Freethought & Rationalism Archive

Bubba · 05-10-2003, 05:52 PM

Socrates on Theologyweb suggested that a "monocoque" wood structure to the hull of the ark would make it seaworthy. My questions are:

1. Has anybody ever tried to do a simulation of a "monocoque" ship of this size, and if so what were the results?

and

2. Lotus built a monocoque automobile out of fiberglass, called the Elite. As I recall there was quite a bit of body flex. I'm not an engeneer, but it would seem obvious to me that

a. Fiberglass is more flexible than steel

b. Wood is usually more flexible than fiberglass

c. The larger the vessel, be it automotive, seagoing ship, whatever, the more of of these little flex inputs will add up...

...and ergo, the idea of a "mponocoque" ark is just pure fantsy. Real input by someone with structural engeneering experience would be appreciated.

In Darwin

Bubba

Vorkosigan · 05-10-2003, 06:46 PM

Quote:

Originally posted by Bubba
[B]Socrates on Theologyweb suggested that a "monocoque" wood structure to the hull of the ark would make it seaworthy. My questions are:

1. Has anybody ever tried to do a simulation of a "monocoque" ship of this size, and if so what were the results?

Is is even possible? I read up on monocoque construction on the net. It doesn't do well against compressive forces. And the Korean engineers Soc cited are hilarious -- a 4,000 ton wooden ship with a 17,000 ton load? I wonder if that article wasn't supposed to be tongue in cheek.

Vorkosigan

Jackalope · 05-10-2003, 09:28 PM

Since I don't read Theologyweb, could someone post the link to the article by those Korean engineers? I'd like to throw it at my husband, who does have a degree in naval architechture. I'm sure he'll find it hilarious. And a change from his usual hobby of stomping on the nuts who believe in the Space Brothers...

Valentine Pontifex · 05-11-2003, 05:56 AM

Quote:

Originally posted by Vorkosigan
Is is even possible? I read up on monocoque construction on the net. It doesn't do well against compressive forces. And the Korean engineers Soc cited are hilarious -- a 4,000 ton wooden ship with a 17,000 ton load? I wonder if that article wasn't supposed to be tongue in cheek.

Vorkosigan

I have not read the thread in question, but it seems unlikely that Sarfati would post anything tongue in cheek. I am not sure he can put his tongue in his cheek.

Kevbo · 05-11-2003, 09:36 AM

http://www.answersingenesis.org/home..._arksafety.asp

Jackalope · 05-13-2003, 02:32 AM

Analysis by George W. Herbert, moderator of sci.space.tech and holder of a degree in naval architechture:

Quote:

>http://www.answersingenesis.org/home..._arksafety.asp

Sure...

On first inspection:

0. Editorial comment

This paper was written by people who looked at a naval
architecture text book and did not understand what they
were seeing; it uses terminology from the profession
but not correctly, and does not use the right analysies.
Either the translation was grossly incorrect or the
paper was the work of not particularly attentive undergrad
students, given that the authors were supposedly at the
Korea Research Institute for Ships and Engineering.

1. "Draft and center of gravity" section

Displacement is given as:
(delta) = 1.025 L B d

That is the correct formula, for a brick.
Perhaps a bad sign of things to come.

Real ships are not perfect rectangular prisms;
they have rounded shapes, and the actual
displacement is some fraction depending on
the curvature of the ship, keel deadrise,
and numerous detail factors. These combine
to give a 'block coeficient' Cb which is simply
the actual volume divided by the volume of
the rectangular shape of the same length,
breadth, and depth. Cb varies from about 0.9
(really blocky huge oil tangers) to 0.55
(light destroyers) but is not 1.0 even for
rectangular barges, which have *some* rounded
off parts...

2. also in "draft and center of gravity" section

These guys calculate the height of the center of
gravity... which is good, and they don't seem to
have completely blown it, but the simplicity of the
analysis jumps out.

*No* mention is made of the height of the center
of buoyancy (the geometric centroid of the displaced
volume).

*No* mention is made of the equally important
Metacentric Height. The metacenter (M) is the imaginary
point around which the geometric center of the
waterplane area rotates as the ship rolls and
pitches. As that area shifts, the actual dynamic
stability of a ship depends on how far above
the center of gravity the metacenter is found.
The metacenter is some distance above the center
of buoyancy, and has to be calculated.

No real ship other than a submarine has its
center of gravity under its center of buoyancy.

The actual moment arm for stability calculations
is the height from the center of gravity G to
the metacenter M (GM).

3. "Comparative hull forms" section

Huh?

Comparative hull dimentions table, maybe.
"Hull Form" implies looking at the curvature,
block coeficient, etc.

4. "Method of Evaluation" subsection in "Seakeeping Performance" section

"A widely used strip method"...

These guys have not even determined KB, BM, or GM, and they
are performing computational motions analysis?

Er.

Ok. This fails the scratch and sniff test, but the method used
is not grossly inappropriate.

5. "General" subsection of "Structural Safety" section

These people do not understand wooden shipbuilding.
Using the terms associated with steel ships is
a gross mistake.

6. "Structural analysis of Ark" subsection of "Structural Safety" section

This fails the scratch and sniff test.

They plug the numbers in to a FEA rather than presenting the basic
by hand back of the envelope calculation. Bzzt.

They assume that they could rigidly attach a 2 dimentional girder
structure to a wooden "shell" ... no mention of how this is made
strong in shear, which is why thick hulled wooden ships are not
made that way.

They do not list the scantlings (thickness and dimentions of
the hull, longitudional and transverse frames, etc).
Without knowing what the actual dimentions are nobody
can crosscheck their numbers. Showing computer program
output without scantlings is the equivalent of lying
with graphics.

"Structural Safety Index" is introduced without any
foundation for what it is supposed to represent
in the analysis and optimization.

7. "Righting Arm" calculations in "Overturning Stability" section

Ah, now we get the metacenter. Except they're calling it Z,
instead of M, and they *integrate* to find the height rather
than simply pulling "Principles of Naval Architecture" off the
shelf and plugging the one line formula in... D'oh.

8. "Overturning stability Index" in "Overturning Stability"

What is this 'overturning stability index' and where is it
coming from? The term is not defined, referenced, etc.
It is not a term of the art in the field.

9. "Voyage Limit of the Arc"

Calculated for rolling motion. Never calculate in roll;
always calculate in pitch and sagging/hogging moment.

"Thickness of wood..." thickness *where*?

10. conclusions

Yet more of these imaginary safety indexes, which are not defined.

Yet more graphs without any supporting explanation of what the
axies mean.

11. my conclusion

This paper fails to show its work.
Almost none of its stated conclusions are supported
with enough documentation to review and evaluate for
technical correctness. Were this a student paper
it would fail on that basis, and it would never
be published in a naval architecture journal for
the same reason.

This paper fails to show basic familiarity with the
standard terminology, rules of thumb, and standards
of practicing naval architects, much less student
naval architects.

This paper fails to reference any of the standard
textbooks in ship design (Such as, Principles of
Naval Architecture 1990 ed). While papers have
certainly been written without reference to PNA,
the inclusion of a bunch of more specific references
without any reference to or use of the basic methods
and overview survey in PNA is bizarre.

Celsus · 05-14-2003, 05:21 AM

George Herbert (via Jackalope): :notworthy :notworthy :notworthy

BWAHAHAHAHA

That treatment was a joy to read--made my day. Does he know that they actually believe that the ark was shaped like a 300m-long brick? Heh. Jackalope, would he be willing to let someone post it to Tweb?

Joel

Jackalope · 05-14-2003, 06:28 AM

I'll ask him this morning. When he's actually awake. I don't tihnk there will be a problem, as one of his hobbies is smacking down idiocy masquerading as science. The thing that frightens me is that they claimed to have used models in the wave tank. I sure didn't see any of that data in the paper. Or any hint of what their actual hull forms were. The "brick" was their computer model. I wonder what their wooden models actually looked like.

edited to add:
He says it's fine to repost it, but you should add the ISBN for Principles of Naval Architecture to it:
ISBN # 0-939773-00-7(I), 0-939773-01-5(II), 0-939773-02-3(III)
This is a three-volume set that's considered the basic reference text for shipbuilding.
You should also add a link to the Society of Naval Architechts and Marine Engineers (SNAME):
http://www.sname.org/

Celsus · 05-14-2003, 07:08 AM

Thanks Jackalope!

I've posted it here: http://www.theologyweb.com/forum/sho...6044#post96044 if he wants to follow the ensuing contortions.

Joel

Jackalope · 05-14-2003, 06:26 PM

I love it. "A feasability study." Using a hull form that has the boyancy of a brick! Is Socrates always this funny?

George says he's honored to be ranked with the talk.origins folks, BTW.

05-10-2003, 05:52 PM	#1
Bubba Veteran Member Join Date: Mar 2001 Location: Orient, OH USA Posts: 1,501	The Ark And Theologyweb Socrates on Theologyweb suggested that a "monocoque" wood structure to the hull of the ark would make it seaworthy. My questions are: 1. Has anybody ever tried to do a simulation of a "monocoque" ship of this size, and if so what were the results? and 2. Lotus built a monocoque automobile out of fiberglass, called the Elite. As I recall there was quite a bit of body flex. I'm not an engeneer, but it would seem obvious to me that a. Fiberglass is more flexible than steel b. Wood is usually more flexible than fiberglass c. The larger the vessel, be it automotive, seagoing ship, whatever, the more of of these little flex inputs will add up... ...and ergo, the idea of a "mponocoque" ark is just pure fantsy. Real input by someone with structural engeneering experience would be appreciated. In Darwin Bubba

05-11-2003, 09:36 AM	#5
Kevbo Regular Member Join Date: Apr 2003 Location: NY Posts: 212	Here is the paper: http://www.answersingenesis.org/home..._arksafety.asp

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05-10-2003, 09:28 PM	#3
Jackalope Veteran Member Join Date: Oct 2002 Location: Hayward, CA, USA Posts: 1,675	Since I don't read Theologyweb, could someone post the link to the article by those Korean engineers? I'd like to throw it at my husband, who does have a degree in naval architechture. I'm sure he'll find it hilarious. And a change from his usual hobby of stomping on the nuts who believe in the Space Brothers...

05-14-2003, 05:21 AM	#7
Celsus Veteran Member Join Date: Aug 2001 Location: Singapore Posts: 2,875	George Herbert (via Jackalope): :notworthy :notworthy :notworthy BWAHAHAHAHA That treatment was a joy to read--made my day. Does he know that they actually believe that the ark was shaped like a 300m-long brick? Heh. Jackalope, would he be willing to let someone post it to Tweb? Joel

05-14-2003, 06:28 AM	#8
Jackalope Veteran Member Join Date: Oct 2002 Location: Hayward, CA, USA Posts: 1,675	I'll ask him this morning. When he's actually awake. I don't tihnk there will be a problem, as one of his hobbies is smacking down idiocy masquerading as science. The thing that frightens me is that they claimed to have used models in the wave tank. I sure didn't see any of that data in the paper. Or any hint of what their actual hull forms were. The "brick" was their computer model. I wonder what their wooden models actually looked like. edited to add: He says it's fine to repost it, but you should add the ISBN for Principles of Naval Architecture to it: ISBN # 0-939773-00-7(I), 0-939773-01-5(II), 0-939773-02-3(III) This is a three-volume set that's considered the basic reference text for shipbuilding. You should also add a link to the Society of Naval Architechts and Marine Engineers (SNAME): http://www.sname.org/

05-14-2003, 07:08 AM	#9
Celsus Veteran Member Join Date: Aug 2001 Location: Singapore Posts: 2,875	Thanks Jackalope! I've posted it here: http://www.theologyweb.com/forum/sho...6044#post96044 if he wants to follow the ensuing contortions. Joel

05-14-2003, 06:26 PM	#10
Jackalope Veteran Member Join Date: Oct 2002 Location: Hayward, CA, USA Posts: 1,675	I love it. "A feasability study." Using a hull form that has the boyancy of a brick! Is Socrates always this funny? George says he's honored to be ranked with the talk.origins folks, BTW.

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