Bismarck draft and displacement

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lwd
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Re: Bismarck draft and displacement

Post by lwd »

Here's a neat little density calculator for water. Note that there's almost a 3% difference in density between ocean water and fresh water at standard temp. A drop in temp of about 15 degrees will yield a similar effect at least at some temps and saliniteis.

http://www.csgnetwork.com/h2odenscalc.html
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Re: Bismarck draft and displacement

Post by dunmunro »

A summary of displacement data for Bismarck:

Image

from another board.
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Re: Bismarck draft and displacement

Post by Dave Saxton »

The archival data states that the draught at the construction displacement, that was 47,253 metric tons, was normally 9.4 meters in sea water.
Entering a night sea battle is an awesome business.The enveloping darkness, hiding the enemy's.. seems a living thing, malignant and oppressive.Swishing water at the bow and stern mark an inexorable advance toward an unknown destiny.
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Re: Bismarck draft and displacement

Post by dunmunro »

Dave Saxton wrote:The archival data states that the draught at the construction displacement, that was 47,253 metric tons, was normally 9.4 meters in sea water.
This is where trying to get a handle on Bismarck's most basic data is so frustrating. I've looked at the published draught versus displacement figures for Hood, KGV and Vanguard. The published immersion per ton figures tally almost exactly for the RN BBs when you examine stated draught versus displacement. I look at the same published data for Bismarck and the figures are all over the place. The Bismarck Class site gives these figures: "10.2 m(at 49.406 tonnes)" so a variation of 2150 tonnes = 80cm! They state 10.61 meters for Tirpitz at at 52.890 tonnes, so then 3500 tons variation = 41cm, which is just as absurd. Schlachtschiff.com claims 10.55m for Bismarck at 53165 tonnes, which is hard to square with 10.61m for Tirpitz at 52890 tonnes, since Tirpitz is a slightly bigger ship. Schlachtschiff.com claims 9.56m for Bismarck at the "construction" displacement which is implied to be 47253 tonnes, however the immersion figure of 57.3 tonnes implies 9.52 meters at 47253 tonnes, but these figures are fairly close. Vanguard has an immersion factor of 140.9 tons/inch which works out to 56.36 tonnes/cm, so 57.3 tonnes/cm seems reasonable for Bismarck.

Without accurate displacement figures it becomes very difficult to estimate performance and it is impossible to run accurate simulations because the various metrics like Block and Prismatic co-efficients can only be calculated correctly when the displacement is accurately known.
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Dave Saxton
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Re: Bismarck draft and displacement

Post by Dave Saxton »

Well we seem to have a dynamic immersion factor in play, probably because of the hull form. The construction displacement is the standard displacement, plus about 1/2 the normal fuel load, and most of the boiler water, so the immersion factor for the construction displacement of about 50.27 represents a fair average. A graph should plot with a slight curve I think. Variations will also occur due to density and tempature compounding the dynamic.

The Baron asked one of the engineers named Otto Riedel about the actual displacements of the Tirpitz and Bismarck. According to Riedel's records, Bismarck was 50,933.2 metric tons at full load, and Tirpitz was 50,955.7 metric tons at full load ( page 34 von Muellenheim) . There was a supplimental fuel load possible of 1,700 metric tons that would normally never be used. German ships were expected to operate between the normal full load displacement and the construction displacement. In practice the draught of Bismarck and Tirpitz in battle trim would flucuate between ~9.3 meters and ~10 meters. In the case of the Bismarck and Tirpitz the displacement would never exceed ~51,000 metric tons in practice, unless they were planning a trip to the Pacific with uncertain re-fueling options or something, and activate the supplimental fuel loading option.
Entering a night sea battle is an awesome business.The enveloping darkness, hiding the enemy's.. seems a living thing, malignant and oppressive.Swishing water at the bow and stern mark an inexorable advance toward an unknown destiny.
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Bismarcks draft in Denmark Strait

Post by JtD »

I know this subject has been covered, certainly more than once, on this board already. I've had my difficulties to find the proper topic, so I decided to start a new one. I'm not sure this was brought up before.

If you're looking at the artificial bow wave, you can quite easily make a good estimate of the draft forward. Judging by what is visible and what not, I'd go for a draft of about 9.50 meters. It might be less because of the waves. Does anyone have a version with a higher resolution?

Image

Please also note this picture. Taken earlier the same day, it shows the bow wave even better. At this picture, the forward draft is not exceeding 9.0 meters. Did Bismarck resupply in any way after this picture was taken?

Image

Based on these pictures I am assuming a draft and displacement shallower and lighter than quoted in several places.

Pictures from www.kbismarck.com.
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Re: Bismarcks draft in Denmark Strait

Post by Vic Dale »

To JtD

Look closely at the second photo and I think you will see that the ship is trimmed by the stern so as to lift the bow for painting out the camouflage dark-grey and the adjust the bow wave. Draught is going to be very hard to judge from this, because we can't see the degree to which the stern has been trimmed.

900 tons has been consumed since leaving Gotenhafen, but I think there is a good chance that forward and aft counter-flooding voids were also filled with fuel adding 2,000 tons and reducing freeboard by 16 inches, which may be very hard to detect in the photo. The hit in the bow was said to have isolated 1000 tons of reserve fuel and there are only two very small bunkers forward of the transverse armoured bulkhead, on the drawings I have to hand.

Vic Dale.
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Re: Bismarcks draft in Denmark Strait

Post by JtD »

Well, yes, but the above picture shows the Bismarck underway, and draft at the bow is not more than 9.50m. Up until Denmark Strait, Bismarck would burn another 1500ts of fuel. And let her have 1 meter trim by the stern in the first picture (which I don't see, even if I look closely), it doesn't change the outcome.

Looking at pictures isn't exactly science, but still, Bismarck very obviously did not have a draft of 10 meters or more during the operation and the corresponding displacement would be closer to 45000ts than to 50000ts.
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Re: Bismarcks draft in Denmark Strait

Post by Vic Dale »

A small observation;

The second photo is taken from two decks above PG's main deck and we should therefore be able to see something of Bismarck's decks. We can't see anything of her decks, not even at the bow and considering that the camera is well abaft her midships we should see something of her fo'csle.

This has me thinking that the ship is heeled to port as well as being trimmed by the stern.

The second photo is going to give considerable trouble because as the ships are in close proximity, the bow will appear out of scale with the freebaord dimension amidships, so I dont think there is much which can be learned here. The ship is on the move and it is very hard to make out what is happeneing to the water as it passes down the ships' side. There is a slight swell running as we can see by the foam at the bow and the way the water cuts the bottom of the false bow wave, so that is going to make an assessment of draught by photogrammetry a bastard of a job.

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Re: Bismarcks draft in Denmark Strait

Post by JtD »

If it heeled to port, you wouldn't see the hull shape as you do. The ratio 3/2 bow height/midship height as you would expect from an heel free ship is there.

A few meters height over several hundred meters distance don't matter anyway.
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Re: Bismarcks draft in Denmark Strait

Post by Vic Dale »

JtD wrote:If it heeled to port, you wouldn't see the hull shape as you do. The ratio 3/2 bow height/midship height as you would expect from an heel free ship is there.

A few meters height over several hundred meters distance don't matter anyway.
Yes, but considering that 2000 tons is only going to add 16 inches to the draught, that is going to be devilishly difficult to spot from a photo.

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Re: Bismarcks draft in Denmark Strait

Post by JtD »

There's also another picture of the Bismarck same day, where you can see the dark waterline paint for the entire length of the ship, with only very small differences in the width, meaning a draft of 9.50m and less over the entire length. That picture is in Breyers book.

I'd be most pleased to see images with better resolution as well as first hand info on the paint job.
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Re: Bismarcks draft in Denmark Strait

Post by Dave Saxton »

I think your off by about a 1/2 meter. I determined from a variety of photos that there's about 1/2 meter of the dark grey showing at Bergen or more or less 10 meters draught. This puts the displacement at about 50000 to 50400 metric tons at Bergen.This leads credence to Ulrich's opinion that Luetjens didn't need to top off Bismarck at Bergen and it would put Bismarck at about 48300 metric tons by DS.
Entering a night sea battle is an awesome business.The enveloping darkness, hiding the enemy's.. seems a living thing, malignant and oppressive.Swishing water at the bow and stern mark an inexorable advance toward an unknown destiny.
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Re: Bismarcks draft in Denmark Strait

Post by JtD »

Eventually, you might be right.

I'd still like to see high res pictures plus info on the paint job. Is it true that the white was painted into the dark grey?
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Re: Bismarcks draft in Denmark Strait

Post by Vic Dale »

JtD wrote:Eventually, you might be right.

I'd still like to see high res pictures plus info on the paint job. Is it true that the white was painted into the dark grey?

Antonio has just posted a very high definition picture possibly from Grimstadt. I am hoping he will post it here.

Vic Dale
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