31' JC Casco Bay

Discussion in 'Downeast Engine Room' started by Radar, Sep 20, 2018.

  1. Radar

    Radar Member

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    Good afternoon Guys .

    Trying to find out what wheel I should be swinging I have a 31' 2002 JC Casco bay powered by a 370hp Yanmar with 2:1 reduction . Presently swinging a 22 x 21 cupped wheel and I am only getting 3200rpm (Tach) WOT.
    Any information would be greatly appreciated.

    Thanks,
    Reggie

    .
     
  2. ARC

    ARC Senior Member

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    that's strange. my 31' has 380 cummins 2:1 and I'm swinging 24x24 . engine is right to specs with full load
     
    ARC,
  3. ARC

    ARC Senior Member

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    QSB data.jpg
     
    ARC,
  4. Radar

    Radar Member

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    Thanks for the information Just came off of slip so I know the bottom and wheel are clean.
     
  5. ARC

    ARC Senior Member

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    What is the history. did the boat ever hit WOT with that prop. To gain the
    RPM you need you would be dropping at least 2" and pitch. Doesn't seem right.
     
    ARC,
  6. Radar

    Radar Member

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    Purchased the boat last year . Been doing some work on it over the winter and started to use it this summer. Sea trial the boat turned up 3250rpm with current prop will
    Thanks for the reply. I have only owned the boat for just over a year so will reach out to previous owner to see if he changed the wheel from original one.
     
  7. ARC

    ARC Senior Member

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    Ok . So you need to start your own history. Your engine and mine should move the boat about the same. I do not have a FB. Use my data sheet and see it your performance comes close. If you see any excessive fuel burn, you may be overloading your engine. Not good for engine. If your speed is higher at a given RPM, you may be overproped. Check RPM with a mechanical tach, your’s may be off. Do this with a fresh set of filters and medium to high load. Post your data so we can look at it. That cup in your prop could really mess things up.
    There are other factors to consider after you do a few runs. Boost, exhaust pressure, engine temp fuel restrictions etc. these boats do not like to run fast. Mine gets crazy bow steer when flat out. If you get good speed similar to mine then your engine is probably making full power. I was told Eastern moved some weight around so you might handle different.
     
    ARC,
  8. Radar

    Radar Member

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    Thanks again for your help. Will try a few of your suggestions and see how things go.
    I will be down to the boat this weekend.
     
  9. Fishbound

    Fishbound Member

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    The difference between the Cummins setup and the Yanmar setup is wide open throttle RPM. The Yanmar turns more RPM at WOT then the Cummins with the same gear. Need less wheel to spin more RPM. Not sure what the WOT is supposed to be on the Yanmar, but I would start by taking some pitch out.
     
  10. Radar

    Radar Member

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    Hi Fishbound thanks for the input. WOT should be minimum 3300rpm's I will try and contact the manufacturer to see if they have any records on prop size and pitch for the boat. Going to check out a few things first this weekend and will let you know how I make out.
     
  11. eyecatcher

    eyecatcher Senior Member

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    Sounds about right the original JC hull would only run a 21 or 22" prop due to hull/skeg clearances. Phototach the engine and the shaft too if your unsure about the ratio. The yanmar tachs are notorious for being off several hundred RPM's.
     
  12. Radar

    Radar Member

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    Thank you eyecatcher. Will get the engine phototached and see what rpm's the motor is actually turning up.
     

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