I've only been through the Straits three times, always at night, always '39/'40. First I carried on then was lost at sea after a save too close to France, the second was during a really heavy storm, tried a few long shots at something in Gibraltar in the distance, no effect, tried some more still to no effect then got out again before daybreak - curiousity got the better of me and I used the external cam - I guess all my shots hit the quay on THIS SIDE of the ship!
Just keep going, we all have crap patrols - you're just getting yours out of the way first!