We need to build a set of shim blocks to place under the subdeck that will allow us to form the subdeck to the sheer of the main deck. I will explain how to calculate the dimension of the shim blocks for a hull with a step deck. It works the same for a flush deck ship its just that each shim block is usually a different size. Measure carefully, record your measurements clearly then convert your measurements for scale. This is one of those times when you must get things right.
Incorrect calculations can result in a deck that is too flat and a keel that sags.
On the hull profile, measure from the top of the bow down to the bottom of the keel. Move aft to the step in the deck. Measure from the deck down to the bottom of the keel. Add this dimension to the bow dimension. Using the scaling formula convert the measurements.