bilge pumps and deck drainage.

Protection Systems:

  • Check the fire suppression system tags to ensure it is up to date and in working order.
  • Check to make sure the fire extinguishers are current.
  • Check to make sure all smoke/fire alarms and CO2 detectors are working.


  • Remove all perishable items from refrigerator.
  • Turn off and defrost freezers, refrigerators, and leave a fresh box of baking soda in each.
  • Prop open fridge/freezer doors that are not in use for better air flow.

Boat Interior:

  • Remove any personal items that you may want to have cleaned, checked or replaced.
  • Open drawers and lockers and clean thoroughly.
  • We recommend small electric oil filled space heaters to keep your boat dry and mildew free if you don't plan on leaving your reverse cycle AC or diesel furnace on.  Plug space heaters into non-inverted AC outlets if possible to avoid depleting house batteries in the event of a shore power failure or outage.

Boat Exterior:

  • Make sure all drains are clear and draining properly.
  • Washing and detailing the boat with a coat of wax will help protect the gelcoat and paint throughout the wet winter months.

Canvas, Cushions, and Fabric:

  • Canvas covers and biminis not being used for winter protection should be cleaned, treated, dried, and stowed.
  • Cushions and mattresses should be stowed on end to allow air to circulate.  Better yet- store them in a climate-controlled environment, if possible.
  • For sailboats, we recommend removing all sails.   Have them cleaned, repaired, and stored in a dry environment.

Electrical cords:

Inspect all power cords, especially shore power plugs and inlets, for corrosion and fit.  Repair or replace any that show signs of corrosion or electrical arching.  Please note that electrical cords are the number one cause of boat fires.

Scheduled Maintenance:

Another option is a scheduled maintenance routine/inspection during the winter months where the vessels engines, generator, heating, fresh water and sanitation systems, and watermaker are all run on a monthly basis and the vessel is inspected for leaks and proper operation.

This routine keeps your vessel’s systems lubricated and in working order and ready to go at a moment’s notice for that Christmas cruise or impromptu trip on a sunny winter weekend.

We at S3 Maritime hope you find this list helpful. We can help with any work you may be unsure of or unable to perform.  From vessel winterization to complete refits we are here for you and are available to contact at