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Putt-Putt outboard motor

"Burns driftwood" boat motor
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Take the design used in the little toy Putt-Putt boats and build it in the form of an outboard motor. Like a woodstove there will be a door on the front where you load in firewood to keep the fire going. Inside there would be a bunch of waterfilled tubes for the steam generation. Maybe some leaf pettal valves in the feed water lines to help lift up the water to the boiler section. A silent and non petroleum power source
darkspeed, Jun 18 2010

to burn or not to burn http://www.motherea...Burn-Driftwood.aspx
[xandram, Jun 18 2010]

Sirius-ly http://en.wikipedia.org/wiki/Blue_Riband
An advantage of wood-burning nautical propulsion. [mouseposture, Jun 18 2010]

[link]






       //Silent// ? I don't think so. The putt-putt boat toy is fairly quiet, but scaled up it might sound more like
!!PUTT--------PUTT!!
  

       I could see trying to build this if I were stranded on a desert Island, though.
csea, Jun 18 2010
  

       Part of the reason that the miniature pop-pop boat works is the scale.   

       The principal relies on the water creating a fluid piston in the tube which is propelled backward when some of it boils. This works OK in small tubes, but becomes less effective when the steam /water boundry becomes turbulent and condensation occurs before much momentum has been imparted to the water. A search for the largest pop pop boat only shows models about a foot long.
Twizz, Jun 18 2010
  

       I'm sorry to disappoint you, but a lot of *driftwood* doesn't burn well, as it has been soaking in water for so long. (from personal experience of lighting beach fires) OR are you carrying a cord of firewood in a tiny boat?
xandram, Jun 18 2010
  

       it's true that wood fired propulsion is going to require frequent stops on shore for re-fueling. (Not something you can do at sea [csea] so a sail and a compass would be a more effective use of your time.)
WcW, Jun 18 2010
  

       As of this writing, if you could make a ship engine that could run on watered-down crude oil, I know of an apparently inexhaustible refueling spot.
normzone, Jun 18 2010
  

       //wood fired propulsion// Well, one good thing about it is: you can cannibalize the structure of the boat to feed the engines. If I recall correctly, this was actually done by one of the first transatlantic steamships. (Quick Wikipedia check shows it was the Sirius, racing the Great Western <link>)
mouseposture, Jun 18 2010
  

       //This works OK in small tubes, but becomes less effective when the steam /water boundry becomes turbulent and condensation occurs before much momentum has been imparted to the water.//   

       Might a larger boat use a bundle of small tubes rather than singular large tubes?
swimswim, Jun 19 2010
  

       Small tubes impart too much friction and may cause pipe cavitation and bursting due to low pressures (due to the energy loss by friction). I know this sounds crazy, but it's true. Pipes will literally implode/explode (air bubbles spontaneously formed inside due to low pressures implode almost immediately and this energy release makes the pipe explode) if there isn't enough pressure, and friction is the number one contributer to the depletion of pressure. You need large pipes for larger ships. It's called scalable design, or some such. And larger pipes equates to turbulence which brings its whole separate bag of problems... Ahh... engineering: full of finicky optimizations.   

       I also believe that the resulting ships will be pretty freakin' loud.
daseva, Jun 19 2010
  

       How about many small tubes?
No scalable design problems that way.
  

       How about 'yes, there will be problems'. For a given flow- rate you will only be increasing the frictional forces with more pipes, decreasing the flow- rate; and the flow-rate is what determines the power output; and the minimization of friction is what increases your power output. I may be wrong, but I'm against this one. People underestimate the amount of friction in pipes and how it changes with diameter.
daseva, Jun 19 2010
  
      
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