Thrust Bearing Source

Discussion in 'Inboards' started by armstpat, Oct 28, 2012.

  1. armstpat
    Joined: Oct 2012
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    armstpat Junior Member

    I'm just about to start building a 25 foot Carolina Skiff. I want to use a thrust bearing and short shaft to the engine. Does anyone know where I might purchase the thrust bearing?
     
  2. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    Any bearing supplier will have them. However, it is up to you to specify which bearing you need.
     
  3. keysdisease
    Joined: Mar 2006
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    keysdisease Senior Member

    That seems like a major overkill for a 25ft boat. $.02
     
  4. Frosty

    Frosty Previous Member

    A thrust bearing needs space your short shaft requirements contradict.
     
  5. michael pierzga
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    michael pierzga Senior Member

    On big boats thrust bearing shaft logs are common. Ive never seen one on a 25 footer.

    You might look at the Evolution marine system for inspiration. I see that they produce the system down to one inch shafting. This is expensive gear.

    http://www.evolutionmarine.com/detail.html?id=3001#info
     
  6. armstpat
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    armstpat Junior Member

    Thanks for the replies. I am new to boat building and only have 'book learning' so far. The setup from evolution marine might fit in my limited space. I really wanted to use a thrust bearing as I wanted to go with a diesel. It's good to know small boats don't normally use bearings If I can't get the thrust bearing to work.
     
  7. FAST FRED
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    FAST FRED Senior Member

    " I really wanted to use a thrust bearing as I wanted to go with a diesel."

    IF your diesel will be using a marine transmission , the thrust bearing is built into the transmission.

    NO extra bearing is required.
     
  8. michael pierzga
    Joined: Dec 2008
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    michael pierzga Senior Member

    An additional thrust bearing is a nice detail. You can use softer engine mounts and achieve better alignment. This equals a much quieter drive train. The small craft that use them are electric boats. You might do some google action around the electric boat clubs for info.
     
  9. CDK
    Joined: Aug 2007
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    CDK retired engineer

    A thrust bearing can actually save space because the gearbox needs not be in line with the prop shaft.
    I have put two small turbo charged diesels in an engine bay made for stern drives. Without thrust bearings and U-shafts that would have been impossible.
     
  10. Frosty

    Frosty Previous Member

    Why do you think a diesel needs a thrust.
     
  11. BKay
    Joined: Jan 2011
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    BKay Junior Member

    Armstapt - I have an Evolution system in my 29' lobster boat. It is a well made system, but I can't honestly tell you how much I benefit from it. I can tell you how much it cost - about $5K more than a conventional system with no thrust bearing. BTW - my builder and I considered some other thrust bearing options (without the integrated shaft that EMSS has) and we didn't have the necessary space. However, he was able to fit the EMSS in.

    My guess is that with the softer mounts and the EMSS - I get a moderate amount of vibration reduction at cruising speed; but nothing phenominal. I like the system and it is well built, but if I was cutting cost, that's the first thing I'd leave out.

    I'm not a technical guy, but if you have any questions about the system, let me know. Also, I've made several calls to the guys at Evolution - they always made time to talk to me. If you have questions for experts on that system, call them.
     
  12. michael pierzga
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    michael pierzga Senior Member

    As your boat ages I think you will appreciate the evolution system. Ive not used that system, but have operated with a similar system from Federal for many years on three different boats. The one Im running now has 14,000 hours on it...zero maintenance and never one drop of sea water in the machine room. Conventionally shafted systems require , coupling, Stuffing box, cutlass bearing and shaft maintenance .This adds up over the log term.
     
  13. keysdisease
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    keysdisease Senior Member

    If you get a good engineer experienced with engine mountings you can achieve very good engine vibration isolation with the correct thrust taking mounts.

    The reason many boats suffer from too much vibration is that the builder just uses the mounts that come with the engine. These are typically on the very conservative side of selection as the engine supplier will not usually know the kind of service the vessel will be in.

    Given the weight, HP, gear, ratio, CG, distance from CG to mounts, prop size and typical RPM range with cruise good vibration isolation can be achieved at minimal expense in a standard installation.

    This usually makes the best sense in a small bout like this

    $0.02 Steve
     
  14. Landlubber
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    Landlubber Senior Member


  15. Frosty

    Frosty Previous Member

    Thrust bearings are for engines that develop thrust and can become a problem. Your 25 foot skiff will not have that thrust.

    I have 2 x 250HP engines that don't have thrust blocks. this is nothing unusual.

    In a boat that small you will feel vibration anyway and I doubt you will achieve expense ballance.
     
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