How good is your math? I don't think there is a simple straight line ratio for pounds to inches since the hull gets wider and longer as it sits deeper in the water. That said lets do some simple math. 1 cubic foot of water weighs 62.43 pound. At the water line the boat is about 25' long and 8 ft wide. Figure the area of an eclipse that is 25' X 8' wide. Multiply it by 1/12' (1"). You will then have a rough idea of cubic feet of 1" of water at the water line
If your boat is out of the water - measure how much longer and wider it is 1" higher than the water line, 2" higher than the water line,etc.
Multiply each of those calc by the wight of 1cubic ft of water. It won't be exact but it will get you in the ball park.