Paddleducks
Paddler Information => Research => Topic started by: Roderick Smith on October 12, 2009, 07:44:08 AM
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This is one of our regular rotating title-page photos.
As it flashed by yesterday, I grabbed it.
Something which I had never really noticed with SWPSs before: why is the smokebox right forard, with the drive wheel fully stern?
How was the transmission effected?
The effect shows very clearly in this photo of SWPS Captain Sturt, one of a folio to which the link was given in a separate thread: http://images.slsa.sa.gov.au/mpcimg/10000/B9965.htm
Is the boiler well forwards for weight balance? for fire safety? for convenience of refuelling? for cooling breezes to keep the engineer from overheating?
Is the engine well astern, with long steam lines from the boiler? That seems very inefficient for use of crew, requiring an engineer to be on duty at each end. It would also result in some energy loss.
Is the engine adjacent to the boiler, but with very long chain drives? That seems very inefficient for energy loss.
What design considerations prevented the boiler and engine being well to the rear?
Regards,
Roderick B Smith
Rail News Victoria Editor
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Hi,
Balance.
Because of the requirement for a shallow draft, the boiler was well forward and the machinery well aft.
Most of the early NZ sternwheelers where thus. Even the last stern paddler on the Waikato River (ps Rawhiti at 300 feet long) had a similar arrangement, and she was built between the wars in 1924.
cheers
kiwi
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With the boiler forward, and the machinery aft, I presume that there were long steam lines.
There would be one engineer (effectively a stoker, also checking water feed) with the boiler, and another astern (lubricator and setting the power and forward/reverse according to bells from the bridge).
Most larger river sidewheelers seem to have two engineers, but smaller ones would run with just one. I haven't been on any paddleboat sufficiently large to warrant three or four engineering crew.
Post edit: What happened to the exhaust steam? There must have been an equally long pipe to bring it back to the boiler to provide the draft, and the familiar 'chuff chuff' noise.
Regards,
Roderick B Smith
Rail News Victoria Editor
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In many cases (I wouldn't presume to say every, or even most cases) exhaust steam was simply lost up the escape pipes - on this model the two shorter, thinner pipes ahead of the paddles and painted the same colours as the smokestacks...
*edit - see this in action on the Julia Belle Swain - http://www.youtube.com/watch?v=ScwIbdM2H8A&feature=related
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...I just had a re-read of http://twaintimes.net/ and it says there that the older boats had a 'non-condensing' boiler/engine setup (and the boiler feed pump used river water to maintain boiler water level) but later ones had a condenser to re-use the spent steam - it didn't make clear wether the steam was ever piped up the smokestack to produce draft for the fires....
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Thanks for the replies so far.
They will lead to further questions.
It is interesting that the model was a sidewheeler, and its boiler was further aft: using exhaust steam for draft would have been quite easy, but perhaps the original had a marine boiler?
A fresh insight came from the video clip: was a Pitman arm direct acting from the piston? The cylinders had to go stern.
In railway boilers, exhaust steam is always used for creating draft, with cunning smokebox design. That could be because a railway boiler is long and thin, and marine boilers usually were not. A boiler would have a blower ring to maintain draft during lighting up when there was no exhaust steam to do the job, and insufficient fire for heat alone to provide the flow. Condensing locos were not common: the most-famous class of these was in South Africa, for desert hauls. They had full-time fans to maintain draft, and sounded quite different from conventional steam locos.
All of the river paddlesteamers on which I have travelled in Australia have noncondensing boilers, and an audible exhaust beat. This is not as loud or crisp as a railway one, as riverboats run at lower pressures. Also, many are compound.
The condensing steamboats on which I have travelled have mainly been tugs with marine boilers: conceivably forced draft isn't required.
In the classic Australian design (nearly all were sidewheelers), the smokebox was almost back to the paddleshafts, and the pistons were almost in line (mix of direct drive, chain drive and geared drive). This put the firebox leading, providing two advantages: ready access to a large hold for the billets of wood for firing (nearly all were wood; I can't recall a coal one, and only a couple of oil-fired ones); plenty of fresh air to keep the engineer cool in our hot climate. Noticeably, engine rooms were open to the front, whereas North American ones were enclosed for the colder climate.
PS Waimarie (NZ) had an enclosed engineroom. It was also coal fired, using side bunkers.
Regards,
Roderick B Smith
Rail News Victoria Editor
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.... was a Pitman arm direct acting from the piston?....
Yes, I believe it was, the twaintimes site has an animation showing how the engine worked - http://twaintimes.net/boat/sbpage3a.html - and the pitman arm is shown as being connected to the 'sliding bit' (crosshead?) where waverley etc. have the connecting rod.
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The NZ paddle steamers usually where non-condensing, makeup direct from the river and steam exhaust overboard directly from the engine. Aussie steamers usually used loco type boilers (from steam traction engines) as opposed to the marine type used in NZ
kiwi
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The str. Golden Girl was an American boat around the turn of the century. I've been trying to fid an article I had on her, but seem to have misplaced it. I'll keep looking.
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Although most has already been said in this thread, let me try to summarize a few facts:
why is the smokebox right forard, with the drive wheel fully stern?
How was the transmission effected?(...) Is the engine adjacent to the boiler, but with very long chain drives?
Nope. Quoting the Marine Iron Works of Chicago (the former market leader for stern wheelers), "There is but one safe and certain method of turning and reversing the paddle wheel, and that is by two direct acting long-stroke engines". This means, the pistons act directly (via the pitman arms) onto the wheel shaft.
What design considerations prevented the boiler and engine being well to the rear?
The heavy cast iron cylinders on the sternmost end of the hull and the very heavy sternwheel, extending even beyond the hull on cantilever wheel timbers, both create a very strong backward momentum. This had to be compensated by putting the boiler to the foremost part of the hull in order to get the thing balanced.
Now you have the two heaviest parts of machinery at either outermost end of the hull, whereas the center of flotation is in the middle. This would lead to high stress and cause the hull to buckle (especially the wooden flat bottom hull of sternwheelers) if it wasn't strengthened by the typical and sometimes sophisticated system of hog chains and hog posts, forming a big girder truss. The weight of boiler and engines was partially supported by the diagonal hog chains, and transferred by the posts to the center of the hull.
With the boiler forward, and the machinery aft, I presume that there were long steam lines.
There would be one engineer (effectively a stoker, also checking water feed) with the boiler, and another astern (lubricator and setting the power and forward/reverse according to bells from the bridge).
Most construction drawings by M.I.W. for small to medium size sternwheelers show the reverse lever quadrant in the boiler pit, besides the fire door. From there a long linkage acted on the actual valve gear of the engines. So in the extreme case, one man could both stoke the fire and operate the engine (and if you ever watched Steamboat Bill by Buster Keaton, he could even put the helm at the same time... ;))
In railway boilers, exhaust steam is always used for creating draft, with cunning smokebox design. That could be because a railway boiler is long and thin, and marine boilers usually were not.
On sternwheelers, locomotive type boilers were as common as Scotch or Clyde type marine boilers. But locomotives have very short stacks for obvious reasons, so forced draft is needed. Tall stacks, however, is kind of a synonym for riverboats. So these don't necessarily need artificial draft, proven by those riverboats (especially of the Mississippi type) with exhaust pipes.
These exhaust pipes aren't visible on the western Canadian steamboats however. An explanation might be what Jack Boudreau writes: "Most sternwheelers discharged their steam directly into the smokestack, creating a draft similar to a forge. For this reason these vessels were able to burn damp to wet wood picked directly off the bars along the rivers."
What happened to the exhaust steam?
Apart from cost or local preference, it was mainly a question of water quality whether the steam became exhausted or condensed. Again quoting the M.I.W.: "When the feed water is salt or brackish it is often advisable to use condensing apparatus with engines of the horizontal tandem compound design (...).The use of it affects the size of boiler and some of the auxiliaries, and being itself an item of expense makes our calculations as to cost of outfit quite different from those intended for boats plying on on good fresh water."
Regards, Moritz
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Just as I felt that all of my questions had been answered clearly and thoroughly, a couple more emerge.
If the western Canadian paddlesteamers were using exhaust steam for draft, how did it get from the cylinders back to the smokebox: another long steam line, but at much-reduced pressure?
If reversing could be handled by the stoking engineer via a long linkage, what stopped the linkage running from the wheelhouse instead? Just a century of tradition? Now it isn't just diesel boats with direct control from the bridge; the rebuilt Swiss lake paddlesteamers use remote control oil fire from the bridge, as well as speed & direction. There must still be a lubrication engineer in the engine room.
Even sidewheelers must have had some long steam lines: to auxiliary engines driving winches (usually foredeck), to power-assisted steering (not common), and possibly also to the galley. I guess that any electrical generator could be fitted into the main engine room, alongside the boiler.
Regards,
Roderick B Smith
Rail News Victoria Editor
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Hi PD's....I believe the engines were double acting...so exhaust steam from an extension stroke is ported to an exhaust chamber & LP pipework to the funnel. then the exhaust steam from the retraction stroke is ported to the same exhaust chamber & LP pipework to the funnel - Derek
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If reversing could be handled by the stoking engineer via a long linkage, what stopped the linkage running from the wheelhouse instead? Just a century of tradition?
That question had also come to my min. Just a few guesses:
- The reverse linkage can run from the boiler pit straight beneath the deck to the engine. From the wheel house, it would be longer and more complicated with redirections.
- The reverse lever and the regulator (or throttle) valve have to be at the same place! To operate also the throttle from the wheelhouse, you would either need another long linkage down to the boiler, or to run the main steam line up to the wheel house, and down and back again to the engine, which would add much length. It seems more logic to me to keep the regulator right at the boiler.
- A conventional boiler has to be manned anyway, for stoking and feeding water. You would not save a hand by simply relocating the reverse lever to the wheelhouse.
- I think it makes sense to concentrate the control over the lateral motion in one place, and over the longitudinal motion in another. And maybe this division of labor had really something to do with tradition?
Regards, Moritz
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This has been a very educational thread. Thanks to all the people who supplied the answers.
I checked one aspect with the railway hobby.
A Garratt was a very long articulated loco, with the rear cylinders quite remote from the smokebox.
Even so, the exhaust steam was piped back to the smokebox to join the exhaust steam from the front cylinders and pass through the blastpipe.
In both this and the sternwheeler cases, there must have been sufficient pressure that the length of the pipe wasn't a problem, and neither was condensation.
Regards,
Roderick B Smith
Rail News Victoria Editor
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Roderick...invariably...be it rail or water...any [full sized] steam engine exhausting spent steam to the chimney would have a blown down valve to drain condensate at the engine or lowest point - Derek
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SWPS Alexander Mackenzie came up on the random opening screen this morning. I couldn't see any exhaust flue, and suspected western Canada (miscued by Mackenzie River, and an early prime minister). Not so: it was Ohio River.
See also
http://images.indianahistory.org/cdm4/item_viewer.php?CISOROOT=/V0002&CISOPTR=905&CISOBOX=1&REC=1
also in the same collection, PS America, almost a quarterwheeler
http://images.indianahistory.org/cdm4/item_viewer.php?CISOROOT=/V0002&CISOPTR=851&CISOBOX=1&REC=6
The funnel is quite remote from the paddles
Regards,
Roderick B Smith
Rail News Victoria Editor
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...probably 'doing this to death' here but I found a few more pics of boats that have escape pipes not condensers...
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I must check Kiwi here, Rawhiti was 190' B.P.203' length on deck and another 23' over the fantails. The boiler is carried as far foreward as possible for trim as it is easy to bog the wheel down and makes steering much easier and responsive.Just keep her head down and bum up. There are or were pics on here somewhere of a boat down on the Murray stated as the slowest thing afloat (diesel powered) with her bows pointing to the sun, I bet if you trimmed her down she would be a different ship.The engine exhausts generally had a cutout directly overboard so when starting from cold the condensate was blown straight out but after warming through exhaust steam was gradually bled to the funnel line and up the stack, and on the waikato boats, when the funnel was lowered for bridges the exhaust was sent back thru the o/b discharge. I really don't think the engine crew were considered at any time but the firebox and bunkers foreward made most sense when you nosed into the bank and wooded up.I don't know of any woodfired boats in N.Z. only coal burners but they were still bunkers foreward. Ray
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Thanks Ray for the correction. Slip of the finger, while half asleep. (which is nearly all the time at present).
cheers
kiwi
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no sweat mate, on your drawings of" Manuwai" in waikato style you may want to include the towing mast and engine frame extensions allowing two more rudders aft of the wheel, these were post 1928 mods when "Free Trader " was stripped down to a barge and was to be Manuwai's dedicated companion. Also she had staggered floats. This stopped wheel slap and vibration. And if Roderick reads this, the "Rawhiti" worked between Port Waikato and Hamilton, designed principaly for trans-shipping general freight from Port Waikato but also as a tug, I have seen her with up to 5 barges alongside.Manuwai also spent her final years as a push tug.
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Hi Ray,
Thank you once again. I will certainly have to do a bit more research and add the mods to Manuwai. Will be doing drawings for the Rawhìti2 next year, as well as the Freetrader. Measured them both up earlier in the year, and will be doing so again in the new year to fill in the bits I missed.
kiwi