The Pilot’s Book · Sea and sailing
Ship's stores
Provisions feed the crew, sailcloth mends the sails, planks mend the hull. They are light, every harbour sells them, and they cannot be sold.
Provisions, sailcloth and «Planks & Pitch» stand first on every market, marked as ship's stores. Every harbour has them without limit. They are light: 0.05 m³ a unit (planks 0.075). 
Instead of «Sell» they show a greyed «Store»: stores are kept for the voyage, not for trade. In return they never count towards overload, the neutral flag's free hold or the passage's limit. 
Cast off short of something, and a window lists what is missing for a normal voyage: food, repairs, shot, hands — with prices. Buy item by item, «Buy all», or «Sail as she is». 
The provisions row shows how much is aboard. At sea the crew eat about half a unit a minute per 40 hands. When the last biscuit is gone, morale slides towards 25. One plank mends 40 points of hull, one bolt of sailcloth 20 points of sails.
See also
RepairsAt sea, out of a fight: «Repair» (R) — the crew mend with planks and sailcloth. In port the yard mends everything for silver.3 steps
The crew and moraleMorale tends to 70. Hunger, curses and black storms lower it, rum raises it. High spirits load faster and board harder; low ones slow everything.3 steps
The hold and overloadTrade goods over half the hold (three quarters on a trader's hull) — overload, −20 % speed. Over the brim — −35 %. Ship's stores do not count.4 steps