[Public-List] Mast Beam Failure

[crufone at comcast.net]

Michael, 

Just remember the beam will continue to flex under load.  The reason   
the original adhesive failed is that it brittle brittle and failed   
under the repeated flexing of the beam.  The AL plates will not flex   
making the entire structure very stiff.  Static load flexing   
(flattening you described) is not as much of a concern as the shock   
load flexing.  This dynamic loading of the structure is what causes   
the beam to fail over time.  and unless you have strain gages I don't   
believe you can measure it accurately. 

The cleats primary purpose is to reduce the torque load of the beam.   
The beam has a tendancy to want to torque away from thebulkhead.  this   
is cause by where the the mast step is in relationship to the   
bulkhead.  Unfortunately the very little of the mast rests on the   
bulkhead.  It is aft of the bulkhead.  This causes the torque loads   
that want to twist the beam away from the bulhead.  The cleats are   
used to minimize this movement. 

I believe if you install a new wood beam in the boat. It will flex and   
in short order that flattening you have now will appear again.   The   
flattening of the beam will occur before laminate failure occurs, not   
the other way around. 



Larry Morris 
Solstice, #501 



Larry, 

Thank you for your assessment of the dynamic loads involved while sailing. It seems that the situation might be cured by using vertical laminations of wood concealing a metal plate as the central lamination.  Your description of the need for the cleats on the bulkhead is the most clear to date. 

Originally, I thought of fabricating a metal 'u' channel and fastening it to the lower side of the existing wooden beam.  I could then camouflage the metal 'u' with a veneer of teak or mahogany. I rejected that plan because I feared the 'u' channel would trap moisture between itself and the wooden beam. 
At this point I believe that I will remove the original beam to assess what the situation is with the upper surface of the beam and interface between the beam and the bulkheads. After that I am not sure how I will proceed. 

As usual this list has been a font of ideas and information presented in a most supportive and helpful manner. 

Thank you....all. 

Unless others wish to go on.......it may be time for another thread to begin, ;-) 

Michael #133 




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