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View Poll Results: What to do?

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Results 11 to 17 of 17
  1. #11

    Re: Repowering my 1980 46C

    When posed with the same question with similar circumstances by my marine clients I always answer "replace with exactly the same."

    In your case, rebuilding the Detroits would be my pick. You know what to expect, you don't have to change anything and there are few unknowns. You have already calculated the time and cost involved to you.
    Last edited by scottinsydney; 09-21-2018 at 04:35 AM.

  2. #12

    Re: Repowering my 1980 46C

    If you want the same or better performance it's not enough to simply look at the horsepower rating for each option. Look at the torque curve for the original 8V71-TI's and then compare that at your typical cruising engine RPM and hull speed to the other options.

    You'll find that those old two stroke Detroit's put out lots more torque compared with a four stroke at any given engine RPM for same (or close). horsepower. So if your DD's are rated at say 425 HP and around 1100 lb-Ft. peak torque you're likely to be in the 550-650HP range or more for similar torque curves on a four stroke.

    My vote would be to rebuild the DD's and call it a day.
    Brian L

    IMPETUOUS - 1984 Hatteras 53 ED MY Hull #CN720
    GOD'S GIFT - 1972 Chris Craft 42 Ft. Commander
    QUEEN B - 1974 Century 24 Ft Buccaneer
    GOD'S LITTLE GIFT - 1962 Johnson 19 Ft. Runabout
    MON AMI - 1984 Catalina 30Ft. Sloop

  3. #13

    Re: Repowering my 1980 46C

    Another factor is that rebuilt Detroits pretty much add zero value to the boat, with a proper repower you may add $.50 on the dollar. I too will be faced with this dilemma when mine wear out.
    1988 Canoe Cove 53 "Lilo Honu"
    1984 Outrage Whaler 22 "Conchyjodyoos"
    Previously owned Hatt 36c

  4. #14

    Re: Repowering my 1980 46C

    $30k to rebuild the DD sounds pretty low, i guess it deoends what is included.

    The gears will have to replaced if you repower, i dont think the C series will work with the allisons. If you rebuild the DD you should rebuild the gears too while youre at it. More $...

    Repowering to the C series / ZF gears will lightened up the boat by about 3500 lbs, maybe closer to 4000 as the TI are heavier than the N. you will probably save quite a bit of fuel which is important for commercial use.

    The cummins dealer will run the numbers, or a good prop shop. Your shafts and props maybe fine. I put new shafts in mine when i repowered earlier this year because i had old two pieces shafts. What material are yours? I was able to stay with the same 2" shafts but they had to be aquamet 22 HS

    You will have to redo the engine beds to accomodate the C series... not a huge deal but a litte extra $

    I got my engines and ZF from Mavex, here in Miami. They re a large dealer / exporters for cummins, yanmar, northern lights, onan, etc...
    Pascal
    Miami, FL
    1970 53 MY #325 Cummins 6CTAs
    2014 26' gaff rigged sloop
    2007 Sandbarhopper 13
    12' Westphal Cat boat

  5. #15

    Re: Repowering my 1980 46C

    Convertible guys only. The motoryacht owners dont understand the needs of a fishing boat.

    Look for a pair of 540 HP or better 6C series. Used or recon. It may be a bit higher cost but

    1) the fuel savings will be significant for your use.
    2) the increase in speed will be nice even if you dont always use it.
    3) the value of the vessel will increase.
    4) You will have a solid and easy to maintain platform with room to move around.

    Im doing maintenance on a 38 rampage with 6C540's. Its nice to work on and at 2500 hours theres no mechanical issues. Just maintenance.

    Id love a pair of these for my boat. Seatrials next week to see if we can hit 38 Kts.
    Scott
    41C117 "Hattatude"
    Port Canaveral Florida.


    Marine Electronics and Electrical Products Distributor.

  6. #16

    Re: Repowering my 1980 46C

    I truly do appreciate all of your feedback. at this moment in time I am going to await results on a compression test of the problematic motor and go from there. If I can get away with another rebuild then I'm all about the path of least resistance. If I find that it's going to be more involved then I'm considering buying a fully rebuilt D and just swapping it out. However, in a perfect world of unlimited funds and time I would rather go with the 6CTA 450's (non electronic). Just need a big bag of money to fall out of the sky. I know I'll make it back in fuel, parts, maintenance, oil, etc; savings down the road. Just need to convince a bank, angel, slot machine to help me out.

  7. #17

    Re: Repowering my 1980 46C

    Cummins c series 8.3 liter are mechanical are going to be too small for a 46c. I have c's in my 41 and it tops out around 30-31 knots and easy cruise at 18knots doing about 18gph total. The 41c is much lighter and much flatter ass and requires way less HP. A 46c needs m11. Save your pennies and do it right.
    FTFD... i drive a slow 1968 41c381

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