Click for Nordhavn Click for Mag Bay Click for Northern Lights Click for Glendinning Click for Abeking

Difference between port and starboard engine

Discussion in 'Technical Discussion' started by Worthy vessel, Sep 8, 2020.

You need to be registered and signed in to view this content.
  1. mapism

    mapism Senior Member

    Joined:
    Aug 9, 2008
    Messages:
    982
    Location:
    Sardinia
    Either I'm not understanding what you mean, or I'm missing something.
    Let's take a typical gearbox like the one below.
    It's directly coupled to the engine, and its only external rotating part is the flange at the bottom, to which the shaft is connected.
    If you put the tape on that flange, or on the shaft connected to it, you certainly can measure the rpm, but with the two caveats of my post #13:
    1) you can't check idle speed with gear disengaged
    2) the rpm that you measure is affected by the g/box reduction ratio

    [​IMG]

    Mind, as I said I normally attach the reflective tape on the pulley, so the gearbox and its layout is totally irrelevant.
    In just one occasion, when the very tight space on the front side of the engine did not allow to keep the photo tach in a decent readable position, I attached the tape to the g/box output flange.
    I did have to consider the reduction ratio for calculating the actual engine rpm, though.

    If there is a third alternative (vs. either the front pulley or the g/box output), I'd be curious to understand what it is.
  2. Capt Ralph

    Capt Ralph Senior Member

    Joined:
    Sep 8, 2004
    Messages:
    9,207
    Location:
    Satsuma, FL
    I have to type slower or your going to have to read the post to the bottom;
    From #19 above;
    Regardless of where the foil tape is placed, just the same place on both engines if just comparing rpm.
    If your checking against your helm tach, Best on the balancer or crank pulley base.
  3. MYTraveler

    MYTraveler Member

    Joined:
    Dec 30, 2014
    Messages:
    40
    Location:
    PNW
    From first hand experience, I learned that there is a third caveat with which one must be concerned. In a prior boat that had high-horsepower J&T 892s, with Alison gears, I burned out a transmission because one of the gears was slipping. A great deal of pressure was required to keep the gears from slipping, but too much pressure and the engine's rear main seal will blow out (with gear oil escaping into the engine's oil pan). I ended up creating my own micro-processor based digital display gauge to indicate slipping on either engine.
  4. Capt Ralph

    Capt Ralph Senior Member

    Joined:
    Sep 8, 2004
    Messages:
    9,207
    Location:
    Satsuma, FL
    There are setups like that already out there. They display the amount of slip in clutches with trolling valves.
  5. MYTraveler

    MYTraveler Member

    Joined:
    Dec 30, 2014
    Messages:
    40
    Location:
    PNW
    Now you tell me. I certainly couldn't find one but didn't mind making my own. And trolling valves (where a high degree of slip is expected) are a sufficiently different application (from my need to confirm that there was to measure even slight slip) that a trolling valve slip monitor would not have performed as well.
  6. Capt Ralph

    Capt Ralph Senior Member

    Joined:
    Sep 8, 2004
    Messages:
    9,207
    Location:
    Satsuma, FL
    Well there ya go. You probably have the much better instrument anyway.
    cr
  7. mapism

    mapism Senior Member

    Joined:
    Aug 9, 2008
    Messages:
    982
    Location:
    Sardinia
    Good point, but did you experience slipping only depending on some conditions, like rpm or load?
    I'm asking because for some occasional checks it would have been sufficient to put the tape on both the front pulley and the gearbox output, and check the consistency.
    Nowhere near as convenient as having a gauge on the dashboard of course, but I would guess (and hope!) that a gearbox doesn't start slipping badly in the middle of a passage with no previous warning signs.
  8. alvareza

    alvareza Member

    Joined:
    Aug 20, 2010
    Messages:
    98
    Location:
    Boston MA
    Got the numbers:
    • Port 138 degrees and 214 psi
    • Stbd 129 degrees and 223 psi
    Fairly sure these have been consistent for two years at cruise. Engines were synchronized. Both engines at 164 degrees. Port engine runs 1 gph higher at cruise 70-80% load. Anything In the temps that merits further investigation?

    All the data is from the DD engine displays, MTU Series 60. Are the RPMs shown on these displays considered accurate?
  9. Fishtigua

    Fishtigua Senior Member

    Joined:
    Jul 20, 2007
    Messages:
    2,768
    Location:
    Guernsey/Antigua
    On one yacht, sadly no longer with us, she had counter-rotating Baudouin diesels. To go astern you had to shut them off, re-fire them to run backwards, and then go in reverse.

    Thank you modern gearboxes.
  10. Worthy vessel

    Worthy vessel Member

    Joined:
    Feb 16, 2019
    Messages:
    55
    Location:
    Sarasota
    I don't think it is an RPM issue with the transmission temps, the temp does not change from cruise at 2600 RPM to WOT of 3000 RPM. I have checked accuracy of gauge with heat gun. I have both analog and digital gauges which show same temp for the engines. Will have to check the spin of the props with engine off. Planning on changing the transmission cooler. Was able to look inside and looked OK so I don't think it will change the running temp.
    Will keep you updated. Thanks
  11. rtrafford

    rtrafford Senior Member

    Joined:
    Jul 13, 2019
    Messages:
    843
    Location:
    Vero Beach
    Consider swapping the coolers to see if the problem follows the cooler?
  12. Capt J

    Capt J Senior Member

    Joined:
    Jul 11, 2005
    Messages:
    13,412
    Location:
    Fort Lauderdale
    Why are you trying to fix a problem that does not exist? The temperature that the port gear is running is well within spec. Leave it alone.
  13. Capt Ralph

    Capt Ralph Senior Member

    Joined:
    Sep 8, 2004
    Messages:
    9,207
    Location:
    Satsuma, FL
    Some folks don't like sleeping dawgs.
    Or, just put on a newer and larger cooler. This would also keep your hands off of the other engine at this time.
  14. Capt J

    Capt J Senior Member

    Joined:
    Jul 11, 2005
    Messages:
    13,412
    Location:
    Fort Lauderdale
    Every boat/yacht I run one gear runs a good 10F hotter than the other and 9 times out of 10, it's the port gear.
  15. rtrafford

    rtrafford Senior Member

    Joined:
    Jul 13, 2019
    Messages:
    843
    Location:
    Vero Beach
    Ok, fine. Don't touch the coolers. Use your heat gun on the incoming and discharge ports of the heat exchanger. Your temperature delta on each engine should be the same if the heat exchangers are performing as they should. But the very fact that the temps aren't climbing suggest that there is no blockage.
  16. DOCKMASTER

    DOCKMASTER Senior Member

    Joined:
    Feb 26, 2012
    Messages:
    619
    Location:
    Ketchikan, Alaska
    Agree with J. Why spend time and $$ on a non-issue? I have brand new engines, gears and all associated components. The gears do not run the exact same pressure and temp. Everything appears well within spec. Surely the OP has other things to spend time and $$ on?
  17. mapism

    mapism Senior Member

    Joined:
    Aug 9, 2008
    Messages:
    982
    Location:
    Sardinia
    +1 on the principle if it ain't broke, etc.

    BUT, the consistency check between the delta temp in/out the cooler that rtrafford suggested makes very good sense.
    Well worth the 3 minutes it takes (if that), imho.
  18. rtrafford

    rtrafford Senior Member

    Joined:
    Jul 13, 2019
    Messages:
    843
    Location:
    Vero Beach
    End of the day, we all must do our due diligence aboard to put to rest issues that bring us concern. If you have an issue that is raising a flag in your mind, you're doing your job as a captain or an owner or a mechanic if you chase down the concern and vet it out. Period. And there are always ways to vet these things out without spending big dollars or using pneumatic tools. If it's in your head, don't merely dismiss it.

    That's my philosophy. Like it or hate it.
  19. alvareza

    alvareza Member

    Joined:
    Aug 20, 2010
    Messages:
    98
    Location:
    Boston MA
    That’s exactly my situation. I‘m done wondering and worrying about it.

    Thank you Capt J!