My submarine suddenly appallingly slow, no idea why. Please help.
 

Sailing an IXB in '42 suddenly it cannot go fast, underwater flank speed is 3 knots, slow is 1 knot, and above the water ahead standard is 7 knots, flank is 10. I have upgraded it with the turbocharged engines too, I have plenty of fuel left, it's in heavy seas but that doesn't explain it since it's been in much heavier seas going much faster, and it's still so appallingly slow 50m underwater.

On 44% hull integrity but otherwise everything is functional, this started mid patrol by the way, I'm now going back to Lorient at a speed of slow.

I've also checked with the engineer, the compressed air, oxygen, fuel and battery levels are all fine, it's not silent running and the pathetic speed persists in recharge mode.

Please help, luckily when it started I was north of ireland, so I can make it back home, the range also was cut down spectacularly, in a type IX with about 55% of the tank left the range has gone to 3000km at ahead standard.

By any chance, did you start the game using SH3Commander, with either malfunctions or sabotage&malfunctions enabled?

I did do that, although I will be disabling that ASAP because I had expected things to not be quite so annoying.

Either way the malfunction reduced all the speeds, if one piston engine were damaged it would just affect the boat on the surface, vice versa for an electric one, and as far as I can tell the engines drive seperate propellors through seperate drive-trains, so that malfunction must have done a lot of damage.

Luckily it seems to be going away, ahead full hits 14 knots, still less than the 20 it usually does.