There are formulas that I can't remember now. I cant even remember the name of some of the yacht design and naval architecture books that I used to use, I'll look through my bookcase and see what I can find.
The jist of it is to calculate the volume of your boat at various depths, from the outside of the hull. You would cut the hull horizontally with an imaginary knife at say 5, 6, 7, and 8 inches. Then compare the weight of the completed boat with motor and complete load against the weight of water at the volumes that you calculated at various drafts. Don't forget salt water is heavier than fresh and will float your boat higher.
The tricky part is calculating the volume of a cuved, tapered shape hull. In yacht design we would calculate the cross section areas at typically ten equal stations along the length of the hull, figure the average of all the below water cross sections and then multiply that average by the length of the wetted area to get cu. ft. Then calculate the weight pf that water (find a table that tells how much 1 cu. ft. of water weighs. I used to use a plantigram to calulate curved areas, but the Devlin sections are close enough to flat vees and sides that you could do it with simple geometry.
Of course you could save yourself a lot of trouble and ask what boats similar to your design draw. It's all a function of weight versus volume. If you add to the freeboard (thus more material = more weight) of a Scaup with adding any width or length, your boat will sit deeper in the water. If you add length and or width without add more weight beyond the extra material, your boat will have greater volume for less depth, so will float higher.
I hope this helps, I apologize if I insulted your intellegence if I told you stuff you already knew.
) Pete