The approx weight of my boat is 665 LBS and the max weight not to exceed 1600 LBS fully loaded according to the brochure. My question is. Should I install foam to float 665 Lbs or 1600 LBS?
Well you should install as much flotation as possible. But to answer your question you should calculate on the loaded number since that's where you will most likely be at least some of the time.