The fantasy world is set in medieval times (1100 A.D - 1400 A.D).
The mission is to travel from the mainland to an ice continent by means of ship, a distance of say from England to the North Pole. The sea being travelled across is tame, though there are some icebergs the closer you get to the arctic continent. The purpose is to mine for precious stones in the ice.
The only outstanding source of technology or magic are stones which generate wind. These stones are used by sailors to give their sails a bit of an advantage over the seas.
What sort of ship could sustain a travel like this (a cog, a galley, etc)? How long would it take? And how many crew members would be needed (and what would their roles be)?
Thanks in advanced.