steel hulls? adding armor to FG hulls
 

On Mar 11, 2:45 am, wrote:
" wrote:
Amen. But, having been tangentially involved in a completely
disastrous attempt to bond Kevlar (tm) fabric to PVC foam with epoxy I
strongly advise getting advise from the fabric provider before
bonding. ...

I wonder why. Incompatible binder in the cloth?
One issue with both carbon fiber & aramids (you're right, Kevlar is a
trademarked brand name) is that the cloth is much lighter than
conventional fiberglass... duh, that's a big reason to use it... but
it also means that the cloth tends to float up out of the resin. ...

Good points. Kevlar has been used with great success. I can only
speculate on the reasons for the failure. I was in the shop where it
happened re-building my dagger boards and the wing was going together
on the other side of a hull of a big cat that was also building. So,
I didn't see every detail. They were building it using Kelsall's KSS
system with Kevlar twill, epoxy and pvc. They bonded one face on a
flat table with a wet lay-up using modest vacuum to clamp it. Then
they cut darts in the pvc, draped the part into mdf formers and hand
laid the inner skin. That's sop for the KSS system and it generally
works quite well. In this case, though, both the hand laid skin and
the bagged skin could be peeled off the pvc (failing at the glue
line). They did it all a second time on the assumption that the
problem was a bad epoxy mix and it failed exactly the same way. Other
parts that came off the same table using pvc from the same batch
before, during and after were fine. I was using the same epoxy to
build my boards and it was also being used in a couple of other
projects around the shop and it was fine. It's possible that they
could have contaminated the pvc skins (boat shops aren't exactly clean
rooms). That's what the guy building the plane though. But both
sides twice? I think that using twill rather than stitched cloth and
bending the parts around very tight molds (the guy wanted to mold
right around the leading edge for some reason) were contributing
factors. But whatever the reason, the epoxy/Kevlar joint was the weak
one and I think that is cause for concern or at least careful testing
when using Kevlar.

... Carbon
is less of a pain to work with but you can't use it to armor existing
hulls.

It would help add compression srength as an outside layer. I dunno if
it would help with impact resistance. ...

The usual argument against carbon reenforcement is that it is so stiff
that it will fail before the glass takes any load. At which point it
might be more sensible to just do away with the glass. Price and
compatibility wise "S" glass might be a better option than either
Kevlar or carbon. In a crash you want strong but flexible to absorb
energy.

-- Tom.

steel hulls? adding armor to FG hulls
 

I am not an expert on bonding neither aramid nor carbon to existing FG
construction, so I cannot add anything there, but you need to think through
the whole scenario. Adding protection aganst puncture is only one aspect of
the required protection. Although my hull is steel and it has collision
bulkheads both forward and aft, it also utilises watertight bulkheads as
well, but even that is insufficient. You must consider the flotation
attitude of the hull under flood conditions. If any part of the deck falls
below the water surface, the boat will most likely be lost before the
flooding can be controlled.. So keeping the boat deck parallel to the water
is really important and in my case I have a rather fine entry forward and if
flooding the forward compartment should occur the bow would sink well below
the deck line. Adding adequate fixed flotation removes too much space, so my
solution, for what it is worth, is to place a 2 ton hyperlon lift bag below
the forward cabin sole that can be inflated in an emergency. Hopefully, this
would buy enough time for the pumps and to effect a repair from the outside.
Steve

wrote in message
...
On Mar 11, 2:45 am, wrote:
" wrote:
Amen. But, having been tangentially involved in a completely
disastrous attempt to bond Kevlar (tm) fabric to PVC foam with epoxy I
strongly advise getting advise from the fabric provider before
bonding. ...

I wonder why. Incompatible binder in the cloth?
One issue with both carbon fiber & aramids (you're right, Kevlar is a
trademarked brand name) is that the cloth is much lighter than
conventional fiberglass... duh, that's a big reason to use it... but
it also means that the cloth tends to float up out of the resin. ...

Good points. Kevlar has been used with great success. I can only
speculate on the reasons for the failure. I was in the shop where it
happened re-building my dagger boards and the wing was going together
on the other side of a hull of a big cat that was also building. So,
I didn't see every detail. They were building it using Kelsall's KSS
system with Kevlar twill, epoxy and pvc. They bonded one face on a
flat table with a wet lay-up using modest vacuum to clamp it. Then
they cut darts in the pvc, draped the part into mdf formers and hand
laid the inner skin. That's sop for the KSS system and it generally
works quite well. In this case, though, both the hand laid skin and
the bagged skin could be peeled off the pvc (failing at the glue
line). They did it all a second time on the assumption that the
problem was a bad epoxy mix and it failed exactly the same way. Other
parts that came off the same table using pvc from the same batch
before, during and after were fine. I was using the same epoxy to
build my boards and it was also being used in a couple of other
projects around the shop and it was fine. It's possible that they
could have contaminated the pvc skins (boat shops aren't exactly clean
rooms). That's what the guy building the plane though. But both
sides twice? I think that using twill rather than stitched cloth and
bending the parts around very tight molds (the guy wanted to mold
right around the leading edge for some reason) were contributing
factors. But whatever the reason, the epoxy/Kevlar joint was the weak
one and I think that is cause for concern or at least careful testing
when using Kevlar.

... Carbon
is less of a pain to work with but you can't use it to armor existing
hulls.

It would help add compression srength as an outside layer. I dunno if
it would help with impact resistance. ...

The usual argument against carbon reenforcement is that it is so stiff
that it will fail before the glass takes any load. At which point it
might be more sensible to just do away with the glass. Price and
compatibility wise "S" glass might be a better option than either
Kevlar or carbon. In a crash you want strong but flexible to absorb
energy.

-- Tom.

steel hulls? adding armor to FG hulls
 

On Mar 11, 10:35 am, "Roger Long" wrote:
... There was a rash of rudder stock failures that had an outer layer of carbon
fiber for stiffness. Turned out the plain fiberglass part of the stock was
plenty strong enough. ...

Funny you should mention that. The guy working just up the bench from
me was building the rudders and stocks for the cat and he had built
carbon/glass stocks which failed exactly as you describe. He was
building the cat's stocks out of S-glass/epoxy around small foam cores
(for forming). He'd also built successful carbon stocks (including
the one on his own boat) but felt strongly that mixing materials in
rudder stocks was a bad idea. He also thought that S-glass stocks
were nearly as good as carbon because carbon had to be over-built to
absorb shock loads that were not a problem for S-glass of the required
stiffness. Carbon that's durable enough ends up being stiffer than
needed. There's still an advantage but not nearly as much as you
would guess just looking at the materials. Adding a bit of spring
into a system that takes sudden loads can reduce the peak forces by a
lot. As you say, the engineering gets complicated. Some materials
suppliers will provide engineering help to builders and designers for
surprisingly reasonable fees (even gratis for small stuff)...

-- Tom.

steel hulls? adding armor to FG hulls
 

Forgive me for replying to myself, but I wanted to add this from the
letters in the February "Yachting World".

"A chairman of the Scottish branch of the Institution of Structural
Engineers once famously defined engineering as: 'The art of modeling
materials we do not wholly understand, into shapes we cannot precisely
analyze so as to withstand forces we cannot properly assess, in such a
way that the public has no reason to suspect the extent of our
ignorance.'"

-- Tom.

steel hulls? adding armor to FG hulls
 

On Tue, 11 Mar 2008 11:48:14 -0400, "Wilbur Hubbard"
wrote:


"Bruce in Bangkok" wrote in message
.. .
That is somewhere around 45,000 N.M. so if he hit two objects in that
distance it averages one object every 22,000 miles. How many people
will cruise that distance in their whole life.


Certainly not you, sir! Pretty hard to get that kind of mileage under your
keel sitting at the Bangkok dock.

Wilbur Hubbard

And also difficult sitting there with the yellow rubber duck in the
bathtub.

Bruce-in-Bangkok
(correct email address for reply)

steel hulls? adding armor to FG hulls
 

steel hulls? adding armor to FG hulls
 

Roger Long wrote:


A single bolt under tension is about the simplest structure on the planet.
The riveted "Titanic" with all those hand fitted parts, highly variable
steel characteristics, joint strength depended on individual workmanship in
riveting, and great flexibility, was arguably one of the most complex
structures to analyse ever built. These quys trying to arrange for their
"official" paper to come out at the same time as the History Channel show
were basing their case on calculations used at the design stage of a ship to
help proportion the steel sizes in the most effecient way and pointing to a
slight difference in stress to strength ratio as "proof" that this guy who
came from nowhere to appear on TV was wrong. The completely ignored the
visual evidence in the steel debris, survivor testimony, and common sense.

I really got some good laughs out of the whole affair.

--
Roger Long




Roger,

Since you have studied this incident so long, has anyone ever considered
the effect of the temperature of the water on the fracture strength of
the steel uesd to build the hull?

In his book "Structures: Or Why Things Don't Fall Down", J.E. Gordon
analizes the changes in physical properties that the near freezing water
would have had on the steels of teh day.

Had the metals retained their ductility, the damage may have been
limited to a single bay, and the ship survive.

I couldn't turn up that piece of text on line, but a sample of the book
may be seen at http://books.google.com

http://books.google.com/books?id=oQB...t%22+fall+down

I think you would enjoy it.


Richard Lamb




^1 Structures: Or Why Things Don't Fall Down by J. E. Gordon

J.E. Gordon’s book is a great read.
Gordon strips engineering of its confusing technical terms,
communicating its founding principles in accessible, witty prose.
Amazing factoids and insights for the lay person abound in this book,
alhought the technical details may a bit heavy for some.

Witty - it will change the way you see the world

steel hulls? adding armor to FG hulls
 

Roger Long wrote:

Another quote from the infamous Roger Long"

"Good engineers understand that the numbers are only a guide to their
judgement. Bad engineers believe them absolutely."

--
Roger Long



that's a keeper!

steel hulls? adding armor to FG hulls
 

These quotes are so good I wanted to include them all (more below)

" wrote:
Forgive me for replying to myself, but I wanted to add this from the
letters in the February "Yachting World".

"A chairman of the Scottish branch of the Institution of Structural
Engineers once famously defined engineering as: 'The art of modeling
materials we do not wholly understand, into shapes we cannot precisely
analyze so as to withstand forces we cannot properly assess, in such a
way that the public has no reason to suspect the extent of our
ignorance.'"


cavelamb himself wrote:
Aircraft design is 90% educated guesses,
worked out to four decimal places.


"Roger Long" wrote:
Another quote from the infamous Roger Long"

"Good engineers understand that the numbers are only a guide to their
judgement. Bad engineers believe them absolutely."


"Roger Long" wrote:
Wow. I wish I had heard that in time to include that in the Titanic
programs

My quote was, "Any idiot can make things strong enough. Engineering is the
science of making them light enough to be affordable and functional in the
real world. The designers of that ship were under enormous pressure to use
the absolute minimum of steel they could get away with."


Engineering is also different from research. Engineers have to figure
out how to build something with the available standard practices of
the day; or provide a practical & workable innovation to standard
practice. It's very easy to say "why didn't you do it like
this" (pointing to some exotic & extreme method which may not even be
a success at the experimental stage).

An official panel of the Society on Naval Architects and Marine Engineers
recently sponsored a paper intended, I believe, to show that I was
completely wrong so as to preserve their standing as the adults and
professionals since I was getting my own TV show, two in fact. They claim
that the ship broke from the bottom up instead of the top down.

That's possible. Further down you say there is a lot of evidence it
didn't happen that way, I'm curious. Wasn't there a RINA paper some
years back on the same subject? Until 1985 the expert opinion was that
the Titanic didn't break in half at all.

I'm also curious if you've ever checked into the newsgroup
"alt.history.ocean-liners.titanic" which is a bit slow these days but
is still a major rivet-counter hangout.

DSK

steel hulls? adding armor to FG hulls
 

Roger Long wrote:
"cavelamb himself" wrote

Since you have studied this incident so long, has anyone ever considered
the effect of the temperature of the water on the fracture strength of
the steel uesd to build the hull?


Yes, and it certainly had a bearing on the details of the event but not the
big picture. She might have broken at 15 - 16 degrees instead of 10 - 12 if
it had been on a summer day.


AH, yeah. :)
Thos balmy summer days in the Norht Atlantic..

I think he probably meant considerably warmer waters.

In his book "Structures: Or Why Things Don't Fall Down", J.E. Gordon
analizes the changes in physical properties that the near freezing water
would have had on the steels of teh day.


Great book. I have read it although quite some time ago.

Why does that no surprise me?

--
Roger Long