Bismarck Speed

[dunmunro]

This doesn't disprove that the Bismarck could do 30 knots though. Actually there are some documented evidence pertaining to the power, shaft RPM's, and the loading. During one documented speed run that has been uncovered to date, the Bismarck was producing about 117,400 HP, and turning the shafts an average of 249.5 rpm. The loading was, IIRC, 75% of payload, and that comes to about 48,900 tons, or within a few % points of normal operational full loads. The speed was 28.374 knots. If the Bismarck could do that speed using only about 117,000 Hp, then surely it could have attained claimed speeds by putting to use the remaining power still on tap.

I do agree that in the right conditions the KGV class could do 29 knots or possibly a bit more, giving a rather small speed differential.

Here's a speed/power curve for Scharnhorst:



from Battleships of Scharnhorst Class, by Koop, page 25.

Note the displacement.

Now, we take Bismarck, add almost 10,000 tons and introduce a much less favourable length to beam ratio and we get a ship that is only about .6 knots slower at the same SHP. Something doesn't add up, and the scarcity of info on Bismarck's speed trials and performance versus SHP make me wonder what was going on.

[Dave Saxton]

I don't see a problem. First of all Scharnhorst is not exactly Bismarck, so it might not be exactly apples to apples. Bismarck was to achieve 29 knots at 138K, not 30 knots as in the case of Scharnhorst. At 150k (or 162K max for Tirpitz) I can see 30 knots as quite plausable. It adds up to me.

[Karl Heidenreich]

Dave:

I don't see a problem. First of all Scharnhorst is not exactly Bismarck, so it might not be exactly apples to apples.

There has been, lately, a lot of "confussions" trying to build up paralelisms from S&G to Bismarck. As I wrote in a post days ago: as if you try to extrapolate Iowa´s performance from the earlier North Carolina or South Dakotas. Which is not only wrong but unnecessary because for each of these vessels we have the info at the very hand.

What if we try, for instance, to extrapolate Iowa´s electrical systems from what happened to South Dakota at Guadalcanal? It´s absurd, isn´t it? So we have to deal separately Iowa from South Dakota. So Bismarck from the Twins.

And then we have to contend with what is a witness account (the Baron) which is a very good and reliable witness.

Best regards.

[dunmunro]

I don't see a problem. First of all Scharnhorst is not exactly Bismarck, so it might not be exactly apples to apples. Bismarck was to achieve 29 knots at 138K, not 30 knots as in the case of Scharnhorst. At 150k (or 162K max for Tirpitz) I can see 30 knots as quite plausable. It adds up to me.

I don't think so:

PoW LWL= 740ft Beam = 103ft, L/B = 7.18, conventional stern, 4 shafts.
111600 shp = 28 knots at 42100 tons (trials)
estimate 120000 shp = ~29 knots at ~42000 tons
estimate 133000 shp = ~29.5 knots at ~42000 tons

Vanguard LWL = 800ft, Beam = 108 ft, L/B = 7.41, transom stern, 4 shafts.
120240 shp = 28.16 knots at 51160 tons (trials)
132950 shp = 30.38 knots at 51070 tons (trials)

crude wetted surface ratio Vanguard/PoW 108x800x35/103x740x32.5 = 1.22

We can see that Vanguard has three major improvements over PoW, a better L/B, a transom stern and a longer LWL to overcome the handicapp of an extra 9000 tons.

Bismarck LwL = 792ft, beam = 118ft, L/B = 6.72, conventional stern, 3 shafts.
117400 shp = 28.374 knots at ~48000 tons (claim since displacement is unknown)
150170 shp = 30.1 knots at 48000 tons (claim)
163000 shp = 30.8 knots (claim - Tirpitz)

Scharnhorst LWL = 741ft, beam =98 ft L/B = 7.53, Conventional Stern, 3 shafts.
117000 shp = ~29 knots at 38950 tons (from the graph), conventional stern, 3 shafts
150000 shp = ~31 knots at 38950 tons (from the graph),
163000 SHP = ~31.2 knots at 38950 tons (from the graph)
160050 shp = 30.7 knots (Gneisenau no displacement given but from graph, probably ~37000 tons)
crude wetted surface ratio Bismarck/Scharnhorst 792x118x32.5/741x98x32.5 = 1.29


We can see the improvements in L/B and hull design that the RN had to use to enable Vanguard to match KGV and pull ahead at the highest power settings, yet Bismarck's only advantage over Scharnhorst is a greater LWL, in the other areas she is at a disadvantage.

I suspect that the claim for 28.37 knots for Bismarck at 75% of load should read 75% of payload at design displacement of 44734 tons - light ship of 38892 tons or ~6000 tons x .75 = 38992ton + 4500 tons = ~43500 tons. Any higher displacement than this simply doesn't make sense.

If we take "payload 75%" and read it literally, we get max displacement x .75 = ~40000 tons and then the numbers are a good match for Scharnhorst, and we must consider this as a real possibility.

[Dave Saxton]

No, 40k is not a real possibility. 40k is less than the ship with nothing. I have a copy of Lindemann's weight break down for March 30, 1940. All tons are metric tons.

The ship with nothing but lubricating oil, and liquids, for the machinery was 41,243 tons.

With ammo, provisions, drinking and wash water, it was 43,646 tons. This was the "standard displacement."

The "construction displacement" with 1/2 the fuel and other oils and liquids required for operation was 47,253 tons.

The remaining 1/2 fuel, oils, liquids, and other supplies, and excluding supplimental loads such as additional fresh water and so forth, brought the full load displacement to 50,900 tons. It was not expected for the ship to carry 100% payload during operations.

If we assume payload is the difference above the construction displacement, the displacement at 75% payload was 49,988 tons.

If we assume that the payload is based on the standard displacement, the displacement at 75% payload was 49,087 tons

If assume that the payload was based on the light ship of 41,243 tons, then the displacement at 75% payload was 48,485 tons.

No matter how it's sliced, the displacement at the time of the speed run we have documented evidence of, was between 48,500 tons and 50,000 tons. The documention of that speed run is indisputable as to power, RPM, and measured speed, so making apples to oranges comparisons to British warships is mute.

If we assume that the curve on the graph for Bismarck was similar in shape to Scharnhorst's, although not exactly the same, then we would expect the curve to be shifted down a little bit by comparison. It is. I understand that your estimating that the shift should be greater, but that's not necessarily the case. The numbers are not out off base at all.

[dunmunro]

Axis BBs gives these numbers on page 304:
Bismarck, Aug 1940/Tirpitz Feb 1941
Light ship: 38992 tons/38915 tons (all in long tons)
Design: 44734/44755
Full load: 48626/48648
Battle load: 49609/49628


Tirpitz at 163000 shp = 30.8 knots at 49000 tons?

Gneisenau at 160000 shp = 30.7 knots at 37000 tons?

Sorry, but this doesn't make sense. The speeds for Bismarck just don't add up at those displacements. There is nothing in Bismarck's design that would allow it to match Scharnhorst's speeds despite another 10,000 tons displacement, with the same power output. Vanguard, by way of contrast, has a greater L/B and a transom stern.

A final comment might be that the calculated 30.1/30.8 knots for the Bismarck class might have been "contract" figures based upon an artificially low displacement perhaps from the original 35000 ton standard displacement design?

[Dave Saxton]

Sorry, but this does make sense. An expert in marine propulsion and hydrodynamics used to drop in here years ago and lead us in some very educational discussions in the complexities of these matters. These factors are very complex. I recall that he mentioned that laymen tend to place too much emphasis on L/B ratio. He also discussed the pros and cons of transom sterns.

Bismarck is a different ship than Vanguard, KGV, and Scharnhorst, so it will have a different set of hydrodynamic and propulsion factors, and efficiencies. The differences in speed per power between Scharnhorst, using the curve you yourself posted, and the larger Bismarck from the specifications during the documented speed run, are noticable, and they are not out of line.

As for the displacement question during that run, the bare minumum displacement that it could operate the propulsion machinery, based on the primary documents on Bismarck's weights, is around 45,000 tons. That is even with completely empty magazines and stores, and almost empty fuel tanks. To operate the boilers and turbines it had to have lubricating oils, and boiler feed water, and other essential fluids. Of course the very idea of Bismarck running sea trials completely empty is ridiculous. The Bismarck was pretty well loaded when it first proceded down the Elbe, as can be seen by the boot topping in the photos of that event.

[Dave Saxton]

...The differences in speed per power between Scharnhorst, using the curve you yourself posted, and the larger Bismarck from the specifications during the documented speed run, are noticable, and they are not out of line..

Just to elaborate and what I'm trying say. Look closely at the Scharnhorst graph.

Notice that at 28 knots the power required is about 103k. From the Bismarck speed run, Bismarck required about 117K.

The Scharnhorst required 120K to attain 29 knots. The Bismarck required 138K to attain 29knots.

The Scharnhorst required 137k to attain 30 knots. The Bismarck and Tirpitz required more than 150K to attain 30 knots.

Notice that the curve is starting flatten out a bit near the top. This reflects the fact that it requires more and more power to attain less and less speed increase. This also explains why the speed differential is becoming less at around 31 knots.

[dunmunro]

Here's some data from Richelieu:

LWL 793 ft, Beam 108 ft, L/B =7.34

power needed for a given speed at a given displacement:

knots/40243/44277/% increase= 10%
29/105540/116385/10%
30/119345/133155/11.5%
31/138085/151695/10%

so we have a 10% increase in displacement requiring a 10% increase in power. By extrapolation an increase in weight to ~48600 tons would require another 10% increase in power to maintain the speed, so 30 knots would require ~146600 shp and 31 knots would require ~167000 shp. Is Bismarck's hull form as efficient as Richelieu's, since this is what would be required for Bismarck to match these figures? This flies in the face of reason. Increases in beam require increases in power all else being equal, and Bismarck's 3 shaft layout places her at a further disadvantage since the centre prop is always less efficient than props that get better waterflow in outboard positions.

Applying this data to Scharnhorst, we can see that she would require about 195000 shp to make 31 knots, if we increase the displacement by 30% to match Bismarck's full load of about 50000 tons. With 150000 shp, at 50000 tons her maximum speed would be about 29 knots and she might make 29.5 knots at 160000 shp. I would suggest that Scharnhorst's power curve can be roughly applied to Bismarck by increasing the power needed in proportion to the increase in displacement.

Another factor is that Scharnhorst's boilers have 8% more steam production than Bismarck. This implies that Bismarck's maximum power output would be about 148000shp, and her maximum speed at 50000 tons would be about 28.6 knots, using Scharnhorst's power curve. It also implies that the trial run that produced 28.37 knots at 117400 shp was run at about 43000 tons displacement, or that whatever speed was achieved was normalized to that displacement, possibly because the manufacturer guaranteed certain speeds at a given displacement.

[Dave Saxton]

Trying to extrapolate data from different ships, such as Richelieu, or Vanguard, and so forth, and applying it to a totally different ship results in a faulty comparison, and is therfore of little value in correctly assessing Bismarck's speed data. Besides, such guesstimates are not needed, because we have hard data from the documented speed run, that set the correct parameters.

[dunmunro]

Trying to extrapolate data from different ships, such as Richelieu, or Vanguard, and so forth, and applying it to a totally different ship results in a faulty comparison, and is therfore of little value in correctly assessing Bismarck's speed data. Besides, such guesstimates are not needed, because we have hard data from the documented speed run, that set the correct parameters.

The data from Richelieu shows that displacement increases must be matched by proportional increases in power to maintain a given speed. A separate question is whether Richelieu would be more easily driven than Bismarck. I suspect that is.

However, the major problem is that the data from the documented speed run on 29.10.40 is not that "hard", since we don't know the displacement and the recorded draft of 8.5meters implies a somewhat lower displacement than you suggest. Why the KM would omit such a key piece of data is hard to understand, and why this data appears to have been expunged from the historical record is also hard to understand, since it is absolutely crucial to any understanding of Bismarck's propulsive efficiency.

by José M. Rico on Sat Nov 18, 2006 4:53 pm

Ulrich Rudofsky wrote:Josef Kaiser said this about Bismarck's speeds:

"The speed data are based on an average output of 39170 shaft HP (WPS =Wellenpferdestärke)) per screw and 249.5 RPM per screw at a load addition of 75% and a draft of approx. 8.50 m.
This is somehow puzzling.
A 8.5-meter draft corresponds to a displacement of about 42,000 tons...

Using Scharnhorst's power curve, a displacement of 42000 tons gives us a very good fit:

from the curve 28.4 knots = ~109000 shp (from the graph) at 39000 tons
from the curve 28.4 knots = ~117400 shp (from the graph) at 42000 tons (39000 x 1.077)

Now Mr Rico suggests that Bismarck's displacement was substantially higher than 42000 tons on 29.10.40, and this seems reasonable. I can only suggest that the contract speeds were based upon a displacement of 42000 tons and the results were normalized to that displacement.

Scharnhorst at 30.1 knots @ 42000 tons = ~148000 shp
Scharnhorst at 30.8 knots @ 42000 tons = ~160000 shp

Again, these are very good fits for the max speed claimed for Bismarck and Tirpitz. I would hypothesize that Scharnhorst is a good analog for Bismarck, and that Bismarck's greater LWL offsets Scharnhorst's better L/B, to some extent.

[José M. Rico]

Now Mr Rico suggests that Bismarck's displacement was substantially higher than 42000 tons on 29.10.40, and this seems reasonable

What I say is that the day of that speed run the Bismarck was loaded with 6,285 m3 fuel oil and 337 m3 feed water according to the KTB, and that equals to a displacement that does not correspond to a 8.5-meter draft.

[dunmunro]

Now Mr Rico suggests that Bismarck's displacement was substantially higher than 42000 tons on 29.10.40, and this seems reasonable

What I say is that the day of that speed run the Bismarck was loaded with 6,285 m3 fuel oil and 337 m3 feed water according to the KTB, and that equals to a displacement that does not correspond to a 8.5-meter draft.

Yes, I agree. Which is why I believe the speeds were normalized to 42000 tons. This is the only way to reconcile the data. Here's the footnote to the test results, which makes it easier to understand what we're discussing:

by Ulrich Rudofsky on Sat Nov 18, 2006 3:50 pm

"Speed 28.374 knots.
Footnote 2.
Data from the protocol of the speed trials on 2 November 1940. The speed data are based on an average output of 39170 shaft HP (WPS =Wellenpferdestärke)) per screw and 249.5 RPM per screw at a load addition of 75% and a draft of approx. 8.50 m. Other documents are not available. (Authors note. The document does not say if this concerns "AK Fahrt" (Äußerste Kraft), i.e. extreme full-power speed. The source of the speeds of 30.4 kn, 30.6 kn or 30.8 kn given in the current literature, is puzzling. Blohm & Voss states 30.1 kn." From: Schlachtschiff Bismarck: Das Original im Detail, Simon Frey Verlag, 2004, page 008.

[Bgile]

obviously the other possibility is the draft is wrong.

[dunmunro]

obviously the other possibility is the draft is wrong.

That's possible but I wonder how Bismarck's engineers and navigators were ever able to predict her performance, since apparently even the most basic data is filled with contradictions?

Here's a crude graph that I prepared showing what I believe to be Bismarck's power curve at 46800 and 50700 tons: