Bismarck Speed

[dunmunro]

There were only 2 British battleships which came at 28kts at the time: KGV and PoW. Bismarck was 2kts faster than them, but 7kts faster than all the other British BBs of the moment.

DunMunro has a fairly good argument elsewhere that Bismarck wasn't faster than KGV, at least not enough faster to make a difference. He thinks they could both do 29 kts on that day in DS.

They did do 29knots on that day, and the evidence for Bismarck being able to make 30knots at a combat displacement simply doesn't exist.

[Herr Nilsson]

Well, is there any evidence that Bismarck was not able to make 30 knots at combat displacement?

[dunmunro]

Well, is there any evidence that Bismarck was not able to make 30 knots at combat displacement?

I have examined the power versus displacement for Bismarck, and I find it unlikely that Bismarck's PP could generate enough power to push her to 30 knots at more than something like 45K tons.

[Herr Nilsson]

Yes, Duncan, I know. We discussed it several times before and you know I disagree.

[Bgile]

IIRC Lutjens ordered both ships to 30 knots. Some time later there was a message from PE that her 30 knots seemed to be different from Bismarck's 30 knots. It's possible this is an indication that Bismarck was unable to achieve the ordered speed on her deep displacement.

[Herr Nilsson]

Almost. It's a statement of Brinkmann:

Ever since leaving Gotenhafen, the revolutions between the ships did not synchronize. Bismarck fully loaded, attained the correct speed as determined by position fixes. Prinz Eugen had to run a knot less under full battle-load-conditions.

I interpret it this way:
28 knots (r.p.m.) of Bismarck were 28 knots, but 28 knots (r.p.m.) of Prinz Eugen were 29 knots in reality. Therefore Prinz Eugen had to reduce speed to 27 knots (r.p.m.) to make the same speed as Bismarck.

[Bgile]

Almost. It's a statement of Brinkmann:

Ever since leaving Gotenhafen, the revolutions between the ships did not synchronize. Bismarck fully loaded, attained the correct speed as determined by position fixes. Prinz Eugen had to run a knot less under full battle-load-conditions.

I interpret it this way:
28 knots (r.p.m.) of Bismarck were 28 knots, but 28 knots (r.p.m.) of Prinz Eugen were 29 knots in reality. Therefore Prinz Eugen had to reduce speed to 27 knots (r.p.m.) to make the same speed as Bismarck.

You can choose to do that, but it could also mean 30 knots for PE was only 29 knots for Bismarck, and the latter was unable to attain the ordered speed of 30 knots. I don't see any way to resolve this.

[Herr Nilsson]

No,I don't think so. Brinkmann stated BS made correct speed.

[alecsandros]

I have examined the power versus displacement for Bismarck, and I find it unlikely that Bismarck's PP could generate enough power to push her to 30 knots at more than something like 45K tons.

There are other factors involved in a ship's ability to mantain a certain speed.

- One of them is the length/beam ratio. Longer ships are faster than "shorter" ships in respect to their beam.
- Another factor is the distribution efficiency from powerplant to the propeller shafts. Most WW2 ships had a 50% efficiency - that is from 100.000 hp only 50.000 - were transferred (this is a gross simplification but I don't have time right now for a lengthy explanation. We all know what it's about, anyway)
- Finaly, a more complex factor is hull shape and hydrodinamic properties. The way the water is pushed out from the front of the bow and moves towards the stern is essential for attaining a large speed.

All those factors, and some others were understood and used by German naval engineers in the 30s. And not only by them, but also by Japanese and American engineers. And they struggled to optimize all of those factors.
The results, as we know them, and as the historical documents depict them, present ships which are faster than one might think if comparing only the displacement/power ratios.

For instance, Yamato only developed ~ 135000 shp, at 70.000 tons, and it still could make 27.5 kts (and there are sources for 28 and even 28.4, faster than KGV, by the way).

[alecsandros]

No,I don't think so. Brinkmann stated BS made correct speed.

An the Barron says they achieved 30.5kts on trials.
Plus, there are several accounts about Tirpitz's top speed at over 30.5kts.
Ignoring them is not a good practice, IMO.

[dunmunro]

For instance, Yamato only developed ~ 135000 shp, at 70.000 tons, and it still could make 27.5 kts (and there are sources for 28 and even 28.4, faster than KGV, by the way).

Trial displacement of 69100 tons @ 153553 shp = 27.46 knots
Yamato's full load displacement in 1941 was 72,809 tons and went up with time.
AoS, Yamato.
WLL = 256m
L/B ratio = 6.94
Would that we had the same info for Bismarck.

Bismarck
WLL= 242m
L/B = 6.72

[alecsandros]

Questions:
1) Does anybody know Bismarck's displacement on the 24th of May?

2) Duncan, have you thought about Yamato's 70.000 tons displacement and 27.5-28kts speed @150.000 shp?

[dunmunro]

Questions:
1) Does anybody know Bismarck's displacement on the 24th of May?

2) Duncan, have you thought about Yamato's 70.000 tons displacement and 27.5-28kts speed @150.000 shp?

Perhaps you can provide specific data on displacement and SHP for Yamato at 28knots? Of course it is possible, but it would require more power, and/or a lower displacement than for her trials data at 27.46 knots which I provided above.

[alecsandros]

The idea is that a 70.000 ton ship achieved 27.5kts on 150.000shp. Bismarck's machinery generated 150.000 shp also, and the ship was 50.000 tons full load.
So the relationship is not linear, there are numerous other variables to consider.

I just re-read some passages from the Baron's book. At the section were he presents the cat and mouse game with Suffolk and Norfolk (May 23rd) he says "our speed was almost 30kts".
This information shows, I think, that Bismarck was capable of 30kts at Denmark Strait.

[dunmunro]

The idea is that a 70.000 ton ship achieved 27.5kts on 150.000shp. Bismarck's machinery generated 150.000 shp also, and the ship was 50.000 tons full load.
So the relationship is not linear, there are numerous other variables to consider.

I just re-read some passages from the Baron's book. At the section were he presents the cat and mouse game with Suffolk and Norfolk (May 23rd) he says "our speed was almost 30kts".
This information shows, I think, that Bismarck was capable of 30kts at Denmark Strait.

Yamato made 27.46 knots at 69000 tons. Yamato's hull form was quite novel and completely unlike any other IJN BB, with a large bulbuous bow and a semi-transom stern. Bismarck's hull form is clearly based upon Scharnhorst although Bismarck's WLL is 15 metres longer, it has a much poorer L/B ratio. The bow and stern design of Bismarck is almost identical to Scharnhorst yet Bismarck is much heavier and has a much wider beam. However we are supposed to believe that somehow Bismarck is actually much more hydrodynamically efficient than Scharnhorst, although there is nothing in Bismarck's hull design that would account for such a surprising increase in efficiency.

Suppose we took KGV and built another ship with exactly the same bow and stern sections, but 6 metres wider in the beam and 15 metres longer, and increased the weight by 12000 tons. Do you really think the resulting ship would be more hydrodynamically efficient than KGV? Vanguard is more efficient than KGV but she had to have a better L/B ratio, 7.41 versus 7.18, and a transom stern to do so. Making the same hull form beamier, with a poorer l/B ratio and ~10000 tons heavier should not make for an increase in hydrodynamical efficiency.