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Old 05-04-2012, 09:28   #76
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Re: Capsize Ratio's



Very funny... Is that long keel glued to the wave or what?

Any boat that finds himself in a huge and steep wave like the one you designed there will try to slip to the bottom of the wave (gravity you know). The main difference between a boat with a small area submersed (foil keel with a torpedo a centerboard or a cat) and a boat with a big submersed area (like a deep full keel boat) is that on doing that downward lateral movement the boat with the large area submersed will trip on it, transforming a substantial part of that gravity force on a rolling movement.





But this as nothing to do with that capsize ratio formula. Even a relatively narrow boat, very light, with a big foil keel (or a long ballasted swing keel) will be very penalized by that formula.
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Old 05-04-2012, 17:21   #77
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Re: Capsize Ratio's

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Very funny... Is that long keel glued to the wave or what?
Funny indeed.

Reading Marchaj casts different light on the subject. He ads the fact that the boat and the wave are in movement - unlike static boats on static waves in a static drawing. Observing a plain float on big swells helps too - it never 'slides', nor does it 'roll'. It just bobs up and down. I wonder why. Perhaps gravity does not apply to small floats as much as it does to big boats. (You know: one pound of lead is heavier than one pound of feathers ;-))))) even though some of us do know that they fall thru the vacuum with the same speed)

BTW boat roll on the wave results from different physics (from different physics of the wave than described in the Spanish dibujitos).

My experience with Spanish seagoing education is that of ... remember Trafalgar? Nothing much changed since ....

OK. Iker Martinez, but otherwise - do not ask peasants about sea monsters ... unless you want to hear some likely stories!

Cheers,
barnie
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Old 05-04-2012, 17:38   #78
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Re: Capsize Ratio's

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...

My experience with Spanish seagoing education is that of ... remember Trafalgar? Nothing much changed since ....

....

Cheers,
barnie
Hi! The Spanish is only because the book is a translation. It is a French book written by one of the best sailors of all times: Eric Tabarly

The two boats on the drawings are two of his boats, the fin keel, one of its racing boats, the full keel boat, the old family boat. He sailed both boats extensively (crossing many oceans and surviving many storms). Those drawings reflect his experience and what he learned with both boats and its behaviour in heavy weather.

But don't take me wrong. He loved the family old boat, so much that he named all his boats after that boat: They were all Pen Duick (II, III, and so on). He died sailing on that boat.
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Old 05-04-2012, 17:45   #79
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Re: Capsize Ratio's

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Hi! The Spanish is only because the book is a translation. It is a French book written by one of the best sailors of all times: Eric Tabarly (...)
I can only repeat the same: Trafalgar.

;-)
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Old 05-04-2012, 17:48   #80
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Re: Capsize Ratio's

Nay, seriously: I admire Tabarly very much and I think French sailors (and their boats and their boat designers) are today at the head of the competition. Alas, I think the drawings and the explanations therein are flawed.

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Old 05-04-2012, 22:44   #81
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Re: Capsize Ratio's

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Originally Posted by Polux View Post


Very funny... Is that long keel glued to the wave or what?

Any boat that finds himself in a huge and steep wave like the one you designed there will try to slip to the bottom of the wave (gravity you know). The main difference between a boat with a small area submersed (foil keel with a torpedo a centerboard or a cat) and a boat with a big submersed area (like a deep full keel boat) is that on doing that downward lateral movement the boat with the large area submersed will trip on it, transforming a substantial part of that gravity force on a rolling movement.





But this as nothing to do with that capsize ratio formula. Even a relatively narrow boat, very light, with a big foil keel (or a long ballasted swing keel) will be very penalized by that formula.
Nice try Paulo, but this is more about hull form than keels.

Do try to keep up.
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Old 06-04-2012, 17:15   #82
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Re: Capsize Ratio's

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Nice try Paulo, but this is more about hull form than keels.

Do try to keep up.

I do keep up with modern design, latest hydrodynamic findings and the work of contemporary Na, it is you that live in the past, full keels and all.
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Old 06-04-2012, 17:42   #83
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Re: Capsize Ratio's

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..3 I wonder why. Perhaps gravity does not apply to small floats as much as it does to big boats. (You know: one pound of lead is heavier than one pound of feathers ;-))))) even though some of us do know that they fall thru the vacuum with the same speed)

BTW boat roll on the wave results from different physics (from different physics of the wave than described in the Spanish dibujitos).

My experience with Spanish seagoing education is that of ... remember Trafalgar? Nothing much changed since ....

....
barnie
This is not very nice for Spanish speaking NA. Some of the greatest today has Spanish has is native language: To you have heard of JK, or SA, not to mention some old school boys like Tony Castro or German Frers?

Regarding that one pound of lead and one pound of feeders, the important is not to know that they "fall" at the same speed in vacuum but that they don't fall at the same speed in water. Actually the feathers will probably float while the lead will sink faster than a stone...you know, Archimedes?
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Old 05-06-2012, 21:19   #84
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Re: Capsize Ratio's

Seems kind of quiet out there now that 8 people have died off the California coast, half the Volvo OR fleet has crashed and is 'racing' to South Africa on the decks of tramp steamers, the Coast Guard has suspended offshore racing until somebody figures out what the hell is going on, and so on.

I just looked at the official web-site for the Pogo ... beloved of Paolo ... on a sea trial it rolled four times, then pitch-poled, loosing the rig -- end of trial. They seemed to think it was pretty cool that the rig held on during four 360 degree rolls.

Do you guys seriously still think that this is the kind of craft that is suitable for offshore cruising? Or anything?
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Old 05-06-2012, 22:45   #85
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Re: Capsize Ratio's

Polux, latest hydrodynamics findings aim for speed and most of the newly desings have happily forgotten the "old" findings. Speaking of the subject boat length, beam, depth of clr and the size of the area itself, depth of cg, displacement and freeboard are what counts.. some lesser things too but these are the essential ones. Now can you figure out how these things do affect to dynamic stability and seaworthiness ?
BR Teddy
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Old 05-06-2012, 23:13   #86
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Re: Capsize Ratio's

You might find some answers in a book by Lars Larssson and Rolf Eliasson called Principles of Yacht Design. He has researched beam length ratios.
Basicly it would appear from tank tests that once the breaking wave hieght exceeds the beam of the boat, the chances are, it will roll.
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Old 06-06-2012, 03:27   #87
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Re: Capsize Ratio's

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Basicly it would appear from tank tests that once the breaking wave hieght exceeds the beam of the boat, the chances are, it will roll.
Nope.. draft to Clr is more relevant in this regard. Beam affects are more depending of the Cg and sometimes quite opposite way you suggest. It's true only if all other things are kept the same and Cg is above waterline.
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Old 06-06-2012, 06:02   #88
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Re: Capsize Ratio's

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Originally Posted by Polux View Post


Very funny... Is that long keel glued to the wave or what?

Any boat that finds himself in a huge and steep wave like the one you designed there will try to slip to the bottom of the wave (gravity you know). The main difference between a boat with a small area submersed (foil keel with a torpedo a centerboard or a cat) and a boat with a big submersed area (like a deep full keel boat) is that on doing that downward lateral movement the boat with the large area submersed will trip on it, transforming a substantial part of that gravity force on a rolling movement.





But this as nothing to do with that capsize ratio formula. Even a relatively narrow boat, very light, with a big foil keel (or a long ballasted swing keel) will be very penalized by that formula.
I'm not trying to pull rank here, but I actually have some relevant experience. I tripped on a very large breaking wave in a modified full keel boat (a Taipan 28 in a typhoon in the S. China Sea). I was knocked down, but did not roll.

I feel quite confident on a gut level that the outcome would have been different in a fin keeler - I probably would have been rolled and might not be writing this now. But, without any empirical data, I can't say for sure what the difference in outcomes would have been.
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Old 06-06-2012, 08:09   #89
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Re: Capsize Ratio's

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Seems kind of quiet out there now that 8 people have died off the California coast, half the Volvo OR fleet has crashed and is 'racing' to South Africa on the decks of tramp steamers, the Coast Guard has suspended offshore racing until somebody figures out what the hell is going on, and so on.

I just looked at the official web-site for the Pogo ... beloved of Paolo ... on a sea trial it rolled four times, then pitch-poled, loosing the rig -- end of trial. They seemed to think it was pretty cool that the rig held on during four 360 degree rolls.

Do you guys seriously still think that this is the kind of craft that is suitable for offshore cruising? Or anything?
Maybe you can post a link for that? This is the official Pogo website and I cannot find anything.

Chantier naval STRUCTURES, constructeur des voiliers POGO (site officiel) :: STRUCTURES Shipyard, construction of sailing boat POGO (Oficial website) | Pogo 10.50, Pogo 12.50, Pogo 40s2, Pogo 50, Pogo 30

What you mean sea trial? It was during the mandatory 360 test for 40class boats? In fact Racing Pogos are able to re-right itself without any outside help, even without waves that is a thing that the vast majority of boats, old and new are not able to do. They are also insubmersible.

Any small boat can be capsized, given the right conditions. Pogos are only one of the more difficult boats to capsize regarding their size, not uncapsizable. They are also one ho the best to recover from an inverted position.

Regarding the VOR 70 you are showing a lot of ignorance: They were put in cargoships not on account of seaworthiness but PIRATE attacks. For their size they are one of the more seaworthy boats ever made, with an incredible stability. They are also one of the strongest boats around. They have to be given the incredible efforts they sustain when for instance they fall from the top of 8m waves at speeds near 30K or more.

Put those boats sailing at 2 times the max speed of your boat and they will not break and will be much more resistant than any old boat.
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Old 06-06-2012, 08:17   #90
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Re: Capsize Ratio's

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Nope.. draft to Clr is more relevant in this regard. Beam affects are more depending of the Cg and sometimes quite opposite way you suggest. It's true only if all other things are kept the same and Cg is above waterline.
BR Teddy
The ones that established that beam was important regarding capsizing and established that relation were specialists (I believe wolfson unit). That is the reason cats are so difficult to capsize. Why do you thing that modern mass production cruisers are beamy boats? Because the best NA don't no what they are doing?
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