Scotch Marine Boiler Plans

[eatonwinks]

Hello all, I am seeking plans/ design for a copper scotch marine boiler, approx 6" diameter or so for steam supply to several stationary engines. Coal or char fired.
There are a few published designs around but a recent design to Aust code is preferred
Advice gratefully received.

[steam4ian]

Are you looking for a true Scotch boiler plan complete with return combustion chamber and wet back?

6" diameter would lead to very small firebox tube/s which for burning coal or char would be very difficult; I doubt a single firebox tube could be much larger than 2" diameter, two tubes even less.

I have seen designs for gas and liquid fuel fired semi scotch boilers with a single fire box tube, dry backs and return tubes. The long fire box tube suits the flame.

[eatonwinks]

Thanks for the reply, I am keen to build a coal burner. Based on this requirement, what do you believe to be suitably proportioned design? Cheers.

[steam4ian]

Eatonwinks

Major caveat, I am no expert but as a professional engineer that has not stopped me successfully on projects where my basic knowledge was minimal.

My references are
Baggo's web site www.modeng.johnbaguley.info/Loco%20design/design1.htm
and "Model Boilers and Boiler Making" K.N. Harris

My personal approach to your problem would be
1/ Work out how much steam you need
2/ Work out what grate area you need for that amount of steam
3/ Work out how many tubes and what size and length you need
4/ Work out what size firebox tube you need to accommodate the grate width
5/ Work out the overall diameter of the boiler, the firebox and flues should not occupy more than the bottom 5/8ths
6/ Get a copy of the drawing of the boiler for a Sweet Violet.

Baggo's web site has some formulae and spread sheets to work them out. You will have to commute cylinder volume and driving wheel diameter to use Baggo's Formula for Ee the Engine Factor. Most miniature steam loco driving wheels turn at 300 rpm in normal service. You need to assess you stationary engines on the same basis; make up a fudge factor for the driving wheel diameter.
The grate area is for locos with loco drafting. Harris implies an 8/20 ratio natural to forced draft so a natural draft boiler will need a grate 2.5 times larger.

The Sweet Violet is a 3.5"G loco with a drum type boiler and tube type firebox. I suggest it works and is a good guide to the minimum diameter of the fire box.
You may be able to get access to plans for a Canterbury Lamb or Invicta which I think had tubular fireboxes; these may be a smaller diameter than Sweet violet.

Decide if you want to go wet back or dry back. You can always put a super heater coil in the dry back.

Regarding fuel. You mention char as an option. In that most UK writers have not heard of it I suggest you are from Oz or NZ. Char is becoming difficult to obtain as the major supplier has shut down their kiln and one alternative has been described as shale. This alternative need significant draft to keep it alight, you can't just bank a fire and walk off for a cuppa, it will be dead by the time you get back. Another option is still being explored.

For your intended us crushed BBQ heat beads might do; you will not be driving the boiler so hard that the ash will fuse and they burn with natural draft.

If you are from the antipodes then what could be more relevant than a Colonial boiler? Alternate name is an under-fired fire tube boiler.
Baggo's calculations still apply only the drum diameter is smaller.

Regards
Ian

[eatonwinks]

Many thanks for your detailed reply, Ian. I certainly will be presenting the plans to the club inspector for approval before I commence the boiler. I'm Qld based.
I'd prefer coal as fuel, yes I've heard the local char more resembles ballast than solid fuel.
To be honest, I have no specific single engine that I need to power, more like a collection of small and large stationary engines that I needed a good supply of steam as well as for experimenting. And I like the look of the scotch boiler and had hoped a 2 pass, wetback would suit.
I just found an e-copy on the net of the K N Harris book which is great reading but I was certainly looking for some input from recent construction.
I do like the look of the colonial style boiler as well, google The colonial type boiler - Land and Marine by William Sinclair from 1916.
Lends itself to some nice scale fittings and support structure.
I'll review all the info
Cheers
Andrew

[steamcoal]

I will send you over some real Welsh Dry Steam coal for your boiler once it is built.

Australia and N.Z have the same problem with all there coal reserves being the wrong type for miniatures.

Always happy to help out our Aussie mates.

[steam4ian]

Coals to Newcastle?

Australia has huge reserves of coal, some of it brilliant steam coal. It is just that you can't purchase it in less than an articulated truck load. Buy 40 tonnes and you can get superb steaming coal from Blackwater in Queensland, fine for a preserved full size railway but a bit difficult for an ME club which uses about 1 tonne per annum.

[steamcoal]

It just seems so strange that you cannot get your hands on the stuff. Why not ask the preserved railway guys for a tonne or two? I am sure they would understand and want to help out if it is the right grade. Your all in it together to make steam.

Maybe a BIG lump might fall off one of those 100 tonne dump trucks and will keep you going for a year.

It seems a real problem, not just in Aussie where every other non-coal substitute is or has been tried in an effort to make steam. It just seems so hard.I was asked if I wanted to import some of that Cooper Char but handling it and bagging it plus the inland haulage from Baccus Marsh to Melbourne would not warrant the effort. I will stay with my remaining tonnage of Welsh even if it does me for the rest of my life, I'll be happy and so will my cobbers.

I must get my vertical FT boiler tested and going just to see what the Welsh Dry stuff does. Might be more steam than I need for the Stuart #10 I fair.

What engine size do you intend to run? I hope my VFT will run both the Stuart #4 and #1 which would be a wonderful sight.

Hayden