Flank speed bug?
 

Running GWX3, SH3 Cdr, Torpedo Damage Final, No continuous "Ship Spotted" and Reduced Mission Orders.

My crew are refusing to go to flank speed. Whenever I select it, the engine-room telegraph just zips round to 'Stop'. This has cost me one contact (hit flank speed, boat floated gently to a halt, I didn't realise until ten minutes and a cup of coffee later) so I'm really tempted to throw my stokers overboard!

I've had this happen before but only with a damaged boat, and I figured then it was something to do with the damage model. However, on this patrol I've seen nothing except unescorted freighters and the boat's in tippy-top condition. Is this a known bug?

Do you have "Malfunctions" and/or "Sabotage" turned on in SH3Cmdr? That sounds like one of the problems created by that option.

Aha, yes I do. But would that happen randomly while out at sea? I could still get flank speed a few (game) hours before this happened.

Any mechanic or engineer will tell you that any machinery is ornery and the REAL basis for Murphy's Laws - either yer engines are feeling a tad outta sorts or ya'll had a sabotuer at yer last base ......... (Malfunction [breakdown] or sabotage)

Did you load a save?

I have had this thing happen in my games also. It happens almost exclusively when I load a game, and I have the "malfunctions" option on in SH3 Commander.
I switch over and click on the number of knots when this happens.

Intermittent malfunction unlike sabotage which would be permanent until you returned to base.

I just had this one and had to redo a career. That was an easy one to fix. I have seen this bug where no matter what speed I set, sub acted as if I was submerged and maxed out at 7 knots (even on surface). It corrupted something and any other sub of the same type (new career, training missions, ect) all acted the same way. None of the files I checked were changed to explain it and I eventually did a complete reload to fix it.

good luck,

Try exiting to windows and reloading the complete game from SH3 commander - but this time with the malfunctions option turned off. I've found that this removes the SH3 generated malfunction.

If you still can't go to flank, then the problem lies elsewhere.