4 thou. measured on the back of a boat? Complete BS.

Cheers MC

DSK wrote:

I remember reading about a New Orleans Marine hotshot racing boat built back in the 1980s, which
had a hull & deck of uncored glass & mat with a subimposed grid of straight S-glass. Everybody
guffawed and said "Those hicks sure don't know how to build racing boats, shoulda used foam
core" but the builder shrugged and said that they measured the bend in the hull/deck with
15,000# tension on the backstay.... it was 4 thousands of an inch....

Fresh Breezes- Doug King

Ever heard of temperature?

MC

DSK wrote:


Sure. Why else would they build expansion joints into the upper decks of big (or even
medium-sized) ships?

They are common in engineering in an pipe system that is exposed to wide
temperatuire fluctualtions.

Cheers MC

otnmbrd wrote:

About the only place I've seen "expansion joints", is on Navy ships
(which is not to say some passenger ships might have them).
On a tanker, the only place you'll see them will be on catwalks and in
piping (G can get downright squeaky).
Tankers, being built with longitudinal framing, tend to bend more, in
that direction.

otn

DSK wrote:

otnmbrd wrote:


Doesn't really matter what size the boat is, you will get some degree of
"flex", especially when you remove it from the water and put it on a
hard stand. BG you want to see flex, you should watch and listen to a
large tanker at sea, or watch one go from hog to sag when loading.



Sure. Why else would they build expansion joints into the upper decks
of big (or even
medium-sized) ships?

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

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

On a tanker, Dresser couplings are used less for temperature
fluctuations, than for longitudinal flexing due to load and or working
in a seaway.
The same would apply to the flex joints that DSK was talking about.

otn

The_navigator© wrote:
They are common in engineering in an pipe system that is exposed to wide
temperatuire fluctualtions.

Cheers MC

otnmbrd wrote:

About the only place I've seen "expansion joints", is on Navy ships
(which is not to say some passenger ships might have them).
On a tanker, the only place you'll see them will be on catwalks and in
piping (G can get downright squeaky).
Tankers, being built with longitudinal framing, tend to bend more, in
that direction.

otn

DSK wrote:

otnmbrd wrote:


Doesn't really matter what size the boat is, you will get some
degree of
"flex", especially when you remove it from the water and put it on a
hard stand. BG you want to see flex, you should watch and listen to a
large tanker at sea, or watch one go from hog to sag when loading.




Sure. Why else would they build expansion joints into the upper decks
of big (or even
medium-sized) ships?

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

"The Captain...cap n all" wrote:

How big was this thing Doug?

It was a Frers designed 1-Tonner, maybe 38' or 39' LOA


Most boats assume a slightly different shape in water as opposed to
land only because they are suppored better.

Sure, but then relatively few boats are built to be as rigid as high-end
custom racers. At one point from the late 1970s through maybe the late
1980s it was fairly common to have a geodesic grid of aluminum struts
inside, completely obstructing the cabin. What a PITA.



I can't see anyone measuring 4 thou in a live environment and assuming
accuracy to that level.

Well, to be honest I don't know how the boatbuilder measured this. It's
not a matter requiring scientific accuracy, but there are several ways you
could measure it with an independent frame or taut wire. Nowadays you
could set up a laser deflection meter easily and quickly.


....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.

They bent.

Shucks, some of them broke! But I meant the hull deflection along major
axis from the rig loads. I suspect that they bent very little (a couple
millimeters or less), or that the hull deflection was designed in as a
tuning feature.... "some chop coming up, let's get the boat a little more
banana-shaped...."

Some of the production boats I've sailed bend visibly, several inches,
when the backstay is on and the rig loaded up.

Fresh Breezes- Doug King

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
|
|
|

.... 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

because you like the feeling of superiority?