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Author Topic:   Something BIG is coming! (AIG trying to build full sized ark)
RAZD
Member
Posts: 18472
From: the other end of the sidewalk
Joined: 03-14-2004
Member Rating: 3.8


Message 196 of 259 (631010)
08-29-2011 9:12 PM
Reply to: Message 194 by Gullwind1
08-29-2011 8:06 PM


Re: terminology
Hi Gullwind1, and welcome to the fray.

It really seems that the problems inherent with wooden ships this large is an argument against the Ark, rather than for it.

The problem here is that the ark does not need to be a ship so much as a floating box. From a naval architectural point of view I don't see that it isn't possible, especially given the extremely vague description (outside dimensions only). One can argue that it must be either able to stay upright in a major storm or be self-righting in some manner.

But the believer can always argue that god/s helped, and in the end belief trumps logic and evidence in the fundamentalist mindset.

Enjoy

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This message is a reply to:
 Message 194 by Gullwind1, posted 08-29-2011 8:06 PM Gullwind1 has responded

Replies to this message:
 Message 197 by Gullwind1, posted 08-29-2011 10:49 PM RAZD has responded

  
Gullwind1
Junior Member (Idle past 1843 days)
Posts: 12
Joined: 04-27-2011


Message 197 of 259 (631024)
08-29-2011 10:49 PM
Reply to: Message 196 by RAZD
08-29-2011 9:12 PM


Re: terminology
The problem here is that the ark does not need to be a ship so much as a floating box. From a naval architectural point of view I don't see that it isn't possible, especially given the extremely vague description (outside dimensions only). One can argue that it must be either able to stay upright in a major storm or be self-righting in some manner.

But the believer can always argue that god/s helped, and in the end belief trumps logic and evidence in the fundamentalist mindset.

The design isn't as important as the strength of the material its built out of. Sure, you could build a wooden ship of the size described, but when that structure is subjected to the stresses of even moderate seas, it is going to break up because no wood is strong enough to withstand the stresses that waves place on the structure of a ship. Even if its just a big box, it is still going to be subject to sagging as a wave lifts the bow and the center rises out of the water, hogging as the wave moves to support the center and the bow and stern are unsupported, and sagging again as the wave lifts the stern but not the middle again. A wooden vessel would have to be almost solid to even have a chance to stay intact, and I'm not sure it could even then. Wooden structures that are constantly flexed back and forth don't stay intact very well, and if the stress is too great the wood simply splinters. I don't deny the proportions given are right, but you can't just scale up a 100-foot barge and say a 450-foot version would be just as good.

Thanks for the tips.


This message is a reply to:
 Message 196 by RAZD, posted 08-29-2011 9:12 PM RAZD has responded

Replies to this message:
 Message 198 by RAZD, posted 08-30-2011 9:15 AM Gullwind1 has responded

    
RAZD
Member
Posts: 18472
From: the other end of the sidewalk
Joined: 03-14-2004
Member Rating: 3.8


(1)
Message 198 of 259 (631078)
08-30-2011 9:15 AM
Reply to: Message 197 by Gullwind1
08-29-2011 10:49 PM


design issues not a problem
Hi Gullwind1, thanks.

The design isn't as important as the strength of the material its built out of.

False.

The (proper) design incorporates the strength characteristics of the material used and equivalent shape characteristics of the individual members.

It may surprise you to know that wood is stronger than steel on a pound for pound basis in the direction of the fibers. Wood is an exceptionally good material to work with if you know and use the characteristics involved. I have a plywood kayak that I designed and built that is stronger than fiberglass ones, stronger than aluminum canoes, and only weighs 35 lbs wet. The plywood uses the cross grain laminations to provide strength in two perpendicular directions.

Traditional construction with framing timbers with the fibers in one direction and plating planks in the other direction do this as well.

To get the same strength all you need is the same (sectional modulus) x (material modulus), where the first comes from the shape characteristics and the second comes from the material used (in the direction under consideration).

... no wood is strong enough to withstand the stresses that waves place on the structure of a ship.

How big are those waves?

As you note, the worst stress condition is either (a) where the ends are supported by waves and the middle is in a trough or (b) where the middle is supported by a single wave and the ends project from the waves.

A free floating vessel (with no power and no means to turn the vessel) will turn broadside to the waves (because of the way the water moves in waves), normally causing the vessels to broach or roll over if they are not stable in that condition (hence the need for self-righting previously mentioned), and thus will not see those critical stress conditions.

You provide the stress and strain conditions to be met and an engineer could design a vessel made out of glued paper to meet them.

Then there is the effect of scale on the equations: the bending stress goes up with the square of the length of a member, the section modulus (geometry strength) of a beam goes up with the power 4 of the scale used. Double the length and the stress goes up 4 time, but double the dimensions of the beam and the strength goes up 16 times, so you can scale by the square root of 2 to match strength to stress (1.414 or 42% increase in size).

The only issue here is that the structure takes up volume inside the vessel, making the available space for animals smaller. Going from 100 ft to 450 ft is a length scale of 4.5 so this creates a stress scale of 4.5^2 = 20.25 and this means a member scale of 20.25^(1/4) = 2.12. I hardly see this as filling the interior with structure.

Ballast in the bilges would further deplete interior volume available and a sea anchor could also be deployed to control the position of the vessel relative to the waves, but this would be adding ad hoc design components that are not mentioned.

This takes us back to the question of what is the passenger list of people and animals and what are the accommodations necessary to carry them, as that is a much larger impact than the structure of the vessel.

Enjoy.


we are limited in our ability to understand
by our ability to understand
Rebel American Zen Deist
... to learn ... to think ... to live ... to laugh ...
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This message is a reply to:
 Message 197 by Gullwind1, posted 08-29-2011 10:49 PM Gullwind1 has responded

Replies to this message:
 Message 199 by Gullwind1, posted 08-31-2011 12:45 AM RAZD has responded
 Message 201 by Theodoric, posted 08-31-2011 6:10 PM RAZD has responded

  
Gullwind1
Junior Member (Idle past 1843 days)
Posts: 12
Joined: 04-27-2011


(2)
Message 199 of 259 (631218)
08-31-2011 12:45 AM
Reply to: Message 198 by RAZD
08-30-2011 9:15 AM


Re: design issues not a problem
False.

The (proper) design incorporates the strength characteristics of the material used and equivalent shape characteristics of the individual members.

It may surprise you to know that wood is stronger than steel on a pound for pound basis in the direction of the fibers. Wood is an exceptionally good material to work with if you know and use the characteristics involved. I have a plywood kayak that I designed and built that is stronger than fiberglass ones, stronger than aluminum canoes, and only weighs 35 lbs wet. The plywood uses the cross grain laminations to provide strength in two perpendicular directions.

Traditional construction with framing timbers with the fibers in one direction and plating planks in the other direction do this as well.

To get the same strength all you need is the same (sectional modulus) x (material modulus), where the first comes from the shape characteristics and the second comes from the material used (in the direction under consideration).

But ships experience stress in all three dimensions and almost constantly, even in calm seas. You'd need so many structural members in so many directions there wouldn't be room for anything else. What you're saying is right, but shipbuilding is a lot different than building a house.

How big are those waves?

In a global flood? With no land to block the wind and waves, swells a hundred or more feet high would be the norm, never mind a storm. I was broadsided by a ninety-footer in the Gulf of Alaska. We rolled 45 degrees and were completely underwater, and this was a 710 foot container ship. The constant back-and-forth motion takes a toll on the structure. How long do you think your kayak would last if it was constantly flexed back and forth, up and down before something gave way? Would it last a year?

As you note, the worst stress condition is either (a) where the ends are supported by waves and the middle is in a trough or (b) where the middle is supported by a single wave and the ends project from the waves.

And this will not be along the grain of the keel, which a ship derives the majority of its longitudinal strength from. Sure, you could laminate it, but its still going to be constantly flexing back and forth. Eventually, it will give.

A free floating vessel (with no power and no means to turn the vessel) will turn broadside to the waves (because of the way the water moves in waves), normally causing the vessels to broach or roll over if they are not stable in that condition (hence the need for self-righting previously mentioned), and thus will not see those critical stress conditions.

So it's constantly rolling over and over? I don't think this is much of a solution. You're just lowering one stress and replacing it with another.

You provide the stress and strain conditions to be met and an engineer could design a vessel made out of glued paper to meet them.

I doubt glued paper would last in sea water for a year. It would probably work better than wood, though, because it is more flexible.

Then there is the effect of scale on the equations: the bending stress goes up with the square of the length of a member, the section modulus (geometry strength) of a beam goes up with the power 4 of the scale used. Double the length and the stress goes up 4 time, but double the dimensions of the beam and the strength goes up 16 times, so you can scale by the square root of 2 to match strength to stress (1.414 or 42% increase in size).

The only issue here is that the structure takes up volume inside the vessel, making the available space for animals smaller. Going from 100 ft to 450 ft is a length scale of 4.5 so this creates a stress scale of 4.5^2 = 20.25 and this means a member scale of 20.25^(1/4) = 2.12. I hardly see this as filling the interior with structure.

Ballast in the bilges would further deplete interior volume available and a sea anchor could also be deployed to control the position of the vessel relative to the waves, but this would be adding ad hoc design components that are not mentioned.

This takes us back to the question of what is the passenger list of people and animals and what are the accommodations necessary to carry them, as that is a much larger impact than the structure of the vessel.

Where are you going to get 450 foot long logs to use as structural members? In reality, you are going to have joints, and those joints are going to be flexing back and forth, all the time.

You make some good points, but history shows that wooden vessels this size just don't work in practice.


This message is a reply to:
 Message 198 by RAZD, posted 08-30-2011 9:15 AM RAZD has responded

Replies to this message:
 Message 200 by Malvern, posted 08-31-2011 11:37 AM Gullwind1 has not yet responded
 Message 205 by RAZD, posted 09-01-2011 5:02 PM Gullwind1 has responded

    
Malvern
Junior Member (Idle past 1733 days)
Posts: 20
From: Mesopotamia, Ohio USA
Joined: 04-22-2011


(1)
Message 200 of 259 (631290)
08-31-2011 11:37 AM
Reply to: Message 199 by Gullwind1
08-31-2011 12:45 AM


Re: design issues not a problem
...and don't overlook the fact that the Ark had to be loaded an balanced properly. Noah and his family, coming from such a long and distinguished line of seafarers would know exactly how to load the solid food, potable water and heavy and light animals in such a way as to maintain proper trim throughout the voyage. And, of course, they had all the necessary ground tackle, ropes and bindings to secure the food and animals in the worst possible sea states. Uh-huh. You bet'cha.

(:raig


This message is a reply to:
 Message 199 by Gullwind1, posted 08-31-2011 12:45 AM Gullwind1 has not yet responded

    
Theodoric
Member
Posts: 5765
From: Northwest, WI, USA
Joined: 08-15-2005
Member Rating: 3.5


(1)
Message 201 of 259 (631338)
08-31-2011 6:10 PM
Reply to: Message 198 by RAZD
08-30-2011 9:15 AM


Re: design issues not a problem
It may surprise you to know that wood is stronger than steel on a pound for pound basis in the direction of the fibers.

Which actually means nothing in this discussion, and I would love to see the data to support this assertion. I have searched the web and have found no evidence for this.

quote:
As a rule of thumb, aluminum is three times heavier, but also three times stronger than wood. Steel is again three times heavier and stronger than aluminum.



http://www.zenithair.com/kit-data/ht-85-12.html

So you need 3 times as much wood to equal strength of steel. That is an awful lot of wood.


Facts don't lie or have an agenda. Facts are just facts

This message is a reply to:
 Message 198 by RAZD, posted 08-30-2011 9:15 AM RAZD has responded

Replies to this message:
 Message 202 by Dr Adequate, posted 08-31-2011 6:29 PM Theodoric has responded
 Message 206 by RAZD, posted 09-01-2011 10:55 PM Theodoric has responded

    
Dr Adequate
Member
Posts: 15929
Joined: 07-20-2006
Member Rating: 3.8


Message 202 of 259 (631345)
08-31-2011 6:29 PM
Reply to: Message 201 by Theodoric
08-31-2011 6:10 PM


Re: design issues not a problem
Don't you mean 9?
This message is a reply to:
 Message 201 by Theodoric, posted 08-31-2011 6:10 PM Theodoric has responded

Replies to this message:
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Panda
Member (Idle past 1125 days)
Posts: 2688
From: UK
Joined: 10-04-2010


Message 203 of 259 (631347)
08-31-2011 6:33 PM
Reply to: Message 202 by Dr Adequate
08-31-2011 6:29 PM


Re: design issues not a problem
Dr Adequate writes:

Don't you mean 9?


'3' was metaphorical and not meant to be taken literally.

Always remember: QUIDQUID LATINE DICTUM SIT ALTUM VIDITUR

Science flies you into space; religion flies you into buildings.


This message is a reply to:
 Message 202 by Dr Adequate, posted 08-31-2011 6:29 PM Dr Adequate has not yet responded

  
Theodoric
Member
Posts: 5765
From: Northwest, WI, USA
Joined: 08-15-2005
Member Rating: 3.5


Message 204 of 259 (631382)
08-31-2011 8:07 PM
Reply to: Message 202 by Dr Adequate
08-31-2011 6:29 PM


Re: design issues not a problem
You are correct I oopsed. Therefore my awfully lot wood comment.

Facts don't lie or have an agenda. Facts are just facts

This message is a reply to:
 Message 202 by Dr Adequate, posted 08-31-2011 6:29 PM Dr Adequate has not yet responded

    
RAZD
Member
Posts: 18472
From: the other end of the sidewalk
Joined: 03-14-2004
Member Rating: 3.8


(2)
Message 205 of 259 (631529)
09-01-2011 5:02 PM
Reply to: Message 199 by Gullwind1
08-31-2011 12:45 AM


Re: design issues not a problem
Hi Gullwind1

But ships experience stress in all three dimensions and almost constantly, even in calm seas. You'd need so many structural members in so many directions there wouldn't be room for anything else. What you're saying is right, but shipbuilding is a lot different than building a house.

Curiously, I am talking about naval architecture and marine engineering design, not houses. You may want to look around at some information available. One site (note mine btw) I found is:

http://twextra.com/afc44y

quote:
FOR more than 40 years, I have worked as a naval architect and marine engineer. My work has involved designing vessels of various shapes and sizes, along with the mechanical and other systems that propel them. In 1963, while I was living in British Columbia, Canada, one of Jehovahs Witnesses showed me that the Bible book of Genesis describes Noahs ark as a long box, or chest. This description intrigued me, and I decided to look into it further.

Now, I don't necessarily agree with all his conclusions, but I don't think you can argue that it cannot be done, especially if you have not gone through the design process yourself.

In a global flood? With no land to block the wind and waves, swells a hundred or more feet high would be the norm, ...

More critical than wave height is wavelength, as that is what determines the hogging and sagging stress loads: these are greatest when the wavelength matches the vessel length, and when the wavelength exceeds the vessel length the stresses are actually reduced from those peak loads.

As long as the waves don't break, this can result in seaworthy behavior in small vessels subject to large waves. Sailboats in the roaring 40's for example. Also:

http://www.waterencyclopedia.com/Tw-Z/Waves.html

quote:
When the wave builds and reaches a steepness greater than a ratio of 1:7, the wave breaks and spills forward. The wave has actually become too steep to support itself and gravity takes over.

So the wavelength of non-breaking (swells) 100+ft high waves would be over 700 ft and could easily exceed the length of the ark by a considerable amount, depending on the energy (height related) of the wave.

Think about Tsunami waves in the open ocean -- they cause very little disturbance to vessels at sea. Without a shore for the waves to run up on, there is no cause for the wave to build to a high peak or breaking wave, unless there is a LOT of wind.

... never mind a storm. ...

What storm? What specifically does the bible say about the weather conditions other than rain? What does it say about wind?

... I was broadsided by a ninety-footer in the Gulf of Alaska. We rolled 45 degrees and were completely underwater, and this was a 710 foot container ship. ...

That would be my point about the ride being uncomfortable, but again this could well be a wave with more energy (height related) than ones in the purported flood.

I also note that a normal container ship does not have the beam to length ratio of the purported ark -- it is made to fit the panama canal after all -- and this makes it more prone to rolling from a broaching sea.

Again, a sea anchor could prevent this broadside condition, but that is ad hoc (not mentioned in the bible), but this is also how small vessels generally ride out storms with waves larger than the vessels.

... The constant back-and-forth motion takes a toll on the structure. How long do you think your kayak would last if it was constantly flexed back and forth, up and down before something gave way? Would it last a year?

Given that it has lasted ~30 years with a lot of that tied to a cartop traveling at 60+ mph I do not see that being a problem. If anything it is stiffer than necessary and thus I could reduce the structure next time.

How long would the ark need to last? The rain purportedly only lasted 40 days.

I doubt glued paper would last in sea water for a year. It would probably work better than wood, though, because it is more flexible.

Laminated paper would be stiffer. Think of fiberglass made with chopped strand -- random fibers in a matrix of plastic.

Where are you going to get 450 foot long logs to use as structural members? In reality, you are going to have joints, and those joints are going to be flexing back and forth, all the time.

The believers will just say that trees grew that big. The other solution is to build up the beams with scarfed and sistered joints, a common practice to solve this very problem.

You make some good points, but history shows that wooden vessels this size just don't work in practice.

The reasons they don't work though are not due to size. Wooden sailing vessels reached their apparent limit with the 4 masted clippers, but the stresses were cause by the rigging.

Enjoy.


we are limited in our ability to understand
by our ability to understand
Rebel American Zen Deist
... to learn ... to think ... to live ... to laugh ...
to share.


Join the effort to solve medical problems, AIDS/HIV, Cancer and more with Team EvC! (click)

This message is a reply to:
 Message 199 by Gullwind1, posted 08-31-2011 12:45 AM Gullwind1 has responded

Replies to this message:
 Message 209 by Gullwind1, posted 09-02-2011 12:09 AM RAZD has responded

  
RAZD
Member
Posts: 18472
From: the other end of the sidewalk
Joined: 03-14-2004
Member Rating: 3.8


(1)
Message 206 of 259 (631604)
09-01-2011 10:55 PM
Reply to: Message 201 by Theodoric
08-31-2011 6:10 PM


Re: design issues not a problem
Hi Theodoric,

So you need 3 times as much wood to equal strength of steel.

Actually it would be 9 times according to your information.

That is an awful lot of wood.

Argument from incredulity.

How much steel would you need? Vessels much bigger have been built out of steel -- look at container ships for instance:

http://en.wikipedia.org/wiki/Ebba_M%C3%A6rsk

quote:
The Ebba Maersk is a container ship owned by the Danish shipping company A. P. Moller-Maersk Group. The fifth of the Mrsk E-class,[1] it and its seven sister ships are the largest container ships ever built as well as the longest ships in use. It has a total TEU capacity of 11,000 TEU 14-ton containers by Maersk definition; however, with standard ratings it can hold 14,770 containers.[2] This rating goes by physical space rather than weight. Her beam is 183 feet (56 m), her length 1,302 feet (397 m), and she has a deadweight tonnage of 156,907. In May 2010, she was reported with 15,011 TEU[3] in Tangier, Morocco, the highest equivalent number of any vessel.

(1) Changing the scantlings to wood with the same resulting deadweight would not significantly affect the carrying capacity or the cargo volume. These vessels have large void areas (double wall sides and bottoms) for damage flooding control, and increasing the wood in these areas would reduce the amount of volume that could be flooded while retaining positive buoyancy, thus actually making them safer (if you could find a boatbuilder that would tackle such a job).

(2) This vessel is ~3 times the length of the purported ark, and so would need to be 9 times as strong for the same longitudinal bending stress, thus the purported ark could have structure about the same as the steel structure in this ship.

Sorry, but I just don't think this line of argument is persuasive.

Enjoy.


we are limited in our ability to understand
by our ability to understand
Rebel American Zen Deist
... to learn ... to think ... to live ... to laugh ...
to share.


Join the effort to solve medical problems, AIDS/HIV, Cancer and more with Team EvC! (click)

This message is a reply to:
 Message 201 by Theodoric, posted 08-31-2011 6:10 PM Theodoric has responded

Replies to this message:
 Message 207 by Theodoric, posted 09-01-2011 11:02 PM RAZD has responded
 Message 208 by Dirk, posted 09-02-2011 12:08 AM RAZD has responded

  
Theodoric
Member
Posts: 5765
From: Northwest, WI, USA
Joined: 08-15-2005
Member Rating: 3.5


Message 207 of 259 (631606)
09-01-2011 11:02 PM
Reply to: Message 206 by RAZD
09-01-2011 10:55 PM


Re: design issues not a problem
Sorry, but I just don't think this line of argument is persuasive.

Unless someone can provide info from actual marine engineers.

This whole post of yours deals with steel not wood. There is a lot more at play here than just inherent strength. I am still waiting for you to show evidence that pound for pound wood is stronger than steel. I am not going to take your word for it.

This vessel is ~3 times the length of the purported ark, and so would need to be 9 times as strong for the same longitudinal bending stress, thus the purported ark could have structure about the same as the steel structure in this ship.

Please show your workings for these assertions.

Facts don't lie or have an agenda. Facts are just facts

This message is a reply to:
 Message 206 by RAZD, posted 09-01-2011 10:55 PM RAZD has responded

Replies to this message:
 Message 210 by RAZD, posted 09-02-2011 12:28 AM Theodoric has not yet responded

    
Dirk
Member (Idle past 1436 days)
Posts: 84
Joined: 08-20-2010


Message 208 of 259 (631609)
09-02-2011 12:08 AM
Reply to: Message 206 by RAZD
09-01-2011 10:55 PM


Re: design issues not a problem
Maybe we should look at some actual wooden ships that approach the supposed size of the ark? See this list, which shows that all wooden ships over 100m in length suffered from severe structural problems, even when they were reinforced with steel.
This message is a reply to:
 Message 206 by RAZD, posted 09-01-2011 10:55 PM RAZD has responded

Replies to this message:
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Gullwind1
Junior Member (Idle past 1843 days)
Posts: 12
Joined: 04-27-2011


Message 209 of 259 (631610)
09-02-2011 12:09 AM
Reply to: Message 205 by RAZD
09-01-2011 5:02 PM


Re: design issues not a problem
Hi Gullwind1

Hi!

Curiously, I am talking about naval architecture and marine engineering design, not houses. You may want to look around at some information available. One site (note mine btw) I found is:

Have you ever taken any classes in these subjects? Even if wood is as strong as steel along the grain, the stresses involved aren't.

Now, I don't necessarily agree with all his conclusions, but I don't think you can argue that it cannot be done, especially if you have not gone through the design process yourself.

I have gone through the design processes, and it doesn't work the way you say it does.

More critical than wave height is wavelength, as that is what determines the hogging and sagging stress loads: these are greatest when the wavelength matches the vessel length, and when the wavelength exceeds the vessel length the stresses are actually reduced from those peak loads.

Reduced does not mean negligible.

As long as the waves don't break, this can result in seaworthy behavior in small vessels subject to large waves. Sailboats in the roaring 40's for example. Also:

http://www.waterencyclopedia.com/Tw-Z/Waves.html

quote:When the wave builds and reaches a steepness greater than a ratio of 1:7, the wave breaks and spills forward. The wave has actually become too steep to support itself and gravity takes over.

So the wavelength of non-breaking (swells) 100+ft high waves would be over 700 ft and could easily exceed the length of the ark by a considerable amount, depending on the energy (height related) of the wave.

But they would still be lifting the bow and subjecting the ship to stress.

Think about Tsunami waves in the open ocean -- they cause very little disturbance to vessels at sea. Without a shore for the waves to run up on, there is no cause for the wave to build to a high peak or breaking wave, unless there is a LOT of wind.

Swells are different than waves. You're talking about apples and oranges. Swells are surface disturbances caused by wind and other things hundreds or thousands of miles away. In a global flood, those swells would have nothing to disperse them and could build on each other, regardless of the local wind conditions. They are nothing like tsunamis.

What storm? What specifically does the bible say about the weather conditions other than rain? What does it say about wind?

As has been said before, if you invoke magic than anything is possible, but if there actually was a global flood then the weather would be drastically affected. Lots of moisture in the air, lots of heat being retained by the water, big storms.

That would be my point about the ride being uncomfortable, but again this could well be a wave with more energy (height related) than ones in the purported flood.

In reality it would be a small one compared to the purported flood.

I also note that a normal container ship does not have the beam to length ratio of the purported ark -- it is made to fit the panama canal after all -- and this makes it more prone to rolling from a broaching sea.

Actually, it was worse than that. It was built in Wisconsin and had to be narrow enough to get through the St Lawrence Seaway. 710' long with a 78' beam. It was a big canoe. I always thought that was a poor choice for a ship intended for the Alaska run.

Again, a sea anchor could prevent this broadside condition, but that is ad hoc (not mentioned in the bible), but this is also how small vessels generally ride out storms with waves larger than the vessels.

Sure, but this increases the hogging and sagging stress. So you either have these stresses, or your doing barrel rolls. Neither option is particularly good.

Given that it has lasted ~30 years with a lot of that tied to a cartop traveling at 60+ mph I do not see that being a problem. If anything it is stiffer than necessary and thus I could reduce the structure next time.

Not a valid comparison. It hasn't been in water for 30 years. I'm willing to be it hasn't spent a single year in the water in those 30 years. Riding on top of a car isn't quite the same thing either. And a kayak is a lot different that a 450' vessel. You can't just scale the equations indefinitely.

How long would the ark need to last? The rain purportedly only lasted 40 days.

But they were in it for a year.

Laminated paper would be stiffer. Think of fiberglass made with chopped strand -- random fibers in a matrix of plastic.

Still don't see it lasting a year.

The believers will just say that trees grew that big. The other solution is to build up the beams with scarfed and sistered joints, a common practice to solve this very problem.

The believers can say anything they want. I'm looking at reality. And joints are not as strong as the beam itself, primarily because of the flexing that takes place. Eventually, there will be a failure.

The reasons they don't work though are not due to size. Wooden sailing vessels reached their apparent limit with the 4 masted clippers, but the stresses were cause by the rigging.

Source for this?

Then why did the Tesseriaconteras stay docked for its entire service life? It wasn't even a single hull, but it was too big to remain intact in anything but dead calm waters.


This message is a reply to:
 Message 205 by RAZD, posted 09-01-2011 5:02 PM RAZD has responded

Replies to this message:
 Message 212 by RAZD, posted 09-02-2011 10:47 AM Gullwind1 has responded

    
RAZD
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Posts: 18472
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(1)
Message 210 of 259 (631613)
09-02-2011 12:28 AM
Reply to: Message 207 by Theodoric
09-01-2011 11:02 PM


Re: design issues not a problem
Theodoric,

Please show your workings for these assertions.

The bending moment is (wL^2/8) now triple L.(1)

This whole post of yours deals with steel not wood. There is a lot more at play here than just inherent strength. I am still waiting for you to show evidence that pound for pound wood is stronger than steel. I am not going to take your word for it.

My 15ft kayak is 35 lbs, an aluminum canoe, with less material (no deck) and the same length weighs more, and the kayak is stronger (doesn't flex as much).

Now I should say some wood rather than all wood, as the strength is variable, but one would tend to use the strong woods rather than the weak ones when building.

http://en.wikipedia.org/wiki/Young%27s_modulus

quote:
Young's modulus is a measure of the stiffness of an elastic material and is a quantity used to characterize materials. It is defined as the ratio of the uniaxial stress over the uniaxial strain in the range of stress in which Hooke's Law holds.[1] In solid mechanics, the slope of the stress-strain curve at any point is called the tangent modulus. The tangent modulus of the initial, linear portion of a stress-strain curve is called Young's modulus, also known as the tensile modulus. It can be experimentally determined from the slope of a stress-strain curve created during tensile tests conducted on a sample of the material. In anisotropic materials, Young's modulus may have different values depending on the direction of the applied force with respect to the material's structure.

For many materials, Young's modulus is essentially constant over a range of strains. Such materials are called linear, and are said to obey Hooke's law. Examples of linear materials are steel, carbon fiber and glass. Non-linear materials include rubber and soils, except under very small strains.

Young's modulus is not always the same in all orientations of a material. Most metals and ceramics, along with many other materials, are isotropic, and their mechanical properties are the same in all orientations. ... Anisotropy can be seen in many composites as well. For example, carbon fiber has much higher Young's modulus (is much stiffer) when force is loaded parallel to the fibers (along the grain). Other such materials include wood and reinforced concrete. Engineers can use this directional phenomenon to their advantage in creating structures.


MaterialGPalbf/in2 (psi)
Steel20029,000,000
Oak wood (along grain) 111,600,000

Ratio of Young's modulii, E, is 200/11 = 18.2, and this means that the geometrical shape for the wood structure (moment of inertia) would need to generate 18.2 times the moment of inertia of the steel structural elements to have the same strength.

The moment of inertia, I, is bd^3/12(2)

For Iwood = 18.2 x Isteel this means that

(bd^3)wood = 18.2 x (bd^3)steel

keeping the same proportion of b to d means we can use 18.2^0.25 times the b and d of the steel structure = 2.06.

The cross-section area would be 2.06x2.06 = 4.41.

http://www.reade.com/Particle_Briefings/spec_gra2.html

quote:

MaterialSpecific Gravitylbf/ft3
Steel, rolled7.93495
Oak, red0.7144

Ratio of weight for comparable structure is 1 cubic ft steel to 2.06 (b) x 2.06 (d) x 1 cubic ft oak = 495/(2.06x2.06x44) = 2.65

THEREFORE: Steel is 2.65 times heavier than oak for the same strength.

QED

Note that doubling the size of the members in a steel ship hardly compromises the interior volume.

Enjoy.



(1) where w is the uniform loading and L is the Length
(2) where b is the width and d is the depth

Note that oak is a heavy wood. This can also be done for pine with similar results:
Pine wood (along grain) = 8.963 GPa =1,300,000 psi
Ratio of Young's modulii, E, is 200/8.963 = 22.3
Iwood = 22.3 Isteel
22.3^0.25 = 2.17 x the dimensions
Pine, Yellow Southern, dry = 0.72 SG, 45 lbf/ft3
Ratio of weight for comparable structure is 1 cubic ft steel to 2.17 (b) x 2.17 (d) x 1 cubic ft pine = 495/(2.17x2.17x45) = 2.33
THEREFORE: Steel is 2.33 times heavier than pine for the same strength.


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This message is a reply to:
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