Winterizing Onboard Systems
In an earlier blog, we outlined the problem with winter and boats, and some defense strategies. Here, we’ll dig more deeply into perhaps the most common tactics to defend against freezing aboard your boat.
When water freezes, either fresh water or salt water, it can’t flow, and its volume expands. This expansion is the primary cause of damage in the winter aboard your boat. Pipes burst, plumbing fittings crack, and engine damage can be extensive, and expensive.
Defense
To reduce the possibility of this kind of insidious damage, the water needs to be replaced with something that won’t freeze at the temps typically seen during the winter in yachting areas, expand and burst things. There are two substances from which to choose that don’t typically freeze: air or antifreeze. Each has their place, which we’ll explore below.
The systems typically requiring winterizing to defend against freezing include the potable fresh water system, the grey and black water systems, and any cooling systems, such as for engines or condensers. A mix of air and anti-freeze will typically be used, depending on the system being winterized, and its summertime use.
Note: flooded lead acid batteries are flooded with an electrolyte that’s a mixture of water, acid and magic. With even as low a state of charge as 60%, they’re good down to around 20 below zero. The simple answer is to keep your batteries charged, then they don’t typically need to be winterized against freezing.
Fresh Water Systems
Fresh water aboard your boat is frequently used for drinking and cooking, as well as washing dishes, showering and sometimes flushing heads.
Replace Fresh Water with Antifreeze
One option to winterizing systems is to displace the fresh water with antifreeze. This involves emptying the fresh water tanks as far as practical, then pour in antifreeze, and pump the resulting mixture through the plumbing. This is the simplest, but there are at least two downsides to this.
First, when using this method, the potable fresh water system is seldom fully evacuated, leaving some fresh water in it, which then dilutes the antifreeze. This diluted antifreeze has a compromised freeze point, meaning its freeze point is higher (worse) than what’s advertised on the jug. How much higher? Who knows?
Second, when spring finally arrives, and it’s time to recommission the boat, all that antifreeze will need to be flushed out. This is seldom fully possible, and virtually always leaves that funny, antifreeze taste in the fresh water. It’s possible to put a little bleach in the fresh water tank, but it’s very difficult to fully get rid of that taste.
Drain And Replace Fresh Water With Air
The other option is to replace the fresh water in the potable water system with air. This can be done by draining, to the extent possible, or by blowing out the fresh water, or a combination/sequence of the two.
Draining as much fresh water as possible is a good start to removing the fresh water, but should not necessarily be considered sufficient to getting rid of all the fresh water. Low points in piping, tank water pick-ups not all the way to the bottom of the tanks, captured water in filter housings, etc., are all places from where water might not completely drain.
Vacuuming can be used to augment or speed up draining, but with the same incomplete caveats as above.
Once a fresh water system is drained, remaining water can be encouraged to leave by blowing out the system. Care must be taken on a couple of fronts when blowing out the fresh water system. The first is over-pressure, the second is the cleanliness of the pressurized air.
Domestic water systems are typically configured for an optimal water pressure in the 40-60PSI range. It’s not a good idea to connect an air compressor at 150PSI to blow out the remaining water, as this over-pressure could be as damaging as letting the fresh water freeze in the first place. Regulating the air pressure in use down to the 30-45PSI range will reduce this risk.
There are a few sources of pressurized air that can be considered to blow out the residual water. Some that come to mind include an air compressor, the exhaust of a vacuum cleaner, or a SCUBA tank.
Use of the fresh water system for potable water means the pressurized air being blown into the system, at a reasonable pressure, should be clean. This pretty much eliminates considering use of a vacuum cleaner exhaust. Shop air compressors quite frequently have oil added to the compressed air, to lubricate the tools they will power. This oiled compressed air will add oil into the fresh water system, which can leave a strange taste, and is difficult to eliminate in the spring. The air in a SCUBA dive tank is about as clean as is readily available, and when regulated down to a safe pressure, is most effective.
Blowing the fresh water out should be done outlet by outlet, starting with the ones furthest from the fresh water tanks, and blowing out until no more fresh water is spurting out of the outlet, then moving to the next outlet.
Sea Water Systems
Sea water is used aboard typically for cooling, e.g. for engines and generators or for refrigeration or air conditioning condensers, as well as when fresh water might too valuable and sea water is used instead, e.g. flushing heads.
Whereas potable fresh water systems draw from an inboard tank, sea water systems, as their name indicates, draw from external water. By virtue of this difference, there is no tank to winterize, just the systems themselves. The reduction of protection due to diluting the antifreeze in a partially still filled tank is not an issue, and, since these systems draw from the outside sea water, they tend to drain the plumbing used to bring the water aboard. Once the water gets to its strainer is when care must be taken.
There are two major classes of equipment that use sea water, typically for cooling. These are internal combustion engines, such as for propulsion or generators, and both diesel and gasoline fueled. These are typically high-volume consumers of sea water. The other class is equipment that has far less sea water draw, and its sea water requirement is intermittent. Examples include air conditioning or refrigeration condensers, washdown systems, and sea water flushed marine toilets.
As these systems have no effect on taste or provide consumable water, the need to avoid the downsides of antifreeze does not exist.
Raw Water Engine Cooling
Marine engines frequently use raw/sea water as their cooling source, either through a heat exchanger, or plumbed directly through the cooling passages in the engine. In addition, it’s quite common for the used sea water to be injected into the exhaust, to both cool it and to be part of the noise muffling system. Water lift mufflers are how this is done, and they hold a fair amount of sea water that must be replaced with antifreeze.
Plumbing into the engine raw water system is frequently easiest right at or after the engine raw water strainer. Pull the hose off the strainer, immerse the end in a bucket of antifreeze, and Bob’s your uncle. Run the engine until only antifreeze is coming out the exhaust or cooling water outlet, and you’re done. Be sure to not let the bucket of antifreeze run out, or you’ll need to replace your raw water impeller.
Other Raw Water Systems
The same process can be used on other raw water-cooled equipment, replacing the sea water pickup with a container of antifreeze, then having the relevant system’s own pumping capability pump that antifreeze. Observing the water exhaust from these systems will indicate when the clear sea water has been displaced by the colored antifreeze. In places where this is difficult, such as the head plumbing into the holding tank, it’s always a good idea to err on the side of too much antifreeze, as that will reduce any dilution effects.
Outliers
It’s always a good idea to review the boat’s plumbing diagram, as well as map out all above and below the waterline through-hulls, to ensure any water entering or exiting the boat has been accounted for. There can be some sneaky ones. These can include bilge pumps, shower sump pumps, head or holding tank macerator pumps, washdown or baitwell pumps, among others. The methods outlined above can be evaluated to choose which will be most effective in each of these cases.
Summary
With a good idea of what’s needed to winterize the water systems on your boat, planning for, preparing and actually winterizing can be a fairly quick, thorough and straightforward job.