Clay,
When a red square pops up move your mouse over it and click. You will notice the time ( 24 hour time ) that the square was positioned in this spot along with it's estimated speed ( slow = 5-7 kts, medium = 9-11 kts or fast = 15-17 kts ) and its estimated direction. If it is a merchant it will say "ship" ( minus the quotes ), if more than one ship it will say "small convoy or large convoy" and also be a larger red square. Same thing if a "diamond" but those are WAR ships.
I do the above with my mouse then I click on the "Protractor" A tool that looks like a triangle left lower part of your screen, zoom in on the square as far as I can go and put the tip of the protractor on the straight line at the rear of the square, note that this is not really accurate but a close guess until he gets closer and then you can zoom down to the silhouette of the ship and draw the protractor from the stern through the bow and this will give you the degree heading the ship is heading. ( although he may change headings before he gets to you ? )
Then I click on the ruler and put it at the front of the square ( opposite of the small straight line running through the square ) and drag it till it crosses the path of my boat ( front or rear as in a minute I'll know how far he will pass me ) and maybe drag the ruler line just a little farther for the sake of it. ( he may change directions ) Lets say the enemy ship is a small lone freighter moving at 7 kts and according to my ruler he is 42 Nautical miles away. I use a calculator and divide 42 by 7 and get 6 which would be a close 6 hours before he lines up with my boat. Now I did say NAUTICAL miles but instead of using fractions I just round it out to an even 42, as 6 hours gives me plenty of time to maneuver to approximately a 1000 yard torpedo shot. As said before this ship may change directions way before he gets to you and may not even be worth messing with.
IF you are surfaced and have no fear of any enemy air craft keep you radar ( F9 ) set to 600 on the left radar screen and you can see just who he is at approximately 21.25 NM. Enemy in game only has about 10 or less NM diameter radar, so you can see him long before he sees you. If you click on the ship at close zoom you will see the radar circle he is transmitting, you will not see your subs radar circle on the 2D map, instead you will see the red square change to a ship silhouette.
Now is a good time to double check ( click on pause if your scratching your head by this time as you can take your time figuring out the mess
) if he's changed course even a little by again using the protractor and zooming in as close to enemy ship silhouette as possible then drag the protractor from stern through the bow, notice the "Degree" and line that same degree up just past the front of your boat. Use the ruler and start at the degree line in front of your boat,drag the ruler toward your boat until it says 1000 yards ( or whatever in "Meters as I'm not a meter man
).
This is only one way of doing it and there is many other ways of doing this task but be warned that the harder the game ( maybe a very strict Mod? ) the harder this task will be to preform, that is until you get used to it.
Of course you may be using a mod that may not let you do some -or any- of this ? as I notice you have a pack of mods listed.
Hope that this may help some Clay.
P.S. I'm sure there are a few things that I missed or should be corrected on so please guys don't hit me too hard just educate me.
EDIT:
When you first notice a red square or diamond pop up and your are in hyper drive ( compression ) hit the backspace twice for 1 time compression ( real time ) IF you really want this bugger, or else you may not even come close. ---or-- If on a death course with your boat it could be Davey Jones time?