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[kiwimodeller]

Hi all, has anybody had any experience running twin steam engines? A member of our club is building a Resolve tug (from Caldercraft?) which he is powering with twin Graham TVR1A engines fed by one large boiler. For simplicity he would like to run just one large lubricator and one throttle. Our main concern is whether the engines will run at near enough to equal speed as otherwise the boat will not run straight without rudder correction. Has anybody tried this set up? Thanks, Ian.

[tobyker]

If you are using just one throttle then I assume you do not want to use engine steering. Presumably you will link the reversing levers together so the cut-off and direction of rotation of both engines are the same. In that case, your only impediment to straight steering will be differing internal friction in the engines. To counteract that you may need to link then in some way, either expensively and noisily by gearing (cross shaft and bevels rather than a straight cut line of spur gears), or quietly but less precisely by a crossed belt in a groove in the flywheels. Or. of course, bya  crankshaft extension on each engine with 90 degree cranks linking the engine - for ultimate version of this see vintage Bentley 3-throw eccentrics to drive cam shaft. But then I'm no engineer, me.

[derekwarner]

Ian...I have no experience with two twin cylinder steam engines with a single boiler, lubricator & steam regulator....but thinking.......
1. We are assuming that the pair of engines were manufactured from the same production run or purposely machined/toleranced from kits at the same time
2. From this we also conclude each engine would consume near identical volumes of steam & steam oil for any given load
3. I know that ANTON will build mirror reversed versions of his engines....this way for twin engine builds the all important identical length, shape & form of steam inlet & discharge tubing can be maintained between each engine
4. As an insurance.......your member build could include a needle valve identically located in the steam inlet line just prior to each engine for discrete throttling if needed
5. We must also remember that each engine will be rotating in opposite directions........I do seem to remember a thread here on Mayhem detailing or asking why the members TVR1A was running at different speeds between ahead & astern..........Pettyofficernick ...may be able to offer comment here..............Derek

[kiwimodeller]

Thanks for the comments so far. They are indeed Graham TVR1a engines assembled as left and right hand engines and rotating in opposite directions. The valve gears will be linked for the purpose of reversing but we have not tried using the valve timing as a means of slowing the engine although I am sure I have read somewhere that it can be done. The simple way of throttling would seem to be to have a steam regulator in the main pipe before the T junction. Derek's idea of a manually adjusted valve (point 4) to adjust one engine seems a little simpler than Bentley ecentrics but I will forward all correspondence. Cheers, Ian.

[essex2visuvesi]

I would have thought being a Tug that one throttle for each engine would be a better option, as it would give better maneuverability

[GreenSteam]

I would have thought being a Tug that one throttle for each engine would be a better option, as it would give better maneuverability

Absolutely!  IMHO, there are few things cooler than watching a big boat come in, directly at the dock, and then, in a sonic extravaganza, punctuated by conflicting wake patterns, slowly rotate itself around while sounding like all h*** is breaking loose.

I can't think of a better reason to have twin power plants except, of course, the safety of redundancy and if you need the power.   

And I speak from experience, having rode in a 30', wooden, twin-six powered gas boat (Hercules power), for many years, in my youth. 

GreenSteam

[Circlip]

Go back to Tobyker's reply, you need to mechanically sync both engines. No matter how carefully the engines are made, they won't synchronise from a common (or separate) steam supply. Another way is to use V/P props adjustable from separate levers. This is why separate throttle levers are fitted in multi-engine boats/A/C etc.
 
  Regards  Ian.
 
  And you'll probably still have to run with constant rudder correction.