Tell me about sea-based trade in 12th century Barcelona

Disclaimer: this is ultimately intended to help with a tabletop roleplaying (D&D) game to be set in 12th century western Europe. However, the point of game is to make the setting as historically accurate as possible, and since I’m asking for factual information I posted this in GQ, but I encourage mods to punt this over to CS if it’s appropriate. ^^

Having said that, here’s the skinny: I’m writing a campaign (basically an interactive story-driven wargame with 2-5 players) that will center around the players working on European trade ships, learning how sea-based trade operates, and eventually buying or stealing their own boat to go into business for themselves. I understand that Barcelona was an extremely large center of trade in the 13th century, so I’m thinking of starting the game in southern Barcelona circa in 1265, 20-30 years after a number of major laws relating to sea trade had been passed. (I’m using the Medieval Sourcebook to assemble information on the relevant laws.)

With that in mind, I have two questions:

  1. How were civilian ships (and fleets) organized? I somehow have this idea that, depending on the individual in charge, the shipboard power structure closely mimicked that of the navy, only with (understandably) less discipline and organization.

  2. What sort of books should I be looking to for: a) a general overview of 13th century nautical laws in Spain and the surrounding area, b) information on the design, function, and distribution of ships in the same period, c) discussion about the Spanish economy from the 10th-14th centuries, and d) information on military technologies common to the same period, preferably in as much detail as possible.

I would appreciate any input that people have… I know there are probably some extremely obvious sources for what I’m looking for, but I obviously know very little about European medieval history.