Input on boiler design

[mtnman]

OK I’m convinced. VFT with a wet firebox, coal fired is my new plan. It looks like 22 tubes 1” in diameter and 20” long in a 16” casing with a 14” diameter firebox. This size boiler also keeps me under the size determined to be a Hobby (miniature) Boiler. Am I right in my figures that this is more than enough boiler for a 2.25x3 HasBrouck #1 engine?

[DetroiTug]

Would that be big enough to run that engine?

This is how I'd determine an answer to that. First you'll need to determine the area inside the boiler that actually sees the fire.

Calculate the firebox at 14" in diameter

14 X 3.14 = 44 (rounded)

You don't say the height, but we'll estimate it at 16" tall

44 X 16 = 704 square inches.

Now the crownsheet or lower tube sheet. It's 14 " in diameter. The area of a 14" circle

(pi)3.14 X 7(rad) X 7(rad) = 154 sq in area.

You have to subtract the tub holes. Area of a 1" circle is .785 square inch

20 tubes X .785 = 16"

So subtract 16" from 154 and that leaves 138

In the firebox you'll have 704 + 138 and that is 842 square inches

Now the 1" tubes, the ID will be less, probably .800, so the equation is

3.14 X .800 = 2.51 Then times the length:

2.51 X 20 = 50 square inches per tube, times 20 tubes, equals 1000

So we take 842 and add the 1000 that equals 1842 square inches, then convert that to square feet:

1842 / 144 = 12.8 square feet

From what I've read about VFT boilers, that is enough for 2 to 3 horsepower.

Having said all that, I was on a guys paddlewheeler this summer and he had a 3 X 4.25" single, and was running it with an old fulton boiler with no tubes and only 12 sq feet of heating surface and the boat ran just fine.

My hunch, is that your boiler plan is about the right size for the Hasbrouck engine.

-Ron

edited the math, I calculated the tube area inaccurately

[87gn@tahoe]

Controls can become an issue with monotubes.

Nope, been mastered here on oil fired ones, not so easy if solid fuel is used. Totally safe too, so little water in them that they can't explode, they only go fizz, believe me, I saw it happen. A friend here in New Zealand has built a number of monotubes using stainless tubing. Superb steamers, and once set up are virtually automatic steamers.
Daniel

Oh, I know monotubes. I have one in my boat. I would not suggest one for a first-timer though.

[dhic001]

A few thoughts on VFT boilers. No one has to agree with my thoughts, but my few pennies worth might be of use.

1) Boiler height: There is no advantage in a tall boiler except in providing steam space. In a small boat there are considerable disadvantages of a tall boiler (stability etc)

2) Diameter: The bigger the diameter the better, more tube plate area exposed to the fire, and more area to fit more tubes, equals greater heating surface ie more power

3) Tubes: Lots of them, relatively small ie inch or so. Big tubes (say over 1 1/2 inch ID needs retarders to be effective)

4) Grate area: as big as possible (while allowing for combustion space(5)) to allow a good fire, and thus allow for some of the fire to not be performing perfectly, being cleaned etc.

5) Combustion space: As much as possible, allow combustion to happen in the firebox, not the tubes. Good combustion allows lots of heat into the boiler, and less soot to remove.

6) Wet or dry firebox:
-Wet firebox means less combustion space outside the diameter of the grate, the heat at the outside of the grate is allowed to be pulled out before the fire is able to get going fully in that area. The area of boiler above the wet leg has no tubes in it, but holds a considerable amount of water in relation to the capacity.
-Dry firebox allows greater diamater than the boiler, creating a larger base to stabilise the boiler in the boat, allows as much grate diameter and combustion space as desired, enables modification to the firebox if needed/wanted. Only disadvantage is the heat output, which can be limited by good modern insulation .

7) Soot: Unless you have amazing coal you'll have to remove soot from your tubes at sometime. Punching tubes is a best avoided if possible, as its messy and hard work. Soot in tubes will greatly reduce performance, even over a relatively short time period (say an hour), more so with smaller tubes. Best to remove it while underway (but not near drying laundry) by using a big diameter blower to create a large draft briefly while firedoor is open. Done regularly you'll go for ages without going near a tube brush.

Hope those thoughts help someone.
Daniel

[mtnman]

Detroitug, thank you for the math. My tubes are 18" long instead of the 16" figure you used, and I think I can squeeze several more tubes into the space allotted. I'd like to have more boiler than I need. I just read your post about draft control and I too wonder about the boilers that draft through the fuel door. Not to efficient in my book ( I heat with wood) you really need to draft under the fire to get the best burn.
Today I bought a 16"x48" piece of pipe, it's the shell for my boiler. It was scrap at a local company that drills BIG wells. What is the optimum height for a firebox that is 14" in diameter? I figure about 12” tall above the grate?
How's your tug coming? Every time I look at your pictures it brings back memories, I had a tug (it wasn't really mine, she belonged to Tampa Ship) when I worked at the shipyard. She was about the same size as yours and powered by a Detroit 6-71. “Miss Tampa Ship” was her name, I used to take her out and play in the river when work was slow. I sometimes wonder where she is now. I think she was sold at auction when the shipyard changed hands back about 1995, I left the yard in 1992.

[DetroiTug]

Detroitug, thank you for the math. My tubes are 18" long instead of the 16" figure you used, and I think I can squeeze several more tubes into the space allotted. I'd like to have more boiler than I need. I just read your post about draft control and I too wonder about the boilers that draft through the fuel door. Not to efficient in my book ( I heat with wood) you really need to draft under the fire to get the best burn.
Today I bought a 16"x48" piece of pipe, it's the shell for my boiler. It was scrap at a local company that drills BIG wells. What is the optimum height for a firebox that is 14" in diameter? I figure about 12” tall above the grate?
How's your tug coming? Every time I look at your pictures it brings back memories, I had a tug (it wasn't really mine, she belonged to Tampa Ship) when I worked at the shipyard. She was about the same size as yours and powered by a Detroit 6-71. “Miss Tampa Ship” was her name, I used to take her out and play in the river when work was slow. I sometimes wonder where she is now. I think she was sold at auction when the shipyard changed hands back about 1995, I left the yard in 1992.

Mtnman, On the height of the firebox, I'm not sure, I know it differs with the type of fuel that will be used. For wood, I'm guessing the same height as the diameter, coal and oil is probably less.

Thanks for the compliments on Iron Chief, I'm getting there slowly but surely. Sounds like a nice tug you use to operate, probably a bit larger though. Not sure I'd want to try a 6-71 Detroit in this one. It would probably work, but I would want to beef up the engine mountings. Sure wouldn't be much room left in the "engine room". This would be a sweetheart with a nice little two cylinder Yanmar or Perkins.

-Ron

[mtnman]

Detroitug, thank you for the math. My tubes are 18" long instead of the 16" figure you used, and I think I can squeeze several more tubes into the space allotted. I'd like to have more boiler than I need. I just read your post about draft control and I too wonder about the boilers that draft through the fuel door. Not to efficient in my book ( I heat with wood) you really need to draft under the fire to get the best burn.
Today I bought a 16"x48" piece of pipe, it's the shell for my boiler. It was scrap at a local company that drills BIG wells. What is the optimum height for a firebox that is 14" in diameter? I figure about 12” tall above the grate?
How's your tug coming? Every time I look at your pictures it brings back memories, I had a tug (it wasn't really mine, she belonged to Tampa Ship) when I worked at the shipyard. She was about the same size as yours and powered by a Detroit 6-71. “Miss Tampa Ship” was her name, I used to take her out and play in the river when work was slow. I sometimes wonder where she is now. I think she was sold at auction when the shipyard changed hands back about 1995, I left the yard in 1992.

Mtnman, On the height of the firebox, I'm not sure, I know it differs with the type of fuel that will be used. For wood, I'm guessing the same height as the diameter, coal and oil is probably less.

Thanks for the compliments on Iron Chief, I'm getting there slowly but surely. Sounds like a nice tug you use to operate, probably a bit larger though. Not sure I'd want to try a 6-71 Detroit in this one. It would probably work, but I would want to beef up the engine mountings. Sure wouldn't be much room left in the "engine room". This would be a sweetheart with a nice little two cylinder Yanmar or Perkins.

-Ron

Miss Tampa Ship was about the same size as your tug. We used her to push fuel barges. She was all engine and a little room for two people to ride. She was the smallest working tug I have ever seen. And about the Yanmar or Perkins...hush your mouth! Your steam plant is beautiful and just what she needs!!!

[artemis]

Ken Brockway, a retired boilermaker has a website at http://www.mysidewheeler.com/boiler.htm and on this page he tells you, step-by-step how a professional designs and builts a vertical fire tube boiler. Laying out out the tube spacing, calculating the heating surface, dry or wet firebox, furnace combustion area, etc. The material on the website was also published - with the author's permission - in the Mar/Apr 2007 Steamboating Magazine, Vol XI, No. 2, pgs 13-25.