[Fr. Frank]

anybody know what gauge wire i should use for a 15-16' run of cable for a 225 fs yami?

Ken is right, the bigger the better. If the chart calls for 2/0 use 1/0, if it calls for 1/0 use O ga.
Also make sure you use tinned aluminim marine grade wire or cable, NOT copper. Copper builds verdigris (copper oxide) quickly in a salt environment, and connectors end up fairly corroded, with significant degradation and impedance, after only a couple of years.

Buying in bulk can save you LOTS of money. I priced 0 ga. tinned aluminum for my boat, and two 12' runs (48' LOA) from West Marine would have cost me over $200. I contacted an electrical supply house in Connecticut, and got the remains of a spool of three-conductor tinned aluminum electrical cable in 0 awg for $105 including truck freight. Originally a 250' spool, there was over 120' left on it. I made the runs for the batteries to under the helm seat, and used the remainder for a cable to hook my 15kW generator to the house, replacing the original 2/0 25' cable, and moving the noisy generator around the corner of the garage. Sweet!