[Public-List] Mast Beam Variation

[John S. Riley]

Jeffrey wrote:
> Have there been any failures of the beam? Any while the lamination was
> still strong? It would have to be early in the boats life to determine
> that I guess.
>
>   

Yes.  This was in 1980 or so (early 80's anyway), so the laminate was 
not 40 years old at that time.  Yves Gelinas was in the Indian Ocean 
aboard his A30 and got knocked down.  This damaged his mast support beam 
and dropped his cabin roof by several centimeters.  As a result of the 
distortion, he could not close his main sliding hatch - not a good thing 
offshore.  His repair when he made it to port?  Aluminum sisters.  Yves 
ultimately completed his solo circumnavigation via Cape Horn.

You might be saying "well, that's offshore in the Indian Ocean." But the 
point is that the rig can be under incredible loads just about anytime 
while sailing - big gusts, squalls, containership wake, etc.  Also, this 
was considerably less than 20 years after his boat was constructed (I 
believe his was a 1967), so I don't think the point of the age of the 
beam ("it's lasted 40 years") is the issue here.

> Not to say the aluminum plates are not a good idea, but wouldn't it
> stand to reason that if the wood itself was in good condition, then a
> new lamination using an epoxy glue likely last another 40 years? Or,
> even a new laminated beam using oak and epoxy?
>   

Why not just make the thing as strong as possible and have confidence in 
it, rather than always wonder if it really will last another 40 years?  
The bottom line is that this beam is a major structural component of the 
boat and there is no way to make it TOO strong.

One question: Is oak really a good construction material for this 
application?  I've read oak does not glue well, does that apply to epoxy 
layups as well?

-- 
John S. Riley, Ph.D.
DSB Scientific Consulting
http://www.dsbscience.com 


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