The following images show how a sunken ship might look if all the water were removed, together with the simulated side scan sonar image of the same scene. (Sonar fish towed along parallel to the length of the ship, simulating one beam or one side only)

However, ships are rarely going to sit upright on the bottom - they will be broken up by tides and currents, and nibbled by wee beasties. The next images show the scene after the ship has sunk a little into the sand and the masts have been toppled.

For the details of the method, please see Publications
I am no longer involved in research in this area. However, Judith Bell at Heriot-Watt is now working on Simulation and Visualisation of the Sonar Process.
vsb1001@cam.ac.uk