[Threadfin]

I've done alot of testing, and a setting of just barely above slow is most efficient IMO. Using the navigator to report range you can see it. What I do is set ahead slow, then click the speed dial just barely above the current speed. Let's say ahead slow gives 8 kts. I then click the speed dial on 9kts. The speed stays at 8kts (sounds confusing I know), but the range increases by about 2000km (in type VII with GW engine).

The most efficient speed is also a function of which engine you have installed on your boat I have found.

Test it for your self. Set ahead slow just after leaving port, and run at relatively high compression to give reliable results (no speed change due to wave action etc). Click the navigator and check his range estimate, get several readings to get a good sample.

Now click the speed dial (not the telegraph) maybe a half knot or a full knot over the ahead slow speed and get some more range reports from the navigator. If you results are like mine, your most efficient speed will be just above ahead slow.

Cobalt~ I'm curious why you submerge at night instead of during the daytime? That's opposite of what I might do. Just interested in your reasoning.