[Public-List] Dynamic Loads while sailing

[J Bergquist]

What I want to know is if you were seeing beam deflections of 1 foot,
what happened to the door between the main cabin and the forepeak? Not
to mention the bulkhead that is attached to the beam? I can't imagine
how those parts survived beam and deck deflections of a foot.

A comment about beam deflections...all materials deflect. The amount
of deflection is a function of the size of the load, the dimensions of
the structural member, and the materials of which it is made, but all
materials (aluminum, wood, steel, carbon, kevlar, hemp, dacron, mylar,
spectra) deflect under load. You may not be able to measure the
deflection, but every structural material which is placed under a load
will deflect some non-zero amount.

So the idea that the aluminum beam sistering fix completely eliminates
deflection in the mast beam of our boats is erroneous. It may reduce
the deflection to levels which we cannot measure with the tools
available to us (tape measure, dial indicator, or what have you), but
there is still deflection. The amount of deflection will depend on
many things...static and dynamic loads are a whole 'nother topic.

J

On Tue, Jan 12, 2010 at 11:42 AM, Lawrence Morris <morris.lc at verizon.net> wrote:
> 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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