Bismarck Speed

[dunmunro]

I find the concept of an ''emergency speed'' curious. Surely there is only one maximum speed a ship can attain for a given weight loading and sea conditions?

This is a difficult thing to pin down. Most warship machinery was designed to produce more steam pressure and volume for short periods of time, than the machinery could safely tolerate for longer periods. The KGV class were designed to run continuously at 110K SHP (KGV made 27 knots for 31 continuous hours during the hunt for the Bismarck) but could operate safely with overload power for several hours at a time and PoW reported a maximum output of 134K SHP, probably just prior to intercepting Bismarck. Normal full power was achieved with 4 to 5 tons of fuel per boiler per hour, but the fuel pumps could deliver up to 6 tons/boiler per hour. Running continuously at overload power ran the risk of damage to the boilers, failure of high pressure steam lines, and turbine blade failure. I read a brief statement regarding an RN DD that conducted an 8 hour overload trial, and at the end of the trial there was some damage to the boiler brickwork and the steel fasteners inside the boilers, due to excessive temperatures. In general the RN did not conduct trials with overload power, although the ability to accept overloads was part of the machinery specification. A ship with worn machinery might not be able to achieve overload power, especially with a foul bottom in tropical waters. The KM had trouble with their HP steam plants and failures were not uncommon, which must have been a factor when deciding how much power to generate.

[dunmunro]

Ciao all,



I have also heard about an addittional boiler added on SH and GU just for that reason, to produce addittional steam for emergency needs, but never found many confirmations about it.

The machinery setup on S&G and Bismarck is interesting. These ships have 12 boilers, each capable of ~50 tons of steam output/hour. The maximum input to each turbine is ~150 tons/hour. In theory, they could attain full power on 9 boilers. One boiler would be required for auxiliary systems, mostly to run turbogenerators, leaving two boilers in reserve. Bismarck reported her maximum speed to be 28 knots after the DS battle, but it seems unlikely that the loss of two boilers would have effected her maximum speed.

[Antonio Bonomi]

Ciao all,

@ Dunmunro,

I agree, the main reason to report the speed being limited to 28 knots after DS battle was not the loos of steam power capability.

I think was mainly the bow received damage and the hull not being perfectly in line anymore due to the 2 hits received, the floooding and the consequent hull mis-alignement.

As you pointed out the factor to determine the speed is the steam reaching the turbines which by design do have defined limits.
Feeding the turbines with more steam results on more speed but you are "overboosting " them and working out of their design specification limits as you described above.
It can be done, but for a very limited period of time, and surely only when absolutely necessary.

The KM warship that surely had the majority of problems when this was done was Scharnhorst with lots of failures thru her life, until her end at North Cape.
Funny to say that the most reliable was Gneisenau, the heavy cruisers were not so reliable with Adm Hipper being the worst, while Bismarck and Tirpitz were never really fully tested about it.

Bye Antonio

[Thorsten Wahl]

Scharnhorst had spent roughly 50% of her living time in port mostly because of machinery problems

[dunmunro]

Whilst reviewing the Bismarck SPS, I realized that Bismarck's SPS would have to be liquid loaded to achieve full protection. A rough calculation shows the SPS tanks to have a capacity of at least 6000 MT. This has implications for Bismarck's minimum operational displacement and it seems likely that her displacement could not fall much under 50000 tons while she was in hostile waters, regardless of how much fuel she burnt off. This might also help explain her poor fuel economy in service versus her trials figures.

[Herr Nilsson]

A rough calculation shows the SPS tanks to have a capacity of at least 6000 MT.

To be exact (and in consideration of the maximum permissible filling level) it was 4166 cubic metres.

[dunmunro]

A rough calculation shows the SPS tanks to have a capacity of at least 6000 MT.

To be exact (and in consideration of the maximum permissible filling level) it was 4166 cubic metres.

Ok, so where is the rest of her 4000mt stored?

[Herr Nilsson]

I don't understand.
The rest of what? Fuel and other liquids?

[dunmunro]

I don't understand.
The rest of what? Fuel and other liquids?

IIRC Bismarck's total fuel load was ~8300 tons so this would require stowage of over 4000 tons outside the SPS tanks.

[Herr Nilsson]

Thank you, now I understand. There were a lot of tanks in the double bottom.

[dunmunro]

Thank you, now I understand. There were a lot of tanks in the double bottom.

When I look at cross sectional drawing of Bismark, and then draw a line to show the SPS tanks 75% full, I see a large gaps in the SPS where splinters could pass right through to the armoured bulkhead without every having to pass through the liquid layer.

[Herr Nilsson]

Only the upper tanks of the SPS had 75% maximum filling level. The lower tanks had just 70%.
AFAIK the Germans built the SPS (apart from the torpedo bulkhead) with steel plates, which were as thin as possible, to avoid splinters of dangerous effect. However, I don't think this discussion belongs to Bismarck's speed.

[alecsandros]

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.

[Bgile]

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 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.

[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.

PoW's log shows that she and Hood averaged 29 knots (and made revolutions consistent with that speed) for the two hours prior to intercepting Bismarck.