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#241
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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 |
#242
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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 |
#243
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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 |
#244
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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 |
#245
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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 |
#246
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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 |
#247
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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. |
#248
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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 |
#249
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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 |
#250
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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 |
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