Winterizing Wisdom from the Chemistry Lab


Each winter sailors must tackle the project of winterizing their potable water system. Our preferred method is to dry the system completely (see PS September 2014, Step-by-Step Winterizing tips. If thats not possible we completely empty the tank and then treat the plumbing with the correct concentration of anti-freeze. The online version of this article provides all the details you need to carry out this process, as does the recent Inside Practical Sailor blog post, The (Cold) Case of the Frozen Anti-freeze.

cracked valves

Photos by Drew Frye

One of the reasons we prefer draining the system is because of the potential harm to neoprene components caused by propylene glycol, the anti-freeze prescribed for potable systems. Some of the vulnerable components, such as water pump impellers, are hidden from view. Other times, the damage is plainly visible.

In lab tests comparing propylene glycol and ethylene glycol (used only for non-potable systems), we found that a clear plastic water strainer housing exposed to propylene glycol was so crazed that we could no longer see through it for inspection. The strainer exposed to ethylene glycol was also damaged, but the crazing was far less severe. Interestingly, in the bowl exposed to ethylene glycol, the crazing appeared several days later, after the bowl had been rinsed and dried.

Winterizing Wisdom from the Chemistry Lab

Although this report focuses on potable systems, the caution regarding propylene glycol applies to engine cooling and other non-potable systems as well. Engine cooling pump impellers are often made of neoprene, as are some joker valves used in toilets. For these and other non-potable systems, ethylene glycol is a better choice. Be very careful not to confuse the two. Ethylene glycol is toxic to humans if ingested and should never be used in potable water systems.

Bottom line:Try to drain your potable system completely each winter. If you must use propylene glycol anti-freeze, make sure it is the right concentration and remove any neoprene components. Otherwise, you should plan to replace them in the spring.

Darrell Nicholson, editor of Practical Sailor, grew up boating on Miami’s Biscayne Bay on everything from prams to Morgan ketches. Two years out of Emory University, after a brief stint as a sportswriter, he set out from Miami aboard a 60-year-old wooden William Atkin ketch named Tosca. For 10 years, he and writer-photographer Theresa Gibbons explored the Caribbean, crossed the Pacific, and cruised Southeast Asia aboard Tosca, working along the way as journalists and documenting their adventures for various travel and sailing publications, including Cruising World, Sail, Sailing, Cruising Helmsman, and Sailing World. Upon his return to land life, Darrell became the associate editor, then senior editor at Cruising World magazine, where he worked for five years. Before taking on the editor’s position at Practical Sailor, Darrell was the editor of Offshore magazine, a boating-lifestyle magazine serving the New England area. Darrell has won multiple awards from Boating Writer’s International, including the Monk Farnham award for editorial excellence. He holds a U.S. Coast Guard 100-ton Master license and has worked as a harbor pilot and skippered a variety of commercial charter boats.


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