[Rana abdo]

I have got some rough surfaces data that i have attached on a ship these surfaces differ from each other one has low density of roughness and the other is very rough. After attaching these surfaces on the ship the ship has become with a rough geometry but the difference of these surfaces are in microns. The problem is when i use fluent to calculate the drag on the ship having these two rough surfaces the values are the same although the roughness have changed.
What could be the problem
Note : when i use different y+ value the drag changes so how can i set the y+ value for the ship surface.
Also there is new cell domain that appears that os called fluid other than the orignal one and a wall shadow so what is the reason behind this.
I couldnt split the domain in space claim the rough ship surface causes error in the geometry