This is a "calories in / calories out" situation.
The human body adapts to the activity it does. They did research on long distance runners, and their bodies burn far less calories doing that activity than a person that doesn't do long distance running. It's because their bodies have hyper-acclimated to the exercise.
Folks working on a boat will have their bodies hyper-acclimate to the activities over years, so they will expend less calories doing them. IE: hoisting sails, etc. So, in the long run, a crew will require less calories to perform activities than, say, a fresh crew that's never sailed before.
Next, while movies have "glamorized" crews working non-stop aboard ships, that would simply be wasting calories / energy for no reason. In some situations, the captain wants to keep the crew busy to keep their mind off boredom at sea (especially, with low / no wind stalling them out). In other situations, the captain is trying to enforce discipline by making the crew do monotonous tasks, like swabbing a deck that's already clean.
But, a smart captain lets the crew rest.
Sailing is a "feast or famine" job. By that I mean there is either too much work to do, or hardly any for long stretches. The crew needs to be fresh and rested when a storm hits, or when they make land to unload / load cargo, etc. They will hit times when the wind stalls out, or they've set a course and just need to wait until the wind takes them where they need to go. The captain will let the crew hang out, play games (dice, cards, etc), play music, work on hobbies (whittling, etc), and possibly have them work on side tasks, like sewing up torn sails, mending rope, etc. The goal is to let the crew relax and enjoy themselves during the down time, because when real work shows up, it often shows up in droves.
These long periods of rest also help the crew conserve calories, because they're not doing hard labor every day on the boat. They're just doing light labor for a week while the ship does all the work (sailing them where they need to go).
So, food isn't that big of a deal. 947
Besides fishing, crews learned to salt meats and create hard-tack biscuits and things. They would take along lard to cook food with, which is high-calorie fat (fat is 9 calories per-gram vs. 4 calories from protein & carbs).
Water would definitely be a big issue, but the crew can use the massive sails to capture morning dew and barrel it for water. Rain storms provide a lot of water. There are times when there's not much rain on the seas, but when out at sea you have a very flat view of the ocean.. you can literally see storms off to the side. You can sail into them and follow them while collecting fresh water by using the sails as funnels. Not every storm at sea is a big-wave destroyer. There are mild storms where it's just rain coming down. Crews would start to know where the rains are during which seasons on the high seas, and decide to make stops there.
What you have to remember is a planet is a closed-source environment. Water evaporates off the oceans, and has to go somewhere. That's where it gets recycled as rain that comes back down. So, if folks are sailing the high seas, they will have opportunities to get fresh water from rain.
If they are stuck out in the sun w/o rain, they can collect sea water and evaporate it into condensation and collect that en masse. 1022