Bismarck draft and displacement

[José M. Rico]

Hello all,

On 21 July 1940, a month before the Bismarck was commissioned, the ship underwent an inclining test (Krängungsversuch). Inclining tests are done to measure the stability of a ship and determine the height of the ship's center of gravity. If you are interested on how this procedure was carried out on German ships and also see how exactly it was done on Bismarck you can download the following file that Ulrich Rudofsky translated for us years ago:

http://www.kbismarck.com/archives/inclining-test.zip

Now, why am I telling you all this? Well, because today looking around at home I found an interesting document that includes some draft figures from Bismarck recorded on different dates during her career. I had this document for years but never put too much attention to it until now. Luckily one page shows Bismarck's draft for 21 July, the same day the inclined test was done. Here it is translated in English for all to see:

Draft on 21 July 1940.
With inclination weights [+400 t].

Port ----------------------------Starboard-------Average Draft
8935 -------Forward-----------8935-------------8.935 meters
8920 -------Frame 187.5------8945-------------8.932 meters
8865 -------Frame 133.5------8915-------------8.890 meters amidships
8885 -------Frame 79.5-------8935-------------8.910 meters
8925 -------Frame 25.5-------8960-------------8.942 meters

Mean draft: 8.92 meters. Displacement: 42,650 (from inclining test report)

Draft on 21 July 1940.
Without inclination weights.

Port ----------------------------Starboard-------Average Draft
8870 -------Forward-----------8870-------------8.870 meters
8860 -------Frame 187.5------8875-------------8.867 meters
8800 -------Frame 133.5------8835-------------8.817 meters amidships
8820 -------Frame 79.5-------8845-------------8.832 meters
8865 -------Frame 25.5-------8875-------------8.870 meters

Mean draft: 8,85 meters. Displacement: 42,250 (from inclining test report)

Draft on 21 July 1940.
With inclination weights on the Starboard side.

Port ----------------------------Starboard-------Average Draft
8940 -------Forward-----------8940-------------8.940 meters
8220 -------Frame 133.5------9550-------------8.885 meters amidships
8640 -------Frame 25.5-------9270-------------8.955 meters

Mean draft: 8,92 meters. Displacement: 42,650 (from inclining test report)

As you can see the draft was recorded from different places of the hull since it could vary depending of the ship's list and/or trim.

I got to go now. More later.

[dunmunro]

Thanks, I was looking through the data on the inclination tests but couldn't find any specifics on draught and displacement, yet it was obvious that this data was recorded during the tests, so this is quite useful.

[dunmunro]

However, IIRC, that test was done in freshwater, in the Elbe river, so Bismarck would have a deeper draught than if done in seawater, and the average draught in seawater would be about 21cm less, if I've done the math right.

[José M. Rico]

Here is another report from Bismarck.

Draft on 10 September 1940 (at 1100 hours).

Port ----------------------------Starboard-------Average Draft
8335 -------Forward-----------8335-------------8.335 meters
8665 -------Frame 133.5------9120-------------8.892 meters amidships
9370 -------Frame 25.5-------9615-------------9.492 meters

You can see that at the time this data was recorded the ship had a list to starboard and the bow was high in the water. Unfortunately no displacement is given for this day but it should be somewhere between 42,500-43,000 mt. According to the KTB, on 10 September the ship was loaded with 1,233 m3 of fuel oil and 521 m3 of feed water.

[José M. Rico]

Draft on 14 September 1940 (at 1100 hours)

Port ----------------------------Starboard-------Average Draft
9255 -------Forward-----------9255-------------9.255 meters
9330 -------Frame 133.5------9335-------------9.332 meters amidships
9480 -------Frame 25.5-------9480-------------9.480 meters

On this day the ship was more or less on an even keel. There is also a handwritten note in the original page that gives a displacement of 45,000 t. (I think it is an approximate figure though). According to the KTB, on 14 September the ship was loaded with 2,330 m3 of fuel oil and 436 m3 of feed water.


Photo. The battleship Bismarck leaving the Blohm & Voss shipyard in Hamburg on 15 September 1940.

[Dave Saxton]

~45k would be about right for 2330 cubic meters of fuel and 436 cubic meters of water. What do make of the reported draught of 8.5 with over 6,000 cubic meters of fuel? It must be typo or something.

[José M. Rico]

What do make of the reported draught of 8.5 with over 6,000 cubic meters of fuel? It must be typo or something.

Who knows?
The reported draft on 29 October for the speed run was as follows:

Draft before sailing: Forward: 8.5/4; Aft: 8.8/4. This gives a mean draft of 8.65.
Draft after sailing: Forward: 8.0/4, Aft: 9.0/4. This gives a mean draft of 8.5.

I don't know what the /4 is.

[José M. Rico]

Draft on 11 December 1940

Port ----------------------------Starboard-------Average Draft
8910 -------Forward-----------8910-------------8.910 meters
9350 -------Admiships--------8960-------------9.155 meters
9590 -------Aft-----------------9365-------------9.477 meters

The mean draft (averaging the forward and aft drafts) is 9.19 meters.
A handwritten note in the original page gives a displacement of 44,500 t.

[dunmunro]

I don't know what the /4 is.

I suspect that it is the draught averaged from 4 positions or 4 readings.

[José M. Rico]

Draft on 6 January 1941 (at 1100 hours)

Port ----------------------------Starboard-------Average Draft
8725 -------Forward-----------8725-------------8.725 meters
9435 -------Admiships--------8805-------------9.120 meters
9805 -------Aft-----------------9500-------------9.652 meters

Mean draft: 9.18 meters
No displacement given.

[José M. Rico]

Draft on 13 January 1941

Port ----------------------------Starboard-------Average Draft
8550 -------Forward-----------8550-------------8.550 meters
8885 -------Admiships--------9185-------------9.035 meters
9600 -------Aft-----------------9750-------------9.675 meters

Mean draft: 9.11 meters
Displacement: 44,240 t.

[dunmunro]

Draft on 13 January 1941

Port ----------------------------Starboard-------Average Draft
8550 -------Forward-----------8550-------------8.550 meters
8885 -------Admiships--------9185-------------9.035 meters
9600 -------Aft-----------------9750-------------9.675 meters

Mean draft: 9.11 meters
Displacement: 44,240 t.

Do you know if this test was done in salt or fresh water?

[José M. Rico]

The ship was moored to the pier at the Blohm & Voss shipyard at that time.

But does it matter? The ship may have less draft in seawater but is going to displace less water as well. For a given draft of let's say 9.3 meters, the Bismarck will always displace the same volume of water, whether that is seawater or fresh water.

[dunmunro]

The ship was moored to the pier at the Blohm & Voss shipyard at that time.

But does it matter? The ship may have less draft in seawater but is going to displace less water as well. For a given draft of let's say 9.3 meters, the Bismarck will always displace the same volume of water, whether that is seawater or fresh water.

It matters when trying to work out the immersion factor, for example, if one draught reading is done in fresh water, and another in salt water, the immersion values will be false.

[Dave Saxton]

The tempature of the water will also effect it's density. There are so many variables involved, that it's virtually impossible to correctly determine specifics with the available information. We can know approximately how much a given fuel load weighs though.