I am watching the film again (excellent film) and at one point the Surprise seems to set sail from the Galapagos islands heading South South West in pursuit of the Acheron. To my limited knowledge there's not much out there and I'm wondering how far they could have gone before having to turn back out of fear of starving before reaching land.
I had a read of the other Master and Commander questions posted but couldn't see anything specifically about food.
Edit: Sorry if it's not a fifth rate ship, that was my best guess from a Wikipedia read.
Also, I didn't ask about water as in the film they end up with a shortage of water but are saved when it rains, so presumably food was a bigger limiting factor.
A ship that size could be stowed with food for up to six months, but it would get fairly monotonous and repetitive at the end of the six months and captains would make every effort to avoid having to use up all their rations. It would have to re-water and get fresh food before the end of that period -- before citrus juice was in wide use as an antiscorbutic, greenstuff was known to be vital in preventing scurvy. Keep in mind that Surprise would have re-watered and bought provisions along the west coast of South America, and would have re-watered and harvested tortoises or other animals in the Galapagos.
Follow up question: how big of a part was fish in a sailors diet?
I was under the impression that beer was the standard drink rather than water? Water would go bad quickly while beer would still be drinkable