Anyone have any information on stability of an oday 27? Vanishing stability, angle of vertical stability etc. I know there are some ways to calculate but am trying the easy way around this first and thought I would start here first. Thanks ahead of time, Doug
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bruce cornell
capsize
capsize is 1.89, anything below 2.0 is considered 'off shore able' and the comfort number is 23.77, not the best number, but better than a mac 26.
capsize is 1.89, anything below 2.0 is considered 'off shore able' and the comfort number is 23.77, not the best number, but better than a mac 26.
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Dennis
US SAILING
Go to US SAILING to find all the formulae. By my reckoning a 1987 shoal keel 272 comes out at "Angle of diminishing stability" = 120 degrees, which I assume to mean 30 degrees of heel. "Cap-size screen" = 2.16 and "Stability" = 2.06 Many similar boats are around the same figures. Reef early!
Go to US SAILING to find all the formulae. By my reckoning a 1987 shoal keel 272 comes out at "Angle of diminishing stability" = 120 degrees, which I assume to mean 30 degrees of heel. "Cap-size screen" = 2.16 and "Stability" = 2.06 Many similar boats are around the same figures. Reef early!
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Doug
Mine is not the shoal draft!
Thanks for the info...I have to look at the reference materials , but guess I was being a bit lazy. I'm not following the second post, but in regards to the first, mine is not the (Well not that I know) the shoal draft, though I can get into the shallows to 4 1/2 feet. 30 degrees heel should be easily rightable I would think ecven in a shoal draft setup. Are you shure this is accurate. My boat wsith the winches in the water would be greater than 45 degrees, but I understood that this--while not a Contessa 32, should still be a self-rightable angle of heel. Correct me if I'm wrong, but most boats should be self-rightable at this kind of angle of heel should they not be? Short of 180 degrees capsize.
Thanks for the info...I have to look at the reference materials , but guess I was being a bit lazy. I'm not following the second post, but in regards to the first, mine is not the (Well not that I know) the shoal draft, though I can get into the shallows to 4 1/2 feet. 30 degrees heel should be easily rightable I would think ecven in a shoal draft setup. Are you shure this is accurate. My boat wsith the winches in the water would be greater than 45 degrees, but I understood that this--while not a Contessa 32, should still be a self-rightable angle of heel. Correct me if I'm wrong, but most boats should be self-rightable at this kind of angle of heel should they not be? Short of 180 degrees capsize.
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Doug
Here it is...
http://www.sailingusa.info/cal__capsize.htm I had been looking for this site! now maybe I can figure it all out! Funny but I could not remember what site it was I saw all the formula calculators on...
http://www.sailingusa.info/cal__capsize.htm I had been looking for this site! now maybe I can figure it all out! Funny but I could not remember what site it was I saw all the formula calculators on...
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Doug
according to formula...
The Stability of the boat is: 1.93 (Stability is predicted !!) The following is the formula used to calculate The Capsize Screening Formula: Capsize Screening Formula = Beam / (Displacement / 64)1/3 Displacement is in Pounds Beam is Measured in Feet
The Stability of the boat is: 1.93 (Stability is predicted !!) The following is the formula used to calculate The Capsize Screening Formula: Capsize Screening Formula = Beam / (Displacement / 64)1/3 Displacement is in Pounds Beam is Measured in Feet
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Dennis
272 Stability
This is an important matter. I hope contributors will give chapter and verse for what they say. For instance what does it mean to say "stability of the boat is 1.93" unless you explain what it means and how it is calculated? I have just run the US SAILING online calculator for the shoal draft 272LE, inserting the following data: LOA 27'; Beam 9'; Weight (i.e. Displacement) 5,375 lbs; Ballast (keel) 1,930 lbs; Hull Draft 1' ("hull draft" was arrived at by eyeballing the boat's schematic elevation found in the Owners Manual and might be an inch out. Note, however that it is HULL draft and NOT OVERALL DRAFT, which is 2'11") Using the above figures the calculator gave: (1) Angle of vanishing stability as 119.64 degrees (which is why I quoted 120 degrees in my earlier post). This surely gives a heeling angle of 30 degrees as the limit of safety. Anyone who disagrees please give full argument and source of information. I'd be happy to be wrong! (2) Stability Value 51.51 (I have no idea what this datum means). Anyone know?
This is an important matter. I hope contributors will give chapter and verse for what they say. For instance what does it mean to say "stability of the boat is 1.93" unless you explain what it means and how it is calculated? I have just run the US SAILING online calculator for the shoal draft 272LE, inserting the following data: LOA 27'; Beam 9'; Weight (i.e. Displacement) 5,375 lbs; Ballast (keel) 1,930 lbs; Hull Draft 1' ("hull draft" was arrived at by eyeballing the boat's schematic elevation found in the Owners Manual and might be an inch out. Note, however that it is HULL draft and NOT OVERALL DRAFT, which is 2'11") Using the above figures the calculator gave: (1) Angle of vanishing stability as 119.64 degrees (which is why I quoted 120 degrees in my earlier post). This surely gives a heeling angle of 30 degrees as the limit of safety. Anyone who disagrees please give full argument and source of information. I'd be happy to be wrong! (2) Stability Value 51.51 (I have no idea what this datum means). Anyone know?
AVS misenterpretation
Your calcualtions seem correct what is incorrect is your interpretation of Angle of vanishing stability(AVS). AVS is in fact the angle to which a vessel can heel before the righting moment becomes zero i.e. The weight of the keel is no longer trying to pull the boat upright, so absent other forces (wind, waves, water sloshing around your bilges) a 272LE will right itself from a 120 degree knockdown. This is not the full story, at some point around 60 degrees of heel the righting moment is maximized (the forces trying to right the vessel are greatest) and from there to 120 degrees the righting moment decreases until finally at 120 the boat will no longer come upright on its own. I have provided a link with a simple explanation of this, you can also look at most yacht design texts. Chris
Your calcualtions seem correct what is incorrect is your interpretation of Angle of vanishing stability(AVS). AVS is in fact the angle to which a vessel can heel before the righting moment becomes zero i.e. The weight of the keel is no longer trying to pull the boat upright, so absent other forces (wind, waves, water sloshing around your bilges) a 272LE will right itself from a 120 degree knockdown. This is not the full story, at some point around 60 degrees of heel the righting moment is maximized (the forces trying to right the vessel are greatest) and from there to 120 degrees the righting moment decreases until finally at 120 the boat will no longer come upright on its own. I have provided a link with a simple explanation of this, you can also look at most yacht design texts. Chris
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Dennis
Many thanks Chris
Many thanks Chris for exposing my error. Your post is just what I needed. Thanks also to Doug for opening this topic.
Many thanks Chris for exposing my error. Your post is just what I needed. Thanks also to Doug for opening this topic.
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Bill Jones
Stability of oday 27
(Quoted) <<By my reckoning a 1987 shoal keel 272 comes out at "Angle of diminishing stability" = 120 degrees, which I assume to mean 30 degrees of heel. ">> I think this engineering term must be misunderstood. "Diminishing stability" I believe, means the extreme angle at which (relative to vertical) the vessel loses its righting ability, which in this case is calculated to be 120 degrees- (The vessel is capsized 30 degrees beyond vertical and at that angle will continue to roll to bottom up.) The weight of the keel and its distance below the center of gravity on well designed ocean sailing vessels over-balances the above waterline weight and some do not reach diminishing stability until they are bottom up at 180 degrees. Even then, the wave motion sometimes returns it to the angle where the keel weight will right the vessel. For lesser stable vessels (daysailers)the lesser keel weight and its shorter distance below the center of gravity makes for a lesser angle of diminishing stability. I would be surprised if the figure of 120 degrees is correct for the Oday 27, which would mean that it can right itself from a complete knock down up to 120 degrees from vertical. Bill *o
(Quoted) <<By my reckoning a 1987 shoal keel 272 comes out at "Angle of diminishing stability" = 120 degrees, which I assume to mean 30 degrees of heel. ">> I think this engineering term must be misunderstood. "Diminishing stability" I believe, means the extreme angle at which (relative to vertical) the vessel loses its righting ability, which in this case is calculated to be 120 degrees- (The vessel is capsized 30 degrees beyond vertical and at that angle will continue to roll to bottom up.) The weight of the keel and its distance below the center of gravity on well designed ocean sailing vessels over-balances the above waterline weight and some do not reach diminishing stability until they are bottom up at 180 degrees. Even then, the wave motion sometimes returns it to the angle where the keel weight will right the vessel. For lesser stable vessels (daysailers)the lesser keel weight and its shorter distance below the center of gravity makes for a lesser angle of diminishing stability. I would be surprised if the figure of 120 degrees is correct for the Oday 27, which would mean that it can right itself from a complete knock down up to 120 degrees from vertical. Bill *o
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