Ahh Janes 688 and the waterfall! Happy days indeed!
I was basing the question on
http://www.subsim.com/radioroom/showthread.php?t=204151
which seemed to indicate that a mod once did have the RPM settings, and a full set of charts for each sound scheme. I wondered if it was included in WoS.
No matter for the actual situation at hand. It was a Costal Boat, so surfaced and sank it with the gun. I wondered why they were not shooting at the target that I though they were, but that was because there was a fishing boat there too. 178 GRT added to my score!