Steam-ship questions. Prizes!

[HareBrain]

I'm hoping the Chrons Collective will be able to answer a couple of questions the internet has failed miserably at. The prize for answering any of the below will be a mention on the expanded version of my acknowledgements page (which will be mailed out to people who request one, so they can paste it over the short version).

1. What determines how much smoke is visible from a steamship's stack? I've seen photos of Chinese steam-engines that look like Mount St Helens, but also photos of restored steam locos that barely show any smoke at all. Someone suggested it was air temperature (or maybe humidity) or is it the quality of the coal?

2. How much time would it take to get a steamship moving from furnaces that were (a) banked, or (b) cold?

3. In a decent-sized ship with a top speed of say 20 knots, how quickly could it stop from full-speed (no icebergs involved), and then how quickly back to top speed again?

I appreciate this requires pretty specialist knowledge, but I have faith that someone out there has it. I'm not after absolute precision, just a general idea.

Thanks in advance.

 

[The Judge]

Just checking here, but do the answers have to be accurate to win the prize? Cos, y'know, I don't think you should discriminate against people who aren't technologically minded...

 

[Susan Boulton]

Sue looks at some old notes:

Scribbled on alongside a picture of a WWII destroyer 33 knots between 1-2 miles engines full astern.

Also in the note; cargo ship in ballast 3 to 5 times its length. Fully loaded 7-8 times, but no mention of speed.

Some one might have more detailed info, but it does depend on ship's displacement, speed and the sea conditions.

I suspect that like a steam train you have to get up a head of steam in the boilers before you can move. As to the length of time depends on the size of the boilers, how many and type of stream turbines used.

As for the smoke a lot would depend on the quality of the coal, some types burn more cleanly than others and give off more heat. Coke, the by product of making coal gas burns with hardly any and burns very hot. Not sure if it was used in steam engines train or ship.

 

[goldhawk]

1. What determines how much smoke is visible from a steamship's stack? I've seen photos of Chinese steam-engines that look like Mount St Helens, but also photos of restored steam locos that barely show any smoke at all. Someone suggested it was air temperature (or maybe humidity) or is it the quality of the coal?

How big the ship is. For one thing, the used steam is routed to a nozzle in the stack which strays it upward, increasing the draft. This pulls more air into the firebox which creates a hotter fire. So a good part of the smoke is actually steam.

2. How much time would it take to get a steamship moving from furnaces that were (a) banked, or (b) cold?

(a) Depends on what you mean by banked. Usually, they are kept at pressure which normally requires a fire. A banked fire would be too small to keep a large boiler boiling. If it is kept at pressure, it can be brought up to operating pressure in a short time, say 5 to 10 minutes.

(b) Depends on (i) how big the boiler is (how much water it has to heat), (ii) how big the firebox is, and (iii) how fast the fire can be fed. A smaller boiler could be brought up to operating pressure in 1/2 hour, a large one, 2 or 3 hours. Don't forget that the RMS Queen Elizabeth 2 is a steamship.

3. In a decent-sized ship with a top speed of say 20 knots, how quickly could it stop from full-speed (no icebergs involved), and then how quickly back to top speed again?

WAG (Wild-Ass Guess): To stop, 1/2 hour and about 5 nautical miles. From stop to top speed, 1 to 2 hours and 10 nautical miles.

 

[ctg]

HB, I tried to search good links to your questions, but no matter how I constructed the queries I ended up with punch of physic links and formulas, which I know wouldn't be no good for you as there's so much in the fluid dynamics etc.

But I can say you that if a captain wants to stop the ship from hitting something, then he will order full reverse if banking doesn't do the trick. He could even order the crew to drop the anchor. So, the full stop could be really, really sudden. And to reverse that, you have rethink the situation as in fluid a full, full stop is nearly impossible to achieve.

 

[reiver33]

A firebox is kept banked up simply to act as an ignition source when more fuel is added, as opposed to the tedium of starting from scratch. Depending on your technology then a boiler (or two) would be kept up to steam to provide power for on-board systems (eg steam turbine generated electricity).

Forget about dropping the anchor if the ship in question is large - you'll just lose it. With a large vessel at rest the anchor works in conjunction with basic inertia versus wind force and tide - which is why in heavy seas/strong winds the anchor will drag. The momentum of any large vessel will easily overcome the tensile strength of your anchor chain.

 

[Pyan]

1. What determines how much smoke is visible from a steamship's stack?

Goldhawk's right about the size of the ship, but it also depends how fast she's going. A big dreadnought in WW1, steaming hard put out so much smoke that they couldn't see from the spotting-tops in some classes, but the same ship idling into Scapa Flow would hardly put out any smoke at all.
This is the US Atlantic Fleet, circa 1913...

Don't forget that the RMS Queen Elizabeth 2 is a steamship.

Was - she was retrofitted with diesels in the mid-Eighties...

 

[goldhawk]

To stop a large ship in open ocean, the best way is to use a sea anchor. The fastest way to turn a ship is to run the screws on one side in reverse.

A lot of this depends on the size of the ship. Any clues?

 

[reiver33]

Re. the above link - the largest ship referred to as using a sea anchor is a commercial fishing vessel of 2800 tons. I wasn't aware they could be used on 'large' ships.

 

[goldhawk]

Large ships are a modern phenomenon and are likely to have good sea charts so they can plan their manoeuvres well in advance. During an emergency, they wouldn't have time to deploy a sea anchor. But if your engines are down, a sea anchor will stop you quicker than letting it coast to a stop.

Of course, a lot depends on the size of the ship, where it is (harbour, open ocean, strait), the weather, and what manoeuvre they're attempting.

 

[J-WO]

Pyan's picture of the Dreadnoughts is awe inspiring. Dreadnoughts are the closest thing to Steampunk ever constructed.

(Sorry I'm no help, HB!)

 

[ctg]

Re. the above link - the largest ship referred to as using a sea anchor is a commercial fishing vessel of 2800 tons. I wasn't aware they could be used on 'large' ships.

20 (45km/h) knots aren't really bad. If you're in sea that deepest point is at the 70 meters, then a 200 meter RORO (Roll-On, Roll-Off) can easily slow them down before hitting ice. And if the Titanic would had build to be a ice-breaker then it would had survived the hit.

A battle-ship* (real steamer) would have double hull, and at least meter on reinforced steel at the sides. It would swim deep as you can see from above picture and just slowing down to full stop wouldn't be a real problem. Just that I cannot imagine a sea-captain ordering such a manoeuvre unless someone would be coming on side.

If she would be arriving to a harbour, she would be swimming in less then 8 knots under a coach command. But she would also be flying flags to declare her peaceful intentions (unless she's fighting in same colours).



* Pyan's picture show them swimming around 6 to 8 knots - judging from the white-heads (is that correct word?).

 

[Pyan]

Yes, they're in Chesapeake Bay, either making for home or going out into the Atlantic, so they'd just be cruising at that sort of speed.

(We'd say white-caps, rather than white-heads. And "swimming" isn't used for ships, only living things as a rule. Use cruising at XX knots, or travelling at...)

In contrast, here's a battlecruiser, SMS Von der Tann, at speed (look at the bow-wave!)
27 knots, on four coal-powered Parsons turbines....

Sorry it's not such a good picture, it seems to be a little faded...

 

[HareBrain]

Thanks for all the ideas and help so far.

The smoke question relates to a pre-dreadnought battleship, about 12,000 tons (though J-WO, you're in luck, I do have dreadnoughts in the story too!) and it's in a warm climate, though no one has said whether that will affect smoke visibility, so I assume not, and it will be visible for plenty of miles.

I'm interested in Sue's point about coke burning with almost no smoke, though. Could that be used in a steamship to be less visible?

The stop/start manouevre is for a light cruiser, about 4,000 tons -- and I'm surprised at all the talk of sea anchors, since I thought the easiest way to stop a ship was to just engage reverse. (This isn't an emergency, BTW, but to lower a ship's boat and then make a quick getaway.)

 

[Boneman]

Q3: My only experience in relation to start/stop relates to diesel engined metal hulled support ships for oil rigs in the 70s. About 75 yards long, these little divills would stop so fast by reversing engines that you could be thrown across the room, or deck. So if you're writing a fantasy, there's be nothing to stop your ship having decent gearing (it's only the prop shaft you'll have to stop, to spin it into reverse) so why not have a good gearing system that engages a cog that reverses the propeller?. Or twin engines, one in reverse, one going forward if you just want to turn round...

 

[Susan Boulton]

(This isn't an emergency, BTW, but to lower a ship's boat and then make a quick getaway.)

From what I have read a ship has to stopped dead to lower a boat safely. On a side note look up info on the RMS Lusitania concerning lowering boats while the ship is still moving. They could not stop her and she was sinking fast.

 

[reiver33]

The ability to bring a ship to a halt by means of reverse thrust (engines full astern) is a function of power versus mass. More accurately, it is the ability to deploy that power via the screws to counteract the forward momentum built up over a period of acceleration.

In a modern, lighter vessel, with large diesel engines - especially those designed for towing - you have a huge excess of power which can be readily deployed for a 'crash stop' if required. With old-style heavy metal ships the margin for a quick response is much reduced.

 

[HareBrain]

I've found some data for HMS Hood and other warships of about 1930 that give a time of between 5 and 10 minutes to 15 knots. Is deceleration likely to be faster or slower than that, do you think?

 

[TheEndIsNigh]

HB: On the smoke question.

Is the smoke and visibility required. The ability of warships to 'make smoke' was a tried and tested defence mechanism. It could also be used in offence, in that if you could signal, to someone in trouble - say a freighter being attacked - that the cavalry was on it's way and put the wind up the enemy. I know if I was a pirate in the gulf attacking an oil tanker - Which I seem to remember takes 10 miles to stop - and I saw Pyan's fleet coming I think a hasty retreat would be called for.

Also I would have thought - I claim the patent if it's not been done - that the ship's stabilizers could be deployed to affect a breaking, sea anchor, slow down.

 

[HareBrain]

HB: On the smoke question.

Is the smoke and visibility required. The ability of warships to 'make smoke' was a tried and tested defence mechanism.

I would have thought it was more undesirable -- the ability to see where a distant enemy ship is without giving away your own position would be a huge advantage, surely?

Also I would have thought - I claim the patent if it's not been done - that the ship's stabilizers could be deployed to affect a breaking, sea anchor, slow down.

Stabilizers are too advanced for the tech-level, alas.