Vessel Winterization

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 that should be accomplished for vessel winterization.

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

Fuel Systems:

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

Engines, Generators and Transmissions:

  • Changethe 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.
  • Checkthe fresh water cooling (anti-freeze) for Ph and adjust or replace as necessary.
  • Ifyou 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.
  • Gasolineengines 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 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.


  • Checkall 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.
  • Turnon the pump and open both hot and cold spigots on each faucet startingwith 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.

Holding Tanks:

  • Pump out the holding tank at a 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-hole.  Pour non-toxic antifreeze into the toilet and pump it throughout the system and into the holding tank.
  • Be sure to label your thru-hole 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:

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


  • Consult with owners manual.  Be sure that the system is either stored withpickling 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 would be happily to advise.


  • Check  operation of bilge pumps and float switches along with any electricalconnections that maybe 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 CO2detectors are working.


  • Remove all perishable items from refrigerator.
  • Turn off and defrost freezers, refrigerators, and leavea 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 dryand mildew free if you don't plan on leaving your reverse cycle AC or diesel furnace on.

Boat Exterior:

  • Make  sure all drains are clear and draining properly.
  • Washingand 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 bimini's not being used for winter protection should becleaned, treated, dried and stowed.
  • Cushionsand 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 themcleaned, 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 and that show signs of corrosion or electrical arching.  Please note that electrical cords are the number one cause of boat fires.

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!