Hello everyone!
I wanted to ask the steamboaters out there about their experiences with different firetube boiler designs. I see that a lot of the firetube operators use a vertical firetube design. Anyone using a locomotive type, or Cochran type? I am curious about the different qualities that they possess. Does a VFT generally draft better than a locomotive type? Does a locomotive boiler generally have a lower center of gravity than a VFT, or Cochran?? Please steep me in your boiler knowledge. Thank you!
Sean
Opinions concerning firetube boilers
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- Lopez Mike
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Re: Opinions concerning firetube boilers
There are all sort of technical considerations as to the different designs. Most are valid.
For me, my choice was determined by the appearance on the market of a junk hull with essentially new machinery. Cheap. And that included a VFT boiler. In other words, historical reasons.
I've had good service out of this unit. Steams fine. Is forgiving and relatively easy to keep on top of. There is something to be said for plenty of reserve water. I gave the old hull and trailer to a local farmer and he is using it to haul cow poop about. Quite appropriate!
One factor I haven't heard much about is real estate. These are mostly small boats and most of us like to take people for rides. My VFT takes up less valuable space than any other design I've seen. A locomotive/scotch design restricts somewhat your choice of firebox door location. Trying to get solid fuel into the firebox with other equipment in the way is frustrating.
A down side of fire tube boilers in general is weight. Water and steel are heavy and the hoop stresses in the shell make for thick walled structures. My 30 sq. ft. boiler weighs around 400 pounds. The weight of two largish passengers.
Since it seems that you are without boat and thinking of getting one, look carefully at the used offerings. I see several boats for sale at far below the purchase price for the parts. And your time has to be worth something.
Mike
For me, my choice was determined by the appearance on the market of a junk hull with essentially new machinery. Cheap. And that included a VFT boiler. In other words, historical reasons.
I've had good service out of this unit. Steams fine. Is forgiving and relatively easy to keep on top of. There is something to be said for plenty of reserve water. I gave the old hull and trailer to a local farmer and he is using it to haul cow poop about. Quite appropriate!
One factor I haven't heard much about is real estate. These are mostly small boats and most of us like to take people for rides. My VFT takes up less valuable space than any other design I've seen. A locomotive/scotch design restricts somewhat your choice of firebox door location. Trying to get solid fuel into the firebox with other equipment in the way is frustrating.
A down side of fire tube boilers in general is weight. Water and steel are heavy and the hoop stresses in the shell make for thick walled structures. My 30 sq. ft. boiler weighs around 400 pounds. The weight of two largish passengers.
Since it seems that you are without boat and thinking of getting one, look carefully at the used offerings. I see several boats for sale at far below the purchase price for the parts. And your time has to be worth something.
Mike
If you think you are too small to make a difference, try sleeping with a mosquito.
Dalai Lama
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- fredrosse
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Re: Opinions concerning firetube boilers
Cochran type boilers, typical to many of the UK “puffers” of the last century are generally considered a manufactured type boiler. While practical, they would generally be a difficult build as a miniature “one-off” project for a steamboat.
The easiest boiler is the Vertical Fire Tube (VFT) with the simplest arrangement having just a group of firetubes, without an enclosed firebox. This mimics the typical Stanley steam car type boiler, with tube sizes according to the fuel used. The Stanley boilers had hundreds of 1/ 2 inch diameter tubes, about 15 inches long, with a kerosene burner under the boiler. My sidewheeler has a similar boiler, but with 48 x 18 inch by 1-1/ 4 inch tubes for wood or coal firing. I ended up with Propane firing, but that works OK too. For firing liquid or gas fuels, this simple type VFT is the most practical for a steam launch and is the easiest to build.
For solid fuel firing, a much better arrangement is for a VFT with a wet firebox below the tube bundle. This allows the enclosed fire to give plenty of radiant heat to the boiling water and is most practical for solid fuel firing. This is probably the most practical type of boiler for a solid fuel fired steam launch. Generally having a large water inventory, these don’t need frequent attention as to maintaining the water level, as well as attending the fire.
Another variant of the firetube boiler is the locomotive (or Gunboat) type of boiler. Technically very similar to the VFT with a firebox, they perform similarly, with the advantage of a lower center of gravity, but a somewhat more difficult build process. Another practical firetube boiler is the Scotch Marine boiler, where the tube pass is a 180 degree reversal of the flue gas passage, as opposed to the loco boiler’s straight thru one direction flue gas flow path. While several of these boiler types are found on UK steamboats, I have not seen them used in the USA steamboats, with only rare exceptions.
As far as watertube boilers go, there are a large number of configurations, and the main advantage is that the heat transfer surface area presented to the hot flue gas is around twice as effective as the firetube configuration. Design thumb-rules dictate that 10 square feet of heat transfer surface area is needed per “boiler horsepower” with firetubes, vs 5 square feet required with a watertube boiler.
The watertube boiler designs generally carry a much smaller water inventory, so they need constant attention to properly maintain water level and firing rate. Automatic controls (electric, electronic, or straight mechanical) can solve these difficulties with proper design features and can be simple if liquid or gaseous fuels are fired.
The design complications are somewhat addressed in this forum’s topic “Bolsover Boiler?”, have a look to get some perspective here about Bolsover and Oldfelt types, potentially good canidates for steamboat boilers. There are dozens of watertube boiler configurations, and several satisfactory designs available for steamboat builders. In general, I think building a watertube boiler is far too much work compared to just building a firetube type with extra surface area. Having said that, I note that my other steamboat has a monotube boiler (yet another watertube boiler configuration), with quite healthy oil firing and high steam generation rate. More details can be found on this forum topic “Monotube Javelin”.
With respect to flue gas draft issues, any of the boiler types can be designed to work well, and this entirely depends on combustion air inlet, and the flue gas flow area through/around the tubes, and the effective stack height.
The easiest boiler is the Vertical Fire Tube (VFT) with the simplest arrangement having just a group of firetubes, without an enclosed firebox. This mimics the typical Stanley steam car type boiler, with tube sizes according to the fuel used. The Stanley boilers had hundreds of 1/ 2 inch diameter tubes, about 15 inches long, with a kerosene burner under the boiler. My sidewheeler has a similar boiler, but with 48 x 18 inch by 1-1/ 4 inch tubes for wood or coal firing. I ended up with Propane firing, but that works OK too. For firing liquid or gas fuels, this simple type VFT is the most practical for a steam launch and is the easiest to build.
For solid fuel firing, a much better arrangement is for a VFT with a wet firebox below the tube bundle. This allows the enclosed fire to give plenty of radiant heat to the boiling water and is most practical for solid fuel firing. This is probably the most practical type of boiler for a solid fuel fired steam launch. Generally having a large water inventory, these don’t need frequent attention as to maintaining the water level, as well as attending the fire.
Another variant of the firetube boiler is the locomotive (or Gunboat) type of boiler. Technically very similar to the VFT with a firebox, they perform similarly, with the advantage of a lower center of gravity, but a somewhat more difficult build process. Another practical firetube boiler is the Scotch Marine boiler, where the tube pass is a 180 degree reversal of the flue gas passage, as opposed to the loco boiler’s straight thru one direction flue gas flow path. While several of these boiler types are found on UK steamboats, I have not seen them used in the USA steamboats, with only rare exceptions.
As far as watertube boilers go, there are a large number of configurations, and the main advantage is that the heat transfer surface area presented to the hot flue gas is around twice as effective as the firetube configuration. Design thumb-rules dictate that 10 square feet of heat transfer surface area is needed per “boiler horsepower” with firetubes, vs 5 square feet required with a watertube boiler.
The watertube boiler designs generally carry a much smaller water inventory, so they need constant attention to properly maintain water level and firing rate. Automatic controls (electric, electronic, or straight mechanical) can solve these difficulties with proper design features and can be simple if liquid or gaseous fuels are fired.
The design complications are somewhat addressed in this forum’s topic “Bolsover Boiler?”, have a look to get some perspective here about Bolsover and Oldfelt types, potentially good canidates for steamboat boilers. There are dozens of watertube boiler configurations, and several satisfactory designs available for steamboat builders. In general, I think building a watertube boiler is far too much work compared to just building a firetube type with extra surface area. Having said that, I note that my other steamboat has a monotube boiler (yet another watertube boiler configuration), with quite healthy oil firing and high steam generation rate. More details can be found on this forum topic “Monotube Javelin”.
With respect to flue gas draft issues, any of the boiler types can be designed to work well, and this entirely depends on combustion air inlet, and the flue gas flow area through/around the tubes, and the effective stack height.
- Lopez Mike
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Re: Opinions concerning firetube boilers
Dead on. As usual.
A consideration, which Fred touched on, is how much attention do you want to pay to your power plant? At first, it seems like that's all steaming is about. On the work bench it's great fun to turn a valve and have this interesting and sometimes complicated mess of machinery react. Fiddling with knobs is fascinating.
But out on the water it's a different situation. The chief engineer is almost always the skipper as well. Navigating. Being a tour guide. In charge of safety for your passengers. Way down on the list of things that you want clamoring for your attention are water level and steam pressure. And the more stable these are, the better and safer job you can do about navigation and whatever else crops up, often with little notice!
As the pilot of that airplane that was so skillfully landed on the Hudson River explained, your priorities must be, "Aviate, navigate, communicate. Since we seldom need to aviate (barring a boiler explosion!), are legally and morally obligated to navigate and usually enjoy communicating with guests, anything that makes your engineering tasks less of a fire drill (joke intentional) is to be welcomed.
Personal prejudices:
I would rather give boat space to a pressure washer, a microprocessor or a wolverine on meth than endure a bipolar and/or mercurial steam generator. Surprises of any sort are unwelcome. If I'm startled or inconvenienced by the behavior of any part of my boat, I redesign or replace. For me, steaming is about relaxation not adrenaline rushes!
Mike
A consideration, which Fred touched on, is how much attention do you want to pay to your power plant? At first, it seems like that's all steaming is about. On the work bench it's great fun to turn a valve and have this interesting and sometimes complicated mess of machinery react. Fiddling with knobs is fascinating.
But out on the water it's a different situation. The chief engineer is almost always the skipper as well. Navigating. Being a tour guide. In charge of safety for your passengers. Way down on the list of things that you want clamoring for your attention are water level and steam pressure. And the more stable these are, the better and safer job you can do about navigation and whatever else crops up, often with little notice!
As the pilot of that airplane that was so skillfully landed on the Hudson River explained, your priorities must be, "Aviate, navigate, communicate. Since we seldom need to aviate (barring a boiler explosion!), are legally and morally obligated to navigate and usually enjoy communicating with guests, anything that makes your engineering tasks less of a fire drill (joke intentional) is to be welcomed.
Personal prejudices:
I would rather give boat space to a pressure washer, a microprocessor or a wolverine on meth than endure a bipolar and/or mercurial steam generator. Surprises of any sort are unwelcome. If I'm startled or inconvenienced by the behavior of any part of my boat, I redesign or replace. For me, steaming is about relaxation not adrenaline rushes!
Mike
If you think you are too small to make a difference, try sleeping with a mosquito.
Dalai Lama
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- barts
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Re: Opinions concerning firetube boilers
Another traditional fire tube steam boat boiler is the Scotch boiler; in small boats these are typically dry-back.
These are more compact than the loco or gunboat designs, and don't require stays for the same reason that a vertical fire tube boiler does not - the tubes act as stays.
A disadvantage of fire tube boilers is that they're slower to raise steam, both because the increased water volume and because the circulation (natural convective currents causing water mixing and temperature equalization) is slower than in water tube boilers. The heat transfer rates in boilers is largely determined by the velocity of fluid flows, both on the water and the fire sides of the tubes, since the film effects at the tube walls present far more resistance to heat transfer than the metal, and higher speeds means thinner boundary layers and better mixing.
Personally, I find the stability and placid behavior of a firetube boiler much better for single operator boats; if one is lucky enough to have a competent helmsman one can spend more time managing the power plant. It's easier to relax with the fire tube boiler.
- Bart
These are more compact than the loco or gunboat designs, and don't require stays for the same reason that a vertical fire tube boiler does not - the tubes act as stays.
A disadvantage of fire tube boilers is that they're slower to raise steam, both because the increased water volume and because the circulation (natural convective currents causing water mixing and temperature equalization) is slower than in water tube boilers. The heat transfer rates in boilers is largely determined by the velocity of fluid flows, both on the water and the fire sides of the tubes, since the film effects at the tube walls present far more resistance to heat transfer than the metal, and higher speeds means thinner boundary layers and better mixing.
Personally, I find the stability and placid behavior of a firetube boiler much better for single operator boats; if one is lucky enough to have a competent helmsman one can spend more time managing the power plant. It's easier to relax with the fire tube boiler.
- Bart
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Bart Smaalders http://smaalders.net/barts Lopez Island, WA
Bart Smaalders http://smaalders.net/barts Lopez Island, WA
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Re: Opinions concerning firetube boilers
Thank you all for the detailed information. I originally did not mention Scotch marine boilers under the assumption that they were impractical for small steamers. After I made the first post, I went to check the mail, and had received my first issue of Steam Gage. Ironically I found an article about a dry back Scotch marine boiler build! I do like the idea that the flue gases get a second pass before going up the stack. The author does mention that the weight put his launch below the designed waterline, perhaps that falls more under qualifying the right powerplant for the boat? Said it "steams like a witch", must be a good thing, so steam generation does not seem to be an issue.
Do any of the aforementioned designs have any liking to a particular fuel? Thanks again for the information.
Sean
Do any of the aforementioned designs have any liking to a particular fuel? Thanks again for the information.
Sean
- fredrosse
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Re: Opinions concerning firetube boilers
"Do any of the aforementioned designs have any liking to a particular fuel? Thanks again for the information."
From a previous post: "For firing liquid or gas fuels, the simple type VFT is the most practical for a steam launch and is the easiest to build." Generally this type boiler is less suited to solid fuel firing, as a firebox with high temperature insulation, or firebrick furnace enclosure is required. Having a furnace inherently close to the bottom of a small boat requires special design considerations.
"For solid fuel firing, a much better arrangement is for a VFT with a wet firebox below the tube bundle. Another variant of the firetube boiler is the locomotive (or Gunboat) type of boiler. Technically very similar to the VFT with a firebox, they perform similarly, with the advantage of a lower center of gravity, but a somewhat more difficult build process. Another practical firetube boiler is the Scotch Marine boiler, where the tube pass is a 180 degree reversal of the flue gas passage, as opposed to the loco boiler’s straight thru one direction flue gas flow path."
From a previous post: "For firing liquid or gas fuels, the simple type VFT is the most practical for a steam launch and is the easiest to build." Generally this type boiler is less suited to solid fuel firing, as a firebox with high temperature insulation, or firebrick furnace enclosure is required. Having a furnace inherently close to the bottom of a small boat requires special design considerations.
"For solid fuel firing, a much better arrangement is for a VFT with a wet firebox below the tube bundle. Another variant of the firetube boiler is the locomotive (or Gunboat) type of boiler. Technically very similar to the VFT with a firebox, they perform similarly, with the advantage of a lower center of gravity, but a somewhat more difficult build process. Another practical firetube boiler is the Scotch Marine boiler, where the tube pass is a 180 degree reversal of the flue gas passage, as opposed to the loco boiler’s straight thru one direction flue gas flow path."
Re: Opinions concerning firetube boilers
I'm the "steams like a witch" guy. I love my scotch - I don't have to think about it or worry about it, in fire-up or underway. She goes from cold to warming-through steam (50 PSI) in an hour (Part of the secret there is to use compressed sawdust, hardware-store bricks during fire-up. They are volatile in a wood stove because of their long-flame quality). If I underestimated her weight (1,000 lbs wet), that is my problem, which could be alleviated in the design process @ the hull.
In addition, the scotch carries a certain reserve with the volume of water. I can quit firing several miles before the boat ramp, and put the dampers on a whisper. The fire is near out by the time we've docked at the ramp, and certainly out by the time of putting on the mooring cover for long-distance hauling. The furnace accommodates normal "supermarket" wood bundles (2' x 4" x 4" pieces).
You read in the article that I am replacing it with a John King WT design. But that is strictly to bring IONA back on her lines. (I'll probably have to build something bigger to put the scotch back in. Or build a shrine in my shop so I can display it under lights ...) I would build it again in a heartbeat except that I lost all of my welding credentials with retirement ...
In addition, the scotch carries a certain reserve with the volume of water. I can quit firing several miles before the boat ramp, and put the dampers on a whisper. The fire is near out by the time we've docked at the ramp, and certainly out by the time of putting on the mooring cover for long-distance hauling. The furnace accommodates normal "supermarket" wood bundles (2' x 4" x 4" pieces).
You read in the article that I am replacing it with a John King WT design. But that is strictly to bring IONA back on her lines. (I'll probably have to build something bigger to put the scotch back in. Or build a shrine in my shop so I can display it under lights ...) I would build it again in a heartbeat except that I lost all of my welding credentials with retirement ...
Steve