Hypothetical crazy turbine steam boat

Discussion in 'Boat Design' started by parkland, Mar 12, 2015.

  1. fredrosse
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    fredrosse USACE Steam

    Rurudyne, I do not understand your last comment?
     
  2. parkland
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    parkland Senior Member

    Also it appears that the VVT turbo based jet engines can reduce air flow quite a bit, using the adjustable nozzles. If the adjustment was connected to an air cylinder, it could remain tight, then start opening after hitting say 30 PSI, and get to fully open at 40 PSI.
    This way, fuel wouldn't be wasted as bad pumping so much hot exhaust away unless it was needed.

    They don't like to start in the tight position though, so it would have to be started in the open position. Need a manual override for that one.
     
  3. Rurudyne
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    Rurudyne Senior Member

    Fred, sorry if I want clear.

    The Doble used the steam to power forced draft, a device basically like a turbocharger.

    This not only drew in more air but also cause introduction of more fuel and increased combustion rate. In that it worked similar to an ICE with a turbocharger. Looking at pictures of the firebox it doesn't seem like it would have been pressurized much.

    My point was just that as the goal of using either a turbocharger or supercharger is to increase the amount of fuel you can burn for a given displacement so too does forced draft permit burning more fuel. The Doble, per one commentator, can run at the ragged edge of burn out as a consequence.

    Btw, there is another way to increase heat exchange: forced water feed. The LaMont (spelling?) boiler, IIRC, forced this at maybe 5 times steam output and not only improved heat exchange rates but reduces stress on the tubes and, with large volume flows prevented scale buildup in the tubes. Personally: do both!
     
  4. parkland
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    parkland Senior Member

    Not sure what you mean by forced water feed?
    Would not every boiler be forced water feed?
     

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  5. Rurudyne
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    Rurudyne Senior Member

    Going from memory again.

    Most of the time water feed in a boiler is not far off from the rate of steam production. By forced then I mean that the rate of feed is greatly increased from that. Because heat exchange is a function of mass flow rate on either side of the equation this improves heat transfer from the fire to the water; however, because so much more water is being pumped through the steam is bubbles within the liquid and under pressure the temperature within the tubes is pegged at not much over the temperature of boiling water.

    So while you're still driving up thermal efficiency for a given steam production rate you don't need special tubing and in fact one of the features of a LaMont boiler is that thin wall tubing will suffice. Likewise, scale can't hold on within the tubing.

    An external vertical reservoir is needed, though only of modest size, as is a feed pump dedicated to this (not the same one returning water to the boiler).

    Maybe then a better term would be "super-feeder" ... like "super-charger"?

    EDIT: I just realized that "doing both" is just increasing the rate of steam production. That lends to more compact boilers, but to maintain the advantages of "super-feeding" you'd need to relatively up that even more. Or would that be keep it where it was in a more compact system? Meh....
     
  6. parkland
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    parkland Senior Member

    So what do you guys think....

    If we had 2 identical boats, lets say they're steel 35' trawlers...
    If one has a 60 hp diesel, (putting out 40 hp)
    The other has a steam system with a 40 hp motor (putting out 40 hp)

    Diesel fuel is about 1.20$/ liter here.
    Waste oil is about 0.20$ / liter or less, especially if ordered in bulk.

    Can a steam boat ever compete price wise?
    I know they are not very efficient, but if you built is using every trick in the book, could it be done?
     
  7. Rurudyne
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    Rurudyne Senior Member

    In terms of price, of course.

    The issue with commercial craft is fuel portage for a given load, range and power. But a non-commercial boat, or one that only does short hops, is not necessarily subject to that constraint.

    And other things can favor steam.

    Take my interest with paddlewheels for example. If a paddlewheel has but one gear ratio it will generally be need to match up with the cruising or flank speed because that's when it's hardest to push the boat through the water. Now as you go slower in a boat it quickly takes a lot less energy to push the same hull. With steam this means at slow speeds the engine is going to be wasting power with a single gear ratio because the torque per rev is pretty much constant. It also may help to explain why some ship seem so slow given their engines, as they are set up to be most efficient at their cruising speed rather than power for some speed they might obtain.

    In a small boat (and smaller engine) there is at least the possibility of using a continuously variable transmission, not of the complex/expensive automotive type but of the kind used in a Shopsmith (v-belts and a couple of adjustable width pulleys) and running in a "tall" gear at slow speeds and a "short" one at cruise. This, I figure, is the functional equivalent of having a controllable pitch prop.

    This would permit a steam engine to better match up low speed power produced with what it actually takes to push the hull and not just how much power is produced when the engine turns at a given rate based on fixed gear ratio. An added benefit is that, at least for a home made craft, it's no big to get the final gear ratio just so ... just get close and learn how to adjust the CVT for best results.

    Of course when accelerating, rather than just maintaining speed, using a shorter gear ratio and increased engine speed would be beneficial. It should be easy to program an app for your smart phone or iPad to help keep track of settings as experience teaches you what they are. Heck, you you'll print them up and laminate the page.

    That wouldn't make the engine as thermally efficient as a diesel, but in terms of skulking around in places small shallow draft paddlewheels are great for it may help them reach relatively good economy, and that doesn't take into account cheaper fuels.

    And while I realize no one sells feathering paddlewheel kits the truth is here in the US nobody is really that far from some plasma cutting service and all the hard to make parts can be cut from a sheet or two of suitable material, machined or tapped or bent as needed with easy to come by tools (which you'll probably already have if you've fitted some boiler and steam engine castings anyway) and a notch up the "she left me because of emotional abandonment" scale or it's equivalent and you've got your wheel., pulley base tranny etc.
     
  8. parkland
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    parkland Senior Member

    A guy could make a little business of collecting used oil from boats haha.
     
  9. Rurudyne
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    Rurudyne Senior Member

    Except that you'd probably be sued you could have a logo of a medieval person pulling a hand cart full of old oil cans and call it "Bring out your oil!" ;)
     
  10. parkland
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    parkland Senior Member

    I'd honestly like a paddle wheel to cruise around on but not sure how practical it would be for a bigger lake.
     
  11. Rurudyne
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    Rurudyne Senior Member

    Fred can help you there! He's got a pretty little paddlesteamer.
     
  12. fredrosse
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    fredrosse USACE Steam

    LaMont

    “Btw, there is another way to increase heat exchange: forced water feed. The LaMont (spelling?) boiler, IIRC, forced this at maybe 5 times steam output and not only improved heat exchange rates but reduces stress on the tubes and, with large volume flows prevented scale buildup in the tubes.”

    Actually, LaMont boilers have very little advantage over “Once Thru” boilers that circulate far less water thru the steam generating tubes. This is because the dominant resistance to heat transfer is the very low hot gas to metal tube heat transfer coefficient. The liquid water rushing thru the inside of the tube has a heat transfer coefficient that is around 1000x the gas side, so the water flow virtually fixes the tube metal temperature near the saturated steam temperature. The high recirculation flow associated with the LaMont type boiler is not necessary.

    LaMont boilers were experimented with about 100 years ago, but were found to be not practical. The circulating pumps needed to drive large quantities of hot water thru the tubes is a design problem still existing.
     
  13. fredrosse
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    fredrosse USACE Steam

    Paddlewheels

    Getting off subject here, but one of the reasons I built a sidewheeler is the shallow draft ability. I like to explore shallow inlets where propeller driven boats dare not go. When the steamboat group goes out, their big propellers and deep draft often results in stuck boats, clogged with underwater grass. Not so with the sidewheeler, my hull draws just 8 inches of water, and the paddlewheels require no more than that.

    I even built articulated wheels to get better performance, proper articulated paddlewheels have efficiency not to far away from modern screw propellers.
     

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  14. parkland
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    parkland Senior Member

    Paddle wheels seem like a joke by modern standards, but in all reality, they do provide many advantages.
    I won't go on to list the ones I know of, but I know that there are many reasons, and situations, where paddle wheel propulsion is ideal.
    Especially for building first time boats, you can totally avoid any holes in the hull.

    I had an idea not long ago; build a dual hull boat, and a paddle system between the hulls, like a snowmobile track, where there are a lot of paddles in the water at a given time, without the constant turning motion.

    What does that steam boat burn for fuel? per hour?
     

  15. Rurudyne
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    Rurudyne Senior Member

    Nice. I notice your articulating wheel keep the thin rods in tension rather than compression. Also nice.
     
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