I agree, you have to find a way to hit him with a torpedo. Set them as shallow as you can and set up an AoB 0 or 180 shot. get him to chase you, even if you have to pop part of the sail out of the water. Make it a max 400 yd, min 300 yd shot and you have a great chance to tag him.
You're toast on the surface unless you're living a real clean life, so I'm afraid you're toast...
You still may end up seeing if you can spread some jelly on that toast and give it back to him, but your advantage is your torpedoes. You have plenty to waste. Go for it!