Boilers per shaft

[Javier L.]

Hello all,

The Bismarck had 12 boilers and 3 shafts, that equals to 4 boilers per shaft. Does this signify that if a shaft was put out of action then its 4 associated boilers were of no use even if they were intact? Could these boilers provide power to any of the other 2 shafts instead?

Javi

[marcelo_malara]

In general boilers provide steam to a steam manifold, not to a particular turbine. So any turbine can take steam from it.

[Javier L.]

That is what I've always thought until someone in another forum said that this was not the case in Bismarck.

[ontheslipway]

That seems highly unlikely. In case of a single boiler failure, distributing steam of 11 boilers of three shafts generates infinitely less trouble than getting an uneven loading.

[Javier L.]

Foeth, I don't understand what are you trying to say.

The person I mentioned says that Bismarck had a conventional distribution of boilers associated to shafts, in other words that each shaft had its associated boilers. If a shaft was lost then its associated boilers couldn't provide power to another shaft. He continues saying that turbo-electric plants didn't have this problem as it was possible to drive the power to any selected shaft.

Anybody knows if Bismarck had this "boiler-shaft" deficiency?

[ontheslipway]

If you have dedicated boilers per shaft, loosing one boiler can result in problems. One prop on 75% and two on 100% results in some speed loss (though very small). To alleviate the power drop on one shaft, you need to drop in rpm, while the two other props will increase their design loading. I'm not sure what the results will be, but for ferry operations one sometimes incorporates running 1 prop on 1 engine and the other on 2. The imbalance often leads to strong of-design conditions with ensuing cavitation and vibration.

[Javier L.]

Thank you Foeth. Point taken.

[_Derfflinger_]

I don't know the details of the three boiler/turbine/shaft arrangements that were in Bismarck/Tirpitz, but I can't imagine any naval design engineers, let alone German naval design engineers, creating a multiple boiler/turbine multi-shaft drive system in a very valuable capital ship, that would not include a cross-over manifold system that would allow steam from one bank of boilers to be fed into one or both of the other turbine drive trains.

But, again, I don't know the details for these ships.

Derf

[Bgile]

I believe the reason for "unit" propusion designs is damage control. If you have steam lines from every boiler connected to every turbine, you have reduced watertight integrity and a more complex system. Sometimes simple is better.

I believe the Iowa class BB's had engine and boilers in the same compartment, and there were no steam lines penetrating a watertight bulkhead at all.