The primary benefit of a second layer of glass on the outside is abrasion/cut resistance. The boat will probably be plenty strong enough for dealing with waves with just one layer of 5 oz inside and out. But an additional layer on the bottom significantly improves its ability to withstand running into stuff. I think it is worth it. It won't add much weight.

: I realize that there are many variables that enter into this but I have been
: debating with myself the need for more than one layer of cloth on the
: outside hull. I am building a 'Cape Ann' for frequent but casual
: recreational use. It won't see a lot of hard use (rocks), mainly just the
: normal wear and tear at the beach (which can be considerable even tho I
: try to be careful). I am using the 5oz cloth from RAKA. The first layer
: goes on tonite.
: How much weight will one more layer of glass add to the kayak?
: Is only one layer just too weak?
: If weight is not a big factor, I will go with two layers. I would sure
: appreciate the opinions of the board.