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Old Dec 16, 2009, 04:32 PM
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Long Island, NY
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WOODIES: Scratch built steam launch w/ two Midwest engines

I've been meaning to do something with these 2 Midwest steam engines that I have geared up to 1 shaft, so today the project was started. An old Sears table saw and a 10 foot length of 1 1/4" sq. mahogany have yielded the pieces for the keel. It will be around 28" LOA.
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Old Dec 16, 2009, 05:13 PM
Grumpa Tom
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United States, CA, Los Angeles
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That's pretty neat, a twin engine steamer! What will you be using for the boiler?

Can you post more pics of your engine and gear drive system? Very interested!
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Old Dec 16, 2009, 07:02 PM
Veni, Vidi, Feci
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Neat. With two cylinders, can you set the cranks at 90 to allow for self starting?
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Old Dec 16, 2009, 07:08 PM
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Long Island, NY
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Kmot, I think the last picture shows you what's happening with the dual engine / single shaft set up if you zoom in enough- I've had this abomination running on the 2 stock boilers on a board so at least I know it works. The reason for the fairly deep reduction is heavy pitch on the propeller. I'll be posting more pix as I get farther along. I pretty much work out solutions to problems as I put the boats together, I'm not one to do a lot of drawings beforehand. This way, everyone's surprised when it's finished...
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Old Dec 16, 2009, 07:15 PM
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patmat, I've actually tried messing with the "timing" that way but it seems to run happiest at a true 180 opposed configuration. If it ultimately runs well enough this way, I may opt for the heritage engines as I've heard that they're a little more efficient. Thanks for the interest..
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Old Dec 16, 2009, 08:16 PM
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Pat, Midwest engines are single cylinder, single acting oscillators; for self-starting with 90deg offset, you need double cylinder, double acting. Peconic's 180deg offset is the best that can be done, but still leaves dead spots (when both cylinders are centered on their frames, none of the 4 ports open). A 180deg offset does not reduce the dead arc per engine, but does cut it in half wrt to the system. With oscillators, if the cylinder port is exposed to either steam or exhaust port, and if you have a reverse valve, you can get the engine running, even if opposite direction to what you desire. Once it's rotating the flywheel, flipping the reverse valve may get the engine going in the opposite, desired direction. btw, 180deg offset is used in modern flat 4 -cylinder aircraft engines.

Peconic, with your gearing, you could install an electric self-starter (Reply #95, down the page):
http://www.modelboatmayhem.co.uk/for...?topic=6781.80

Are you going to use twin Midwest boilers? I've thought of that, to get more run time. I think they should have a transfer pipe near the bottom to ensure that if one boiler produces more steam (and thus uses up water faster) it does not go dry while the other is still operating - this was full size, multiple-boiler practice. I don't have enough practice silversoldering to install such a pipe, myself.

Looking forward to your build!
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Old Dec 16, 2009, 08:59 PM
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Long Island, NY
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Hi Brooks, I probably will be using a cross-connect tube so both engines are supplied by both boilers. I could rig up a small emergency kick-start electric motor to the gearing; I've built such a system for an electric start IC plant but I think I'll be a purist and not go that route. Plenty of rescue boats at the ready! When this plant is run on the test board I measure out 2 oz. of pre-heated h2O per boiler, and load up the pans with sterno so that the fuel expends itself with ~ a half oz. of h2O remaining in each boiler at the end of the run. I've had a fair amount of experience with the larger steam plants and this will be a bit of a retro, simplistic build to get through the early winter-
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Old Dec 16, 2009, 11:18 PM
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Looks like an interesting project, inexpensive engines would be great for twin engine boats.

Steve
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Old Dec 17, 2009, 03:40 AM
I SEE NO SHIPS
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Somerset England
Joined Feb 2007
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Geared twin steam madness !
Just the sort of inventive experiment we want on a steam forum
Looks good , and with the correct settings should be self starting.
Good luck with the build.
Dunc2504
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Old Dec 17, 2009, 05:51 AM
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A single cylinder double acting (scda)motor is not self-starting at all pts in the arc of the crank. Sidewheelers used those engines, one per paddle. The engineer and his assistant had to "bar-over" such an engine if it happened to stop in it's dead spot. That is, they had to physically turn the paddle to reposition the engine out of it's dead spot. Paddle boxes had a hatch exposing the paddle to the engineer so that he could apply a lever to a blade to move it. Or there was some other way to lever the system to turn it, say by prying on the crosshead. Or, there might be a way to manually work the valves to introduce steam in the normal dead spot.

Peconic has essentially made a single cylinder double acting motor. An additional hampering factor for oscillator self-starting is the automatic steam cutoff inherent in the design of simple ones. That gives a greater dead arc than a slide valve scda (set for full steam for entire stroke, with the johnson bar), making self-starting even harder to achieve for the simple oscillator. Double cylinder double acting oscillators can be made self-starting - several companies sell them. So they have designed to reduce the dead spot, possibly by opening ports &/or changing timing so that the cutoff is no longer present. Anyone who has such an engine might care to look at the ports to see if they are not symetrically placed. Such an engine might not be self-starting for both forward & reverse.

Saito made a v-4 scsa, I have one. It's self starting, but not an oscillator.
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Old Dec 17, 2009, 11:12 AM
Grumpa Tom
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wrt

pts

scsa

?????

What is this? Cell phone texting shorthand?
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Old Dec 17, 2009, 12:54 PM
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Kmot, I think it's: with respect to, points, and single cylinder/single acting. Now, about that "johnson " bar ....
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Old Dec 17, 2009, 04:58 PM
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In cold parts of the country, so I've been told, Johnsons spend a lot of time at the bar :-).

In Loco-Lingo, the Johnson bar is the forward/reverse lever. It's a big handle in the cab that the loco engineer hauled on. It's big because you need lots of omph to move the loco's connecting links and arms to a new position; later engines took some of the work out by connecting a steam cylinder to the mechanism; nowadays, we'd use hydraulic cylinders. You can tell the Johnson bar by the serrations along an arc near the top and the latching handle that keeps it in position. The extreme end positions on the arc give maximum force forward and reverse. By positioning the Johnson bar closer to the center of it's arc, you "latch up" or "hook up", making the cylinder valve cutoff flow from the boiler to the cylinder before the piston has traveled it's full stroke. Since steam expands, you can reduce the amount flowing into the cylinders and still get the piston to complete it's stroke. This saves steam, which the fireman will appreciate. On the other hand, latching up widens the dead band. Oscillators are always latched up to some degree, so they have a wider dead band than other steam engines.

During the steam era, this was the shorthand: -.- /-- /--- /-//-- /-.-- // ..-. /.-. /../ ./ -./ -..
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Old Dec 18, 2009, 01:06 PM
Grumpa Tom
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Thanks for the close-up photo of the engine package.

Questions:

What is the thumb lever on the one engine for?

Will the engines be connected in series on the steam pressure line?

If so, will the lube in the steam line be enough for the second engine after the first engine consumes some of it?

Are you intending to offset the engine package in the hull for the gear to contact the prop drive, or are you going to use idler gears and center the engine package over the prop drive?

Oh, on a second look it seems as if the angle of the prop drive will allow it to be centered on the engine package that is installed lower than the prop drive gear?
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