Thordon Shaft Bearings – Not Just for the Big Boats

Thordon Shaft Bearings

We are going through the running gear system on a 36 foot Glasstech built fishing boat – a classic looking walk around.  The shafts are out for straightening and engine alignment to cure a persistent problem with a port side vibration.  We are also replacing the shaft bearings.

The vessel was built with Thordon plastic shaft bearings.  Thordon material is a hard compound that is an alternative to rubber cutless bearings.  Thordon bearings are common in large commercial vessels (over 1,000 ton) and we see them in our yard on Trinity’s and other vessels from 120 foot and larger.

It is not so common to see Thordon’s in smaller vessels although they can be found in many Hatteras’.  One advantage with Thordon bearings is the elimination of bearing squeal or, more technically, “stick-slip”.  Bearing squeal is sometimes found with rubber bearings on stainless prop shafts when the shafts are turning extremely slowly.  The shaft is not spinning fast enough to get the hydrodynamic lift of water between the rubber and the stainless steel.  The result is a squealing sound.  Not a big deal, unless you are in trolling mode or drifting, trying to catch fish.

Liquid nitrogen process for Thordon Bearings

Thordon bearings are installed with an interference fit.  The bearing OD is machined larger than the strut barrel and frozen down to shrink the OD for installation.  We use liquid nitrogen (minus 270 degrees) to shrink the bearing.  It only takes a few minutes in the liquid nitrogen to shrink and 15 to 30 seconds in the strut barrel to warm up and fit tight.  You have to move fast to get it right the first time.