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Old 01-26-2020, 03:45 PM   #1
GreyLynx
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Default Weight and Trim Procedure

Before heading to the open sea / combat area, the Weight and Trim Procedure should be carried out (Sea Trials) as described in the "Diving Regulations for U-boats" document (uboatarchive.net/Diving/DivingRegulations.htm).

In the Wolfpack game, this is how I do it:
1. On the surface, Conning Tower Hatch closed, engines stopped, I flood the Main Tank Ballasts, I purge the Trim Tank and the Negative tank if necessary.
2. I check the depth on the "Water above base of keel Meter" next to the Trim Meter. This is the Base Depth which is proportional to the weight of the boat (Archimedes principle). In the game, it varies randomly from 7.6 m to 9.8 m, based mainly on the amount of fuel on board. I assume that at a Base Depth of 9.8m, the boat is fully loaded.
3. I adjust the Trim Tank to lower the boat to a depth of exactly 11.6 m, which is the Neutral Buoyancy setting. Beyond this point, the boat has a Negative Buoyancy and starts sinking. BTW at the beginning of the game, the Trim setting is automatically set to this value (more or less).
4. The Base Depth and Trim Setting are kept in the Diving logbook (for those who play by the book).

If the Base Depth is 9.8, then the Neutral Buoyancy Trim setting is 4 m. If the sub weights 761 tons on the surface and 865 tons submerged, then adding 100 m in the MBTs will add 100 tons to the surfaced sub, and the Trim tank will add 4 more tons.

Note: When torpedoes are fired, the boat becomes lighter, therefore the Dive Officer must adjust the trim setting accordingly to maintain Neutral Buoyancy. The trim setting may also need adjustment based on speed and Dive Planes positions. On the other hand, water density (salinity) is not taken into consideration in the game (yet).

The following table shows the Base Depth / Trim setting I measured during testing:

Base
Depth Trim
----- -----
7.6 m - 11 m
7.9 m - 9 m
8.2 m - 8 m
8.5 m - 7 m
8.9 m - 6 m
9.4 m - 5 m
9.8 m - 4 m

May I suggest that this procedure be added to the responsibilities of the Dive Officer.
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Old 01-26-2020, 04:28 PM   #2
derstosstrupp
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This is the kind of stuff I always love to see, and what makes Wolfpack so great, great post!
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Old 02-03-2020, 12:16 PM   #3
GreyLynx
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Here's a table showing the Trim Tank setting for Neutral Buoyancy:
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File Type: jpg Wolfpack - Trim Tank.jpg (85.3 KB, 17 views)
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Old 02-03-2020, 01:55 PM   #4
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Here's a table showing the Basic Depths (MBTs full, no Trim) for the different random sub weights at the beginning of the game, and the Trimmed Depth (Neutral Buoyancy) in red.
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Old 02-12-2020, 09:52 AM   #5
Jonas Grumby
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Default Ballast and Diving

You are making the dive complicated with that formula man.
In my experience, when you spawn the trim tank always has a random amount of water in it. It also is very close to neutral buoyancy every single time you start a new sub. Doesn't matter what depth, the sub will be trimmed. There is no "sea pressure" modeled that I can see.
I take note of that number, then I "trim dive" my boat after flooding negative and blowing ballast out of the trim tank so I am hovering. Take note of that number on the trim tank gauge after dumping the weight overboard and you are set.
Now, when I need to get down in a hurry all I need to do is flood the trim tank completely and down on both planes. There is no negative effect I have been able to notice in running the boat in this manner.
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Old 02-13-2020, 03:54 PM   #6
GreyLynx
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Hi Jonas Grumpy, you are right concerning the effect of sea pressure at various depth or the salinity of the sea on buoyancy. They are not modeled in the game. Maybe one day...

Now let's take an example: The initial trim at the start of the game is 8.6 m. With MBTs full and Trim tank empty, I get a base depth of 7.9 m. I trim the boat for neutral buoyancy with 9.15 m for a depth of 11.6 m. There is 6% error between the initial and actual trim value.
This is the standard procedure (more or less) for trimming the boat according to the "Diving Regulations for U-boats" document, Section V.

Your method is equivalent and was actually used later during the war when the threat of surprised air attack was increased. You fill up the Negative tank with 4.5 m and remove water from the Trim tank to reach Neutral buoyancy. The volume left is 4.65 m. The total amount of "trim" is the same, ie 9.15 m.

Crash Dive is meant to go from the surface to below the surface (depth of 15 m) quickly.

Test 1:
- Negative tank empty.
- Trim tank set for Neutral Buoyancy (9.15 m)
- Electric Engines at Full Speed, Dive Planes Down. Start timer.
- Fill MBTs (100 m)
- Fill Negative Tank (4.5 m)
- Total Ballast = 113.65 m
- Depth of 15 m reached. Stop timer: 40 sec.

Test 2:
- Negative tank full (4.5 m)
- Trim Tank set for Neutral Buoyancy (4.65 m)
- Total "Trim" = 9.15 m
- Electric Engines at Full Speed, Dive Planes Down. Start timer.
- Fill MTBs (100 m)
- Fill Trim tank (15 m)
- Total Ballast = 119.5 m
- Depth of 15 m reached. Stop timer: 30 sec.

There is a gain of 10 seconds, which could be a matter of life or death in the case of an air attack.
On the other hand, the rate of descent if much higher, which could be difficult to stop before hitting the bottom or reaching the crush depth. More compressed air is used.

Conclusion: Both methods are correct and specific to the level of threat from an air attack.

Good point Jonas Grumpy!
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Old 02-14-2020, 10:17 AM   #7
GreyLynx
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Test 3:
- Negative tank full (4.5 m)
- Trim tank set for Neutral Buoyancy (9.15 m)
- Electric Engines at Full Speed, Dive Planes Down. Start timer.
- Fill MBTs (100 m)
- Total Ballast = 113.65 m (same as Test 1)
- Depth of 15 m reached. Stop timer: 32 sec.

In Test 1 and 3, the same Negative Force (4.5 tons) is applied, but in Test 3, Negative Buoyancy is reached sooner because the Negative tank is already filled up at the start.

Historically, this is how it was done ("Diving Regulations for U-boats" document, Section VII).

But Hey, I once met an XO who told me: "There's the Right way, there's the Wrong way, and there's the Navy way; but on MY ship, you do it MY way!". "Aye Aye Sir".
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