You're not picking up a Collins on passive unless you run him over or he steps on the gas. Using LW/Ami will help make him more detectable if he does put on the speed (+13 NL instead of +5 when at flank).
Active sonar is your best friend when you're taking an SSN against an SSK with no friends. The Collins is going to be the toughest SSK though, because it has a good sonar and carries the ADCAP instead of crappy short-ranged torpedoes. But, you can take advantage of the fact that the AI doesn't resteer its torps.
So go ahead and ping away, and be ready to get shot at after you do. When you get shot at, clear datum until the torp is no threat, then close a bit and repeat the process until you're close enough to shoot. You might be able to get him on the TA when he starts running, so keep an eye out for that happening too.
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