Can't slow to crawl without sinking - help!

[9emini]

Greetings friends - it's been a while. I am as I write this plea in a Type IIa 110km directly east of Hull, UK. It is Feb 6 1940. I am attempting to intercept a convoy but after an ugly incident earlier with an ASW trawler (subsequently dispatched with the humble flak cannon ), appear to have been rendered unable to e.g. rig for silent running without the boat sinking to the nearby sea floor (resulting in more damage, of course). I've repaired all damage possible but the stern quarters appear to have taken on a little water (it is visible in the 'crew' screen). I wonder if this is to blame. I appear to be able to travel no slower than 3-4kts before losing 'altitude' uncontrollably. I don't know why this water remains. Suspiciously, clicking on the stern quarters under the damage control team (top left of 'crew' screen) turns the stern quarters yellow, while reporting 'no damage to repair'. The large text box near the bottom of the 'crew' screen says all is well with the stern quarters too. But (and this too is odd) I am unable to select the stern quarters by clicking on the 'crew' screen's "large" sub image.

Running GWX3.0 @ 100% realism. Please help, fellow submariners.