Capsize Screen? At what angle does this refer for my Hunter 30? Is that what they call being knocked down?
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Capsize Screen Definition
The capsize screen is not an angle. It's a nondimensional ratio used to indicae the ability of a boat to recover from a 180 degree capsize. A very light and beamy boat such as a catamaran would have a very igh capsize screen -- indicating that it is extremely stable in the inverted position -- a condition noted by famous yacht designer Weston Farmer as "not a particularly desirable characteristic for a boat." A narrow, heavy displacement boat would have a low capsize screen value. The heavy displacement boat may have less initial stability, but it would be more likely to recover to an upright position once rolled over (provided it didn't fill with water and sink). This site also has info on the capsize screen on the Performance Ratios page. Also, the site http://www.anyboat.com/capsize.htm has a capsize screen calculator that calcultes the value based on the following definition: " According to the capsize formula published in the May 1997 issue of Practical Boatowner, anything less than 2 is considered "good". If you would like to find the capsize "value" of your vessel divide the displacement of the vessel by 64, then take the cube root of that number and divide into the beam of the vessel, or just use the form below! Just a word of caution, anyboat does not recommend the use of any one formula for determining vessel stability or if a vessel's design is seaworthy." ________ Paul
The capsize screen is not an angle. It's a nondimensional ratio used to indicae the ability of a boat to recover from a 180 degree capsize. A very light and beamy boat such as a catamaran would have a very igh capsize screen -- indicating that it is extremely stable in the inverted position -- a condition noted by famous yacht designer Weston Farmer as "not a particularly desirable characteristic for a boat." A narrow, heavy displacement boat would have a low capsize screen value. The heavy displacement boat may have less initial stability, but it would be more likely to recover to an upright position once rolled over (provided it didn't fill with water and sink). This site also has info on the capsize screen on the Performance Ratios page. Also, the site http://www.anyboat.com/capsize.htm has a capsize screen calculator that calcultes the value based on the following definition: " According to the capsize formula published in the May 1997 issue of Practical Boatowner, anything less than 2 is considered "good". If you would like to find the capsize "value" of your vessel divide the displacement of the vessel by 64, then take the cube root of that number and divide into the beam of the vessel, or just use the form below! Just a word of caution, anyboat does not recommend the use of any one formula for determining vessel stability or if a vessel's design is seaworthy." ________ Paul
Three or four comments
I suspect angle of vanishing stability is more indicative of capsize recovery than capsize screen. Measurements of hull shape, knowledge of a boat's center of gravity, and good software are needed to calculate the AVS. There is no magic to the value 2.0. Ever since the capsize screen was developed, shortly after the Fastnet disaster, there have been a lot of modern designs with capsize screens of 1.9x. Are designers simply pushing to the edge of what people will buy? Stability is not the same as stiffness. Very beamy boats are stiff. They might or might not be stable. If you are concerned about a boat's stability, in addition to capsize screen, you should look at its ratio of ballast to displacement, and for other clues of how its weight is distributed. The best thing would be for us to persuade builders to publish more data on their designs.
I suspect angle of vanishing stability is more indicative of capsize recovery than capsize screen. Measurements of hull shape, knowledge of a boat's center of gravity, and good software are needed to calculate the AVS. There is no magic to the value 2.0. Ever since the capsize screen was developed, shortly after the Fastnet disaster, there have been a lot of modern designs with capsize screens of 1.9x. Are designers simply pushing to the edge of what people will buy? Stability is not the same as stiffness. Very beamy boats are stiff. They might or might not be stable. If you are concerned about a boat's stability, in addition to capsize screen, you should look at its ratio of ballast to displacement, and for other clues of how its weight is distributed. The best thing would be for us to persuade builders to publish more data on their designs.
Getting data from Hunter
I've e-mailed Hunter on a number of occasions to get details of stability curves etc, with no success. I guess they don't want to let people know the details. I wonder why not?
I've e-mailed Hunter on a number of occasions to get details of stability curves etc, with no success. I guess they don't want to let people know the details. I wonder why not?
Opening a can of worms, eh? Here is your homework!
The discussion about capsize screen formulas and other "magical numbers" pops up with some regularity on the newsgroups (e.g. rec.boats.cruising; search the deja.com archives) and even on the Cruising World bulletin board (which is a cross between a cocktail party and a serious discussion board). Recently, this issue received some very serious consideration there, with several Hunter owners taking part in the discussions. I am attaching a copy of my personal response (entitled "Aw, c'mon guys!!!") as well as the titles of 90, or so, other entries. Read especially Jeff H's comment. He is generally acknowledged as the professor of sailboat design issues on that board. To find this discussion, try the following URL: <http://www.sailingworld.com/cgi-bin/arch_049.pl?read=52728>. If that does not work, just go to the bulletin board and look in archive #49, October 30, 1999. Have fun! Flying Dutchman (copy of own CWBB discussion contribution and headers of other contributions) Thanks for this enlightening discussion. My vessel only calculated out at 1.85, or so. However, I have already ordered a load of bricks that will be paved over the teak decks and am looking at ways to make bath room tiles stick to the mast (or should I take lead?). Yes, I know this may not make my Hunter legend 43 quite equal to crab crushers that were designed and built like that from scratch, but it will go a loooong way...... (including the sailing characteristics). An guess what? My CSF will have gone all the way to 1.67 after making these reinforcements!!! Now I will finally be able to sleep better (as long as I stay home, of course)... Ever heard of "magical thinking"? This is where most of these vaunted empirical formulas and dimensionless numbers really belong. For the numerically and/or physicochemically challenged among us (and who, including myself, does not fit into that group at one level or other?) it is a great solace to be able to put our hopes and believes into magical thinking. Of course, you might also try PRAYING. That, at least, is an honest admission that we really know clue about most of these issues. Have fun! Flying Dutchman "Rivendel II" Messages in This Thread Stability issue revisited -- Greg Kozlowski -- 10/30/99 One thing pointed out ... -- kaj -- 10/30/99 Yeah but, people buy the boats and have responsibiliy.. -- Tom Jessop -- 10/30/99 just a matter of time -- billy -- 10/30/99 Competitive ocean racers are usually lightweight or even ultralightweight boats ... -- dougjnn -- 10/30/99 passing the buck -- Greg Kozlowski -- 10/30/99 Greg's Boat is a __________? -- Nelson -- 10/30/99 SHERPA -- Greg Kozlowski -- 10/30/99 Live and Learn.... -- Voss -- 10/30/99 I have to disagree about light boats, Voss .. -- Russell -- 10/30/99 I agree that light and heavy are relative terms... -- Voss -- 10/30/99 Voss, my friend...you are indeed wise enough to know... -- Steve Honour -- 10/30/99 Displacement vs. construction weight... -- Voss -- 10/30/99 Absolute agreement on the bottom line. -- Steve Honour -- 10/30/99 Voss... I'll let you know if my "light" boat ever "crumbles under the fury of the ocean!"(nm) -- KevinG -- 10/30/99 Stability Formula -- Catalina Kids -- 10/30/99 Here is the capsize screen .. -- Russell -- 10/30/99 in simple language -- Greg Kozlowski -- 10/30/99 I guess we are ok -- Catalina Kids -- 10/30/99 Low Capsize-Risk + High Comfort-Factor = Great Boat -- Ernie A -- 10/31/99 Thanks Ernie A -- Catalina Kids -- 11/1/99 Aw, c'mon guys!!! (ROTFLMAO) -- Henk Meuzelaar -- 10/30/99 You said the same thing more effectively, probably, with ridicule ... -- dougjnn -- 10/30/99 Did you calculate the transverse moment of inertia as well ... -- kaj -- 10/30/99 I think that formula is ridiculous. I think the issue of lateral ... -- dougjnn -- 10/30/99 doup, where did you obtain the righting... -- h40.5bob -- 10/30/99 I was trying to remember that, and can't so far ... -- dougjnn -- 10/30/99 For the record -- Greg Kozlowski -- 11/1/99 To be fair ... -- kaj -- 11/1/99 With you all the way on this -- Greg Kozlowski -- 11/1/99 GZ curves - Practice and Reality -- NigeCh -- 11/1/99 Loose the righteous indignation, Capsize screening is not a cure all... -- Jeff H -- 10/30/99 I've always had a question about that formula.... -- JohnH -- 10/30/99 The Capsize screening formula ... -- kaj -- 10/30/99 That formula is a joke. See my post above, Henk's and the ... -- dougjnn -- 10/30/99 John, your well educated "intuition" is spot on some ... -- dougjnn -- 10/30/99 Don't think the deeper keel helped in those specific conditions. -- Bev Clary -- 10/31/99 It's fun to argue about yacht design and survival storms, but there are many more important parts to safety -- Russell -- 10/30/99 If ... -- kaj -- 10/30/99 My answer to this one of your "if's" : -- dougjnn -- 10/30/99 Wise post Russell. You don't sound so "green" to me ... -- dougjnn -- 10/30/99 Hard to argue your points Russel... -- Voss -- 10/30/99 You are simply wrong about the relative utility of ... -- dougjnn -- 10/30/99 Now hang on there a minute doug... -- Voss -- 10/30/99 I will concede some hyperbole in my closing paragraph ... -- dougjnn -- 10/30/99 One thing everyone seems to have missed... -- Jon -- 10/30/99 Let's take that back a bit further ... (Medium long) -- NigeCh -- 10/30/99 Nige, did you read any estimates of at what angle to the prevailing wave ... -- dougjnn -- 10/30/99 Here are 2 URLS that may help -- NigeCh -- 10/30/99 “There is no evidence that any particular style or design ... -- kaj -- 10/31/99 Stability issues - Fastnet -- NigeCh -- 10/31/99 Ok - thanks for clarifying. -- kaj -- 10/31/99 The first Marchaj quote is incomplete! -- NigeCh -- 11/1/99 Catalina-42 with a 1.97 CSR finishes 8th in '97 Sydney-Hobart - go figure... -- Ernie A -- 10/31/99 Extremes Aside, The Screening Formula is Valid... -- John -- 10/30/99 a question....are all you guys engineers?... -- h40.5bob -- 10/30/99 Does this look that serious
(nm) -- kaj -- 10/31/99 yes, i'm afraid so...this is great..since the ratio for my h40.5 is less than 2, i'm now a ratio snob.... -- h40.5bob -- 10/31/99 I am.(nm) -- Tom Jessop -- 10/31/99 Many contributors to this discussion missing the point -- Greg Kozlowski -- 10/31/99 Are you looking for the holy grail? -- Brian Grant -- 10/31/99 What? -- Greg Kozlowski -- 10/31/99 the size of your living room is more important if your wife won't go at all otherwise, and you don't want a divorce.... -- h40.5bob -- 10/31/99 Can't argue with that! -- Greg Kozlowski -- 10/31/99 Let's not be so hard on the messinger! -- Harold -- 10/31/99 you're welcome...my pathetic attempts at humor rarely come across....nm -- h40.5bob -- 10/31/99 Living Room? PLEASE!!!!! -- Nelson -- 10/31/99 Yes, let's stick with the proper terms, like "stick" and "pointy end" (nm) -- Russell -- 10/31/99 In my experience there are two kinds of people who sometimes .. -- dougjnn -- 10/31/99 That wasn't what I got from your original post -- Brian Grant -- 10/31/99 Brian, did you miscalculate, or do I have the wrong specs ? -- Russell -- 10/31/99 OH, thank goodness, I'm safe -- Brian Grant -- 10/31/99 Knowing how to use storm tactics and carrying yes a series drogue and ... -- dougjnn -- 10/31/99 Knowing how to use storm tactics and carrying yes a series drogue and ... -- dougjnn -- 10/31/99 this is a very interesting discussion, but.... -- h40.5bob -- 10/31/99 A lot of this board is feeding the dream -- Brian Grant -- 10/31/99 You want stability, you got it ... -- JAX -- 10/31/99 If I never sailed more than a day's distance from the nearest ... -- dougjnn -- 10/31/99 Kate's got a thread above. Now come on, -- NigeCh -- 10/31/99 Vast majority of time is not bluewater. I thought I was the poster boy ... -- dougjnn -- 10/31/99 If I never sailed more than a day's distance from the nearest ... -- dougjnn -- 10/31/99 I reject the idea that there is a "best" set of performance criteria for a boat. -- Tom Jessop -- 10/31/99 Agree. -- Bev Clary -- 10/31/99 'THE Posiden adventure thread' a study in human nature... -- billy -- 10/31/99 Did you find any ... -- Brian Grant -- 10/31/99 i'd gut out the interior, sand most of the jell coat -- billy -- 10/31/99 Hey up, billy ... -- NigeCh -- 10/31/99 Why do boats sink? A few thoughts on safety .. -- Russell -- 10/31/99 Some simple methods re (1) -- kaj -- 10/31/99 Kind of modified Miesian ... (?) -- NigeCh -- 10/31/99 Cannot resist -- kaj -- 11/1/99
The discussion about capsize screen formulas and other "magical numbers" pops up with some regularity on the newsgroups (e.g. rec.boats.cruising; search the deja.com archives) and even on the Cruising World bulletin board (which is a cross between a cocktail party and a serious discussion board). Recently, this issue received some very serious consideration there, with several Hunter owners taking part in the discussions. I am attaching a copy of my personal response (entitled "Aw, c'mon guys!!!") as well as the titles of 90, or so, other entries. Read especially Jeff H's comment. He is generally acknowledged as the professor of sailboat design issues on that board. To find this discussion, try the following URL: <http://www.sailingworld.com/cgi-bin/arch_049.pl?read=52728>. If that does not work, just go to the bulletin board and look in archive #49, October 30, 1999. Have fun! Flying Dutchman (copy of own CWBB discussion contribution and headers of other contributions) Thanks for this enlightening discussion. My vessel only calculated out at 1.85, or so. However, I have already ordered a load of bricks that will be paved over the teak decks and am looking at ways to make bath room tiles stick to the mast (or should I take lead?). Yes, I know this may not make my Hunter legend 43 quite equal to crab crushers that were designed and built like that from scratch, but it will go a loooong way...... (including the sailing characteristics). An guess what? My CSF will have gone all the way to 1.67 after making these reinforcements!!! Now I will finally be able to sleep better (as long as I stay home, of course)... Ever heard of "magical thinking"? This is where most of these vaunted empirical formulas and dimensionless numbers really belong. For the numerically and/or physicochemically challenged among us (and who, including myself, does not fit into that group at one level or other?) it is a great solace to be able to put our hopes and believes into magical thinking. Of course, you might also try PRAYING. That, at least, is an honest admission that we really know clue about most of these issues. Have fun! Flying Dutchman "Rivendel II" Messages in This Thread Stability issue revisited -- Greg Kozlowski -- 10/30/99 One thing pointed out ... -- kaj -- 10/30/99 Yeah but, people buy the boats and have responsibiliy.. -- Tom Jessop -- 10/30/99 just a matter of time -- billy -- 10/30/99 Competitive ocean racers are usually lightweight or even ultralightweight boats ... -- dougjnn -- 10/30/99 passing the buck -- Greg Kozlowski -- 10/30/99 Greg's Boat is a __________? -- Nelson -- 10/30/99 SHERPA -- Greg Kozlowski -- 10/30/99 Live and Learn.... -- Voss -- 10/30/99 I have to disagree about light boats, Voss .. -- Russell -- 10/30/99 I agree that light and heavy are relative terms... -- Voss -- 10/30/99 Voss, my friend...you are indeed wise enough to know... -- Steve Honour -- 10/30/99 Displacement vs. construction weight... -- Voss -- 10/30/99 Absolute agreement on the bottom line. -- Steve Honour -- 10/30/99 Voss... I'll let you know if my "light" boat ever "crumbles under the fury of the ocean!"(nm) -- KevinG -- 10/30/99 Stability Formula -- Catalina Kids -- 10/30/99 Here is the capsize screen .. -- Russell -- 10/30/99 in simple language -- Greg Kozlowski -- 10/30/99 I guess we are ok -- Catalina Kids -- 10/30/99 Low Capsize-Risk + High Comfort-Factor = Great Boat -- Ernie A -- 10/31/99 Thanks Ernie A -- Catalina Kids -- 11/1/99 Aw, c'mon guys!!! (ROTFLMAO) -- Henk Meuzelaar -- 10/30/99 You said the same thing more effectively, probably, with ridicule ... -- dougjnn -- 10/30/99 Did you calculate the transverse moment of inertia as well ... -- kaj -- 10/30/99 I think that formula is ridiculous. I think the issue of lateral ... -- dougjnn -- 10/30/99 doup, where did you obtain the righting... -- h40.5bob -- 10/30/99 I was trying to remember that, and can't so far ... -- dougjnn -- 10/30/99 For the record -- Greg Kozlowski -- 11/1/99 To be fair ... -- kaj -- 11/1/99 With you all the way on this -- Greg Kozlowski -- 11/1/99 GZ curves - Practice and Reality -- NigeCh -- 11/1/99 Loose the righteous indignation, Capsize screening is not a cure all... -- Jeff H -- 10/30/99 I've always had a question about that formula.... -- JohnH -- 10/30/99 The Capsize screening formula ... -- kaj -- 10/30/99 That formula is a joke. See my post above, Henk's and the ... -- dougjnn -- 10/30/99 John, your well educated "intuition" is spot on some ... -- dougjnn -- 10/30/99 Don't think the deeper keel helped in those specific conditions. -- Bev Clary -- 10/31/99 It's fun to argue about yacht design and survival storms, but there are many more important parts to safety -- Russell -- 10/30/99 If ... -- kaj -- 10/30/99 My answer to this one of your "if's" : -- dougjnn -- 10/30/99 Wise post Russell. You don't sound so "green" to me ... -- dougjnn -- 10/30/99 Hard to argue your points Russel... -- Voss -- 10/30/99 You are simply wrong about the relative utility of ... -- dougjnn -- 10/30/99 Now hang on there a minute doug... -- Voss -- 10/30/99 I will concede some hyperbole in my closing paragraph ... -- dougjnn -- 10/30/99 One thing everyone seems to have missed... -- Jon -- 10/30/99 Let's take that back a bit further ... (Medium long) -- NigeCh -- 10/30/99 Nige, did you read any estimates of at what angle to the prevailing wave ... -- dougjnn -- 10/30/99 Here are 2 URLS that may help -- NigeCh -- 10/30/99 “There is no evidence that any particular style or design ... -- kaj -- 10/31/99 Stability issues - Fastnet -- NigeCh -- 10/31/99 Ok - thanks for clarifying. -- kaj -- 10/31/99 The first Marchaj quote is incomplete! -- NigeCh -- 11/1/99 Catalina-42 with a 1.97 CSR finishes 8th in '97 Sydney-Hobart - go figure... -- Ernie A -- 10/31/99 Extremes Aside, The Screening Formula is Valid... -- John -- 10/30/99 a question....are all you guys engineers?... -- h40.5bob -- 10/30/99 Does this look that serious
(nm) -- kaj -- 10/31/99 yes, i'm afraid so...this is great..since the ratio for my h40.5 is less than 2, i'm now a ratio snob.... -- h40.5bob -- 10/31/99 I am.(nm) -- Tom Jessop -- 10/31/99 Many contributors to this discussion missing the point -- Greg Kozlowski -- 10/31/99 Are you looking for the holy grail? -- Brian Grant -- 10/31/99 What? -- Greg Kozlowski -- 10/31/99 the size of your living room is more important if your wife won't go at all otherwise, and you don't want a divorce.... -- h40.5bob -- 10/31/99 Can't argue with that! -- Greg Kozlowski -- 10/31/99 Let's not be so hard on the messinger! -- Harold -- 10/31/99 you're welcome...my pathetic attempts at humor rarely come across....nm -- h40.5bob -- 10/31/99 Living Room? PLEASE!!!!! -- Nelson -- 10/31/99 Yes, let's stick with the proper terms, like "stick" and "pointy end" (nm) -- Russell -- 10/31/99 In my experience there are two kinds of people who sometimes .. -- dougjnn -- 10/31/99 That wasn't what I got from your original post -- Brian Grant -- 10/31/99 Brian, did you miscalculate, or do I have the wrong specs ? -- Russell -- 10/31/99 OH, thank goodness, I'm safe -- Brian Grant -- 10/31/99 Knowing how to use storm tactics and carrying yes a series drogue and ... -- dougjnn -- 10/31/99 Knowing how to use storm tactics and carrying yes a series drogue and ... -- dougjnn -- 10/31/99 this is a very interesting discussion, but.... -- h40.5bob -- 10/31/99 A lot of this board is feeding the dream -- Brian Grant -- 10/31/99 You want stability, you got it ... -- JAX -- 10/31/99 If I never sailed more than a day's distance from the nearest ... -- dougjnn -- 10/31/99 Kate's got a thread above. Now come on, -- NigeCh -- 10/31/99 Vast majority of time is not bluewater. I thought I was the poster boy ... -- dougjnn -- 10/31/99 If I never sailed more than a day's distance from the nearest ... -- dougjnn -- 10/31/99 I reject the idea that there is a "best" set of performance criteria for a boat. -- Tom Jessop -- 10/31/99 Agree. -- Bev Clary -- 10/31/99 'THE Posiden adventure thread' a study in human nature... -- billy -- 10/31/99 Did you find any ... -- Brian Grant -- 10/31/99 i'd gut out the interior, sand most of the jell coat -- billy -- 10/31/99 Hey up, billy ... -- NigeCh -- 10/31/99 Why do boats sink? A few thoughts on safety .. -- Russell -- 10/31/99 Some simple methods re (1) -- kaj -- 10/31/99 Kind of modified Miesian ... (?) -- NigeCh -- 10/31/99 Cannot resist -- kaj -- 11/1/99- Status