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Bertram 68 motoryacht repower

Discussion in 'Bertram Yacht' started by Trinimax, Dec 14, 2021.

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  1. Trinimax

    Trinimax Senior Member

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    My buddy finally finished up his repower project on his bertam 68 Cockpit MY, boat was a 58 aft cabin with a 10 foot cockpit added.

    The boat originally had 12v 71 TIs at around 650 hp and the rough numbers were as follows
    1400 rpm, 10 kts 21 gph
    2000 rpm, 18 kts, 60 gph
    2300 rpm, 21 kts, 76 gph

    The new engines installed are twin C 12.9 cats at 850 hp, spinning 4 blade 32 x 35 props
    the new rough numbers are as follows
    1200 rpm, 12 kts, 18 gph
    1900 rpm less than 80 % load, 20 kts, 50 gph
    2300 rpm, 25-26 kts, 86 gph

    The fuel capacity of the boat is about 2200 gallons, so she has some pretty good range. The owner simplified the fuel system by using the center tank ( original aft tank) as a day tank, and then fuel is transfered to that tank from the forward and aft cockpit tank.

    due to the marginal increase in HP, the shaft and exhaust size remained the same, which made the project a bit easier.

    Attached Files:

    cleanslate likes this.
  2. Trinimax

    Trinimax Senior Member

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    Here are the cats installed

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  3. Trinimax

    Trinimax Senior Member

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    here she is launching and at speed

    Attached Files:

  4. Capt Ralph

    Capt Ralph Senior Member

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    I'll be studying these pictures for a long time to come.
    What clutch was used? I can see it had a down angle.
    Big ole coach roof hatch works darn good.

    Is this the boat that had 3412s originally planned?

    Send in more pictures. Of the extension also please.

    Thx
    Ralph
  5. motoryachtlover

    motoryachtlover Senior Member

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    Do you engine guys think the owner should have gone with larger displacement engines? Are those 12.9s going to be stressed pushing that boat at cruise speed? Maybe the owner just wants to cruise at idle speed.
  6. mapism

    mapism Senior Member

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    No idea about if and how much oversized the original shafts were (or not) vs. the original power.
    But the exhaust size depends more on displacement and rpm, rather than power.
    And here we are talking of a 40% displacement increase, with the same max rated rpm...
    Good luck with that.
  7. mapism

    mapism Senior Member

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    20 kts at 1900 rpm with less than 80% load doesn't sound too bad, actually.
    I guess that aiming at a much faster speed with that hull would be pointless.
  8. cleanslate

    cleanslate Senior Member

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    Looks great ! Nice job. I wish you guys would wear some better footwear while working on those bilge monsters! Ouch!
  9. Capt Ralph

    Capt Ralph Senior Member

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    Like my 58, those were low restriction 10 inch exhaust lines. From a old design 14L to a modern 13L may be a loss in engine displacement but doable. Those one piece 2.5 inch shafts with an extra strut should be around the safe max but doable well also.
    The grace in added hull displacement, the beam to length ratio just improved big time. It is not unusual for speed increases with the same engines when cockpit extensions are added. I remember a 58 Bert that was lengthened to 80. Turned the same speed.
    I do look forward to a 1000 hour report and I anticipate good news then.
    Last edited: Dec 14, 2021
  10. YachtForums

    YachtForums Administrator

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    LOVE threads that document refits. Thank you Trinimax!
  11. Capt Ralph

    Capt Ralph Senior Member

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    One design item I question, moving the rudders back and not the props.
    You will get no wash on the rudders and poor slow speed operation. I used to run a Roamer house boat with an extension, just the rudders moved back. Ended up upgrading to large stablizer fins for rudders. Still throttles and clutches needed in slow speed areas. The owner may consider moving back to the original locations.
    YachtForums likes this.
  12. jhall767

    jhall767 Senior Member

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    You're forgetting that the switch was from detroits which exhaust on every stroke to 4 cycle so the volume of exhaust is actually less.
  13. mapism

    mapism Senior Member

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    Doh! Don't ask me why, but when I wrote my previous comment I calculated by heart a displacement of around 9L for the V12 DD 71 - hence my comment on 40% increase.
    Not sure of what I was thinking...
  14. Trinimax

    Trinimax Senior Member

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    Thanks fellas glad you like the pics. in answer to some of your questions.
    @Capt Ralph
    1. the new gears are ZF 1.97:1 with a 10 degree down angle, where the original gears were straight, so the stringers up forward had to be cut down a bit. this worked well as there is a good bit of headroom above the front of the engine.

    2. The owner bought this boat about 15 years ago with the extension. so fortunately that wasnt one of his upgrades. The rudders were also moved aft by the previous owner. Funny enough there is another 70 ft stretched 58 bert in Trinidad and this had the rudders in the original location, and the low speed steering wasn't very good, and the owner moved the rudders aft. So far the steering is good at displacement and planning speeds, and the bow thruster helps for close quarters maneuvering.

    @motoryachtlover

    there is a boat called the Sirena 64 that is similar size and weight as this bert and she has the 1000 hp versions of the C12.9 cats and the performance numbers are similar. This 58/68 bert has only 15 degrees of transom deadrise, so she is not as deep a V as the other berts



    I have uploaded some pic of the early part of the installation of the custom D angelo exhaust risers. I would have to say that they were really helpful. they sent us a template form with the required measurements to take. Fortunately I took accurate measurements, and the completed product fit perfectly.

    I will try get you all some more pics of the other upgrades carried out on this boat

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  15. cleanslate

    cleanslate Senior Member

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    Looks good. I do not know, so I'm asking, That white exhaust elbow looks the same on the out side as on the inside? Or does it have a turning vane or defection point in it? Or does it just dump into the '' Tee''?
    How does it work?
  16. motoryachtlover

    motoryachtlover Senior Member

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    I think it is a T to allow room to keep water from surging up the exhaust and into the engine.
  17. DOCKMASTER

    DOCKMASTER Senior Member

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    Correct. They are called Surge Tee's. I have the same from DeAngelo as I went with them for my exhaust for my Repower.
  18. chesapeake46

    chesapeake46 Senior Member

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    + 1 on DeAngelo
  19. echo charlie

    echo charlie Member

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    How much weight was saved ?
  20. Trinimax

    Trinimax Senior Member

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    About 1300 lbs per engine, and maybe a litle bit on the transmission. so around 2700 lbs total