Mark, Interesting. I have used clash of arm Baltic Arena as my primary source. You have inspired my to try coastal patrol again.
Chuck, great question! I haven't found a good set of torpedo rules especially for solitaire play. I finally wrote my own. You don't track their movements you trust that your boat knows how to aim torpedoes just like you trust they aim guns. You might have to wait a turn but then you roll to see if it hits. Simple.
Unfortunately I have it bundled with some other rules for cruel seas. I titled it Crueler Seas and it is available for the princely sum of 50 cents. At wargame vault. [ 100% of money I make goes to the local food bank.] Sorry for the commercial but it is an honest answer to your question and I make no money.
Thanks
Joe