I'm no expert either, but I've been in a few in my life, including some replicas (viking ship and "knarr")
The first impression is that it's very wide. While this makes it stable and able to carry lots of cargo, it'll make it sail like a dog. Definitely a boat only for inshore sailing and short voyages. Slimming it down one square would make it more seaworthy, at the expense of cargo capacity (see also rowing later)
The mast is a bit too far in front, the best placement (with a single mast) is just a little bit in front of the centre. Move it back at least one (possibly two) squares.
Most of the wind pressure will be from the back, you need far stronger support ropes from the main mast fastened in the main body of the boat. You also need a smaller angle on these ropes, thus they need to be fastened further back on the boat. Finally, with a square sail (the "worst"/least advanced type of sail) you must be able to adjust the angle of attack for the sail, thus a separate rope and pulley (sp?) system for the sail is necessary.
With a square sail you need oars, as these boats are almost impossible to sail upwind. However the ship is a bit big (and wide) for rowing, especially with only 6 oars (I assume 2 persons per oar). In addition the cabin hinders communication between the rowers on each side, making it very hard to coordinate. And you need something stable to sit on when rowing, which seems hard to do with your design. I would either have removed the oars completely (but then you need a different type of sail), put the oars below deck, or gone for a slimmer design without the cabin between the rowers.
The cabin is a bit big for a ship this size, and with the mast in the middle you probably need to slim it a bit down and put it further back. I would also have put the entrance door on the short end, that seem to be the common arrangement on all boats I've been on (probably because it's easier to get a good layout of the cabin).
All in all its not bad, it'll probably sail but not very well. The biggest goof is the mast (placement and support ropes), you need to fix that. Apart from that it depends on what you are aiming to use it for. It'll do for inshore trading, but if you want to go outshore (and longer voyages) you need either a slimmer boat with a better oar system, or a proper ship (i.e. larger).
.Ziggy
