Hmm, when the DD drifts around the corner, will he be able to shell you? In other words, do you have a direct line-of-sight to where he will be when he 'runs out of' pier?
If so, turn your boat, and submerge as far as it will go so you will be ready to give him a torp when he breaks free and come for you. Mind the depth, though: For a bow shot, you'll need magnetic trigger and you should only try this, if there is enough water to have the torp pass under him.
Another solution would be to use your gun as a mortar: I don't know how far it can be elevated, but perhaps enough for you to shoot over the buildings and hit him!
BRGDS
Sven