What is a quick answer for the meaning of "Capsize Ratio" as it relates to sailboats?
Our boat has a ratio of 1.95.
Thanks
Our boat has a ratio of 1.95.
Thanks
Capsize Ratio?
- Thread starter Ducati
- Start date
- Status
it is just the boat
You are a significant factor in wither the boat capsizes or not.
Learn weather and weather handling skills before you need them. Practice in a gale near home first.
FWIW
You are a significant factor in wither the boat capsizes or not.
Learn weather and weather handling skills before you need them. Practice in a gale near home first.
FWIW
Thanks
My quick math tells me that most boats have a beam that is about 1/3 that of the length.
Our boat has a beam of 11.4' x 36. So is this a good or bad ratio.
Regards
My quick math tells me that most boats have a beam that is about 1/3 that of the length.
Our boat has a beam of 11.4' x 36. So is this a good or bad ratio.
Regards
Designers Intent
Experience and testing make it clear that if a boat is hit broadside by a breaking wave taller than its beam, it willl capsize, regardless of its design, or low capsize screening ratio.
Capsize ratio indicates the likelihood that a boat will recover from an inverted, capsized position. It was developed during tank tests conducted after the Fastnet race disaster.
Because it has been around for a while, the capsize ratio tells you about the designer's intent for a design. Boats designed for blue water cruising will have many features to support that purpose, including a capsize screen below 2.
On the other hand, a beamy design with a capsize screen over 2 has some real advantages for coastal cruising:
- Higher form stability, supporting more sail as winds move up to 20 knots.
- More interior room, especially when the beam is carried aft.
- Depending on the hull shape, a beamy boat may be more likely to plane on a reach.
And coastal cruisers can usually return to port before conditions build breaking waves tall enough to capsize the boat.
Experience and testing make it clear that if a boat is hit broadside by a breaking wave taller than its beam, it willl capsize, regardless of its design, or low capsize screening ratio.
Capsize ratio indicates the likelihood that a boat will recover from an inverted, capsized position. It was developed during tank tests conducted after the Fastnet race disaster.
Because it has been around for a while, the capsize ratio tells you about the designer's intent for a design. Boats designed for blue water cruising will have many features to support that purpose, including a capsize screen below 2.
On the other hand, a beamy design with a capsize screen over 2 has some real advantages for coastal cruising:
- Higher form stability, supporting more sail as winds move up to 20 knots.
- More interior room, especially when the beam is carried aft.
- Depending on the hull shape, a beamy boat may be more likely to plane on a reach.
And coastal cruisers can usually return to port before conditions build breaking waves tall enough to capsize the boat.
I think a good sailor doesn't put him or the boat in a situation where the boat will get hit broadside with a wave that big and breaking. Things tend to happen like mast breaks when the boat rolls regardless if the boat is blue water or not. Perfect example is the big 50' boat that some rich advenerer took to solo non-stop circumnavigate with. He rolled his boat and lost both masts. Called CG and sunk the boat. Bye Bye beautiful blue water boat 
Stuff happens
Franklin, in the Fastnet race, there were some good skippers who were caught when the storm blew up. Blue water sailing means you have to take the weather that comes - and unseasonable storms do happen. If a helmsman loses contol of the boat for a moment, or if fatigue, injury or illness force lying ahull, or a wave comes from an unexpected direction...then a boat can be capsized. A larger wave can capsize a boat without catching it broadside.
Once inverted, a boat with a low capsize ratio is more likely to recover to an upright position. With or without the mast and rigging, that's a whole lot better than staying inverted!
Franklin, in the Fastnet race, there were some good skippers who were caught when the storm blew up. Blue water sailing means you have to take the weather that comes - and unseasonable storms do happen. If a helmsman loses contol of the boat for a moment, or if fatigue, injury or illness force lying ahull, or a wave comes from an unexpected direction...then a boat can be capsized. A larger wave can capsize a boat without catching it broadside.
Once inverted, a boat with a low capsize ratio is more likely to recover to an upright position. With or without the mast and rigging, that's a whole lot better than staying inverted!
Stuff happens
Like David said, stuff happens and happens and happens.
http://www.youtube.com/watch?v=eiRgKXs92fc&NR=1
Like David said, stuff happens and happens and happens.
http://www.youtube.com/watch?v=eiRgKXs92fc&NR=1
dserelle,
Are you saying that the capsize ratio and the capsize screening factor are different? Your post seems to say the capsize ration is a measure of resistance to capsize and the capsize screening factor is a measure of how a boat may recover from capsize. Is that correct? Can you supply the parameters of both?
Are you saying that the capsize ratio and the capsize screening factor are different? Your post seems to say the capsize ration is a measure of resistance to capsize and the capsize screening factor is a measure of how a boat may recover from capsize. Is that correct? Can you supply the parameters of both?
When I was looking at boat designs 30 years ago "righting moment" was the charictaristic that we looked for. iIrealize it is but one factor and the engineers have combined righting moment with several other factors to come up with the capsize factor or ratio. Degrees of stability was another factor that concerned us. How far could you roll a boat and expect it to recover and not continue to roll until it was turtled?
As it relates to a sailing vessel the ratio by itself is worthless. Ratios can be misleading as they are based in proportions and the winds and seas just come in one size. If you provide us with the size and make of your boat perhaps we can best advise on its capabilities.
Keep in mind, some say if a wave comes long and capsizes you and it stays down, another wave will come by and right you as long as the sheets are released.
Personally, I will never be taking a wave on the beam like that. At the very worst, I'lll deploy the jsd and go below and sleep it out.
Personally, I will never be taking a wave on the beam like that. At the very worst, I'lll deploy the jsd and go below and sleep it out.
The next wave
Actually, the capsize ratio indicates the chances that the next wave(s) will right the boat.
A chief value of the different ratios we use to describe a boat design is that they _do_ apply to widely different designs.
Actually, the capsize ratio indicates the chances that the next wave(s) will right the boat.
A chief value of the different ratios we use to describe a boat design is that they _do_ apply to widely different designs.
Testing the extremes
Capsize ratio is telling us about the impact of form stability versus righting moment in a boats designed shape.
With extreme beam, and no ballast, a catamaran has the form stability to stay upright in high winds - but once it's turned over its going to stay that way.
On the other hand, a cylinder with a lead keel on it is always going to return to an upright position. The Island Packet design comes to mind.
Capsize ratio is just an elegant way of indicating where a design fits between those two extremes.
Capsize ratio is telling us about the impact of form stability versus righting moment in a boats designed shape.
With extreme beam, and no ballast, a catamaran has the form stability to stay upright in high winds - but once it's turned over its going to stay that way.
On the other hand, a cylinder with a lead keel on it is always going to return to an upright position. The Island Packet design comes to mind.
Capsize ratio is just an elegant way of indicating where a design fits between those two extremes.
Wind speed is a big issue also My J24 is a tender boat and due to racing the windex has gotten submerged a few times
It always pops right back up BUT if its windy enough the large surface area of the hull when exposed can make it stay over a LOT longer
It always pops right back up BUT if its windy enough
the large surface area of the hull when exposed can make it stay over a LOT longer- Status