That is the point you don't need to measure AoB with the protractor,
All you need to do is get a good target course and measure it's true heading(course line) with the compass rose and put that course into the TDC using the AoB input dial. It's really that simple. By using the three minute rule you get both speed and course, 2/3 for your firing solution and you may not have even seen the target yet. You don't even need to raise the periscope to do this, sonar or later radar is all you need to get to this point.
All you need than is range/bearing, get this with the steadimeter once the target gets closer. When it's in a comfortable shooting range turn on the PK and start inputting your data. Speed, that shouldn't have changed Second use a AoB input dial to set in the course, that should not have changed either and last steadimeter range/bearing, check the firing solution on the attack map and adjust as necessary.
Get to where you can hit with some consistency and than you can try more difficult shots later.
There are other ways to do all this but this is the simplest, try it first.
Good luck and good hunting.
Magic