Why does set course = set speed?
 

It would be nice if setting a course did not automatically set your speed to "normal". I was in a port, all quiet like, using waypoints to line up my shot perfectly. I adjusted one of the waypoints and WHOOAH, I'm full speed ahead! I caught it after 2 seconds, but I was using the improved escort mod and they heard me right away, came in and DCed me. I reloaded, since this wasn't MY goof-up, it was the game's. Anyway, I do remember it was the same in SH3 and there's just no reason for it.

It only sets your speed if your at all stop. Whenever in that situation - needing to stay quiet - set your speed to 1 knot - then do your navigational chores. This will keep you from increasing speed. Just make sure your not at all stop or in reverse. If you are - you get ahead standard automatically. Shouldn't do it - but does. Sh3 did the same thing, and was never changed. Probably not high on the list of things to
"fix" as it isnt really a bug. Hope this helps.