Maybe its sh3 commander enabling this? with sh3 commander, at times my surface speed will decrease, hit flank in a upgraded IXD yet shes only doing 5knots this is suppose to happen, or my periscope is blurry usually when i have a destroyer charging towards me. Im sure Jonesy made these events to happen just when the crap hits the fan
But yeah maybe something is mess up and SH3 Cdr has now enabled your boat to run at 11knots submerged?