Hull Flexing
 

Welcome back, Peter. How were the elephant seals? (present
company excluded of course)
--
Flying Tadpole

-------------------------
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Hull Flexing
 

But the boat is not solid steel is it?

Cheers MC

Peter Wiley wrote:

Actually quite a few sailboats *are* much more rigid than you seem to
know. You're taking your experience on plastic boats and assuming it is
generally applicable. The flex in a steel or ferrocement hull is
certainly there (everything flexes to some degree), but it's a fraction
of what is common in lightweight toy racing boats which are built to
minimal standards of seaworthiness and do, indeed, flex. In fact, the
toy boats often break when coming off a fairly moderate wave, as recent
Sydney-Hobart races have shown so well.

The remark about water being much less compressible than the boat is
pure & utter bull****. Even frozen water is a lot more compressible
than steel. Also has lower shear strength, tensile strength etc.

As to measurement of a boat to 0.005", I can easily believe that this
is possible. It's not even all that difficult. Whether there's any
point and whether the measurement is repeatable are different issues.

Peter Wiley

In article ,
The_navigator© wrote:


That boats are built differently has nothing to do with it. Sail boats
are not rigid nor even near it. To be as rigid as you suggest would
probably mean they would not float. If you had ever been in a real boat
beating to windward your would know they are *not* rigid. Put your hand
on the forstay and look at it unloading when she buries her bow and look
at it going tight on the crest (that's revealed by the luff bending).
It's loading up/unloading because the boat is flexing. If you ever get
the chance (assuming that any boat owner could put up with your big
mouth and BS) have a good hard look at the hull of a boat pounding hard
to windward and look and feel hull panels flexing. The boat needs has to
flex to reduce impact loadings because water is much less compressable
than the boat. Once again you reveal your lack of experience with big
boats by suggesting otherwise. This typifies your inability to grasp
even simple ideas.

As for measurent of a boat to 5 thou, look at the coefficent of
expansion of say GRP or even Al (which expands muchg less) and then tell
me how much a boat moves during a typical day/night temperature cycle.
Now you want to tell me it's easy to measure a 5 thou deflection over a
40' boat? Even if the boat builder had access to interferometric
equipment (which I'm sure they did not use -as there would be no point
in such an accurate measurement) it would still be hard. If you think
it's so easy how come you need a 'crew'. Lets face it this is yet more
Doug Kig (I'm a ****ing hero) BS. Have'nt you ever wonder why you don't
make more money -after all, you are such an expert...

My point is that Ella is not a large racing boat and yet still has more
than 1 ton rig tension.

Cheers MC

DSK wrote:

The navigator© wrote:



I'd say It's BS because boats are simply not that rigid


Oh yeah, and all boats are built to the same structural standard, aren't
they.



and it's hard to
measure to an accuracy of 4 thou on big objects.


Now that is total BS. It costs, but if you're willing to pay, I'll bring a
crew and and gear, and show you how to measure movement in any axis on
objects of any size & orientation down to 5 ten thousands +/- 1

It's part of what I do for a living, thanks very much. The NIST has
occasionally asked me for advice on this type of thing.




.... Even Ella has a backstay
tension of 2,500 lbs when beating.


Gee, and there's no difference between "2500#" and 15,000# is there?

Why do I bother answering your posts?

DSK

Hull Flexing
 

Yes, repeatability is the whole issue. Since you agree that steel and
ferro hulls flex, how much do they typically flex (sag/hog)?

Cheers MC

Peter Wiley wrote:

Actually quite a few sailboats *are* much more rigid than you seem to
know. You're taking your experience on plastic boats and assuming it is
generally applicable. The flex in a steel or ferrocement hull is
certainly there (everything flexes to some degree), but it's a fraction
of what is common in lightweight toy racing boats which are built to
minimal standards of seaworthiness and do, indeed, flex. In fact, the
toy boats often break when coming off a fairly moderate wave, as recent
Sydney-Hobart races have shown so well.

The remark about water being much less compressible than the boat is
pure & utter bull****. Even frozen water is a lot more compressible
than steel. Also has lower shear strength, tensile strength etc.

As to measurement of a boat to 0.005", I can easily believe that this
is possible. It's not even all that difficult. Whether there's any
point and whether the measurement is repeatable are different issues.

Peter Wiley

In article ,
The_navigator© wrote:


That boats are built differently has nothing to do with it. Sail boats
are not rigid nor even near it. To be as rigid as you suggest would
probably mean they would not float. If you had ever been in a real boat
beating to windward your would know they are *not* rigid. Put your hand
on the forstay and look at it unloading when she buries her bow and look
at it going tight on the crest (that's revealed by the luff bending).
It's loading up/unloading because the boat is flexing. If you ever get
the chance (assuming that any boat owner could put up with your big
mouth and BS) have a good hard look at the hull of a boat pounding hard
to windward and look and feel hull panels flexing. The boat needs has to
flex to reduce impact loadings because water is much less compressable
than the boat. Once again you reveal your lack of experience with big
boats by suggesting otherwise. This typifies your inability to grasp
even simple ideas.

As for measurent of a boat to 5 thou, look at the coefficent of
expansion of say GRP or even Al (which expands muchg less) and then tell
me how much a boat moves during a typical day/night temperature cycle.
Now you want to tell me it's easy to measure a 5 thou deflection over a
40' boat? Even if the boat builder had access to interferometric
equipment (which I'm sure they did not use -as there would be no point
in such an accurate measurement) it would still be hard. If you think
it's so easy how come you need a 'crew'. Lets face it this is yet more
Doug Kig (I'm a ****ing hero) BS. Have'nt you ever wonder why you don't
make more money -after all, you are such an expert...

My point is that Ella is not a large racing boat and yet still has more
than 1 ton rig tension.

Cheers MC

DSK wrote:

The navigator© wrote:



I'd say It's BS because boats are simply not that rigid


Oh yeah, and all boats are built to the same structural standard, aren't
they.



and it's hard to
measure to an accuracy of 4 thou on big objects.


Now that is total BS. It costs, but if you're willing to pay, I'll bring a
crew and and gear, and show you how to measure movement in any axis on
objects of any size & orientation down to 5 ten thousands +/- 1

It's part of what I do for a living, thanks very much. The NIST has
occasionally asked me for advice on this type of thing.




.... Even Ella has a backstay
tension of 2,500 lbs when beating.


Gee, and there's no difference between "2500#" and 15,000# is there?

Why do I bother answering your posts?

DSK

Hull Flexing
 

Completely & utterly impossible to say without knowing design &
construction details and doing some sort of finite element analysis
which is way beyond my technical competence. That'd only give you a
theoretical measurement anyway.

Think about it for 5 seconds, Nav. How thick is the plating? How many
longitudinals and frames and what spacing? How many welds and at what
spacing? What sort of keel? Is the deck a different material or not? Is
the shell monococque or not? Etc etc. Steel (I know little about ferro)
boats are typically a monococque construction with steel decks attached
to the hull by welding. Plastic boats may have their decks 'glassed to
the hull but usually it's a handful of self-tappers and a tube of
sikaflex. No rigidity there.

I do know that some steel boats can be easily lifted by a couple of
eyebolts welded internally without any worries about deformation, and
others are built with their stiff, heavy keels only supported in 2
places and the plate tolerances are typically 1.5 to 2mm before
welding, to minimise possible weld distortion. They don't sag or hog as
you're using the term. Maybe a few millimeters at most.

The issue isn't repeatability at all. You're merely trying to shift
goalposts. Your Ella is a racing boat and built like one - minimum
weight and what you see WRT flexing is what you'd expect. As a class
they break in really bad weather because they're outside their design
envelope.

PDW

In article ,
The_navigator© wrote:

Yes, repeatability is the whole issue. Since you agree that steel and
ferro hulls flex, how much do they typically flex (sag/hog)?

Cheers MC

Peter Wiley wrote:

Actually quite a few sailboats *are* much more rigid than you seem to
know. You're taking your experience on plastic boats and assuming it is
generally applicable. The flex in a steel or ferrocement hull is
certainly there (everything flexes to some degree), but it's a fraction
of what is common in lightweight toy racing boats which are built to
minimal standards of seaworthiness and do, indeed, flex. In fact, the
toy boats often break when coming off a fairly moderate wave, as recent
Sydney-Hobart races have shown so well.

The remark about water being much less compressible than the boat is
pure & utter bull****. Even frozen water is a lot more compressible
than steel. Also has lower shear strength, tensile strength etc.

As to measurement of a boat to 0.005", I can easily believe that this
is possible. It's not even all that difficult. Whether there's any
point and whether the measurement is repeatable are different issues.

Peter Wiley

In article ,
The_navigator© wrote:


That boats are built differently has nothing to do with it. Sail boats
are not rigid nor even near it. To be as rigid as you suggest would
probably mean they would not float. If you had ever been in a real boat
beating to windward your would know they are *not* rigid. Put your hand
on the forstay and look at it unloading when she buries her bow and look
at it going tight on the crest (that's revealed by the luff bending).
It's loading up/unloading because the boat is flexing. If you ever get
the chance (assuming that any boat owner could put up with your big
mouth and BS) have a good hard look at the hull of a boat pounding hard
to windward and look and feel hull panels flexing. The boat needs has to
flex to reduce impact loadings because water is much less compressable
than the boat. Once again you reveal your lack of experience with big
boats by suggesting otherwise. This typifies your inability to grasp
even simple ideas.

As for measurent of a boat to 5 thou, look at the coefficent of
expansion of say GRP or even Al (which expands muchg less) and then tell
me how much a boat moves during a typical day/night temperature cycle.
Now you want to tell me it's easy to measure a 5 thou deflection over a
40' boat? Even if the boat builder had access to interferometric
equipment (which I'm sure they did not use -as there would be no point
in such an accurate measurement) it would still be hard. If you think
it's so easy how come you need a 'crew'. Lets face it this is yet more
Doug Kig (I'm a ****ing hero) BS. Have'nt you ever wonder why you don't
make more money -after all, you are such an expert...

My point is that Ella is not a large racing boat and yet still has more
than 1 ton rig tension.

Cheers MC

DSK wrote:

The navigator© wrote:



I'd say It's BS because boats are simply not that rigid


Oh yeah, and all boats are built to the same structural standard, aren't
they.



and it's hard to
measure to an accuracy of 4 thou on big objects.


Now that is total BS. It costs, but if you're willing to pay, I'll bring a
crew and and gear, and show you how to measure movement in any axis on
objects of any size & orientation down to 5 ten thousands +/- 1

It's part of what I do for a living, thanks very much. The NIST has
occasionally asked me for advice on this type of thing.




.... Even Ella has a backstay
tension of 2,500 lbs when beating.


Gee, and there's no difference between "2500#" and 15,000# is there?

Why do I bother answering your posts?

DSK

Hull Flexing
 

Oh Yeah... that's right you always have the engine on so it's irrelevant!

CM

"The_navigator©" wrote in message
...
| ?
|
| Cheers MC
|
| Capt. Mooron wrote:
|
| Oh about 32 degrees in a pinch... You?
|
| CM
|
| "The_navigator©" wrote in message
| ...
| | What's your point?
| |
| | Cheers MC
| |
| | Capt. Mooron wrote:
| |
| | How does that differ to her usual condition of standing by outside a
| harbour
| | with a fouled prop?
| |
| | CM
| |
| | "The_navigator©" wrote in message
| | ...
| | | I'd say It's BS because boats are simply not that rigid and it's
hard
| to
| | | measure to an accuracy of 4 thou on big objects. The flexability
of
| most
| | | boats is such that the side stays limit the spread of the hull
as
| the
| | | backstay is tightened (this is naval architecture 101). Current
rig
| | | tensions are much higher than they used to be. Even Ella has a
| backstay
| | | tension of 2,500 lbs when beating.
| | |
| | | Cheers MC
| | |
| | | DSK wrote:
| | |
| | | The_navigator© wrote:
| | |
| | | 4 thou. measured on the back of a boat? Complete BS.
| | |
| | |
| | | "The Captain...cap n all" wrote:
| | | I would have thought so.
| | |
| | |
| | | AFAIK there was no reason to BS about it, the boat was a one-off
| | | and paid for. If I am interpreting the article about the boat
| | | correctly, the distortion was measured at the mid length along a
| | | straight from stem to center transom.
| | |
| | | If one is installing high powered hydraulics to control the rig,
| | | it makes sense to make the hull & deck structure as rigid as
| | | possible, within reasonable weight limits. I haven't seen any
| | | figures for the distortion measured on the newest IACC boats but
| | | the early 1990s boats had very high rig loads (10K kg and up)
| | | and very little (if any) distortion.
| | |
| | | Fresh Breezes- Doug King
| | |
| | |
| | |
| |
| |
| |
|
|
|

Hull Flexing
 

Peter Wiley wrote:

Completely & utterly impossible to say without knowing design &
construction details and doing some sort of finite element analysis
which is way beyond my technical competence. That'd only give you a
theoretical measurement anyway.

But it is possible (not that difficult) to measure the hull's deflection along any
axis in the real world. Not everybody has a dial indicator handy, though.



Think about it for 5 seconds, Nav. How thick is the plating? How many
longitudinals and frames and what spacing? How many welds and at what
spacing? What sort of keel? Is the deck a different material or not? Is
the shell monococque or not? Etc etc. Steel (I know little about ferro)
boats are typically a monococque construction with steel decks attached
to the hull by welding. Plastic boats may have their decks 'glassed to
the hull but usually it's a handful of self-tappers and a tube of
sikaflex. No rigidity there.

I disagree. Most structures are essentially the same, a box girder. Steel is
surprisingly limp all by itself. That's why they make I-beams instead of just steel
planks.

You're right that the details of the hull-deck joint are important to the boats
structure. A lot of mass-produced boats do not have a very good hull deck joint,
but others do. It is not inherent in the material.



I do know that some steel boats can be easily lifted by a couple of
eyebolts welded internally without any worries about deformation

So can many fiberglass boats. But this wasn't really an argument about the relative
merits of steel vs fiberglass, was it?


The issue isn't repeatability at all.

It is to Navvie© since his knowledge of engineering (among other things) is
limited. Besides, when you 'discuss' things with him, you have to accept his
tendency to bring up irrelevant oddities as though he were playing some kind of
trump. It's one of his more amusing character traits.

Fresh Breezes- Doug King

Hull Flexing
 

Peter Wiley wrote:

snip

The issue isn't repeatability at all. You're merely trying to shift
goalposts. Your Ella is a racing boat and built like one - minimum
weight and what you see WRT flexing is what you'd expect. As a class
they break in really bad weather because they're outside their design
envelope.


Was it so bad a voyage/tour of duty, Peter, that even on your
return you insist on clubbing insensible elephant seals?

--
Flying Tadpole

-------------------------
Learn what lies below the waves of cyberspace!
http://www.internetopera.netfirms.com

Hull Flexing
 

The navigator© wrote:

Yes, repeatability is the whole issue.

Why?

Repeatability is always an issue when measuring things, but is there some
specific reason why a boats rigidity should be uniform & consistent? To what
standard should it be?



.... Once again you reveal your lack of experience with big
boats by suggesting otherwise.

Really? Is it you that's been following me around all my life? Maybe you can
really tell me how many big boats I've sailed, I never did keep a written tally
myself.


....This typifies your inability to grasp
even simple ideas.

You mean like how to measure things?


As for measurent of a boat to 5 thou, look at the coefficent of
expansion of say GRP or even Al (which expands muchg less) and then tell
me how much a boat moves during a typical day/night temperature cycle.

Why is that an issue? BTW did you miss the thread about how much an aluminum mast
expands or contracts due to temp variation?


Now you want to tell me it's easy to measure a 5 thou deflection over a
40' boat?

Sure is. All you need is a yardstick slightly longer than the boat.

Even if the boat builder had access to interferometric
equipment (which I'm sure they did not use

Now you're claiming you were there? How do you know what they used?


.... -as there would be no point
in such an accurate measurement) it would still be hard.

Not really, if you know how.



My point is that Ella is not a large racing boat and yet still has more
than 1 ton rig tension.

Umm, Navvie©..... did you think that the terms '1-Ton' and the like refer to the
rig tension carried by the boats of this particular class?

BTW the specific boats I had in mind, which had aluminum struts forming a big
truss inside, were 'IMP' (designed by Ron Holland IIRC) and 'Ydra' (which was a
German entry in the Admirals Cup IIRC) and the Canada's Cuppers which I already
mentioned. Ben Lexcen (Bob Miller) designed at least one boat with the same type
structural elements. There were a bunch of less successful copies. A few years
later the advent of practical carbon fiber laminations made truss frames seem too
heavy.

There was also an early 1900s America's Cup contender with one.

Do you still think it's all BS? Will you never learn?

Fresh Breezes- Doug King

Hull Flexing
 

BTW Peter welcome back. As you can see, we've kept a boot warm for you...

DSK

Peter Wiley wrote:

Completely & utterly impossible to say without knowing design &
construction details and doing some sort of finite element analysis

Hull Flexing
 

"Capt. Mooron" wrote:

Oh about 32 degrees in a pinch... You?

Bad pun.... bad bad bad!

DSK