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Bertram 42 Detroit 6v-92TA Repower with Yanmar or Cummins

Discussion in 'Bertram Yacht' started by etang789, Jul 5, 2017.

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  1. etang789

    etang789 Member

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    Ok understood! Where do you guys get your AQ22HS? Directly or dealers?

    Any comments on the gearbox choices? One is at the limit another one is over kill... of course budget will come into play

    And I need recommendation on propeller choices, will order them after first sea trial.
  2. Pascal

    Pascal Senior Member

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    I ordered the shafts from a good local prop shop who machines the stock. They get the stock from a distributor in Alabama or Georgia and I was surprised to find the stock came from Italy ...

    I got new ZFs with the factory recons Cummins. That was another consideration in the decision. The old 500lbs Allisons had to go, I don’t think rebuilding these dinosaurs makes sense. The gears are that expensive anyway

    Again a good prop shop can run the numbers and advise you. I was lucky that my spare props were close enough and cold be repitched. And they were Nibral....
  3. etang789

    etang789 Member

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    I have just double checked the current old shaft size is 56mm (2.2 inches) diameter, and about 12 foot in length. If I use normal Aquamet 22 it will just fall short of 493hp at 491hp. But I dont see any where that supplies Aquamet 22 High Strength below 2.5 inches.
  4. Capt J

    Capt J Senior Member

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    While severely limiting buying used props etc. if you go with a splined prop shaft you can go with a smaller diameter shaft. I know of a 75’ sf with 2000hp 16v2000s and 2.5” splined shafts instead of 4” and a normal key way.
  5. PacBlue

    PacBlue Senior Member

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    56mm (2.205") is awfully close to a US 2.250" (57mm) shaft diameter. Assuming it would still be the factory 2.250" shafts?

    But for conversation sake, using 56m (2.205") and regular AQ 22 (63,000 psi yield strength in torsion for shafts 2" - 2-1/2") at a gear ratio of 2.20 /1, you get a Safety Factor of 5.20 and therefore have no need to go to AQ 22 High Strength. Bertram did their home work and has the right set-up for your needs.

    For reference:

    upload_2018-8-27_8-49-50.png
  6. PacBlue

    PacBlue Senior Member

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    How is the project going, are you in the water and running yet?
  7. etang789

    etang789 Member

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    So you saying that the Bertram 42 came with AQ22 or with the shaft diameter is US 2.250" (57mm) ?

    Thanks for asking the project was on hold back in 2018. Restarting the project now, need to update on myself if the previous engine and gearbox and genset choices are still the way to go...

    Previous final choices:
    • QSC8.3 493bhp @ 2,600rpm –Int. Rating (Int)
      • Smart Craft 2.5, DTS Control Head, Vessel View Display (7”, 2 pcs)
    • ZF 286A 2.208:1
      • Coupling, 12V Electric Shift; SAE#3, ratio 2.208:1
    • Whisper Power M-SQ 12 Marine Generator
    • BEP Battery Management Panel with Twin Engines
  8. PacBlue

    PacBlue Senior Member

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    It’s been awhile, glad to hear the project is up and running again.

    As far as the shaft goes, I was commenting on your information regarding shaft diameter, it appears to be unknown what material was supplied by the factory unless you can get access to the manual.
  9. etang789

    etang789 Member

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    Ok understood so I will just order AQ22 with the shaft diameter of US 2.250" (57mm)

    anything else I should pay attention with the propeller? Was thinking to do sea trial after Repower before I order a new propeller...
  10. Capt Ralph

    Capt Ralph Senior Member

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    Using a good propeller will offer a guide where to adjust.
    Please insure the wheels are matching the stamp. I personally prefer diameter adjustments over pitch on first tries. I just like surface and bite of the water and adjust from there.
    Your not building a race boat, but something to go fishing, diving, touring on. Not in a hurry (well so much).
  11. PacBlue

    PacBlue Senior Member

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    Well you could possibly use the original propellers for a baseline sea trial, but you would still have to recondition them at a prop shop and ensure their pitch and diameter are correct and balanced.

    The best thing to do is work with a good prop shop, they should be able to predict a good size from the get go (maybe require one adjustment) and give you a better sea trial.
  12. etang789

    etang789 Member

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    Yes, I would recondition the current one first for the first sea trial.

    If i want to purchase a completely new propeller which brands should I look into?

    There's no real prop shop in where I live, basically they just gonna grind it down and call it a day.
  13. PacBlue

    PacBlue Senior Member

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  14. etang789

    etang789 Member

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  15. PacBlue

    PacBlue Senior Member

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    So what is the nearest boating center near your Bertram?
  16. etang789

    etang789 Member

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    Hong Kong has a decent boating industry but the quality of their work is non existent...

    Zhuhai is nearby and they do some good stuff, but asked a few shipyard there and they werent interested in working on the Bertram
  17. etang789

    etang789 Member

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    just want to double check with you guys the ZF 286A 2.208:1 is the preferred / correct gear ratio to go with?
  18. PacBlue

    PacBlue Senior Member

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    From Post #7:

    2300/2.0 = 1150 shaft rpm.
    For the Cummins, 2600/1150 = 2.26 gear ratio.
    So continue with a gear as close to 2.26 as possible. ZF will be lighter.

    But as always, the buy-on you really need is from ZF. Have them run the numbers to confirm as they are the warranty provider.
  19. etang789

    etang789 Member

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    Many Thanks! Im just worried that the dealer didnt do the math right.