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380 flybridge / 3126 cats

Discussion in 'Luhrs Yacht' started by hannah rose, Nov 8, 2020.

  1. hannah rose

    hannah rose New Member

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    Greetings,
    Just picked up a '98 tournament 380 which will only pull 2300 rpm's WOT the props are
    26by27 four blade. Is it possible the boat is not pulling close to spec WOT which is 2850 due to
    being over propped? In neutral the motors spin up to 3k easily and the motors run great.
    Grateful for any assistance.
  2. NYCAP123

    NYCAP123 Senior Member

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    That could definitely account for it as could a dirty bottom, bent shaft, bad cutlass bearing or struts.
  3. hannah rose

    hannah rose New Member

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    Thanks for the reply
    The survey included a haul out and according to mechanic and surveyor everything looks good so that leaves the props which they felt were over propped. I’ll begin with a change in props.
    If anyone runs the same boat and motor I’d love to hear what props you are using.
  4. Capt J

    Capt J Senior Member

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    DID you have engine survey done??? If not I would do that first, 550 RPMS shy of WOT is A LOT. I would also try to do another seatrial, make sure all fuel filters are new, air filters are clean and see what rpms each engine makes by itself WOT (1 at a time), I would also measure what boost is at cruise and WOT as well as fuel pressure. If the current mechanic is not a CAT dealer mechanic I would get one. If the bottom was clean, I'd be very wary that there isn't something major going on with 1 of the engines or both. Honestly I wouldn't move forward with the deal at this point without verifying it's not something in the engines. You can't even cut the current props enough to get the rpm's you're looking for as they're so far off. So you're looking at buying new props. What was speed at WOT. What did the boat weigh? Is it within spec?
  5. hannah rose

    hannah rose New Member

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    certified cat mechanic was on boat for sea trial, he felt the motors were good, he did a full inspection including oil samples. Oil samples were taken in July and again last week and shows no issue. Motors spin up to 3k RPM individually in neutral.
    I'm being told that props can easily account for the difference but again I'm relying on others as I have no personal experience.
  6. Slimshady

    Slimshady Member

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    Running diesels that over loaded is not good at all. I smell problems cooking
  7. hannah rose

    hannah rose New Member

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    please elaborate as your comment is very vague thanks
  8. Capt J

    Capt J Senior Member

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    Running diesels that only make 2300 RPMS when they're supposed to make 2850 RPMS WOT is very bad for them. In my mind a 550 rpm loss of what the motors should turn is HUGE. To me this tells me there is something wrong with the motors not making enough power due to a mechanical issue than it does props. I would imagine that these props origionally turned 2850 rpms when the boat is new. 550 rpms is a sign of a serious problem.
  9. Slimshady

    Slimshady Member

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    Diesel motors do not like being over loaded. 100 rpm raises flags. 500+ is huge. The pistons, crank, bearings are under much higher stress with less coolant flow on top of that. Ride your bike up a steep hill in to high a gear, that grinding and popping sound is what is happening in the motor. It also hints at poor maintenance from previous owner, why did they let it get that bad. Diesels are great powerplants if maintained properly
  10. hannah rose

    hannah rose New Member

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    the motors have never been run hard the owner babied them and used them regularly, they have 3K hours, Certified cat mechanic did full inspection and was on sea trial claims they are good and RPM loss is due to props
    is he wrong?
  11. hannah rose

    hannah rose New Member

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    motors start right up, little to no smoke on starting, runs very smooth and no smoke under way, the prior owner ran them at about 1800 RPM's when running, but mostly used for trolling for salmon
  12. Capt J

    Capt J Senior Member

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    The motors have lived a very hard life if they only turn 2300 rpms WOT, no matter what rpms you run them at, they are being run in an overloaded condition.

    You don't just lose 550 rpms. The original props, just don't become over propped without a legitament reason, such as boat weighing considerably more or engines no longer performing (making the same power as they did new), or an issue such as the bottom being dirty. 100 rpm's difference between rpm and WOT rpm's, given the age I could see, 550 rpms lost, is a GLARING red flag that you have a big issue somewhere. Are the props that are on the boat the factory prop specs when the boat was new?
  13. hannah rose

    hannah rose New Member

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    I just got off the phone with Wilmington props who confirmed that the props are way out of spec and need to be reduced to 23 from 27 and according to them is the likely culprit. Like I said in my earlier post the engines had oil
    samples taken and were inspected during the sea trial by certified cat mechanic. Not sure what else I can do. And the bottom is dirty
  14. boatpoor

    boatpoor Member

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    I would clean the bottom ( everything below the waterline) and run it up to wot again before I started trimming the wheels.
  15. mapism

    mapism Senior Member

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    What?!?
    Neither the surveyor nor the mechanic suggested to clean the bottom and the underwater gear while the boat was out, before going for a seatrial?
    Did you already pay them...?
  16. DOCKMASTER

    DOCKMASTER Senior Member

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    Wow this whole situation sounds bad. As others have mentioned, 550 rpm loss is huge. You say Michigan says the props are out of spec. What are they basing this on. If spec is 23”pitch, how did they ge to 27”? Did previous owner change props and just throw on some used wheels he bought on EBay that for the shafts? And your “certified” CAT mechanics didn’t make a big deal of this overloaded condition? You have the wrong mechanic doing your survey. When CAT recently came to trial and certify my new CATs, the main thing they were interested in was ensuring I reached WOT + a little extra under fuel load. And by the way, quit running them WOT at idle. That doesn’t mean anything and will only cause issues.
  17. DOCKMASTER

    DOCKMASTER Senior Member

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    Curious- did you already complete the purchase of this boat? I’m guessing yes based on your comment that you just picked it up. Is this correct?
    You really need to look at this in perspective, you are a whopping 20% overloaded and you need to know why. What are the complete original boat prop specs - diameter, pitch, # of blades and any cup. And what is on there now?
    How bad is the bottom? Got any pictures from when hauled?
  18. mapism

    mapism Senior Member

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    I agree with everything you wrote, but actually running at wot unloaded is one of the normal checks for diesel engines. Didn't they do that with yours?

    If and when the engines don't reach the max unloaded rpm, it's pointless to even make a seatrial, but that's not the case here.
    Actually, I'm not sure of what the number should be for the 3126, but 3000 sounds about right for an engine rated for 2800 rpm under load.
    Which in fact is what the 3126 is, not 2850.

    That said, of course running at WOT unloaded is something you only want to do upon engine check, with all the fluids up to normal running temp, and just for some seconds.
    I'm not suggesting to do that upon every stone cold startup, to warm the engines faster! :D
  19. DOCKMASTER

    DOCKMASTER Senior Member

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    Hannah Rose I hope we didn't chase you off. I would really like to hear more about what you found and if you have made any progress toward correcting the overloading?
  20. hannah rose

    hannah rose New Member

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    turns out that with the bottom cleaned the numbers changed dramatically at WOT it made 2650 rpm's with wheels that are still slightly
    over propped according to Wilmington props. Bought the boat and ran it for hours to my home port and it ran beautifully.
    Thanks for all the feed back