I’m sure it’s a simple answer. I have a rudimentary knowledge of distillation (collection of condensed vapor if I’m not mistaken), and I would think that salt would be left behind as the vapors rise. Perhaps this is not the case. Was it too dangerous, inefficient, or ineffectual?
Distillation requires heat, and heat requires fuel. Possibly - I’m guessing - the amount of fuel needed to distill a useful amount of desalinated water was prohibitive; it was easier to carry fresh water than it was to carry the fuel needed to distill sea water.
Correct. In fact if you are making boiler water and the evaporator flashes over and the water has salt in it it does not get dumped it becomes domestic water. Ever have salted coffee or salted cool aid?
Fire was a huge risk when you’re at sea in a wooden ship. Even a small fire could cause a large amount of damage before it could be put out and a large one would burn the ship to the waterline. And if a small spark should happen to stray anywhere near the powder magazine…
There’s no way they’d have been able to set up a fire heated distillary. Ships typically banned smoking pipes entirely or limited them to a small section. Other then a few lanterns above deck and the cook’s fire, which would have remained unlit in rough seas, they didn’t have much to do with open flames.
A solar still would simply have taken up far to much room to try and provide for the crew in any meangingful way.
Whaling ships had huge fires in them to render blubber, and I’d venture to say that all ships had cooking fires in the galley.
Not saying that fires weren’t and aren’t a particular hazard aboard a vessel. Just saying.
Where distillation was employed, it tended to use waste heat from the cooking fire. This didn’t really make for much distillation, but it could supplement supplies of stored fresh water or, in extremis, produce amounts of fresh water which, while tiny, were a great deal better than nothing.
(As noted above, the cooking fire was extinguished in rough seas.)
Things changed when steamships arrived. A still powered by waste heat from the engine came to be standard equipment. It still served to supplement stored fresh water, though, not to replace it. And, of course steamships made journeys much faster, so the problems of long-term storage of fresh water were greatly reduced.
It was not really waste heat that ran the evaps. The evaps on a lot of ships could supply the needed fresh water, but it is cheaper to purchase the water than make it.
As a side bar
How many have heard of either shower hours or a ship board shower?
Shower hours are used to save the expence of making water. On a ship with shower hours the water is turn on only during a short time each day. It encourages everyone to take quick showers, in and out so the next man can shower.
A proper ship shower, turn the water on wet down turn water off. Soap up turn the water on to rinse off turn the water off and you are done.
I had a friend, mid-twenties at the time, once remark that he did not understand how anyone, ever, could run out of hot water in the shower. It just seemed impossible: it had certainly never happened to him. Knowing his dad was career Navy, I said “Do you turn the water on and off in the shower as needed?” and he said “Uh . . .yeah?” and I was like “normal people don’t do that.” He truly had no idea.
Thank you for that beautiful illustration of the proper use of “just sayin’”. 
In the Navy, this is known (unsurprisingly) as a Navy shower.
The alternative - much anticipated after a long time underway - is a Hollywood shower. That implies unlimited water at any temperature you like, and unlimited time to enjoy it.
On a Navy ship in the tropics could you get a cool shower?
Of course the primary purpose was to make water to replace what was inevitably lost during operation of the steam plant, without which the ship grinds to a halt.
On mine, the fresh water tanks tended to be at more or less the temperature of the ocean, which I always found plenty cool enough for comfortable showering. Someone crazy enough to enjoy truly cold showers might have been disappointed.
But the most tropical place I ever spent much time was the Caribbean. I expect that the Red Sea would be a different story.
On the training ship at the maritime academy the water came off the evaps at 120 degrees. Stored in a deep tank with machinery spaces on three sides, The Boiler room the fourth side. After standing watch in the boiler room or the engine room I wanted a cold shower. I learned to salt water showers until I cooled off. The finish with a frresh water shower.
The freighters and tankers less people and in port more often and I had my own room and shower.
I seem to recall 105 degrees as the outlet temperature. The evaps were really good, and we almost always had nearly full tanks.
This has nothing to do with the OP, just an added thingie to Xmea’s
contribution.
In 1969 I was in Vietnam. In September I got R&R and was able to met my wife in Hawaii. Even today, from time to time, she will comment on how much time I would spend in the shower in our hotel room.
Great responses guys. This question was inspired by a viewing of the latest Pirates of the Caribbean movie in which they ran out of potable water. I think I can safely surmise that in an emergency situation, distillation via controlled and monitored fire could have been a last resort option, as opposed to going without drinking water.
As far as the danger of fire on a ship goes, a bucket of saltwater is always handy and I’d assume that any surface nearby would be soaked just in case.
It could have been a feasible, if not efficient, emergency source of drinking water then?
You’re seriously underestimating the danger of fire on a sailing ship in the 17th century. It was the number one danger for a ship. Remember that many sailors at the time did not know how to swim, so going overboard meant drowning. And it sounds easy to say, “but you’re surrounded by water,” until you try hauling up enough water to put out a fire. The only way the ocean helps is by stopping the fire at the waterline. Remember that the ship is almost entirely made out wood, rope, and linen. The whole thing is waterproofed with oakum, which is made of hemp fiber and pine tar. And don’t forget the magazine full of gunpowder.
In 1669 Henry Morgan’s flagship, the Oxford, was lost while at anchor because of an errant spark. More than 300 people died.
Yes, they had flames onboard in the form of lanterns, candles, and the galley fire. These were all strictly regulated. Most ships at the time would only serve one hot meal a day for the sailors and the galley was extinguished in bad weather or even on sighting a potentially hostile ship.
Yes, they could build larger fires if they needed it for activities like whaling. That didn’t mean that all or even most ships would have been able to handle larger fires. And when you think of whaling ships most people think of ships that were almost 200 years later than your OP, with the “Golden Age of Whaling” (the era Moby Dick takes place in) occuring roughly from 1800-1850.
Running out of water would have been far less of a priority than the danger of a fire. A still would simply have not been worth it.
People minus water = death, after what 5 days, less?
So there were regulated fires onboard, yet an errant spark could kill 300 men. Sounds like a freak accident to me, given the common practice of having fire onboard.
Would a distillation unit be under any less scrutiny that a galley fire? I’d think it might be part of the galley fire.
If I’m gonna have a fire on a wooden boat, you’d better believe that there are numerous buckets of water right there within a foot or so of the fire. Everything within 20 feet would be soaked with seawater, and the fire would be isolated to an extreme.
If one is planning to have a fire in a flammable boat, one should have waaay too much water on hand to quench it. People weren’t retarded back then, just old timey.