Quick question about crush depth?

I have SH3 and GWX and I seem to remember one randomizes crush depth. when it randomizes it does it stay the same for each boat in a career Ie if I have a IIB that goes to 150 If I use the IIB throughout my whole career will it continue to go 150? or is based on patrol?

The only reason I ask is because in my new campaign / patrol I took my IIB down to 157 when in deeper water and the only reason I couldnt go deepr is because I bottomed out.