Steam Engine Decision Choice

[sunworksco]

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[Alan Stepney]

The triple expansion will only work well with high steam pressure, at least 180psi and preferably over 250psi.
That means a thicker and heavier boiler, and that you dont want in a boat.

Stick with a "simple" rather than compound engine, and 2 or more cylinders so that it will start on its own.


There is no good reason to use stainless steel, in place of cast iron, bronze, etc.
There are a few items that could be made from SS, such as valve gear mechanism, but even then it is doubtful what benefits it has, and you will have to ensure it is the correct grade.
Overall, it is rarely worth the extra effort.

[sunworksco]

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[Alan Stepney]

Their boilers only run to between 50 and 80psi (depending upon model) so certainly wouldnt suit a compound engine.

The Twin Launch is a better bet, but I dont know if it will have the power you need. (I dont know enough about the helical drive system to even hazard a guess!)

[sunworksco]

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[Alan Stepney]

The twin launch is only about 1" bore and stroke (from memory) and I doubt that even two of them will give the power you need.

If it was a 54" long boat, with conventional drive, they would suffice.

However, I suspect (but have no definate knowledge os them) that the helical system will be less efficent, plus running on snow (for example) will consume VASTLY more power.

Before spending money, I would try to get some idea of the power required, and then see which engines can supply it.

[sunworksco]

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[Alan Stepney]

I'm not sure if they would give enough power, but I have no idea what power that type of drive requires.

I suggest getting some figures, at least of the full size versions, to see what the model will need before spending money.

[watt-steam]

I would hazard a guess that at least 40 HP will be required to haul a twin helical screw drive vehicle and one person on snow or water, and probably 60 HP on sand or rock, due to the enormous friction of helical drive drums.

This helical drive idea was done as adapter kits for model A fords in the 1930's. Pontoon drums with helical screw like fights welded on were used. The pontoons were mounted lengthwise under each side of the car and driven by a sprocket and chain controlled by a clutch for each one, the centre sprocket being attached to a gearbox where the differential would normally be. I have seen several U toob videos of them. In snow or a peat bog they will work OK but otherwise friction catches up with the idea.

There is a video of a tractor based 1926 Screw Drive Snowmobile at

http://www.liveleak.com/view?i=568_1233111054

The vehicle will need to be light, too. Big water filled steam boilers are not really the ideal power source for such a thing.

A launch or a nice steam wagon/truck powered by a compound launch engine with conventional wheels will likely be far easier to make and much more gratifying, as it is very likely to work well.

[sunworksco]

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[Jan-Eric Nystrom]

That's one curious machine!

How come we don't see any of that type today??

[sunworksco]

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[Alan Stepney]

At least we have some numbers now.

You wont get much over 1/10 HP from the Twin Launch engine.
Yep, one tenth HP.

So, two of them, and being generous, you may get a total of 1/4HP.



watt-steam, that Model A might have been OK on snow, but I bet it would make a mess of the roads!

[sunworksco]

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[sunworksco]

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[willy]

as it is noted in this video, tracked vehicles literally screwed the alternative drive. The screw drive was not good for snows in the west coast as they would bury themselves, where the track type machines had a better "footprint"

http://www.youtube.com/watch?v=MCC0VT6_jVo&feature=related

[sunworksco]

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[watt-steam]

Sunworksco, you obviously want to build one, so go ahead. Let us know when you're done, send us a video. You obviously know far more about the propulsion requirements than anyone here.

Watt

[sunworksco]

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