Engine RPMs and hydrophone speed calculation question

[ETR3(SS)]

Originally Posted by commandosolo2009

Now, I wanted to ask if there was a RPM guide around here, much like RPM over speed in kts?, for trained ears to use.. I kinda like the idea of staying low and not exposing myself at all, and this is what I also hope to get your advice on.

To be exact, is there a chart or not necessarily a chart, but a rule for rpms vs speed (kts) here? And, if I put my hydrophone operator on monitor, he leaves all the targets and focuses on the warships which are naturally ahead of the convoy, so is there a way to let him monitor that specific screw on the telegraph? I guess there aint, but I'm just spitballing here..

Yes there is a rule. Shaft RPM heard through the hydrophones does not correlate to an exact speed of target. The best you can get is a slow, medium, or fast speed report from the operator. Besides if you could accurately count the shaft rpm you would need to classify the contact in order to determine the turns per knot ratio.