VIIB crash dive time tests results

[Abd_von_Mumit]

Warning!
Do not read this post unless you want to know how the tests were conducted and what are the results. I warn you because I know that for some Kaleuns this would work as a spoiler (immersion killer) - many of us wish to gather such knowledge based on own experience.

Starting every patrol I conduct comprehensive set of tests to be sure everything works fine, my crew is combat ready and no French saboteur had access to my boat. Recently after being seriously bombed by British aircraft, I conducted tests of crash dive times - the purpose was to find the fastest way of avoiding the airborne threat.

Tests were conducted in medium weather conditions (sky clear, precipitation none, visibility unlimited (aka fog none), wind 7 mps, direction 177) at deep seas.

Purpose: find the optimal depth of cruising and speed of cruising to make the crash dive time as short as possible.
Every single test was prepared in exactly the same start condition: 5 minutes after setting tested speed and depth, batteries and engines were checked (to be sure batteries are full and both the engines propell the boat) and then crash dive ordered. Time measured is the period between the moment of pressing C button and reaching depth of 15 metres as shown below the Tiefenmesser (right bottom of the screen in default GWX 2.0 GUI).
Boat tested: VIIB with GW Kapselgeblase engine upgrade.

Results:
- [starting speed], [starting depth] - [average time of dive].

- 0 knots, surfaced - 37 s
- 0 knots, 6.9 metres - 21 s
- 0 knots, 7.9 metres - 28 s

- 8.5 knots, surfaced - 34 s
- 8.5 knots, 6.9 metres - 20 s
- 8.5 knots, 7.9 metres - 24 s

- flank speed, surfaced - 36 s
- flank speed, 6.9 metres - 19 s
- flank speed, 7.9 metres - 22 s

Interpretation is obvious: starting speed has very little impact on crash dive time; the faster the start speed, the faster you go down. The most important factor is the starting depth of your boat. At any speed the best results were achieved when the depth (set manually) was 6.9 m. I found it a bit surprizing, as I believed before that the deeper you go, the better. This belief however prooved to be false. Probably the reason is that 7.9 metres depth makes the boat acceleration too slow because of the drag, and the boat is unable to reach a high enough speed to dive efficiently (after ordering crash dive). 6.9 metres is a "compromise" depth - your tanks are allready partially flooded, so it takes less time to fully flood them, and at the same time the boat is still able to get enough speed before breaking the surface to dive efficiently. Depth of 7.9 metres is still much better for crash diving than 5 metres (surfaced), but it cannot compete with 6.9 m.

Some more exact test followed to find the very optimal depth. Speed of 8.5 knots was chosen as it's the optimal speed for everyday cruise with VIIB type with GW Kapselgeblase engine upgrade.

- 8.5 knots, 6.0 metres - 23 s
- 8.5 knots, 6.3 metres - 21 s
- 8.5 knots, 6.6 metres - 20 s
- 8.5 knots, 7.0 metres - 20 s
- 8.5 knots, 7.3 metres - 19 s (and the best time of 15 s!!)
- 8.5 knots, 7.6 metres - 26 s

Given the results I can quite safely asure you, that the best way of cruising areas heavily patrolled by enemy aircraft is to be at 7.0 depth and optimal speed. That, however, shortens the maximum range of your boat, as cruising decks awash consumes much more fuel than when surfaced. In my opinion shortening the crash dive time from 37 seconds to 20 seconds is worth that price.



EDIT: No Bernard or animal were killed or hurt during the tests.

[KeptinCranky]

Excellent info Herr von Mumit

one minor quibble:
why call it spoiler info? I'm sure every Kaleun who took a boat out to sea knew exactly how long it would take for his crew and Uboat type to crahsdive, this is something that was excercised constantly I'd imagine, and done over and over again until they got it right, the lives of the entire crew depend on it after all so you'd want this to be done as fast as possible.

I wouldn't be surprised if there was such a thing as the unofficial title of "fastest diver in the Kriegsmarine"

[Abd_von_Mumit]

Next sets of tests were conducted, this time the type VIIC boat was put to the limit.

All tests were conducted in the same weather conditions, with wind at 4 km/h. Results follow.

VIIC type, no engine upgrades, with deck and flak guns mounted.

Crash dive time

- [speed], [depth] - [result, i.e. time in seconds to reach 15 m depth]
- 0 knots, surfaced - 34 s
- 0 knots, 6.1 metres - 22-24 s
- 0 knots, 7.0 metres - 21 s
- 0 knots, 7.9 metres - 20-21 s

- 8 knots, surfaced - 33-34 s
- 8 knots, 6.1 metres - 22-23 s
- 8 knots, 7.0 metres - 19-21 s
- 8 knots, 7.9 metres - 20-21 s

- flank speed, surfaced - 32 s
- flank speed, 6.1 metres - 21 s
- flank speed, 7.0 metres - 17-19 s
- flank speed, 7.9 metres - 20-21 s

As with the type VIIB, speed doesn't matter a lot. Initial depth is the main factor. The optimum cruise depth is 7.0 metres (reduces diving time by ~40%). Remember though, that not only diving speed is important when patrolling enemy territories - fuel efficiency is also a very important factor (the deeper you go, the more fuel you burn), as well as keeping your above water profile as low as possible. I think a depth of 6 m would be more useful for cruising, as it's quite economic with fuel and it still reduces diving time by as much as 30-35%.

Optimal speed regarding fuel efficiency

8.1 knots, not even 0.1 more or less.


VIIC type, all available '40 upgrades: GW Kapselgeblase engine upgrade, and 800 bttery; deck and flak guns mounted.

Crash dive time

- [speed], [depth] - [result, i.e. time in seconds to reach 15 m depth]
- 0 knots, surfaced - 33 s
- 0 knots, 6.1 metres - 23 s
- 0 knots, 7.0 metres - 19-20 s
- 0 knots, 7.9 metres - 19-20 s

- 8 knots, surfaced - 33 s
- 8 knots, 6.1 metres - 22-23 s
- 8 knots, 7.0 metres - 19 s
- 8 knots, 7.9 metres - 20 s

- flank speed, surfaced - 32 s
- flank speed, 6.1 metres - 21-22 s
- flank speed, 7.0 metres - 18 s
- flank speed, 7.9 metres - 18 s

Here the results vary a bit frm the previous - there is almost no difference between 7.0 m and 7.9 metres diving time. I don't know why. It could be possibly caused by higher power electric engines that propell the boat efficiently even underwater.

Optimal speed regarding fuel efficiency

8.3-8.4, less than upgraded VIIB type, slightly more than no-upgrade VIIC.


And the last test: a user claimed on these Forums, that there IS a difference in boat performance between sailing "surfaced" and sailing "at 0 meters" depth (i.e. after you point 0 m on the depth gauge). No test proved this to be true, not even a slightest difference was noticed in any aspect of U-Boot's performance. "Surfaced" is totally equal to any depth between 0 and 4.5 metres (possibly even 5.0 metres).



I'm not going to do IX nor II type tests, as I don't use these types. If anyone is interested, feel free to post your results in this thread, so that all the info is stored in one place.

Thank you.

[Chad]

Great research and information! Thanks

[Abd_von_Mumit]

I kindly ask the moderators to change the topic of the thread to:
VIIB & VIIC type tests: crash dive time, optimal speed tests and more

I don't know why, but I'm not able to change the topic. Thanks.

[danlisa]

Nice bit of analysis.

So the result, running 'decks awash' with any boat is the fastest way to crash dive at any speed.

Don't want to be a boob here but I'd assumed most knew this already. LOL, at least, we've tried to tell everyone.

[Brag]

In type IXB, decks awash at 7 meters, dive time 20 sceonds.

[Abd_von_Mumit]

Originally Posted by danlisa

So the result, running 'decks awash' with any boat is the fastest way to crash dive at any speed.

Don't want to be a boob here but I'd assumed most knew this already. LOL, at least, we've tried to tell everyone.

:hmm: I didn't know. Idea of running decks awash hadn't rise in my head before I finally read about it on this Forum. So I suppose there are others who don't know too (if not it would mean I'm an extreme dumb, which is not true of course ).

And I doubt a bit everyone here knew the details. For example, did you know that your crash dive time is shorter at 7 metres than at almost 8 metres?

Anyway, I would do the test no matter how useful they are to "the public". I'm just the type of commander who feels he must know his boat as well as possible. I also try to do some role-playing for variety's sake, so I keep training my crew and do many 'useless' crash dives with no particular reason, maneuvres at depths of 200 m, I erform regular service of the boat and so on.

As the Kriegsmarine "Submarine Commander's Handbook" says (1):

[...] In order [...] to understand and master the tactics (i.e., of submarine warfare), it is necessary to be thoroughly familiar with the weapon, and its characteristics and peculiarities; for it is on these that the tactics depend.

In addition, complete success as a result of a thorough exploitation of the possibilities of the weapon can only be achieved if all the officers in charge of it are trained to think along the same tactical lines.

[Jimbuna]

Originally Posted by danlisa

Nice bit of analysis.

So the result, running 'decks awash' with any boat is the fastest way to crash dive at any speed.

Don't want to be a boob here but I'd assumed most knew this already. LOL, at least, we've tried to tell everyone.

Have you also tested with the forrad torpedo compartment full of crew to see if the weight of said crew quickens the dive ? :hmm:

[Abd_von_Mumit]

Originally Posted by jimbuna

Have you also tested with the forrad torpedo compartment full of crew to see if the weight of said crew quickens the dive ? :hmm:

No, but might try tonight. I doubt this will work. The best test path I could think about is to place them in the aft compartments, make a few measures, than replace to bow compartments and compare the results. Diving from surface at medium speed. :hmm:

[Fincuan]

Originally Posted by Abd_von_Mumit

No, but might try tonight. I doubt this will work. The best test path I could think about is to place them in the aft compartments, make a few measures, than replace to bow compartments and compare the results. Diving from surface at medium speed. :hmm:

That's basically what I did here: http://www.subsim.com/radioroom/show...8&postcount=26

No effect whatsoever

edit: Good job with the test btw

[Abd_von_Mumit]

Originally Posted by Fincuan

That's basically what I did here: http://www.subsim.com/radioroom/show...8&postcount=26

No effect whatsoever

edit: Good job with the test btw

And I confirm your results. No noticeable difference in boats performance.

Warning: Following paragraph possibly contains an exploit description
BUT I found an issue I think, however being sure about it would take me looong hours of testing: I think pausing your game for a long time during dive can signicficantly shorten your diving time. Yesterday night, when testing dives, I had to pause for a real long talk with my mate, and when I unpaused, the boat went down like a stone, 30% faster than normally. Pausing for short periods didn't cause such large variation. Any tips?

Another explanation of this observation would be problems with in-game clock when the game is lagging. :hmm:

[Reece]

Can these times be changed? Wierd, all this time running slow then pressing "C" seemed to me to get down a lot faster than hitting flank & "P", must have been an illusion. Useing "C" certainly takes a lot longer to "pull up", or is that an illusion as well?
Is there any difference in time getting to a depth of say 50 meters?

[snwcrsh]

Abd: Just a short question, did you take the fatigue of the crew in the engines sections into account? How strong would fatigue influence the results?

Ans a rather lame question, I cannot try it out currently as I am in shallow waters: If you crash dive, is there a depth you aim at? Or will you just go down until you command to level the boat?

[melnibonian]

Originally Posted by snwcrsh

If you crash dive, is there a depth you aim at? Or will you just go down until you command to level the boat?

If you Crash Dive (Key C) you go for 80m before the boat levels itself out.