No difference between full and flank?
 

My Gato class sub has absolutly no difference in speed in totally calm water between flank and full. I am assuming this is not supposed to be like this?

The differenece between those 2 speeds was most noticable if the sub was returning from a war patrol. All Ahead Pearl Harbor usually could induce a little extra speed from the engines ;).

There is actually only a couple knot difference that I've noticed in game and I "think" that's not inaccurate. You have to wait for the sub to build up the speed though and it is most noticable in calm seas.

Stock speed settings are off somegiving too small a difference between flank and full. LeoVampire came up with a mod for this that also improves all the EO telegraph settings. Note this is already in RFB for ROW with slight changes:
http://www.subsim.com/radioroom/showthread.php?t=115260

Speed
 

Calm seas as mentioned above will show it best. That extra knot can make all the difference!

I think way back in SH1 if you ran at flank speed too long the engines would over heat/damage...but hey that was a long time ago

is that true here? no desire to test it on my boat, it is still shiny

Nah you can run slap full out till you run out of either diesel or batteries or both. Then your screwed.

ah, thanks!