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Re: Next prop question

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  • Pat
    Hi Barge Pis did not get through (thanks Yahoo!!) Please open a photo folder (let us know which one) and try to upload them there. Very anxious to see them, I
    Message 1 of 21 , Apr 30, 2013
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      Hi Barge

      Pis did not get through (thanks Yahoo!!)

      Please open a photo folder (let us know which one) and try to upload them there.

      Very anxious to see them, I got a Chinese 125cc m/c manual today which did not help much except to learn that most are Honda or Suzuki copies and that some are water cooled.

      Pat

      --- In multimachine@yahoogroups.com, michael broadbent <bargemaster24@...> wrote:
      >
      > Hi Pat,
      >             Trying to send some pictures one shows the mounting boss for power unit
      >
      >
      > ________________________________
      > From: Pat Delany <rigmatch@...>
      > To: "multimachine@yahoogroups.com" <multimachine@yahoogroups.com>
      > Sent: Tuesday, 30 April 2013, 4:00
      > Subject: Re: [multimachine] Re: Next prop question
      >
      >
      >
      >
      >
      >
      > Good points all!!
      >
      > The prop I am going to try to buy (along with the engine to shaft adapter) is the one Thai boat racers use on their 150cc motorcycle engine, long tail boats. I know the pitch will be wrong but 100mph performance is nothing to sneeze at for a motor this small.
      >
      > Pat 
      >
      >
      > ________________________________
      > From: Shannon DeWolfe <sdewolfe@...>
      > To: multimachine@yahoogroups.com
      > Sent: Monday, April 29, 2013 9:03 PM
      > Subject: Re: [multimachine] Re: Next prop question
      >
      >
      >
      >  
      > Pat and all,
      >
      > I have read all the posts concerning the motor and prop design for
      > Jeremmy to try. This is probably the most ambitious project he could
      > possibly tackle. The propeller design is crucial to the success of the plan.
      >
      > I know very little about propellers. But I do know a few things about
      > engines.
      >
      > The 4stroke engine shown in the demo video early-on in this thread has a
      > wide flat torque curve and is governed to about 3200 RPM. A 2stroke
      > scooter motor rated to the same HP will have a very narrow powerband,
      > probably peaking somewhere north of 6000 RPM. The strength of a 2stroke
      > is the ability to rev. You can make a lot of HP from a small motor if
      > you can spin it very fast. But the trade off is no power down low in the
      > RPM range.
      >
      > A prop that works on a 5HP 4stroke will not work on a 2stroke rated at
      > 5HP. The pitch will be too coarse for the scooter motor to overcome. It
      > will not get up to speed to utilize the narrow powerband. If the motor
      > actually gets to it's powerband, the prop will likely cavitate.
      >
      > Will the boat move? Yes. But it will have high fuel consumption and very
      > high wear on the motor.
      >
      > What I am trying to say is, don't copy a prop used on a 4stroke engine.
      > Better to use a prop off of an older 2stroke outboard motor as a
      > starting point -- if one can be found. I haven't seen a small 2stroke
      > outboard motor in a long time. But, if memory serves, the prop pitch was
      > much finer than the prop in the video of the 4stroke on a stick.
      >
      > Of course, if Jeremmy has access to 4stroke scooters this post was
      > useless. ;-)
      >
      > Mr. Shannon DeWolfe
      > --I've taken to using Mr. because my name misleads folks on the WWW. I am a 57 year old fat man.
      >
      > On 4/29/2013 8:50 PM, Johnny wrote:
      > > I would suggest that you determine the appropriate pitch, diameter,
      > > shaft size, etc, and find a locally available aluminum screw
      >
    • David G. LeVine
      ... Whatever else you do, USE A HEAT EXCHANGER with a water cooled engine, do not use raw river water. Dave 8{) -- A word to the wise ain t necessary - it s
      Message 2 of 21 , May 1 1:48 PM
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        On 04/30/2013 10:52 PM, Pat wrote:
        > Very anxious to see them, I got a Chinese 125cc m/c manual today which did not help much except to learn that most are Honda or Suzuki copies and that some are water cooled.

        Whatever else you do, USE A HEAT EXCHANGER with a water cooled engine,
        do not use raw river water.

        Dave 8{)

        --

        "A word to the wise ain't necessary - it's the stupid ones that need the
        advice."

        Bill Cosby
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