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emc wrote:

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Ed wrote:

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How long does it take to fire up (from cold) and build enough steam to move a BB at 6 knots to clear the harbour? Is the time different for coal fired vs. oil fired boilers? Would all 3 or 4 engines be used to manuver within the harbour and how many boilers? Once clear of the harbour, how long does it take to get to a cruising speed of 15 knots? Are these time periods different for different classes, or ships with a class (like the Nevada vs. the Oklahoma)? Could the USN Fast BBs (NC, SoDak, and Iowa classes), build enough steam to get to cruise speed (15 knots) faster than the standard USN BBs?

There probably isn't a single answer, as it would depend on the condition of the boilers and how urgent was the need. I remember reading, in an article about the Italian Capitani Romani class cruisers that getting the boilers started was about an eight-hour task, with emergency startup being possible in as little as one.

I suspect that the fast battleships would take longer than the USN standards, as the boilers were likely more complex, thereby more sensitive to rough handling.

The fast BB boilers were identical in design and operation to all the other 600 psi/850 deg F M-type boilers in the USN of the time. They were little different in size to DD boilers (or so they look up close). For these boilers the normal period from cold to ready to cut the boiler into the main steam line is about 3.5 hours. This time period is this long to allow proper warm up of the plant (and all its associated piping). It's not just a boiler thing - the main engines and the generators are in this process.

The process can of course be speeded up, but there are risks as a trade off. To answer your question, I think about an hour, maybe two to get to six knots from cold-iron.

It gets better if, like all the BBs moored to the "F" moorings at Ford Island on The Day, one is already steaming at least one boiler supplying hotel services. Inter alia, the other boilers are under a steam blanket and thus already warm to a degree. The time line thus to get a main engine(s) warmed up is shorter - note Nevada's performance. I don't know the details, but suspect she was moved on one boiler, with the others lit off and building up to operating pressure. Had she sortied I am guessing she would be ready to answer all bells within the hour. And, backing out of her berth required IMHO both engines; it is hard to back a two shaft ship in a straight line with only one operating shaft. Not impossible, but hard.

The difference between the fast BBs (600 psi plants) and say Nevada and her chronological sisters is probably not great. The earlier ships after their big interwar upgrades were probably running 250 psi plants at about 400 deg F (this is a guess). The earlier ships may well have had a shorter time line.

BTW, big ships are hardly ever 'cold' except during extended repair periods. To go 'cold' one needs a source of shore power and at least an auxiliary steam source. These services are not that commonly available and for big ships the transition process to and from 'cold' is not trivial.

BOBC59 - chime in where you think appropriate - I need a 'check' on 600 lb plants.

Fermi2 wrote:

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Probably 3 to 4 hours. Usually USN Boilers are limited to less than 100 F/Hr heatup rate to protect the tubes. I'd have to look in PINE as it has the recommended heatup rates for USN Boilers.

Mike

Sounds about right.. EOSS specs for 1200 ships was about 3+ hours. Lighting off sprayer plates were drill size 32; normal steaming 20. Soooo, if one were in a bit of hurry, 20s might go in at hour two or so. Probably no log entries, however.