Desalinaztion on board.

And by all means catch rainwater. Before RO became practicle I would always catch rain water with either a modified sun awning or a purpose built water catch.

In the tropics its easy to catch 10 or 20 liters of water in afternoon cloud burst .

 

Regarding technical specifics, I would think:
-double glaze the evaporator to reduce heat loss and condensation on the solar collector.
-use a porous medium as evaporation surface rather than a "pool". Imagine a damp black carpet. This would reduce contamination of the distillate by not having free liquid water.
-a continuous flow dripper system could apply moisture to the evaporator and brine could simply drain out of the bottom. If a counter-current heat exchange between input water and output brine is used then the lost heat through having a continuous flow system should be trivial.
-have a separate seawater-cooled condenser with a small air transfer pump between evaporator and condenser.


Michael, good point. Rain is also a good option for a top up. The down side there is predicting when it will (or won't) rain, but actual "droughts" at sea are rare.

 

There is an alternative for topping up tanks and that is collecting rainwater, its how it was done in years gone by before the advent of RO, some folks such as the Pardeys still do it. Obviously this will work better in some geographic area than others. No its not going to give you as much water as a larger RO system but would likely be competative with smaller manual units and solar stills. It would require being prepared to take advantage of opportunities as they present themselves. Just a thought.

Steve.

 

I sailed to Tahiti from San Francisco in '95 on a 36 footer we had 40 gallons on board plus a emergency reserve of 20 gallons at all times we ran a power surviver 35 to top up the tanks it was more than adequate for the job. Now there are even better RO makers like any of the Spectra models. 1 gallon pp p/day is easy to remember but is more than you need. Although having that cap. Easily keeps your mind at ease if there is a problem. We also had survival solar stills for each person thankfully we did not have to use them. That passage was 19 days. Sent from my I phone

 

Nothng wrong will RO its just that they are expensive and over the lifetime of the boat they are the least used piece of equipment. Ive got about 600 hrs on mine... over 19 years. Id prefer to spend the money on other equipment


If the area youre sailing has absoluty no facilty to fill up your water tanks then they make sense. How many people sail in areas with no access to water ?



As for ocean passages, ive never had a problem with water shortage . Use a big tank, be a water miser and carry bottled water sufficent for two times the expected passage time . 3 crew. 1 bottle per day, 30 day supply...90 bottles.


A hand watermaker for liferaft use is a good addition.

 

Some boats will tolerate the weight of large tanks of water , others less well and a watermaker makes sense.

 

True, but normal folks dont often cruise in speedsters.

Most folks dont cross oceans .


As for extra tanks in a normal coastal cruiser..the guys who like to take hot showers....its the way to go. Who cares if you start a three week cruise overloaded, with your waterline submerged or bow down.

Too many times on cruising sailboats I see tank ratios backwards. Big fuel tanks and small water tanks. The designer has automatically required a watermaker be fit. The watermaker or generator is going to break and ...well...there goes your three week cruise.