[Public-List] Dynamic Loads while sailing

[Lawrence Morris]

Michael,

There are a number of components that flex in the system: sails,  
halyards, sheets, standing rigging.  I think you want to minimize  
flexing in structural elements of the hull and deck.  if the beam  
flexs the deck flexs and the bulkhead flexs.  I want something above  
the deck to fail in case of extreme dynamic loading.  rigging, sails  
halyard or even mast.  What I don't want is that the beam is flexing  
and then fails during complete knockdown and punch the mast through  
the deck.  I want that beam to be the strongest element on the boat  
and as stiff as possible.  This has 2 benefits one is it makes the  
boat safer and it improves performance.  The less flex in the rig and  
structure the more thrust is delvered to the water the faster you go.




Larry Morris
Solstice, #501




On Jan 12, 2010, at 10:40 AM, crufone at comcast.net wrote:

>
>
> 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.
>
>
>
> Larry Morris has got me to thinking with his response above.  Is  
> there any support for the argument to design in some flex in the  
> mast beam as it transfers the load from the mast butt to the hull? I  
> know that structural engineers design in flexible components for  
> tall buildings so that they can resist various wind load  
> conditions.  If the buildings were rigid the wind load would exceed  
> the strength of the materials and the buildings collapse?
>
> So is there some merit in allowing the mast beam some flex?  I  
> wonder if the mast beam were too rigid  might something else fail?
>
> I assume while in a strong gust that the rig loads up in some sort  
> of sequence, i.e., sails, running rigging, mast, shrouds, chain  
> plates, couch roof, mast beam , bulkheads, hull, keel.  This might  
> only take part of a second, but it does happen in sequence.  My  
> thought is if each component has some flex or elasticity then the  
> opportunity for the whole to absorb more load is greater. Is this  
> true or am I just out to lunch?
>
> Michael #133
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