engine mounts- rigid or dampers?

Discussion in 'Inboards' started by Joris, Dec 20, 2014.

  1. Joris
    Joined: Mar 2013
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    Location: belgium

    Joris Junior Member

    I started preparations to put the engine in my hull and while looking for parts and info i stumbled across a boat build by Kane Custom Boats. To prevent flexing under heavy load he used rigid engine mounts, not the damper-type i was planning on using.
    Obviously not an amateur (like me), an engine with much more torque and hp and a set-up with a V-drive while my is inline, should or can i consider rigid mounts?
    I have about 4-5 feet between strut and coupling, a 1" shaft and a PSS-seal.
    http://s1296.photobucket.com/user/blancoracing/library/?sort=3&page=1

    Joris
     
  2. CDK
    Joined: Aug 2007
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    Location: Adriatic sea

    CDK retired engineer

    Rigid mounts transmit all engine sounds and vibrations to the hull. That increases the noise level and may cause resonance in the weirdest places. The amount depends on engine power vs. hull mass.

    Quite acceptable in a tug boat or ferry, but not in pleasure craft.
     
  3. Joris
    Joined: Mar 2013
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    Location: belgium

    Joris Junior Member

    Thanks, CDK.
    That was what i was expecting but nice to be sure now;)

    Joris
     
    Last edited: Dec 22, 2014
  4. TANSL
    Joined: Sep 2011
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    Location: Spain

    TANSL Senior Member

    Maybe I misunderstand the question and I'll say something stupid but can't you mount the engine elastically mounted on a rigid longitudinal bench?
     
  5. CDK
    Joined: Aug 2007
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    Location: Adriatic sea

    CDK retired engineer

    Yes you can, but it wouldn't do much good.
    Anything elastic between the hull and the propulsion is subjected to torque and thrust. The latter can be avoided with a separate thrust bearing, the torque remains. Flexible engine mounts are not symmetrical but oblong to better cope with thrust.
    My favorite construction is a thrust bearing, universal shaft/joints and round or square engine mounts. It gives maximum isolation and avoids alignment errors, but it is more expensive than a straight shaft.
     

  6. TANSL
    Joined: Sep 2011
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    Location: Spain

    TANSL Senior Member

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