BOAT SHOW REPORT.. MC & capsize screen
 

DSK wrote:

Also, be prepared to explain why _your_ explanation disagrees with the
explanation of the professional naval architects who devised this measure.

MC wrote:
Oh but it does. It is closely related to the definition of the
metacentric radius. Do you know what that is?


No but I know several different ways of calculating, and few methods of
approximating with less rigorous measurements, metacentric height. If you
calculate metacentric height for a series of all angles through 180, you would
get a sort of radius. And it is a very very different thing from the capsize
screen. Let's make sure we're talking about the same thing...

Well that explasins everything. The metacentric radius is really basic
naval architecture -look it up and then you'll understand the most
common capsize screen formula -which is not what you've posted below.


CSR==(Beam / Disp ) ^ 0.333

with a lower result being more desirable when comparing similar vessels. Ring
any bells?


Yes, but you got the equation wrong. LOL The correct equation is
directly proprtional to the metacentric radius (the formula of which I
gave you before and which defines the initial stability) with the
assumption that the boat is quite slab sided (tumblehome is small). The
idea of the screen was to try to give a simple estimate (from numbers
that most people have readily to hand) of how stable the boat might be
upside down with the assumption that the water plane lateral moment
would not be very different from that expected from just the beam and
typical prismatics and sections. Empirical tests showed that this
assumption was reasonable for a rough and ready estimate -but only as a
guide. It's not an estimate acceptable here for offshore certificates.
In fact, if one were to follow the logic of this formula there would be
almost no difference between the initial stability inverted and the
right way up as it does not take any account of the VCG or coach roof.
For example, it predicts some inverted stability for a vessel with a 180
lps -e.g. a life boat -and that's clearly wrong! That anyone would
seriously use this formular in trying to decide seaworthiness is a most
unwise practice -naval architects don't!

OK?


Cheers

BOAT SHOW REPORT.. jaxineering
 

dougies, I never used the term "order of magnitude" in this context. It just
is not appropriate, and if you knew what one is you would know that as well.

btw, look up the term "asymptote" -- AND frickin' understand its meaning --
before you use it again.

Last week, in a discussion on another newsgroup, he said "Hull speed doesn't
have an
asymptote, unless it gets up to within the order of magnitude of infinity."
Cost a
fortune in spilled coffee, that one did.

DSK

BOAT SHOW REPORT.. MC & capsize screen
 

.... Ring
any bells?



MC wrote:
Yes, but you got the equation wrong.

No, that's the right equation. I see the problem... you don't know WTF
you're talking about.

The correct equation is
directly proprtional to the metacentric radius

Instead of blabbing about the metacentric radius, how about looking at a
well known and widely used formula, and taking the time to understand it?

But no, you'd rather babble, that way you can continue to feel smart.

.. That anyone would
seriously use this formular in trying to decide seaworthiness is a most
unwise practice -naval architects don't!

In the absence of more detailed measurements, it's better than nothing.
And it is a useful measure when comparing vessels of similar size and form.

BTW the CSR is not used anywhere I know of for an offshore rating
certificate, but it is occasionally used as a screen for allowing
vessels to enter a particular race.

DSK

BOAT SHOW REPORT.. MC & capsize screen
 

MC wrote:

Well if you know the answer then post it.

I may or may not know the answer, but at least I know the question.

... I'll be impressed

Impressing you is not among my concerns.

.... if you can
correctly state the boundary conditions for vortex shedding.

Are you talking about a starting vortex, a tip vortex, or trailing edge
turbulence?

DSK

BOAT SHOW REPORT.. jaxineering
 

MC wrote:
He had a good point but his argument became unglued.

That's not all that has come unglued

DSK

BOAT SHOW REPORT.. MC & capsize screen
 

dougies, the capsize ratio is widely discredited as a predictor of anything but
being the capsize ratio. You can find some pretty horrible boats with ratio's
as low as 1.75 and far better boats with 1.95+.

the capsize ratio takes too little into consideration to be much more than a
quite guide.

.... Ring
any bells?



MC wrote:
Yes, but you got the equation wrong.

No, that's the right equation. I see the problem... you don't know WTF
you're talking about.

The correct equation is
directly proprtional to the metacentric radius

Instead of blabbing about the metacentric radius, how about looking at a
well known and widely used formula, and taking the time to understand it?

But no, you'd rather babble, that way you can continue to feel smart.

.. That anyone would
seriously use this formular in trying to decide seaworthiness is a most
unwise practice -naval architects don't!

In the absence of more detailed measurements, it's better than nothing.
And it is a useful measure when comparing vessels of similar size and form.

BTW the CSR is not used anywhere I know of for an offshore rating
certificate, but it is occasionally used as a screen for allowing
vessels to enter a particular race.

DSK

BOAT SHOW REPORT.. MC & capsize screen
 

a tip vortex, or trailing edge
turbulence?

a tip vortex is not th same thing as trailing edge tubulence, though each
orginates for the same reason. Different dynamics, different effects.

go read another Popular Mechanix article.

BOAT SHOW REPORT.. MC & capsize screen
 

JAXAshby wrote:

dougies, the capsize ratio is widely discredited as a predictor of anything but
being the capsize ratio.

"Discredited"? By whom? Please explain... as of the fall of 2003, there
were a number of offshore races around here that required a certain CSR
for certain classes.


... You can find some pretty horrible boats with ratio's
as low as 1.75 and far better boats with 1.95+.

Well, that's very true given the wide lattitude in defining "horrible"
and "better."


the capsize ratio takes too little into consideration to be much more than a
quite guide.

Kind of like your posts, huh?

DSK

BOAT SHOW REPORT.. MC & capsize screen
 

a tip vortex, or trailing edge
turbulence?


JAXAshby wrote:
a tip vortex is not th same thing as trailing edge tubulence,

Very good Jax! I can see why MC refers to you for these difficult
questions.... a tip vortex forms at the tip, and a vortex formed by
trailing edge turbulence is at the trailing edge... shucks why didn't I
think of that!

... though each
orginates for the same reason.

Which is? (sound of Jeapordy music)

.. Different dynamics, different effects.

Wait a minute, I thought you said they formed for the same reason?


go read another Popular Mechanix article.

Is that where you get your technical info?

DSK

BOAT SHOW REPORT.. MC & capsize screen
 

... You can find some pretty horrible boats with ratio's
as low as 1.75 and far better boats with 1.95+.

Well, that's very true given the wide lattitude in defining "horrible"
and "better."

I'm afraid he's correct. Quite a bit of junk out there with good capsize
ratings. And quite a few nice boats on the margin or outside of it.

RB