: My partner and I are preparing to build 17ft fiberglass sea kyaks. We were
: told that one layer of 17oz double bias stich mat

Matt is usually specified in oz/ft2, cloth in oz/yd2. Do you know which you have?

To get an idea if your advisor is in the ballpark, try weighing a piece of what you layed up. From this, calculate what a square foot would weigh and multiply that number by 50 or 60 square foot, the likely surface area of your boats. Most commercial boats are pretty close to 50#.