Stuart No:3 Launch Engine?

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mahking51
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Stuart No:3 Launch Engine?

Post by mahking51 » Sun May 20, 2018 7:18 am

Hi All,
I am new here so hope this is the correct place to post?

I have just acquired this engine along with a bunch of old tools and it is not really my thing but would love to know more about it and its potential use.
It is at the moment very dirty so I will clean it up and try to run it on air if possible to check it out before selling it.
Not sure how to add images here, some help please if possible?
Regards,
Martin
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Re: Stuart No:3 Launch Engine?

Post by mahking51 » Mon May 21, 2018 11:51 am

Hi Again!
Am I doing something wrong here please as no reply at all?
Regards, Martin
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Re: Stuart No:3 Launch Engine?

Post by RGSP » Mon May 21, 2018 12:27 pm

The Stuart No.3 is a compound twin, quite a lot smaller than Stuart's other main compound, the ubiquitous 6A. Castings sets have just become available for it again (at £1000 per set) and Stuarts give a rating of 1HP at 950 rpm: I don't disbelieve that figure, but 950 rpm is much faster than most of us would like to run a launch engine, partly because it will be quite noisy at that speed, and partly because it is likely to have a very short life run that fast. I'm guessing, but I suspect a more realistic operating regime would be 1/3 HP at maybe 350 rpm. That's still plenty for a boat perhaps 12' long, and capable of taking 3 adults comfortably.

The reason for compound engines is their improved efficiency compared with simple singles or twins. However, at this tiny size, thermal losses through the cylinder walls are relatively large, and I may be wrong, but I doubt the efficiency would be noticeably better than Stuarts No.1 or No.5A engines, both of which are single cylinder designs of comparable power to the No.3, and both of which have been employed very successfully as small launch engines, admittedly normally with enlarged bearings.

I think it's fair to say that the No.3 is an enthusiasts engine, rather than one aimed at practical use, but it's a very nice little engine all the same. For use in a small launch it would really need reversing gear, and if your engine does not have this, I would think very hard before fitting it. In its original state it has considerable value as a period piece, which would be partly spoiled if new parts were fitted (even though you can buy them again now).
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Re: Stuart No:3 Launch Engine?

Post by mahking51 » Mon May 21, 2018 2:36 pm

Hi, RGSP,
Thanks very much for the helpful info.

I have today cleaned most of the gunk off of the unit and tightened a few loose bolts on the reversing gear, (which it does have!)
It seemed quite hard to turn over by hand so I have oiled all the points I could find and swung it over quite a few times with an improvised hand crank and it certainly went a lot smoother.
I then hooked up my compressor to the intake and gently let in some air and lo and behold it turned over at once and seems to my totally inexperienced eye to run very sweetly indeed.
I have only run it slowly as I am not certain about the oil needs etc.

I have no idea how to try out the reversing gear? Is it straight forward please?

I will have no interest in using this engine and will dispose of it in the near future, hopefully to a good home.
I would post some pics but do not know how I am afraid.

I am about half way through making the STUART 10V as a way of learning machining from a novice level which I enjoy enormously, but slow going with other things going on.
Regards,
Martin
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Re: Stuart No:3 Launch Engine?

Post by RGSP » Mon May 21, 2018 3:07 pm

If it has reversing gear, it will be of the Stephenson link type, and there will be TWO PAIRS of eccentrics on the crankshaft, one pair under each valve stem approximately. Assuming this is true, there will also be two curved, slotted bars, one for each valve chest, both of the bars will be connected via links to the same "reversing rod", so that they're pushed backwards and forwards together. The reversing rod will also have a hand lever connected to it: the reversing lever. In practice the engine will normally run with the lever locked at one extreme or the other, operating the valves by one eccentric or the other, and giving forward or reverse. In full sized ship practice, and also for steam locomotives, the reversing lever will be set at the extremes only when maximum torque is required, and otherwise will be set nearer the centre, which gives improved efficiency. In practice with launch sized engines, especially small ones, there is often little to be gained by setting away from the extremes.

In order to post a picture here you need to use a picture hosting service, and post a link to it - I would have said Photobucket, but they've decided to charge a fortune for their service, which nobody I know is willing to pay, so you'll need to choose one of the others. Google search should find one.
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Re: Stuart No:3 Launch Engine?

Post by Mike Rometer » Mon May 21, 2018 3:07 pm

Don't worry about any delays in reply. On here some folks only look in every few days or once a week, so the ideal answerer may just not have looked in when you check. This definitely isn't Faceache or Twaddle, with replies every second. We are also a lot fewer in number. :lol: :lol: :lol:
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A BODGE : - A Bit Of Damn Good Engineering.
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Re: Stuart No:3 Launch Engine?

Post by fredrosse » Mon May 21, 2018 7:58 pm

Posting pictures is easy and direct on this forum. Below the reply windowyou can post a file, for me usually a JPG or JPEG file. The only issue is file size, I believe 100k is the limit, but the many photos I have posted here all look OK with that file size limitation. If your picture is too big, most photo software allows you to resize the photo, and save it with lower resolution.

Note that a small steamer would not need reverse, if you are comfortable with an ordinary paddle for maneuvering while docking, etc.

Also note that my sidewheeler has been operating for years with only 0.6 horsepower, and it weighs more than a tonne, with an obsolete, and relatively low efficiency propulsion system: paddlewheels. So in a small steamer, fractional horsepower may be completely satisfactory.
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RGSP
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Re: Stuart No:3 Launch Engine?

Post by RGSP » Tue May 22, 2018 11:24 am

Fred is quite right about posting photographs on the forum: I'm sorry but I'd forgotten the obvious way!

I'm sure Fred is also right about manoevering a steamboat with a paddle if the engine doesn't have reverse. My own boat is 21' long and displaces a bit over a ton, and I have to say that the paddle is near-useless in any sort of wind: on a calm day it's fine.

Running a slightly larger steamboat using very little power is fine in lakes on calm-ish days, but on the rivers with currents, and estuaries with tides, that many of us frequent, a bit more power is useful, and a bit of a safety factor.
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Re: Stuart No:3 Launch Engine?

Post by fredrosse » Tue May 22, 2018 10:29 pm

"......but on the rivers with currents, and estuaries with tides, that many of us frequent, a bit more power is useful, and a bit of a safety factor."

I agree, when I go out on the Delaware river I must consult the tide tables for a reasonable launch time, or travel takes too long. As a matter of fact I plan to push my steam plant up to over 1 horsepower this summer, adding an exhaust steam feedwater heater, and an economizer. That should allow extra steam generation, enough to get main steam pressure up 25%, which should do fine.
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