What is meant by immersion at load draft for a ship , how is it calculated?

Question

what might be the approx value for 180 m ship dead weight 45kt

Answer 1

There is no one answer, depends on the shape of the hull and loading of the ship.  It also depends on fresh/salt water and time of the year.  Water densities vary with location and season.  Your question needs to be more specific.  When a ship's waterline, at even trim, matches its Primsoll Mark then that is the deepest the ship should be loaded.