Marine steam engines

[Mark F. Jenkins]

I must confess that formerly, I had less interest in the steam engine part of a steamer... I usually glanced past it, my eye attracted more strongly to the casemate, armor, and gun (thinking here especially of my viewing the Cairo at Vicksburg). But as I've started to learn more about steamboats and steamships in general, I've begun to realize that this was a rather sizable hole in my understanding!

Years ago, I'd read Louis C. Hunter's magisterial Steamboats on the Western Rivers, but not much had stayed with me. It was actually my ride last year on the Belle of Louisville that got me thinking more about it. I re-read Hunter and began collecting some books here and there on the topic.

I bring this up because currently, I'm reading James H. Ward's Steam for the Million, a book with a double attraction: first, because the author was a U.S. naval officer (killed early on in action along the Potomac), and second, because he was consciously writing a text to be an introduction to steam engines for non-engineers. His intended audience may actually have been fellow (non-engineer) naval officers, but either Ward or the publisher saw a potentially larger audience, hence (perhaps) the title. Anyway, I just came to the realization, thanks to Commander Ward, that the steam drum and the steam chest are two separate structures. I had always assumed that they were two names for the same thing. (D'oh!)

Ah, well. If I knew it all already, it'd be dull.

(Reading plan ahead: move on to Alan L. Bates Western Rivers Engineroom Cyclopoedium, and then to a set of biographies-- Benjamin F. Isherwood, James B. Eads, and John M. Brooke.)

 

[AndyHall]

Bates is outstanding, although you should also look for his Western Rivers Steamboat Cyclopoedium, which although intended for modelers, is a top-to-bottom guide to how the real boats were built.

Hunter also wrote a book, Steam Power, that was (and probably still is) a classic industrial history, although it does not focus on marine application per se.

 

[Mark F. Jenkins]

Yeah, I have the "Steamboat Cyclopoedium" on my Wish List. The one I have (Engineroom Cyclopoedium) I actually picked up in the gift shop at the Howard Steamboat Museum in Jeffersonville... I noticed last night that it's a first edition, though I'm not sure if that's notable in this case or not.

 

[Mark F. Jenkins]

Another interesting note in Ward's book was his discussion of converting a low-pressure condensing engine into a high-pressure engine simply by disconnecting the condenser.

Some of the science in Ward is questionable-- there's a lot of discussion of "caloric," for instance-- and it's in the usual sort of needlessly-flowery 19th century language, but it's actually a quite good basic intro to the topic. (There's also a notable reference to John Ericsson, a year or two before his name became a household word because of USS Monitor, and both his "caloric engine" experiments and his screw propeller.)

E-book: http://books.google.com/books?id=12dCAAAAYAAJ&dq=Ward "steam for the million"&source=gbs_navlinks_s

(I had to score an original copy, being addicted to actual books...)

 

[yankee hoorah]

Wish I knew more on the topic....

 

[Mark F. Jenkins]

Well, maybe I'll take some notes and present them here... "Steam Engines for the Uninitiated" or something like that. We can learn together.

(I'm not an expert. If anyone spots an error, please let me know...)

 

[Mark F. Jenkins]

Starting with the logical place... the boiler. One has to make the steam to begin with, in order to use it.

1. Grate bars and ash pan
2. Furnace
3. Flue
4. Return flue (when present)
5. Smoke box
6. Smoke pipe or chimney
7. Water level
8. Water bottom (when present)
9. Steam room

9a. Steam chimney (when present)
9b. Steam drum (when present)
9c. Steam dome (when present)
​

[Diagram adapted from James H. Ward, Steam for the Million, pp. 39-40]

There were many different configurations of boiler; this is a very generalized and simplified diagram. The earliest boilers were simple containers for water heated over a flame, but as demands and sophistication increased, variations began to appear. The general type shown is a "fire-tube" boiler, where metal flues or pipes containing hot gases from the furnace are routed through the body of the boiler, increasing the heating surface area inside. The flue might simply go through the boiler once, or loop back again, depending on the design.

In some designs, a "steam chimney" abutted or surrounded the smoke pipe/chimney to utilize remaining heat that otherwise would be lost up the chimney. Likewise, in some arrangements, a "water bottom" would abut or surround the furnace, both partly insulating the furnace and also capturing heat that might otherwise be wasted. Although fuel efficiency was not the most important factor in most engine designs, there were some steps taken in that direction.

Boiler management was generally the province of the class of engineers known as "firemen," but responsible chief engineers kept a close eye on the boiler too. As well as being the principal source of power for the vessel, the boiler was also by far the greatest source of potential danger. Weaknesses in design or construction, boilers in poor repair, and inattention to proper water levels could all result in a catastrophic explosion, particularly in the non-condensing "western rivers" type engines which typically ran at very high steam pressures.

The principal method of monitoring the water level in the boiler was a series of valves, typically three, known as "try-cocks" or "gauge-cocks," with one mounted above the optimum water line, one at the line, and one below the line. Opening the valves briefly was a rough method of estimating the water level within the boiler, and the goal was to keep it consistently at or near the optimal level. Introducing too much new water into the boiler at any given time could cause a number of problems, not the least of which was decreasing overall average temperature in the boiler and thereby losing power, so ideally water was added at the same rate that it was lost.

Boilers had to be cleaned periodically; sediments, salts, and minerals would tend to boil out of the water and build up on the walls, forming what was known as "scale." Scale both reduced boiler efficiency and increased the risk of explosion, so regular maintenance and cleaning was vital.

Boilers had practical upper limits in terms of size and weight; by the Civil War, most steamers had multiple boilers, the steam from which was collected through a common connection or manifold known as a steam drum. This often looked like an additional boiler, sometimes of smaller diameter, lying crosswise (athwartship) and on top of the other boilers.

 

[Mark F. Jenkins]

What with the importance of getting the right amount of water into the boilers at the right rate, the feedwater system should be covered next…

1. Sea Chests
2. Cold Well
3. Strainer
4. Pump
5. Feedwater Heater
6. Expansion Loop
7. Boiler Battery
8. Hand Pump
9. Donkey (auxiliary) Boiler

Water is drawn in from the outside of the vessel through screens via the "sea chests" and into the cold well. A pump draws the water through a strainer system and forces it into the feedwater heater (for several reasons, it is desirable that the water be heated prior to being introduced into the boilers). Piping conveys the pre-heated water to the boilers, where it is injected or pumped in. Due to the expansion and contraction of pipes, boilers, and other components from heat, allowance must be made for components changing alignment with each other slightly; constructions like the expansion loop in the pipe allow leeway for this. An auxiliary boiler, usually of simpler design than the main boilers, is used as necessary, both for feedwater and for other uses.

[Diagram adapted from Alan L. Bates, Western Rivers Engineroom Cyclopoedium, p. 26]

 

[Mark F. Jenkins]

And a bit about the nature of steam itself...

We're all familiar with steam in the settings of cooking, steam-rooms, and other "ordinary" manifestations; what's important to remember is that steam has some properties that are important to its role in propulsive systems.

Most know that, at different altitudes, water boils at lower temperatures due to the reduction in ambient air pressure. At about 2,000 feet (600 meters) above sea level, the boiling point is approximately 208 degrees (98 Celsius), rather than the more familiar 212 (100) degrees. With higher pressure, the boiling temperature increases.

In a boiler, especially a high-pressure boiler like a Western Rivers-style steamboat used, the water temperature was heated to well above what we would think of as "boiling point," but it was held largely in liquid state by pressure. If a boiler in operation was made of transparent material, you would see a seething (but not bubbling) mass of water with a clear, apparently empty space above it. However, this space was not empty, but filled with high-pressure, noncondensed steam; steam (and water vapor in general) only becomes visible when it cools and condenses into small droplets, which it could not do under the conditions within a working boiler.

If you were to suddenly make a hole in the boiler at this time, not only would the steam-under-pressure in the top of the boiler suddenly escape and expand through the room, but a large measure of the water that had been held in its liquid state by pressure would suddenly expand into steam as well. This gives an idea of the problem confronting engineers (and steamboat passengers and crew) when a weak point in a boiler failed; the steam would expand to many times its liquid volume, spreading throughout the ship at high speed.

On the other hand, when taken out of the boiler under controlled conditions, steam could be made to work. The same powerfully-expansive (or "elastic") nature of steam was what made it capable of driving a piston in a cylinder.

 

[Mark F. Jenkins]

As mentioned above, steam engines, particularly the ones used on the western rivers, were not especially efficient. A steamer that turned as much as 5% of its heat energy into propulsive force was extremely efficient. Adapted from a chart in Alan L. Bates' Western Rivers Engineroom Cyclopoedium, p. 13:

From this, it can be seen that only about a quarter of the heat energy from burning fuel was turned into useful work (a certain amount, 12.8% in the above chart, being used to keep the fires going). About another quarter was wasted in the process, and half was simply thrown away.

 

[DaveBrt]

Excellent explanations, Mark.

 

[Mark F. Jenkins]

If you get into the topic any distance, you'll rapidly come into contact with the terms "high pressure engine"/"low pressure engine" and "condensing engine"/"noncondensing engine". Ignoring a few spurious cases (and it was a period of experimentation, so there were lots of variations), in a nutshell, it comes down to this:

A "low pressure" engine was a "condensing" engine. The steam, at higher than atmospheric pressure, was sent into the cylinder, then, upon being taken out, was sent through a condenser, an apparatus to cool it down. This condensation caused a reduction in pressure. The pressure differential (the higher of the new steam, and the lower of the being-condensed-steam) drove the piston, as it were, one side pushing and the other pulling. The condensed steam was routed back into the boiler and cycled through the system again.

A "high pressure" engine was a "noncondensing" engine. The steam, at much higher than atmospheric pressure, actually drove the piston in the cylinder (just a push, no pull), and upon exhaust, was sent up into the atmosphere.

There were pluses and minuses to both types. The low-pressure/condensing engine was somewhat safer (due to lower pressures being involved, boiler failures were less common and less catastrophic when they occurred) and more economical, since less water and less heat energy was thrown away in its operation. On the other hand, the extra equipment meant extra weight and expense, and also meant more equipment to maintain and repair, being a more complex machine.

The high-pressure/noncondensing engine was more lightweight and had fewer parts involved, so it took up less weight/room that could be used for cargo, and was simpler and cheaper to build and maintain. But it could be more dangerous, and was less efficient, requiring more fuel for the same work, as well as a constant large-scale supply of water.

As a result of these pros and cons, the two types of engine found their niches... on the seaboard and on the oceans, where larger vessels operated over longer distances, the problems associated with condensing engines were relatively minimized, and the strengths, particularly in terms of economy, were more important. On the rivers, with plenty of fuel and fresh water at hand, economy was less important, but since the vessels had to be smaller and lighter, every ton of engine meant a ton of cargo that couldn't be carried... so the high-pressure engine was more advantageous. (This was also true of locomotive engines, for the same reasons, and so these were also high-pressure/noncondensing.)

This was not an invariable rule, and some engines of each type found their way into the other environment, but they were then at a relative disadvantage.

 

[rebelatsea]

Don't forget Mark ,that at the time frame we are in "engine" always meant one cylinder, so if a ship had "engines" it had two cylinders - or more.

 

[vikingbear]

Excellent explanations, Mark.

Agree with you DB.
Picked up a several books in a second hand store a couple of years ago and one turned out to be about steam (hay was short on time). Still have it , but after a quick skim haven't been brave enough to dive in, was impressed though about river boat boilers and how they use a simple acid mix to bond or repair boilers.

GRIZZ
(well back to the "ic e box"!)

 

[Republican Blues]

This is a fascinating subject!! the netherworlds of the engineering spaces were a place I have not learned much about and this is a good tutorial! awesome stuff...

Now as to our instructor...

Hello Engine... Im Mark Jenkins.