Hit... something... in the channel

[bsalyers]

After transferring from Kiel to Wilhelshaven (seen enough Norwegian neutrals for awhile), I was eagerly heading to my new patrol zone West of Britain in my Type IIA. Wanting to save fuel, I decided to go through the channel. I've done this before, both in SHII and the stock SHIII. Yeah, it's pretty hairy, but it's possible, and going north around Scotland kills your diesel level. Now, with the GW mod installed, I keep colliding with... something that destroys my boat just northeast of Calais. The first time it happened was under time compression, so I assumed I'd been detected and depth-charged. The second time, I made sure to slow down and determined what I could. It was no destroyer; the game definitely called it a "collision". I was running at periscope depth at ahead slow, no ships in sight. Would hitting a mine be called a "collision"? Did the Brits build a brick wall across the channel?
Has anyone else experienced this?