There is no point in doing that, all it will do is just add unnecessary weight to your kayak.

The direct answer to your question is yes, you can do that, but Jeepguy2 is right that you should not. It will not only add unnecessary weight, but it will also add a lot of extra work.

You should, however, wrap the deck sheathing an inch or so over the shear. For photos and description of a neat way to do this, see my blog at http://twofootartist.com/ganymede-construction-notes/ Scroll to the May 16, 2010 entry.

-Wes

Thanks gents.  The reason for the extra sheathing would be expected use off the northern California coast, which can get pretty rocky, and the fiberglass that came in the kit seems a hair thin at 4oz. weight.  An extra few pounds of weight seems a reasonable price to pay for some peace of mind.  

Twofootartist, great idea on the masking tape "curlup" !    

If you are really looking to add strength and some flex after running into rocks from the sides or bottom, I would consider lining the inside at least around the cockpit with Kelvar 49/epoxy.  Side and bottom impacts/crashes causing compression from the outside and expansion of the material on the inside.  So impacts that causes leaks are many times due to failure of the material on the inside, caused by sudden material expansion beyond it tensil strength.   Kelvar provides both strength and some flex due to impacts that is far superior to fiberglass.

Your deck can be strengthen with strips of carbon fiber around the cockpit or back of the cockpit or any place you my sit on your kayak. 

Good Luck