Cutlass bearing power consumption

Discussion in 'Inboards' started by rfleet1066, Jul 13, 2021.

  1. rfleet1066
    Joined: Feb 2012
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    Location: New Kent, VA USA

    rfleet1066 rfleet1066

    We recently pulled the long tail drive from my river boat for inspection/refit. Originally the boom had five antifriction flange bearings along the shaft and one cutlass bearing at the prop. I installed two more cutlass bearings in place of the flange bearings on the wetted section of the boom/shaft. Re-installed and tested, I notice a difference in output power. Just wondering if the cutlass bearings consume energy. Ideas?
    Ryland
     
  2. rfleet1066
    Joined: Feb 2012
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    Location: New Kent, VA USA

    rfleet1066 rfleet1066

    This is the longtail boom IMG_4136[1].JPG
     
  3. bajansailor
    Joined: Oct 2007
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    Location: Barbados

    bajansailor Marine Surveyor

    Re the difference in output power, were you able to measure this difference, or were you simply noticing that the boat was running more slowly?
    How much 'difference' is this?
    How many hours have been clocked up since you installed the new cutless bearings?
    Are there any signs of wear on them yet, possibly indicating slight mis-alignment?
    Do you have any vibration on the shaft while underway?
     
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  4. kapnD
    Joined: Jan 2003
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    Location: hawaii, usa

    kapnD Senior Member

    The rubber may be heating up and swelling around the shaft where it does not get constant water cooling.
    There are “hard” types of cutless bearings that might be less susceptible.
     
  5. BlueBell
    Joined: May 2017
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    Location: Victoria BC Canada

    BlueBell "Whatever..."

    Ryland,
    Did you look at the bearing manufacturers spec sheet online?
    Or, there may be independent reviews (even better).
    What's the brand name and model on the bearings you installed?
     
  6. jehardiman
    Joined: Aug 2004
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    Location: Port Orchard, Washington, USA

    jehardiman Senior Member

    Cutless bearings are designed to be run wet for cooling and lubrication. As kapnD suggested, you may be destroying the bearings as well as the shaft due to overheating. As far as shafting goes, a cutless bearing should only be used as the last one because it is designed to wear due to the overhanging weight of the prop. Intermediate bearings should not be as long and should spin freely. They are to prevent shaft whirl only.
     
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  7. rfleet1066
    Joined: Feb 2012
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    Location: New Kent, VA USA

    rfleet1066 rfleet1066

    I notice a 50 RPM top speed.
    About 15 hours have been run on the new bearings.
    I used a tensioned .010" piano wire in mandrels at both ends with dial indicator measurement to align. Most likely not misaligned.
    There is vibration above 1800 engine RPM during forward propulsion. No vibration in reverse.
    Anti-friction bearings are used in the section of boom that is not submerged.
    Fuel consumption shows .3 GPH increase with the new bearings.

    Ryland
     
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