The extra glass is not a bad idea.  Put it on the outside.  If you put it under the full layer then when you feather it all out you will cut through the full layer.  Not a good deal.

Better yet, coat the bottom with 50/50 epoxy & graphite powder.  Then you can drag it up a gravel beach.

Enjoy your new Duck and, you'l love the Shearwater.  Is it a hybrid?

PAG

I put an extra layer of fiberglass on the entire flat bottom area of the Wood Duck I'm currently building.  Based this on the scratch pattern on my Shearwater (built about 1.5 years ago) that shows scratches across the entire bottom panel.  I would recommend a third narrow layer on the very V-shaped parts of the bottom bow and stern also (the middle seam you refer to) - this area will get lots of abrasion since it's so thin and sharply pointed.  Again, based on my experience with the Shearwater that has a similar, although narrower bottom shape. 

As PAG mentioned, always put the smallest pieces on outside and bigger pieces closer to wood. 

You'll see in the Shearwater instruction manual that they recommend this same lay-up for the bottom; I basically copied it for the Wood Duck.  Of course it depends on the bottom characteristics of where you'll be paddling.  We have quite a few rocks in my area. 

Or you can do the graphite coating.  I would have, but I really like to see the wood. 

After having just built a boat, I would have done things slightly differently than what I did.

Next boat, I would put a tape over the keel both front and rear at least 2' on each end.  Sand this in on each edge. 

Then put the glass over the whole hull and then put another abrasion tape on the outside as well.

Thanks everyone for the guidance...I know what I'm going to do now.

PAG..Shearwater will be a another Stitch and Glue boat..love the strip method, but I don't think I have the time just now...but would love to build a strip boat in the future at some point.