All stop when gathering tac data?
 

When I take my two range and bearing marks should I be still in the water or will when I press 'estimate speed and heading' will the ai into account where I'm moving? It's really foggy and there are warships escorting some merchants so I didn't want to use sonar and I need to keep up.

i think that if you have the position kepper on it will estimate for your movement
atleast thats what ive observed

As I said here, it works even if you're changing speed and/or course. So the sub doesn't have to stay still.

Remember that the position keeper must be OFF if you're going to use the "estimate speed and heading" feature, or it won't work. You can and should of course switch it on after you have used the feature and entered all data into the TDC.

Can you elaborate further on why the PK must be off to use the "estimate sourse and speed" command? I've never done that and have never had any problems.

Copy/Paste from here:
make sure the Position Keeper is OFF since it changes the TDC data that you just sent for the new target using the heading/speed determined for the previous ship you attacked, so the longer it takes to send all data, the more the PK ruins your solution.

If you are not an experienced skipper, it may take some time and your torpedos will be way off.