Does anyone know the capsize screen ration for the Hunter 450? It is not listed under the technical specs for that model. I would also like to know the angle of "limit of positive stability" for the Hunter 450.
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450 capsize screen
the capsize screen for the 450 is 1.89 which is rather conservative for a modern design.. 2.00 or below is supposedly the standard for an offshore boat...wiser people than i feel that calculation is just one factor in deciding to take a boat offshore
the capsize screen for the 450 is 1.89 which is rather conservative for a modern design.. 2.00 or below is supposedly the standard for an offshore boat...wiser people than i feel that calculation is just one factor in deciding to take a boat offshore
Builders hide a whole world of data
It may be that no one has calculated the limit of positive stability for the Hunter 450. It is not something that has to be calculted in the process of designing the boat. If the Hunter 450 had ever raced under IMS, the rating certificate will give one version of the LPS, calculated from righting arm measurements of the boat raced. Be careful of comparing LPS values, unless you know they are calculated in the same way! The sad thing is that there is a world of data that IS part of boat design that designers and builders typically keep secret. For example, designers have to calculate the righting arm at small degrees of heel, to know that the boat will stand up to its sail plan. The designer must know the center of gravity (CG), and the center of buoyancy (CB), the latter at different angles of heel. The center of effort tells where the sails work, and the center of lateral resistance (CLR) tells where the hull pushes back. The former is easy for anyone to calculate from sail plan. Wetted surface (WS) tells how much resistance the boat has at low speeds, and how many gallons of antifouling you will need to buy. Then there is prismatic coefficient, polars from a VPP, etc. And that's just hull and sail abstractions. On top of that, there are the engineering data on how the boat is built: lamination schedules, the steps used to join parts, plumbing and electric schedules, etc. Finally, there is data on how the boats generally, and how a specific hull, varies from the design and engineering specifications. Production boat builders have a book of data on each model they produce. But they are NOT telling you, the buyer. Why not?
It may be that no one has calculated the limit of positive stability for the Hunter 450. It is not something that has to be calculted in the process of designing the boat. If the Hunter 450 had ever raced under IMS, the rating certificate will give one version of the LPS, calculated from righting arm measurements of the boat raced. Be careful of comparing LPS values, unless you know they are calculated in the same way! The sad thing is that there is a world of data that IS part of boat design that designers and builders typically keep secret. For example, designers have to calculate the righting arm at small degrees of heel, to know that the boat will stand up to its sail plan. The designer must know the center of gravity (CG), and the center of buoyancy (CB), the latter at different angles of heel. The center of effort tells where the sails work, and the center of lateral resistance (CLR) tells where the hull pushes back. The former is easy for anyone to calculate from sail plan. Wetted surface (WS) tells how much resistance the boat has at low speeds, and how many gallons of antifouling you will need to buy. Then there is prismatic coefficient, polars from a VPP, etc. And that's just hull and sail abstractions. On top of that, there are the engineering data on how the boat is built: lamination schedules, the steps used to join parts, plumbing and electric schedules, etc. Finally, there is data on how the boats generally, and how a specific hull, varies from the design and engineering specifications. Production boat builders have a book of data on each model they produce. But they are NOT telling you, the buyer. Why not?
But the capsize screen is easily calculated
All you need is the boat's displacement and maximum beam. For the 450, it works out to 1.89.
All you need is the boat's displacement and maximum beam. For the 450, it works out to 1.89.
very interesting - and my question, too
That's interesting stuff, BT, although I would think they'd have to make those calculations to get the European certification, wouldn't they? I also wonder why they wouldn't release data they have? I doubt that they're trying to hide anything - I mean, it's not like production boats are capsizing every week. Perhaps they think most consumers aren't interested in that degree of data. Do you know of any significant builders who do make all that data available? Interesting thoughts, indeed. p.
That's interesting stuff, BT, although I would think they'd have to make those calculations to get the European certification, wouldn't they? I also wonder why they wouldn't release data they have? I doubt that they're trying to hide anything - I mean, it's not like production boats are capsizing every week. Perhaps they think most consumers aren't interested in that degree of data. Do you know of any significant builders who do make all that data available? Interesting thoughts, indeed. p.
Several points
I don't think builders' stinginess with data has anything to do with ultimate stability, which just isn't that big an issue for most people. You're right, also, that most people would not delve much into it. Wouldn't it be good if more sailors learned more about these things? This kind of data would be most useful to reviewers and writers, and through them it would percolate into the sailing community, along with help interpreting it. But what is good for the sailing community may not be good for the individual builder, who would prefer to control what potential buyers know about their product, and have the first opportunity to "position" this information. I know of no builder who makes public much of their design data. My impression is that they each give about the same minimum set of information that they think the market demands.
I don't think builders' stinginess with data has anything to do with ultimate stability, which just isn't that big an issue for most people. You're right, also, that most people would not delve much into it. Wouldn't it be good if more sailors learned more about these things? This kind of data would be most useful to reviewers and writers, and through them it would percolate into the sailing community, along with help interpreting it. But what is good for the sailing community may not be good for the individual builder, who would prefer to control what potential buyers know about their product, and have the first opportunity to "position" this information. I know of no builder who makes public much of their design data. My impression is that they each give about the same minimum set of information that they think the market demands.
Capsize screen follies
Here is a tip for those Hunter owners who would like to have a better Capsize Screen number: pave the deck with lead bricks! (Of course, it is wise to tie your boat firmly to the dock on both sides or she may turtle before you are completely done). Another interesting "thought experiment' is to disconnect the keel ballast and hoist it high into the mast (same precautions apply here). Now repeat your capsize screen calculation and see what you get...... Right! Worshipping at the altar of these dimensionless empirical numbers without taking a hundred other factors into account is as likely to give you a false sense of security as to needlessly scare you. Flying Dutchman "Rivendel II" (Legend 43, hull #1)
Here is a tip for those Hunter owners who would like to have a better Capsize Screen number: pave the deck with lead bricks! (Of course, it is wise to tie your boat firmly to the dock on both sides or she may turtle before you are completely done). Another interesting "thought experiment' is to disconnect the keel ballast and hoist it high into the mast (same precautions apply here). Now repeat your capsize screen calculation and see what you get...... Right! Worshipping at the altar of these dimensionless empirical numbers without taking a hundred other factors into account is as likely to give you a false sense of security as to needlessly scare you. Flying Dutchman "Rivendel II" (Legend 43, hull #1)
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