For a small boat at sea, a water maker is an amazing luxury. Aboard Oso, we shower every day, we don’t think as much about conserving water while washing dishes or preparing food, and our toilets even flush with fresh water.
All of that is enabled by our water maker, which pumps out about 35 gallons/135 liters per hour of delicious desalinated water. The theory behind a water maker is pretty simple – sea water is filtered and then pushed across a membrane at high (~800psi) pressure. About 90% of the water is pumped overboard, but 10% of the water makes its way through the membrane, leaving its salt and other impurities behind.
In practice, it’s a bit more complicated. A feed pump supplies a high volume of sea water to a second pump that increases the pressure. That pressurized water is sent to the membrane housings, where a salinity meter decides if the quality is high enough to divert to the tank. All of that pumping and pressurizing requires energy, so we run our small generator to power the process, essentially converting diesel fuel to fresh water.
Oso carries ~280 gallons/1000 liters of freshwater in two independent tanks, each with its own pump for redundancy. Our strategy is to always keep both tanks nearly full – by doing this we sacrifice a small amount of light wind sailing performance that we’d achieve with less weight onboard, but we have more days of autonomy should something happen to the watermaker that would prevent us from making more water.
So we run the watermaker every four days or so for an hour and a half, making about 50 gallons/200 liters. That works out to about 12 gallons/50 liters per day of consumption for the two of us, so our definition of onboard “luxury” is very different from normal water usage on land!
All’s well aboard.
Day Nineteen
19 23.6S 121 45.5W
175nm
