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what size steam engine?

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  • what size steam engine?

    hi fella's, i cant seem to find much info on model steam engine sizes, i have the bug to build another steam engine but at a loss to how big it needs to be, its going to power a 68" long x 12" wide boat hull, the engine just needs to just push the boat through the water at a slow speed, as far as power to weight ratio would it be best for a single cylinder engine or a multiple cylinder engine?

  • #2
    Have you tried this site?

    Or, something different.
    Last edited by PSD KEN; 11-12-2006, 01:52 PM.


    • #3
      Plenty of formulae for full-sized boats available via Google although it's questionable whether they can be successfully extrapolated to model boats.
      Regards, Marv

      Home Shop Freeware - Tools for People Who Build Things

      Location: LA, CA, USA


      • #4
        Steam is quite scalable. Otherwise, the model live steam railroad engines would not be successful.

        The Tiny Power 2V-10M will handle a 5'-6' model and has reversing gear. The 1V-10 would probably be adequate to move a boat of that size, but would require reversing gear to be added if that feature is desired.
        Jim H.


        • #5

          Are these engines the same as the ones from Stuart Turner?:

          All of the gear, no idea...


          • #6
            They are different engines, being all brass castings, but are equal to the Stuart models in power, or maybe a bit more as they have a longer stroke.

            This is the twin cylinder marine engine version;
            Jim H.


            • #7

              You did not mention the desire of a casting kit or plans. Seems like a twin cylinder double action 3/4 bore by 3/4 stroke is what you need. Rudy Kuhoupt has a nice set of plans for a marine engine. Villiage press has just published a set of books featuring Rudys engine plans. This engine is a 5/8x 5/8 so may be a little under powered, or you could scale it up some. Rudys engine was so well build he could blow in it and it would run. One of the advantages in these designs is that they are self starters. You want this since is a little hard to spin a flywheel to get an engine going while the boat is in the middle of a pond. Remember in models the power and weight of an engine is proportional to the cube. In other words doubling the size say changing a 1/2 inch bore to 1 inch produces 8 times the power requres 8 times the material by weight and requires 8 times the steam.
              Ad maiorem dei gloriam - Ad vitam paramus


              • #8
                thanks for the info, im in the uk so stuart engines are an expensive option, but me been me i like to make everything from scratch, my last engine and boiler was made from stock materials, and the boiler was also scratch made, im thinking on the lines of a 1" bore and a 3/4" bore engine, but im also toying with the idea of a big bore engine of around 1 1/2" diam.


                • #9
                  Double expansion??

                  Originally posted by billyboy
                  im thinking on the lines of a 1" bore and a 3/4" bore engine, but im also toying with the idea of a big bore engine of around 1 1/2" diam.
                  Does that mean you are considering a double or triple expansion engine? That would be a good option and these were used in the larger marine engines of old. IIRC there is a Rudy Kuhoupt design for one of those as well. One of the guys I know from the ME shows built one, runs great on steam but not compressed air. Like i mentioned earlier a single large piston will have dead spots. If it stops for any reason you may not be able to restart it. Aslo if you are talking about 1-1/2 inch at boiler pressure a single cyinder double action is still 4 times the engine you need. And it will have large steam requirements.
                  Ad maiorem dei gloriam - Ad vitam paramus


                  • #10
                    There are some very good plans available from Ray Hasbrouck;


                    Engine Number Nine will fit your needs exactly. Most of the others are larger, but can be easily scaled down.

                    Ray's engines are designed to work, not as shelf decorations. They are attractive and very practical engines.
                    Jim H.


                    • #11
                      HasBrouck #9 engine

                      I have built this engine except for the water pump addition. It is a powerful little engine that is a workhorse, although I am not sure it would be enough to power a boat as large as you mention. In any case it would be an interesting project.


                      • #12
                        hi, thanks for all the links, im really after scratch building from bar stock, a model boat hull of 5 or so foot needs to have a power plant of substantial size, i just need the size of bores and stroke size, a good point brought up by Tin Falcon was to have more than one cylinder for self starting, im not too bothered of material weight or size as i will have plenty of room to accommodate the engine and boiler.


                        • #13
                          Actually, you probably really need the mean effective pressure also.....

                          That will allow you to get an estimate of the power of the engine. It would be about halfway between the boiler pressure (less flow losses) and the exhaust pressure.

                          You would need an estimate of the power needed to move the hull, when at its nominal draft. I assume there are people with formulae on their sites......

                          Keep eye on ball.
                          Hashim Khan


                          • #14
                            5 ft boat? I would assume the equivelent of a 1.5" scale 2-8-2 live steamer.
                            Just a wild guess off the top of my head though. Do a search on Google books for marine steam applications. Not everything scales down, like steam whistles, but most everything else does.


                            • #15
                              i would think pressure and boiler's rate of producing steam are more important, that and the prop. figure out what boiler will fit and or looks right and size your engine to that. Tin's point is good, you want your boiler to easily to keep up to the engine. remember, the big cylinder's on triple or double are the low pressure ones and do nothing without a condenser, the high pressure (first) cylinders are small!

                              boats always bothered me because there's no easy way to monitor the boiler, have you some automated scheme to automatically keep up the water level?

                              Bill, just a guess, but I think boat would need small fraction of what a loco would, there is so much friction with the loco, only takes the tiniest of hand pushes to send a 5' boat off, not so with the loco.
                              Last edited by Mcgyver; 11-13-2006, 12:29 AM.