I made the decision to build the aluminum skiff 17ft long and strong enough to hold an outboard motor with a mass of 141kg (approx. mass of 90Hp Mercury).  Knowing the amount of material I would need; I then went on to estimate the mass of the boat when finished to be 239kg.  I also made the decision to build a fuel tank in the front of the boat holding 141kg of gasoline (≈ 38gal).  The design of the boat permits the boat bottom to have an estimated area of submersion of 5.55m2 (L= 3.7m  W=1.5m).  With these measurements in hand I knew I needed a way to determine the height from the bottom of the boat at which I should build my second deck and drain plugs.  I got a value from a veteran boat builder but surely there was an equation to help me out.  Click here for Archimedes Principle and to see how it could help to design this boat.  Below is a sketch of the approximate boat dimensions.