1974 Chris Chraft Rebuild

Discussion in 'Gas Engines' started by Dean R. Jarvis, May 11, 2012.

  1. Dean R. Jarvis
    Joined: May 2012
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    Dean R. Jarvis renovator

    i have a chris craft 38' coho
    existing engines are 427 ford 300hp with paragon transmissions
    converting to a commercial fish/dive boat by gutting entire interior
    22,000lb new 1974 reduce wieght by 4-5000 lbs
    i am cutting off the tri-cabin structure and adding alum. trawler style top over upper helm with upper deck from upper helm to extend to stern
    Question:idea:i will install new 1/8 inch aluminum floor
    repower with new gas engines or used 5.9 cummins diesels
    diesels burn rate 7.5 per hour 2800 rpm versus gas
    boat was sunk. engines and paragon trans missions to come out
    existing 400 gal. tanks in good shape. hull is like a tank. question with stripped down boat will old transmission bolt up to new engines? obviouly transmission need rebuild and probably have ratio reductions
    i have two 440 chrylers marine in various state of repair. should i use them or go with newer gas motors. i don't have 40 grand for new diesels.
     
  2. mydauphin
    Joined: Apr 2007
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    mydauphin Senior Member

    I would try to find two good used diesels with trannys. You got to figure what horsepower you want. You might need new shafts and props. Or stay with similar engines you have.
     
  3. Dean R. Jarvis
    Joined: May 2012
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    Dean R. Jarvis renovator

    1974 Chris Craft

    Thanks for your advise! your are correct, thats what i would really like to do. there was/is 300 ford gas 427's in there now. the shafts are 1.5 - 1 3/8" props that were used 22x24 pitch 4 blade. i probably need to stay with 300hp. the torque is what I was looking at. Big block gas 430-500 ft lb's
    From what I read 1265 ft. lb's for 5.9 cummins. Do I need to get different transmissions? Am i wasting time with Paragons to diesels. Do velvet drives tie to diesels ok? What is most cost effective:?:
     
  4. mydauphin
    Joined: Apr 2007
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    mydauphin Senior Member

    Velvet drives can't handle alot if I recall, not familiar with Paragon. Also remember gearing has to do with shafts too. All else being equal diesel would run slower because of lower rpms. To compensate you go with bigger props, but that puts more strain on shafts. You either match engine/tranny to props you have. Or match engine/tranny and buy props and possibly shafts. That is upto your budget. What speed do you want to go?
     
  5. Dean R. Jarvis
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    Dean R. Jarvis renovator

    Again, thanks for your advice. 25-30 mph would be great with a lighter boat. that would be al out to speed. cruising 15-20. the most i had out of my Trojan with chrysler 440 is 25 mph. in calm seas. Props are gone. I belive the paragon tranys are reduced ratio. they would have to be to turn 4 blade props 22x24. my Trojan has 18" props and 18 pitch. Top speed on the 38 COHO was 16 mph. gas was cheep back then. i remember gas wars at .25 per gallon!
     
  6. mydauphin
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    mydauphin Senior Member

    There is a major difference between designing propulsion system for 25-30 than for 15-20. Figure out how much pain you are willing to suffer and work from there. Pain = Money

    I would go with lower figure, much lower on costs including fuel.
     
  7. Dean R. Jarvis
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    Dean R. Jarvis renovator

    obviously you have felt the pain. as a contractor in Florida it hurts when I sit down. I want to do something smart. Diesel is more pain. I got other boats running at the marina. it seams the desiels are apart more often than the gas engines. of course the desiels are beat more.
     

  8. mydauphin
    Joined: Apr 2007
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    mydauphin Senior Member

    I was a marine contractor in Miami, FL. Pain isn't the word. Today it is cheaper to be semi-retired than have a construction company.
     
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