Winterizing a sailboat involves preparing the engine for winter, removing or protecting gear, and winterizing the head and water systems before covering the boat. You can expect serious problems when the temperature drops below freezing if you fail to correctly winterize all systems. Pipes can burst in the most unexpected places, resulting in costly repairs and potentially letting water inside when you launch in the spring.
Start by buying a supply of nontoxic, environmentally safe RV-type antifreeze at a marine or hardware store. Choose one rated to a temperature low enough for your area. Make a list of every water line and hose in the boat that ever carries water (fresh or waste). Then methodically treat each part of the system one step at a time. Following is a list of areas to treat on a typical mid-size cruising sailboat. Most important, don’t overlook any hose or water passage, even those you think may drain straight out of the boat, because a low place may accumulate enough water to freeze and burst the hose.
1. Start at the water tanks.
Pump out all the water from all water tanks. You may have to close a valve on one tank to ensure that another tank drains completely once the pump starts sucking air. Get them as dry as you can. Then pour the antifreeze full-strength into each tank, putting the most in the main tank. Close the valve to any secondary tanks for now.
If you have a hot water heater, drain it completely, then close the drain so that antifreeze flushes through the tank in the next step. For all sink drains, open seacocks to allow antifreeze to drain outside.
Then, one outlet at a time, pump the antifreeze out each hot water outlet until the tap water turns the color of the antifreeze. Do the galley sink, the head sink(s), and shower nozzle. Shut off the power to the pressurized water pump so that you don’t fill the hot water heater full of antifreeze. Disconnect or block the inlet to the hot water heater (or use a small fitting to connect the tank’s inlet and outlet hoses together to completely circumvent the tank); then open its drain.
Now run antifreeze out every cold water tap, including again the shower head. If you have a freshwater foot pump or hand pump in the galley, pump it as well. You may have to add more antifreeze to the water tank to displace the water in all these lines to all taps.
If your marine head is plumbed for fresh water flushing, pump water into the bowl until it turns the color of the antifreeze. (If your head uses lake or ocean water for flushing, wait until the later step.)
Finally, close the main tank valve and open the valve to the secondary tank. At the nearest sink, pump through the cold water tap until the water changes color. You should not have to pump out the other outlets again, since the water lines to those are still full of antifreeze. Now all lines and hoses through which your freshwater system flows should be winterized.
2. Winterize the head and holding tank.
Hopefully you already pumped out your holding tank, since this is difficult or impossible to have done ashore. Before winterizing, depending on your tank, you may want to flush the system first with a soapy bleach solution to get it as clean and antiseptic as possible.
Begin by winterizing the water line to the head(s). If the head uses lake or ocean water for flushing, disconnect the inlet hose from its seacock. Put the end of that hose in a bucket of antifreeze, and pump the head until the incoming water changes color. (If the head does not have sufficient suction, you may have to raise the end of the inlet hose, or attach an extension piece, high enough to make it easier for the antifreeze to be pumped into the bowl.)
Your marine head likely pumps directly into the holding tank rather than overboard, as required by US regulations. Pumping a gallon or so in through the inlet hose and out into the holding tank winterizes this part of the system.
Don’t forget the holding tank outflow, however. Some tanks can only be pumped out via a deck fitting; in this case, because the tank outlet hose rises up from the tank to the deck, the hose should not contain fluid and thus does not need further winterizing. (If it may collect waste water in a low spot, pour some antifreeze into the outflow hose at the deck outlet.) If your tank can be pumped overboard, whether manually or through a macerator pump, you need to winterize that part of the system also. Run that pump until the antifreeze from the holding tank is pumped out.
3. Winterize the bilge pumps.
This is an easy one to forget—until you split a hose or rupture a pump! Manual and electric pumps in the bilges often have a backflow valve that keeps water from flowing back into the bilge—which means there is likely water in these hoses. Suck the bilge as dry as you can, then pour in some antifreeze and run each pump until the water being pumped overboard changes color.