Durham Donkey Boiler

[VANYA]

Hi,

A long time since I posted anything but I would like to build a simple (Small) VFT Steamboat boiler and see the Bill Durham Donkey Boiler listed in the January-February 1962 edition of Stemboat and Modern Steam launches.

I have located a length of 14" Schd pipe for the barrel and will have the design verified before construction.

Does anyone know of this boiler or its abilities?

Its for a small personal steamboat, not an ocean liner!

thanks.

[DetroiTug]

Hello,

Points to consider.

If it's a standard VFT (Don't have the Durham book with me), they are great boilers and most commonly used for small steamers. They are great boilers and for new firemen to learn on. They do everything slowly allowing a new fireman to stay ahead of it. Very stable water level. Plus, they fit the bill for an historically correct boiler. If built properly, easy to get state certification and Insurance. Better supply of stable dry steam. That's the good stuff.

The con's are:

- Heavy when compared to their counterpart boilers such as some Watertube types and especially the Monotube. Much of that weight is carried up high which raises the center of buoyancy of the craft.

- Expensive to build, much more material than a small Watertube or Monotube boiler.

- Lower steam generation per square foot of heating surface, about half that of a Watertube. And much less than a Monotube. Increased time to raise steam, increased time to shut down.

- Not very good internal circulation, it's all up and no real deliberate route down

- Higher fuel consumption per pound of steam generated.

Watertube pro's are:

- Fast steaming, better overall steam generation, less fuel consumption

- "Safer" They work with lower amounts of boiler water and generally referred to as "safer", although all boilers are "safe" if built and operated properly.

- Typically lighter.

- Typically less expensive to build.

- Lower center of gravity.

- Natural internal circulation. One of the key factors that make them better steam generators. Velocity varies by design.

Watertube con's:

- Difficult to get government certifications, varies by design.

- Often erratic water level readings, making safe water tending difficult.

- Piping is more difficult i.e. installing isolation valves at the boiler surfaces, which are completely in the fire in some designs.

- Some WT types more difficult to build than a standard VFT.

- Prone to carry over (water in the steam line under high demand), caution should be used with piston valve engines and consideration for watery whistles.

- Require shorter intervals of manual water tending - really better suited for automatic water level controls.

Monotubes.. Great steam generators, but they are the real hot rod boilers and require sophisticated electric or heat/pressure analog automatic controls. The control schemes can be very difficult to design and problematic in operation. See White, Doble, Serpolet and others steam cars.

Pro's: Inexpensive, easy to build and great steam generation for their size - very light.

Con's: Very unstable. Very prone to carry over.

-Ron

[VANYA]

Hi Ron.

Thank you for all the information. It is good to hear that they are considered good steamers.

I have the essential specifications from the page in the book, no of tubes, tube dia etc to give to my designer.

The boiler would be made under the Australian Miniataure Boiler Safety Code (AMBSC) which specifies maxiumum barrel Dia of 14" and < 50 litres of water and W.P of 100 psi.

As for the fuel I have an unlimited supply of Welsh Dry Steam Coal so this should be fine and this is what I want to design the firebox around.Now that I have the steel barrel I will proceed.

Ron, do you know if this boiler is being used these days or if any other members may have photos of this boiler even though it is from a long time ago in the 60's.

Thank you so much.

Hayden

[fredrosse]

From Ron: "Monotubes.. Great steam generators, but they are the real hot rod boilers and require sophisticated electric or heat/pressure analog automatic controls. The control schemes can be very difficult to design and problematic in operation. See White, Doble, Serpolet and others steam cars.

Pro's: Inexpensive, easy to build and great steam generation for their size - very light.

Con's: Very unstable. Very prone to carry over."

I have built monotube steam generators that have none of the problems you mention. No sophisticated electric or heat/pressure automatic controls, (well, perhaps sophisticated, but very simple with no moving parts, no electricity, and no magic involved) stable continuous operation with 100% continuously flooded coils, and virtually no chance of water carryover into the steam pipe, and no moving parts in the entire steam and feedwater circuits, except for a conventional reciprocating feed pump.

The only disadvantage with these boilers is that they need to have the option of fast flame shutdown, which is no problem if Propane or liquid fuel is used for the burners. A VFT, or conventional Water Tube Boiler can have a coal or wood fire that is slower to shutdown, as the contained inventory of stored water allows some level of continued heating after steaming (and feedwater flow) is interrupted.

Advantages similar to those espoused for Lamont type monotube boilers, except there is no need for a waterside high temperature water circulating pump, which I believe is the basic nemessis of the Lamont style boiler.

[DetroiTug]

Hi Fred,

"I have built monotube steam generators that have none of the problems you mention."

Judging from my reading of books, various internet posts and many discussion with steamfolk, your results are more of an exception. Monotubes are typically problematic for most builders, especially those with limited understanding of steam systems and are attempting to operate them manually.

Type of demand is important, as in pulling a generator, the load is mostly constant. Road engines and marine engines too have a varying demand which makes the Monotube more difficult to control.

If you happen to have it, I would like to see a schematic of your Monotube system. I may try one in the future.

-Ron

[fredrosse]

An attached boiler drawing, suitable for a small steamboat, with 16 inch diameter shell. Probably your 14 inch shell could be adapted, being about 12% smaller. What is the material of your shell, and actual dimensions, Outside Diameter, Wall Thickness, Length, and material specification (if available)?

[Lopez Mike]

Nice drawing, Fred.

I would build it with a water leg. Except for the firebox penetration there are no drawbacks that come to mind and the steam producing area of the boiler are so much improved.

just two rings and the firebox hole and you easily double the area that receives radiant heat from the fire.

[VANYA]

Fred.

The barrel is 14" OD with a wall thickness of 8mm.

The pipe is drawn seamless drill casing of similar standard to Sched 40. I was told verbally the specs but cannot remember just now. I was just looking for the pipe first before I did any further planning.

The boiler can only be maximum of 14" dia to be built under model engineering (AMBSC -Australian) miniature boiler code. I am not doing the design myself but have an engineer in Australia who is a boiler designer and AMBSC Code author. he has built his own steel boilers of 10" dia. i just do not want to cross over into the >50 litre certified boilers. This is almost a model engineering project.

The length will be similar to Durham Donkey boiler to keep the C.G low. There are basic measurements on the drawing in the book but the code will provide other criteria.

As for the engine I have two unmachined casting sets for a stuart 5A but can decide on the bore to suit the boiler. It will be smaller than the standard 5A.

I will see if I can attach the Durham Drawing in another post.

Hayden

[VANYA]

Durham Donkey Boiler from Steamboat Book

[Ethelred]

Nice drawing, Fred.

I would build it with a water leg. Except for the firebox penetration there are no drawbacks that come to mind and the steam producing area of the boiler are so much improved.

just two rings and the firebox hole and you easily double the area that receives radiant heat from the fire.

One often reads this argument in favour of water leg VFT boilers, however if it were true, i.e. the only radiant heat on a dry wall VFT is the tube base sheet, then they would hardly work at all. The fact is that besides Bill Duhram, Strath Steam sold dry wall VFTs for years and even Simpson Strickland made them in the early 20th century and I've not read of any complaints.
I think what happens in the dry wall boiler is that the casing becomes very hot and, as anyone who's held a piece of metal whilst the other end is heated will testify, the heat transfers upwards, thus to the boiler surround. A correct calculation as to the heating area should include the entire drum circumference, which would actually be greater than that of a water leg version.
Added to the much simpler construction of the dry wall and the well publicised problem of sediment accumulating in the legs of water walls, I think I'd prefer a dry leg.
It would be interesting to hear from anyone with experience of a dry wall VFT as to its characteristics.