Weight and Trim Procedure

Jonas Grumby · 02-12-20, 10:52 AM

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.

GreyLynx · 02-13-20, 04:54 PM

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 m³ 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 m³ and remove water from the Trim tank to reach Neutral buoyancy. The volume left is 4.65 m³. The total amount of "trim" is the same, ie 9.15 m³.

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 m³)
- Electric Engines at Full Speed, Dive Planes Down. Start timer.
- Fill MBTs (100 m³)
- Fill Negative Tank (4.5 m³)
- Total Ballast = 113.65 m³
- Depth of 15 m reached. Stop timer: 40 sec.

Test 2:
- Negative tank full (4.5 m³)
- Trim Tank set for Neutral Buoyancy (4.65 m³)
- Total "Trim" = 9.15 m³
- Electric Engines at Full Speed, Dive Planes Down. Start timer.
- Fill MTBs (100 m³)
- Fill Trim tank (15 m³)
- Total Ballast = 119.5 m³
- 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!

GreyLynx · 02-14-20, 11:17 AM

Test 3:
- Negative tank full (4.5 m³)
- Trim tank set for Neutral Buoyancy (9.15 m³)
- Electric Engines at Full Speed, Dive Planes Down. Start timer.
- Fill MBTs (100 m³)
- Total Ballast = 113.65 m³ (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".

02-12-20, 10:52 AM	#1
Jonas Grumby Watch Join Date: Feb 2017 Location: Retired in Rapid City, South Dakota Posts: 23 Downloads: 126 Uploads: 0	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.

02-13-20, 04:54 PM	#2
GreyLynx Duplicate account Not Allowed Join Date: Mar 2019 Location: The Great White North Posts: 18 Downloads: 22 Uploads: 0	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 m³ 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 m³ and remove water from the Trim tank to reach Neutral buoyancy. The volume left is 4.65 m³. The total amount of "trim" is the same, ie 9.15 m³. 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 m³) - Electric Engines at Full Speed, Dive Planes Down. Start timer. - Fill MBTs (100 m³) - Fill Negative Tank (4.5 m³) - Total Ballast = 113.65 m³ - Depth of 15 m reached. Stop timer: 40 sec. Test 2: - Negative tank full (4.5 m³) - Trim Tank set for Neutral Buoyancy (4.65 m³) - Total "Trim" = 9.15 m³ - Electric Engines at Full Speed, Dive Planes Down. Start timer. - Fill MTBs (100 m³) - Fill Trim tank (15 m³) - Total Ballast = 119.5 m³ - 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!

02-14-20, 11:17 AM	#3
GreyLynx Duplicate account Not Allowed Join Date: Mar 2019 Location: The Great White North Posts: 18 Downloads: 22 Uploads: 0	Test 3: - Negative tank full (4.5 m³) - Trim tank set for Neutral Buoyancy (9.15 m³) - Electric Engines at Full Speed, Dive Planes Down. Start timer. - Fill MBTs (100 m³) - Total Ballast = 113.65 m³ (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".