[safa_pl]

Hello everybody. I'm new in steam world and so far I have no experience. I'm interested in constructing marine steam boat and I would like to ask you a question.
According to "Model Boilers & Boilermaking" of K.N. Harris watertube bore to lenght ratio should be not greater than 1:50 or better 1:40.
But do you know how far this rule can be taken? For example can I use copper pipes 2mm bore 0,5mm wall and 40mm long in building small yarrow boiler? In this case ratio bore to lenght would be like 1:20 which is (at least in theory) twice as good as reccomended. What concerns me is maintaining water flow in such narrow pipes. Do you have any ideas?

Such short lenght of watertubes is result of restricted height of model vessel. I prefer to keep main waterdrum in normal size to prevent rapid running out of water.

ps I am not native english speaker

 

[34C]

You need a specialist model boiler site covering marine and/or static types: water tube boilers didn't meet with much success on the railway.

I would try your question on sites such as these:
http://www.modelboats.co.uk/
http://www.model-engineer.co.uk/

 

[safa_pl]

Thank you! I'll ask there.

 

[andrew]

A little off to the side here, but if you are interested in studying this subject in a bit more depth to understand the practical background, probably the best resource available is the book published by Babcock & Wilcox, Steam, Its generation and use. The current edition from B&W is rather expensive, but a perfectly serviceable version is available free at http://www.gutenberg.org/ebooks/22657. I find it very absorbing reading!

andrew

 

[LTSR]

Rather more detail needed! ..Can you provide the size and type of hull, power plant and fuel type being considered?

There have been many proven designs published and with more details it should be possible to point you at something suitable.

 

[safa_pl]

LTSR
Hull type - hms Dreadnought 1:100 scale
so: 10 cm height, 20 cm width and 20 cm lenght space is available for boiler.
In Yarrow type boiler model I consider silent burner or blowlamp. Rather gas than anything else. And this still can be changed because copper-watertube-core will stay the same, only casing should be different.
As far as I get the whole conception.
For the power plant I want to make small steam turbine.
I know that whole project may take me quite a lot of time and effort but this is the thing I really want to achive.

 

[LTSR]

QUOTE (safa_pl @ 8 May 2014, 15:37) <{POST_SNAPBACK}>LTSR
Hull type - hms Dreadnought 1:100 scale
so: 10 cm height, 20 cm width and 20 cm lenght space is available for boiler.
For the power plant I want to make small steam turbine.

"For the power plant I want to make small steam turbine."

A long, long, LONG time ago I helped a guy with some of the more difficult machining on a small single stage turbine. It eventually ran well, if I remember correctly, at well at over 100,000 RPM.

The turbine wheel, again from memory, was 40'ish mm dia., I was told that the blade tip speed at that RPM was more or less supersonic! In other words a serious bit of kit requiring some serious maths (not mine!) and careful choice of materials.

The problem is however that while the turbine is a compact unit the rest is not, the boiler for a start has to produce a LOT of steam which means that the burner must be big too. Then there are things like a reduction gearbox, water feed pump, oil pump, (the turbine bearings and reduction box require a lot of lubricating) and that in turn means an oil separator, particularly if a condenser is included which in turn would mean an air pump. If radio control is in the plan then there is all that actuator gubbins too!

To be honest I think the stated available space is marginal at least but I will see what I can find.

 

[safa_pl]

1. Space.
The mentioned 10x20x20 cm space is just a space between P,Q and X turrets, under the rear funnel. This is the space just for boiler. Turbines and auxillary machinery can be located in other places. For example between turets X and Y there is about 10x15x15 cm space. Also displacement limit is high in this scale - it should be 18kg if hull will be made properly.
2.Turbines.
I hope that reasonable efficiency can be acquired with relatively simple means. Like here:

This will require some precise CNC machining but seems to be possible.
The casing of turbine will be 2mm thick brass pipe. Additional steel protection belt may be added so that in an event of fatal failure this part can be some kind of bulletproof.

And I want to repeat this: It is just a project, first attempts may be failure. Not big enough, not powerful enough but i believe that it is not impossible

 

[LTSR]

Sent you a PM.