[Public-List] Mast Beam Failure on #133

[Lawrence Morris]

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




On Jan 11, 2010, at 12:27 PM, crufone at comcast.net wrote:

>
>
> Hello all,
>
>
>
> On my boat the failure of the mast beam has been the failure of the  
> original Resorcinol glue and not the wooden components of the beam.   
> I know from experience that as Resorcinol glue ages it crumbles into  
> a grainy powder.  When the beam was in the collapsed position I  
> could actually see light through (between) the laminates.
>
> In a discussion with Philip Beigel Sr. in 2004 he told me that was  
> possible to remove the mast beam because that on the early boats it  
> was basically bolted to the main bulkhead.  There is some tabing but  
> that is easily cut and removed.  This discussion encouraged me to  
> persue the removal, repair and replacement approach to this issue.
>
> Since the Resorcinol glue had failed and become brittle I felt that  
> the laminates on my boat could be separated once the beam was removed.
>
> I have done some tests while sailing and using measured reference  
> points have determined that the entire beam does not flex/move  
> downward in my boat.  Rather it tends to 'flatten' in the middle,  
> (as between the door jambs).  This also suggests that the beam as a  
> whole may not extend in length athwartships. The failure of the glue  
> allows the laminates to slide against each other and the beam to  
> loose it's arch. As the arch flattens the rig loosens.
>
> This observation leads me to question if the 'cleats' added to the  
> bulkhead jambs to increase the surface area supporting the beam at  
> that point have much of an effect on mitigating the flattening of  
> the center of the beam. Hummmmmmmmm....
>
> As I am removing my beam I will inspect carefully the bolt holes in  
> the bulkheads to determine if the beam has actually elongated the  
> holes and moved in relation to the bulkhead.  If not, then the task  
> is to retain the arch of the beam, particularly in the span between  
> the door jambs.
>
> I assume this can be accomplished with metal, adhesives, mechanical  
> 'keys' or a combination there of added to the original or a  
> replacement wooden beam.
>
> I know that the aluminum plate sistering method is a time tested and  
> durable repair.  I also don't wish to be irresponsible and use a  
> method which is any less durable and sea worthy.  I also don't  
> question the fact that the aluminum plate method is a relatively  
> efficient way to affect this repair. What I don't appreciate is what  
> it does to the appearance of the interior of the boat.
>
> Perhaps I am just a frustrated plastic boat owner who wished his  
> boat were made of wood!! I believe that the original mast beam was  
> engineered well enough. The glue failed and I can replace the glue  
> with a stronger more durable adhesive and she can sail on with that  
> minor modification for another 43 years.
>
> Michael #133
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