Here is a list of boats to compare. I have a 1981 Hunter 27. I know from sailing my boat that it feels very stable when it is rough out. I have been comparing the capsize factor and the comfort factor of my boat with other boats. Here is what I have found. "Note" anything with a capsize factor over 2 I did not do a comfort factor on as they are more able to capsize so I didn’t figure it made much difference if you were comfortable. What surprised me is that a Hunter 27’s capsize and comfort rate is right up there with a Hunter 35.5 and is better than an Islander 32!!! If your boat is not here and you want to check it go to the related link. Hunter 27 1981 Capsize factor of -1.94 Comfort factor - 23.39 Hunter 31 1985 Capsize factor - 1.9 Comfort factor - 24.55 Hunter 28 1986 Capsize 2.21 Not acceptable Hunter 30 1983 Capsize factor of -1.89 Comfort factor - 25.21 Hunter 33 1981 Capsize factor of -1.86 Comfort factor - 25.56 Hunter 35.5 1995 Capsize factor of -1.97 Comfort factor - 24.57 Irwin Citation 31 1979 Capsize factor of -2.09 Not acceptable Pearson 31 1978 Capsize factor - 2.03 Not acceptable Allied Seawind 30 1965 Capsize factor of - 1.62 Comfort factor - 36.86 Bristal 32 1966 Capsize factor of - 1.74 Comfort factor - 32 Endeavour 32 year? Capsize factor of -1.76 Comfort factor - 30.25 Islander 32 year? Capsize factor of - 2.03 Not acceptable Islander Iona 32 year? Capsize factor of -1.9 Comfort factor - 23.17 Alberg 30 1968 Capsize factor of -1.71 Comfort factor - 30.97 O’Day 32 1977 Capsize factor of -1.91 Comfort factor - 25.38 Pearson 323 1983 Capsize factor of -1.74 Comfort factor - 30.88 Kettenburg K32 1978 Capsize factor of -1.86 Comfort factor - 27.76
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Another fun Sail Calculator
Another fun Sail Calculator with an extensive database of boat models can be found at the Related link below. The program outputs a number of different categories in a bar chart format in a separate window. But remember, these are just numbers! Have fun, Trevor
Another fun Sail Calculator with an extensive database of boat models can be found at the Related link below. The program outputs a number of different categories in a bar chart format in a separate window. But remember, these are just numbers! Have fun, Trevor
Be Careful With The Numbers
Looking at these numbers are all well and good but they are derived from simple formulas and don't take into account many factors. And, additionally, how you setup your boat will change the numbers. For example: Capsize Ratio = Beam / (Displacement / 64)**0.333 Notice the only factors involved are Beam and Displacement. This means that, for the same displacement, a boat with a light-weight construction and a deep fin keel will have the same number as boat with heavy construction and a shoal-draft keel. To test what a few hundred pounds difference makes in displacement just run it through the formula and you will see that it makes a difference. If that little change in displacement makes that much difference just imagine what a difference taking into account the center of gravity and the lever arm would make. Think about that 8 or 9.9 hp outboard hanging on the stern rail, life raft and dingy on the coach roof, jerry cans of gas and water lashed to the life lines, etc.. Your numbers just changed big time. The formulas are "no brainers" but one needs to use a lot of judgment when using them. They make a good starting point for discussion, though, if you know what is behind them but don't treat them as gospel.
Looking at these numbers are all well and good but they are derived from simple formulas and don't take into account many factors. And, additionally, how you setup your boat will change the numbers. For example: Capsize Ratio = Beam / (Displacement / 64)**0.333 Notice the only factors involved are Beam and Displacement. This means that, for the same displacement, a boat with a light-weight construction and a deep fin keel will have the same number as boat with heavy construction and a shoal-draft keel. To test what a few hundred pounds difference makes in displacement just run it through the formula and you will see that it makes a difference. If that little change in displacement makes that much difference just imagine what a difference taking into account the center of gravity and the lever arm would make. Think about that 8 or 9.9 hp outboard hanging on the stern rail, life raft and dingy on the coach roof, jerry cans of gas and water lashed to the life lines, etc.. Your numbers just changed big time. The formulas are "no brainers" but one needs to use a lot of judgment when using them. They make a good starting point for discussion, though, if you know what is behind them but don't treat them as gospel.
Rough Numbers
As John indicated, the MCR & CR don't consider all the numbers & variables, and should only be used for a very rough preliminary consideration of very similar boats. For instance (I'm paraphrasing Jeff_H from another forum): An extreme example: You could move a significant weight from a boat's deep keel to it's masthead, without affecting the formulaic outcome (very different boat realities, but same resulting ratios). Regards, Gord
As John indicated, the MCR & CR don't consider all the numbers & variables, and should only be used for a very rough preliminary consideration of very similar boats. For instance (I'm paraphrasing Jeff_H from another forum): An extreme example: You could move a significant weight from a boat's deep keel to it's masthead, without affecting the formulaic outcome (very different boat realities, but same resulting ratios). Regards, Gord
Is there a better formula out there?
I couldn't agree more. I wonder if there is a formula that takes the draft and keel weight into consideration. If there isn't why does'nt someone come up with one? It would be much better I would think.
I couldn't agree more. I wonder if there is a formula that takes the draft and keel weight into consideration. If there isn't why does'nt someone come up with one? It would be much better I would think.
Isn't the CR really a righting ratio
Richard, I am going to go off and confirm this info, but wasn't the capsize ratio developed by Ted Brewer to be an indication of a boats ability to recover from a capsize (the 180 position) and not specifically to be an indication of its initial stability? The factor favours less beamy boats which have less initial stability when upright, but when turned turtle the lack of beam means they can be uprighted more easily. And of course the greater and deeper the ballast the easier the righting process. I seem to recall Ted pointing out that today's modern beamy boats may not be able to right themseleves when inverted due to their wide beam. Kevin
Richard, I am going to go off and confirm this info, but wasn't the capsize ratio developed by Ted Brewer to be an indication of a boats ability to recover from a capsize (the 180 position) and not specifically to be an indication of its initial stability? The factor favours less beamy boats which have less initial stability when upright, but when turned turtle the lack of beam means they can be uprighted more easily. And of course the greater and deeper the ballast the easier the righting process. I seem to recall Ted pointing out that today's modern beamy boats may not be able to right themseleves when inverted due to their wide beam. Kevin
I've seen different numbers...
...right on this site. The capsize factor for a Hunter 31 is 2.13.
...right on this site. The capsize factor for a Hunter 31 is 2.13.
The capsize screening formula is useful
because wide light boats don't roll back up as quickly as narrow heavy boats. There are other numbers that can be calculated to give the range of positive stablity. It is odd that boat manufacturers almost never include this data. But for the few boats that I've compared if the CSF is low the boat is generally considered seaworthy. But even the range of positive stability may not be a better indication in that capsizing is a dynamic event and the RPS is a static measure. The CSF came about by looking at boats that survived the Fastnet?? disaster as opposed to those that didn't. It is an empirical observation rather than a theoretical calculation. BTW I have a book that has a photo of a beamy fin keeler in the turtle position with the crew standing on the hull. Yes the keel is still attached!! Once that mast is underwater with sails it would take a lot to bring it back upright.
because wide light boats don't roll back up as quickly as narrow heavy boats. There are other numbers that can be calculated to give the range of positive stablity. It is odd that boat manufacturers almost never include this data. But for the few boats that I've compared if the CSF is low the boat is generally considered seaworthy. But even the range of positive stability may not be a better indication in that capsizing is a dynamic event and the RPS is a static measure. The CSF came about by looking at boats that survived the Fastnet?? disaster as opposed to those that didn't. It is an empirical observation rather than a theoretical calculation. BTW I have a book that has a photo of a beamy fin keeler in the turtle position with the crew standing on the hull. Yes the keel is still attached!! Once that mast is underwater with sails it would take a lot to bring it back upright.
does not compute
That capsize screening formula is almost universally criticised for being overly simplistic. It does not take into consideration the all-important ballast/displacement ratio, nor does it factor ballast/draft. If my boat displaces 20,000 pounds, it makes a tremendous difference whether 6,000 of those pounds are in ballast or 8,000 are. My H410, which displaces 20,000 pounds, has a bulb keel of 7,500. Surely this bulb keel gives it superior capsize stability than a fin keel would, but the formula doesn't take that into consideration. Neither does it factor whether I have the deep keel version or shoal draft. To simply factor beam verses displacement is ludicrous.
That capsize screening formula is almost universally criticised for being overly simplistic. It does not take into consideration the all-important ballast/displacement ratio, nor does it factor ballast/draft. If my boat displaces 20,000 pounds, it makes a tremendous difference whether 6,000 of those pounds are in ballast or 8,000 are. My H410, which displaces 20,000 pounds, has a bulb keel of 7,500. Surely this bulb keel gives it superior capsize stability than a fin keel would, but the formula doesn't take that into consideration. Neither does it factor whether I have the deep keel version or shoal draft. To simply factor beam verses displacement is ludicrous.
Please give me an example
of a cruising boat generally recognised as a seaworthy blue water cruiser that has a CSF greater than 2!!!! Check out allied seawind,Pacific seacraft,swans,cape dorys, etc etc I haven't done an extensive survey but every one that I have looked at had a CSF of 1.8 or less.
of a cruising boat generally recognised as a seaworthy blue water cruiser that has a CSF greater than 2!!!! Check out allied seawind,Pacific seacraft,swans,cape dorys, etc etc I haven't done an extensive survey but every one that I have looked at had a CSF of 1.8 or less.
IMHO, the calculation is so simplified...
that it is useless. From an engineering viewpoint, so many relevant variables have been left out that any conclusions drawn using the formula presented are essentially false. While beam and displacement are important numbers, they certainly aren't the only ones that need to be considered and given a place in such a complex analysis. Kind of reminds me of the old 'skid charts' the police would use to determine the speed of a vehicle immediately prior to a colision. They would take the length of a skid mark, determine the type of road surface and then look it up on a little chart to get the estimated speed. No accounting for such things as vehicle weight, tread width, condition of tread, inflation pressure, etc. was done. While I'm certainly not a naval architect, it would seem that determining a boats inherent ability to self-right after going inverted would require complex computer modeling, tank testing and perhaps other sophisticated methodology to get anywhere near a correct answer. Even then, one would have to look at variables such as type and size of sails aloft during the event, actions taken by the crew immediately prior to and after the event and a myriad of others. Sorry, but I just can't buy into a calculation so inherently flawed. P.S. Has anyone ever heard of or contemplated something along the lines of an auto-inflating PFD that would be mounted at the top of the mast and deploy after being submerged? I wonder what (if any) effect this would have, given a few hundred pounds of positive bouancy, on initiating a self-righting action? Perhaps I'm crazy (although it's never been proven in court!) but would something along the lines of a 4' diameter inflatable mooring ball tied to the top (bottom) of an inverted mast do much to get a 10 ton boat headed back onto her feet? What if it also had, via some mechanical means, the ability to 'blow' the main and jib halyards to remove the resistance of the sails to the righting movement? Just wondering.
that it is useless. From an engineering viewpoint, so many relevant variables have been left out that any conclusions drawn using the formula presented are essentially false. While beam and displacement are important numbers, they certainly aren't the only ones that need to be considered and given a place in such a complex analysis. Kind of reminds me of the old 'skid charts' the police would use to determine the speed of a vehicle immediately prior to a colision. They would take the length of a skid mark, determine the type of road surface and then look it up on a little chart to get the estimated speed. No accounting for such things as vehicle weight, tread width, condition of tread, inflation pressure, etc. was done. While I'm certainly not a naval architect, it would seem that determining a boats inherent ability to self-right after going inverted would require complex computer modeling, tank testing and perhaps other sophisticated methodology to get anywhere near a correct answer. Even then, one would have to look at variables such as type and size of sails aloft during the event, actions taken by the crew immediately prior to and after the event and a myriad of others. Sorry, but I just can't buy into a calculation so inherently flawed. P.S. Has anyone ever heard of or contemplated something along the lines of an auto-inflating PFD that would be mounted at the top of the mast and deploy after being submerged? I wonder what (if any) effect this would have, given a few hundred pounds of positive bouancy, on initiating a self-righting action? Perhaps I'm crazy (although it's never been proven in court!) but would something along the lines of a 4' diameter inflatable mooring ball tied to the top (bottom) of an inverted mast do much to get a 10 ton boat headed back onto her feet? What if it also had, via some mechanical means, the ability to 'blow' the main and jib halyards to remove the resistance of the sails to the righting movement? Just wondering.
Just asked Bob Perry on cruising world's BB
He didn't put much value on the CSF in and of itself. He said that bigger is better in that a longer boat is less likely to capsize. He also said that for cruisers that if you stay away from radical designs and have a moderate beam and displacement/length or 220 or better you'll probably be alright. But if you think about it a heavier boat D/L>220 and a moderate beam will probably give you a CSF of less than 2.0. Bob Perry please forgive me if I misquoted. My only attraction to the CSF is that it is a readily available number to compare boats. If you look at SA/Displ,Disp/wll, motion comfort ratio beam/length,PHRF etc you get an idea of what the boat is like. Of course all of these numbers are indications of how the boat probably will perform. Ideally you would have the time and money to hire an expert designer to evaluate the boat. But for some boats this would cost more than the boat!!!!!!
He didn't put much value on the CSF in and of itself. He said that bigger is better in that a longer boat is less likely to capsize. He also said that for cruisers that if you stay away from radical designs and have a moderate beam and displacement/length or 220 or better you'll probably be alright. But if you think about it a heavier boat D/L>220 and a moderate beam will probably give you a CSF of less than 2.0. Bob Perry please forgive me if I misquoted. My only attraction to the CSF is that it is a readily available number to compare boats. If you look at SA/Displ,Disp/wll, motion comfort ratio beam/length,PHRF etc you get an idea of what the boat is like. Of course all of these numbers are indications of how the boat probably will perform. Ideally you would have the time and money to hire an expert designer to evaluate the boat. But for some boats this would cost more than the boat!!!!!!
So the verdict is
According to what I’m reading, This capsize formula is pretty much worthless to really determine if your boat will capsize or if it will right itself. That said, generally speaking a boat with a higher number is probably less capable of staying upright than one that has a lower number. So when someone is looking at boats, I guess, use this formula but keep in mind that the lower the keel and the heavier the keel the better. Also you should keep in mind mast height and how much freeboard there is above the water line. Now why doesn’t someone come up with a better formula? While it may not be perfect I’m sure it could be better than this one.
According to what I’m reading, This capsize formula is pretty much worthless to really determine if your boat will capsize or if it will right itself. That said, generally speaking a boat with a higher number is probably less capable of staying upright than one that has a lower number. So when someone is looking at boats, I guess, use this formula but keep in mind that the lower the keel and the heavier the keel the better. Also you should keep in mind mast height and how much freeboard there is above the water line. Now why doesn’t someone come up with a better formula? While it may not be perfect I’m sure it could be better than this one.
Uncomfortable truths about "comfort factors".....
What is the point of even discussing the value of such dimensionless empirical numbers when one is unlikely to find two sailors who completely agree on what "comfort" (or rather: "comfortable motion") at sea really is? Just try to start a rational discussion on this topic between avowed mono- and multi-hullers and you will soon see the futility of such an exercise. Perhaps we should all remember one other fact as well: there is currently no model (i.e. quantifiable level of understanding) that even begins to describe the dynamic behavior of a sailing vessel at sea. If that sounds like a bit of an exaggeration, just consider the fact that current models for boat speed at different points of sail and wind strengths are only valid for flat water! In other words, no one is even able to fully describe what the effects of seastate on something as straightforward as BOAT SPEED are...... IMHO, anyone who accepts the claim that some magical formula can predict the effect of seastate on something as complex as "comfortable motion in a seastate", while at the same time acknowledging that our current level of understanding is insufficient to predict something as comparatively simple as the effect of seastate on boat speed, would appear to have some issues to deal with that fall well outside the scope of this board. Have fun! Flying Dutchman
What is the point of even discussing the value of such dimensionless empirical numbers when one is unlikely to find two sailors who completely agree on what "comfort" (or rather: "comfortable motion") at sea really is? Just try to start a rational discussion on this topic between avowed mono- and multi-hullers and you will soon see the futility of such an exercise. Perhaps we should all remember one other fact as well: there is currently no model (i.e. quantifiable level of understanding) that even begins to describe the dynamic behavior of a sailing vessel at sea. If that sounds like a bit of an exaggeration, just consider the fact that current models for boat speed at different points of sail and wind strengths are only valid for flat water! In other words, no one is even able to fully describe what the effects of seastate on something as straightforward as BOAT SPEED are...... IMHO, anyone who accepts the claim that some magical formula can predict the effect of seastate on something as complex as "comfortable motion in a seastate", while at the same time acknowledging that our current level of understanding is insufficient to predict something as comparatively simple as the effect of seastate on boat speed, would appear to have some issues to deal with that fall well outside the scope of this board. Have fun! Flying Dutchman
You're Right Richard - Take With A Grain of Salt
By jove I think you've got it! These formulas make a good starting point for discussion purposes. If nothing else, if your post got you thinking about what's going on that's good. You've started asking questions - that's good. Not taking everything hook-line-and sinker, that's good. I'm thinking about my own boat which is much the same as the Hunter 35.5 and has an aluminum toe rail. The Toe rail is bolted onto a flange on the hull and deck and sticks out about 2 or 3 inches. The beam is the width to the outside of the toe rail. So, do you plug in the manufacturers published number for the beam or use the beam measured to the outside of the hull? At 2" x 2 that's 1/3 of a foot, 0.333. At 3" x 2 that's 0.500 feet. Hey! That's significant! Then there are the other things that don't even fit "The Formula", like how one loads the boat, things one can do to rectify a bad situation (creative flotation devices were mentioned). So the point is there are a lot of variables that aren't in the formula. I guess if a point can be made that this MAY true with all the other formulas too so take the formulas with a grain of salt. The PHRF formula isn't exact either and it incudes many more variables but for speed on a race course, as a rule, it gets pretty darn close. There are exceptions, though, such as the handicap factor for a fixed-blade prop. Not only should one think about and question the forumulas, one should always be thinking when you're on the boat. Things happen and you have to be creative with ways to work your way out of a bad situation. Whether it's a squashed pinkiy up the inside passage (this happened to the Pardey's), getting a boat up-righted, or just getting between those two boats coming toward you in a narrow channel. We are really on our own out there, some times more than others, and you can't necessarily just call 911 to be taken care of. Bottom line - use the info with a grain of salt and think for yourself. And .... if your boat isn't reasonably water tight the best number in the world won't mean a thing. Now go out there and have fun.
By jove I think you've got it! These formulas make a good starting point for discussion purposes. If nothing else, if your post got you thinking about what's going on that's good. You've started asking questions - that's good. Not taking everything hook-line-and sinker, that's good. I'm thinking about my own boat which is much the same as the Hunter 35.5 and has an aluminum toe rail. The Toe rail is bolted onto a flange on the hull and deck and sticks out about 2 or 3 inches. The beam is the width to the outside of the toe rail. So, do you plug in the manufacturers published number for the beam or use the beam measured to the outside of the hull? At 2" x 2 that's 1/3 of a foot, 0.333. At 3" x 2 that's 0.500 feet. Hey! That's significant! Then there are the other things that don't even fit "The Formula", like how one loads the boat, things one can do to rectify a bad situation (creative flotation devices were mentioned). So the point is there are a lot of variables that aren't in the formula. I guess if a point can be made that this MAY true with all the other formulas too so take the formulas with a grain of salt. The PHRF formula isn't exact either and it incudes many more variables but for speed on a race course, as a rule, it gets pretty darn close. There are exceptions, though, such as the handicap factor for a fixed-blade prop. Not only should one think about and question the forumulas, one should always be thinking when you're on the boat. Things happen and you have to be creative with ways to work your way out of a bad situation. Whether it's a squashed pinkiy up the inside passage (this happened to the Pardey's), getting a boat up-righted, or just getting between those two boats coming toward you in a narrow channel. We are really on our own out there, some times more than others, and you can't necessarily just call 911 to be taken care of. Bottom line - use the info with a grain of salt and think for yourself. And .... if your boat isn't reasonably water tight the best number in the world won't mean a thing. Now go out there and have fun.
Nah, HL43. Tell us about your Windship, though!
Flying Dutchman is just the nickname my crew gave me (probably because I am such a nice guy ;D). For the past decade, or so, I have been using this handle faithfully in order not to give anyone a chance to change it into Captain Bligh...... The name of our Hunter Legend 43 (hull #1) is Rivendel II. Just type "Rivendel" under Search as far back as Phil's archives go these days and you will get a pretty good idea about what she's been up to. Have fun! Flying Dutchman
Flying Dutchman is just the nickname my crew gave me (probably because I am such a nice guy ;D). For the past decade, or so, I have been using this handle faithfully in order not to give anyone a chance to change it into Captain Bligh...... The name of our Hunter Legend 43 (hull #1) is Rivendel II. Just type "Rivendel" under Search as far back as Phil's archives go these days and you will get a pretty good idea about what she's been up to. Have fun! Flying Dutchman
Great thread,
What did we say? *o And John, I can call 911 anytime. My wife works there.
Again, great thread.
What did we say? *o And John, I can call 911 anytime. My wife works there.
Again, great thread.CSF
I still believe in formulas that are used with caution. Take my chick screening formula as an example. weight X height in inches/ageX150. Usually women with a CSF of 2.2-1.8 are acceptable. If the number gets too high she is too fat or young. If the number gets too low she is too old ,short or skinny. If I throw in a couple of qualifying limits the results are better. Say older thatn 18 and younger than 35. But then you might get a perfect number and the girl be unacceptable for other reasons such as she doesn't like old farts!!!! Example a 62" woman weighing 120#s and 25 years old = 1.98 if she is 55 that number changes to =0.90 which is clearly an unacceptable number. Maybe I should factor in red hair and a large bank account???? But heck it's hard enough to get a woman to devulge her weight and age!!!!!!! Maybe a beer factor where .25 is added or subtracted for each beer consumed in the last hour????
I still believe in formulas that are used with caution. Take my chick screening formula as an example. weight X height in inches/ageX150. Usually women with a CSF of 2.2-1.8 are acceptable. If the number gets too high she is too fat or young. If the number gets too low she is too old ,short or skinny. If I throw in a couple of qualifying limits the results are better. Say older thatn 18 and younger than 35. But then you might get a perfect number and the girl be unacceptable for other reasons such as she doesn't like old farts!!!! Example a 62" woman weighing 120#s and 25 years old = 1.98 if she is 55 that number changes to =0.90 which is clearly an unacceptable number. Maybe I should factor in red hair and a large bank account???? But heck it's hard enough to get a woman to devulge her weight and age!!!!!!! Maybe a beer factor where .25 is added or subtracted for each beer consumed in the last hour????
And Tom, also factor in,,,
Bitch formula. And don't forget, they are doing the same thing. But, for them, first and foremost are your bank account numbers! Aw hell, just have more beers. You won't need that formula until morning. *yks
Bitch formula. And don't forget, they are doing the same thing. But, for them, first and foremost are your bank account numbers!
Aw hell, just have more beers. You won't need that formula until morning. *yks- Status