while i can't speak definitively to canoes, the typical kayak has concepts of light, regular and heavy-duty builds....which typically relate to how many ounces of cloth one will use over a normal core (cedar strips or marine ply).  so a typical kayak (regular build) will have 6 oz on the hull and 4 oz on the deck....and a light build might go 4 oz on the hull and 3 oz on the deck.

i routinely have done light builds and since i don't make it a practice of banging my boats into things, i have had no issues with this practice and have enjoyed the weight savings that have resulted.

i would have no problem working with 3 oz cloth becuase, if you think you need some more strength in certain areas, it's easy to double it up.  so on even a light kayak....while the overall hull may be 4 oz,   you might double it up just on the bottom of the hull.

at the end of the day it's only a 12 foot craft, so there is not going to be a lot of load on such a small boat.  so i think you will be fine with 3oz.  if it strikes you as too flimsy in a section (e.g., the middle bottom-flatish section) once you have a single layer in place, you can just add another layer.

h

Chris,

Also keep in mind that 6-oz cloth obscures the wood grain more than the lighter cloths. In my builds I don't use it on portions that will be finished bright. If I must use it then I plan on painting that portion. Same for multiple layers.

Laszlo

   Chris, I think for the S-12 you only glass the bottom of the hull, not the lapstrake sides. So, the ammount of glass you use is not very much. It is already a light craft.

Ralph

   Thanks everyone. I decided a simple solution of 6oz on the bottom & 3oz inside which is close to the same as having 4oz top & bottom. Cheers, Chris