Ship Performance after Reboilering

  • #1
I'm trying to do some rough estimates of how much additional performance a steam powered warship (World War I to 1950 or so) could get from receiving new engines. I'm aware that different hull designs have different impacts on drag in the water, but for the rough estimate I'm focusing on the propulsion systems. The largest changes for performance seem to be fuel type (coal or petroleum) and boiler pressure.

Presumably the ships of this era were using bituminous coal, as its been said that the switch to petroleum doubled a ship's energy density. Anthracite coal has been used to power some ships (it was used as a stealthy fuel in the American Civil War due to its cleaner burning) but it has about as much energy density as petroleum. Does that mean that switching from coal to petroleum would allow most ships to double their horsepower?

Also, it seems that boiler pressures were constantly increasing throughout the era. What kind of relationship does that have with power density and performance of the engines?
 

Answers and Replies

  • #2
anorlunda
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I think you can get your estimates from the historical record. The most relevant parameter is horsepower per ton of displacement for the same hull form and waterline length. You should be able to find the data, horsepower, displacement, and top speed for historical warships.

As a rough guess, I would say that the change in weight of power plants, as a fraction of total displacement is a minor factor. Tonnage of fuel carried must also be a factor, but performance gains could come in terms of speed or range or munitions carried.

I once visited the USS Texas (circa 1910). I think the plaque said it was the last steam-piston engine warship.

Higher pressures certainly add a lot of power/weight. But other big factors were the improvement in design of steam turbines, and speed reduction gears.

What about the weight of armor?
 
  • #4
Nidum
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Starting right back in Newcomen beam engine days there have always been schemes proposed to uprate the power output and increase the efficiency of steam power plant .

One of the earliest was devised by a Scottish engineer called William McNaught . He upgraded low pressure beam engine plants to use higher pressures by supplying replacement high pressure boilers and by fitting an additional high pressure cylinder to the original beam engine . This allowed the engine to work at the higher pressure and effectively to work as a compound .

This procedure did allow the engine to develop more power but only within the limits of the engine mechanical construction . The real advantage was the improvement in efficiency . There are credible reports that coal consumption for a McNaughted engine supplied with steam from the new boiler could be less than half of what it was previously .
 
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