Hey there! Okay, you don't have enough information there to definitively help you but I can go through the whole thing.
There are two kinds of attacks you can manage here, the check bearing (conventional US attack method) and the constant bearing attack (ala U-boat, but we don't talk about U-boats in this context, we talk about Dick O'Kane, who "invented
" them)
Your check bearing or conventional attack works using the position keeper. The position keeper uses a clock, hooked to your supplied enemy position, course and speed to predict his position at all times after you give the TDC the information. If your data is correct (capitalize, underline, bold and italicize the word "if.") you can shoot at any time and hit the enemy. You could even dive to 99 feet, change your course and speed, shoot and blub, blub, blub.
To do this conventional (for US boats) attack, first turn on your position keeper. Then determine and enter the target speed. Next enter the AoB, which is your bearing in German nomenclature from the target. Quickly take a stadimeter sight, setting the enemy's position (range and bearing). Now check with your attack map to ensure that the enemy's position and the TDC position are the same and moving together at the same course and speed. If that checks out you're ready to go. Just wait until the target is at the position you want to shoot from and send him your greetings.
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The second attack method is the constant bearing method. Typically, this would be done from a course 90 degrees from the target track and with fleet boats we call this the Dick O'Kane technique. Range doesn't matter much but the game TDC freaks out if your range shows zero.
In this case you pick a shoot bearing. We'll use your example, with the ship coming left to right, 7 knots. First you determine target speed and enter that into the TDC. Ensure the position keeper is OFF! Then pick your shoot bearing, 15 degrees before straight ahead in your case, and enter your AoB as 90-15 or 75 degrees starboard, because you're looking at the starboard side of the target. Get this wrong and bad stuff happens. Finally, just grab the range dial and rotate it as far as you can in a positive direcction (comes about to 1400 yards), then sight the periscope down the 360-15=345 bearing and hit send to TDC. You're set.
Now all you have to do is sight the periscope down the 345 and shoot when the parts of the target you want to hit cross the wire.
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Pay very close attention to starboard or port AoB. Pay very close attention to whether the position keeper is on or off. Always use the attack map to check your solution, not the numbers on the TDC. Graphics are self-validating, numbers are just numbers. There are other pointers in the video.