Trimming boat up for more range

[bert8for3]

Out on patrol for 21 days now, and down to about 1/3 fuel remaining, I've only expended two torpedoes on a couple of targets very early on in the patrol. Since then, nothing except two fast transports that I couldn't catch. So I need to stay out a good while longer.
I'm about 1500 km from base at Lorient in a VIIB, and with knot indicator set for 9 knots (clicked on halfway between the 9 and 10 marks), and in calm or pretty near calm weather (so speed on setting was 9 knots), my navigator was reporting about 4500 km range remaining (average, i.e. asking him several times over several minutes 'cause he never gives the same answer).
I guess I could drop my speed down and get considerably more range, but I wanted to see if I can squeeze out more range and still maintain a decent cruise speed to sweep a bigger area for targets. So I did a little experimenting and found that if I drop the knot setting to 8 knots (clicking halfway between the 8 and 9 marks), and trim the boat higher by clicking 3 or 4 metres on the depth gauge, as opposed to running on default "S" draft, I get an additional knot of speed (9 knots), but the range projection boosts considerably to about 6000 km. So depending on the weather I'll be able to stay out longer.
I haven't tested this in different weather conditions yet. Also, I don't know if this was done in RL, but to my own idea of realism (everyone's being different) perhaps they had to sometimes. BTW, it doesn't seem to make a noticeable difference on dive time.

[Abd_von_Mumit]

You've jus rediscovered what was widely discussed many times here - optimal speed of a boat. FOr VIIB type it's 8.25 knots (and 8.5 knots after GW Kapselgeblase engine upgrade), for other types the speeds are different, individual (about 6 knots for type IIB, almost 9 for IXB and so on). Unless in rush or in need I always travel at optimal speed to save fuel. 8.25 Knots is decent enough for cruising in my opinion.

I really doubt there is a real difference between "surfaced" and "0 m" depth, as surfaced allready means that the boat has as much positive bouyancy as possible, and setting depth to 0 m will not add anything. But I might be wrong, especially if there are some game engine issues I don't know about. SH3 behaves strange in some situations.

[Brag]

In RL they did lighten the boat as much as possible to obtain longer range. Though I havent tried lightening, I think it may work in the game as fuel consumption does go up when you have more wetted surface by going decks awash. Good find! Thanks for sharing.

[DS]

I believe there is a RL difference between "operationally" surfaced, and surfaced with all tanks blown dry.

Operationally, I believe that some ballast tanks were kept flooded for safety reasons (call it reserve potential bouyancy), and the boat sat lower in the water, which is what we see with most photos.

With all tanks blown dry, the boat would obviously sit higher in the water, be less stable (pitch and roll), and may have better speed/efficiency characteristics as less hull in the water means less drag.

Sub experts please feel free to correct the above.

Giving the first post here, it seems this is moddeled by SH3, which is cool.

[Abd_von_Mumit]

Originally Posted by DS

I believe there is a RL difference between "operationally" surfaced, and surfaced with all tanks blown dry.

Operationally, I believe that some ballast tanks were kept flooded for safety reasons (call it reserve potential bouyancy), and the boat sat lower in the water, which is what we see with most photos.

With all tanks blown dry, the boat would obviously sit higher in the water, be less stable (pitch and roll), and may have better speed/efficiency characteristics as less hull in the water means less drag.

Sub experts please feel free to correct the above.

Giving the first post here, it seems this is moddeled by SH3, which is cool.

1. I've performed tests of speed and diving time for "surfaced" and for "depth 0 meters" - no difference in performance at all. More on that in post #3 here:
http://www.subsim.com/radioroom/showthread.php?t=129286

2. From Kriegsmarine "Submarine Commander Handbook":

29.) The danger of a surprise attack exists, in particular, when the submarine comes to the surface, especially after traveling long distances at considerable depth. When coming up from a considerable depth, an all-round sound location should therefore be carried out at a safe depth, where the submarine cannot be rammed; i.e., at a depth of approximately 20 m, at "sound-location speed." Next, the submarine should go rapidly through the danger zone at periscope depth, with the periscope raised; careful all-round look-out with and without magnification - submersion up to 9 m, depending on the weather, then lower the periscope altogether (see No. 23) and surface at high speed. The manhole of the conning tower is opened as quickly as possible, and the commander - with, at the most, one man who is especially good as a look-out - goes up. It is not until the surface of the sea has again been examined with binoculars, in every direction, that the compressed air cells can be completely emptied of water.

The bolded sentence firmly suggests, that surfacing for a longer time always meant full emptying of tanks.