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Go Back   SailNet Community > Out There > Vessels Lost, Missing, or in Danger
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  #31  
Old 06-30-2013
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Re: 6 Americans, 1 Brit vanish at sea

Many materials display linear elastic behavior, defined by a linear stress-strain relationship, as shown in the figure up to point 2, in which deformations are completely recoverable upon removal of the load; that is, a specimen loaded elastically in tension will elongate, but will return to its original shape and size when unloaded.

After the yield point, ductile metals will undergo a period of strain hardening, in which the stress increases again with increasing strain, and they begin to neck, as the cross-sectional area of the specimen decreases

The study of strength of materials often refers to various methods of calculating stresses in structural members, such as beams, columns and shafts. The methods employed to predict the response of a structure under loading and its susceptibility to various failure modes may take into account various properties of the materials other than material yield strength and ultimate strength; for example, failure by buckling is dependent on material stiffness and thus Young's Modulus.

n materials science, the strength of a material is its ability to withstand an applied stress without failure. The field of strength of materials deals with loads, deformations and the forces acting on a material. A load applied to a mechanical member will induce internal forces within the member called stresses. The stresses acting on the material cause deformation of the material. Deformation of the material is called strain, while the intensity of the internal forces is called stress


Transverse loading - Forces applied perpendicular to the longitudinal axis of a member. Transverse loading causes the member to bend and deflect from its original position, with internal tensile and compressive strains accompanying the change in curvature of the member.[1] Transverse loading also induces shear forces that cause shear deformation of the material and increase the transverse deflection of the member.
Axial loading - The applied forces are collinear with the longitudinal axis of the member. The forces cause the member to either stretch or shorten.[2]
Torsional loading - Twisting action caused by a pair of externally applied equal and oppositely directed force couples acting on parallel planes or by a single external couple applied to a member that has one end fixed against rotation.



\sigma=\frac{F}{A}, where F is the force [N] acting on an area A [m2].

Compressive stress (or compression) is the stress state caused by an applied load that acts to reduce the length of the material (compression member) in the axis of the applied load, in other words stress state caused by squeezing the material. A simple case of compression is the uniaxial compression induced by the action of opposite, pushing forces. Compressive strength for materials is generally higher than their tensile strength. However, structures loaded in compression are subject to additional failure modes dependent on geometry, such as buckling.

Tensile stress is the stress state caused by an applied load that tends to elongate the material in the axis of the applied load, in other words the stress caused by pulling the material. The strength of structures of equal cross sectional area loaded in tension is independent of shape of the cross section. Materials loaded in tension are susceptible to stress concentrations such as material defects or abrupt changes in geometry. However, materials exhibiting ductile behavior (most metals for example) can tolerate some defects while brittle materials (such as ceramics) can fail well below their ultimate material strength.

Shear stress is the stress state caused by the combined energy of a pair of opposing forces acting along parallel lines of action through the material, in other words the stress caused by faces of the material sliding relative to one another. An example is cutting paper with scissors[4] or stresses due to torsional loading.

A material's strength is dependent on its microstructure.

In materials science, fatigue is the progressive and localized structural damage that occurs when a material is subjected to cyclic loading.

Fatigue occurs when a material is subjected to repeated loading and unloading. If the loads are above a certain threshold, microscopic cracks will begin to form

Damage in wood is principally the result of fatigue. Fatigue is the process of progressive localised irreversible change in a material, and may culminate in cracks or complete fracture if conditions that initiated or propagated the process persist.


Although wood is the world's most widely used structural material, whether measured by volume consumed or value of finished construction, its behaviour is not well understood even by people who have spent their careers studying it.
  #32  
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Re: 6 Americans, 1 Brit vanish at sea

So- an 80+ year old wooden boat with a length of 60' LWL in 26' seas and hurricane strength winds for days as well as the fact the boat dried out while undergoing engine refit makes WOOD FAILURE the MOST LIKELY SCENARIO.
Thank you come again.
  #33  
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Re: 6 Americans, 1 Brit vanish at sea

Quote:
Originally Posted by MarkofSeaLife View Post
Could an old boat fully dry for the first time in many years have been a contributing factor in either popping a plank on a wave, or a catastrophic situation bordering on what Harborless opines?
Anything is possible. We're looking at probabilities here and the objective isn't to decide or guess what happened but what we can learn can make us safer.

I've never heard of a plank "popping" and a boat going down so quickly that there wasn't time to trip a manual EPIRB or make a radio call. Of course, we probably didn't hear about cases like that even if they happened.

A lot of wooden ships and boats have put to sea in truly atrocious condition over the centuries. Their sinking is usually proceeded by terrifying hours of pumping during which there is plenty of time in the modern world to call for help. The Bounty, which certainly was more prone to wracking and straining because of her size and nature of construction, is an excellent example.

A friend of mine hit something like a container and went down so fast that only he (singlehanded) and his dog made it into the dinghy. He still got off the radio call that prevented him from becoming one of those mysteries. No EPIRB because he was near coastal and it was before they were common.

One of the horrifying aspects of the Bounty tragedy was the unforgivable delay in telling the Coast Guard about taking on water. When unexplained water starts coming in, or ingress due to normal working and infiltration below starts getting close to the capacity of the pumps, itís time to make a call so they are at least standing by and starting to think about options if you have to declare an emergency. I suspect Wallbridge put off that call because it meant admitting to himself what he had done. I canít imagine the Ninaís master not making a Pan Pan call if there was leakage that the pumps could not keep up with.

A dry hull may be more prone to spitting some caulking or simply leak a bit more than normal when working hard but, absent some other severe structural issue, would not be at significantly greater danger of a catastrophic hull breach.
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Re: 6 Americans, 1 Brit vanish at sea

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Originally Posted by Harborless View Post
Now I will post the physics
I rest my case
  #35  
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Re: 6 Americans, 1 Brit vanish at sea

Quote:
Originally Posted by Harborless View Post
So- an 80+ year old wooden boat with a length of 60' LWL in 26' seas and hurricane strength winds for days as well as the fact the boat dried out while undergoing engine refit makes WOOD FAILURE the MOST LIKELY SCENARIO.
Thank you come again.
Might be best to actually establish the fact that the engine swap was done with the boat on the hard, no?

A series of photos on Dyche's Facebook page documenting the removal of the old engine would appear to indicate otherwise, showing the boat in the water, at Town Centre in Whangarei...







Last edited by JonEisberg; 06-30-2013 at 03:09 PM.
  #36  
Old 06-30-2013
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Re: 6 Americans, 1 Brit vanish at sea

This does not look like a boat that came apart without some sort of catastrophic event!
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  #37  
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Re: 6 Americans, 1 Brit vanish at sea

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Originally Posted by smurphny View Post
This does not look like a boat that came apart without some sort of catastrophic event!
Yup, every photo I've seen of her is a clear indication that she was magnificently maintained...

Here's something you don't see every day...


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  #38  
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Re: 6 Americans, 1 Brit vanish at sea

You act like i want to be right. I said b4 i hoped i was wrong. I backed my logic. Stop being blockheads (yes thats a pun).
  #39  
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Re: 6 Americans, 1 Brit vanish at sea

Quote:
Originally Posted by JonEisberg View Post
Yup, every photo I've seen of her is a clear indication that she was magnificently maintained...

Here's something you don't see every day...


You can see the EPIRB secured in the background.

Would someone inform the ignorant of us about what the purpose of that crank in the photograph is?
  #40  
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Re: 6 Americans, 1 Brit vanish at sea

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Originally Posted by Shinook View Post
Would someone inform the ignorant of us about what the purpose of that crank in the photograph is?
I think it opens the skylight.
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