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Old 01-31-2005
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Bluewater defined?

I said that it was controversial...

Some confusion (it is confusing) between RORC STIX and STIX as it is defined by ISO 12217-2 (and mandatory by Directive 94/25/EC of the European Parliament). The second is the one that is important, being actually taken with dynamic tests with the boat on the water.


The Classes stated by GordMay are the ones that are defined by the European Directive and every boat sold in Europe has to pass tests to conform to one of them.

Those classes are better than nothing but unfortunately the A class has (in the general opinion) too low standards for the definition of an oceangoing boat.

Almost all light construction European 36ft are A boats, I mean the Bavaria 36, The Beneteau 36, The Jeanneau 36, etc.

Fact is that the specialized press doesn’t call them Oceangoing boats or bluewater boats and I agree. They are basically good coastal boats. That doesn''t mean that they can not make passages, it only means that they weren''t designed for that.

On the other hand, Stix value and AVS ( or LPS) found by dynamic tests are very important to determine the seaworthiness of a boat.

"For ocean-going and offshore yachts one of the most easily seen and meaningful aspects of a GZ curve is the AVS.
But a GZ curve and its AVS are by no means the whole transverse static stability story. A boats mass (displacement) is also very important.

A lever, when multiplied by the force pushing it, becomes a moment. With a boat the lever is the GZ and the force is the boat’s mass. So by multiplying GZ by the boat’s mass gives a righting moment (RM) curve. As the area under this curve represents the energy needed to heel the boat, then for the same GZ curve, a boat of double the mass will need twice the energy to capsize (and twice the energy to re-right after capsize).

ISO 12217

It is for this reason that the recently launched International Standard dealing with the stability of monohull ballasted sailing yachts (ISO 12217-2) uses both AVS and mass as its two main static stability limits.
RCD* Category A boat limits are a minimum mass of 3.0 tonnes and an AVS greater than (130 – (2 x mass)) but always equal to or greater than 100"....

"STIX

STIX, which scores a boats stability on a scale of 1 to 100, uses a boats length as it’s prime factor adjusting this by seven other factors including assessment of a boat’s

• ability to withstand a capsize by considering the area under it’s GZ curve,
• recovery from inversion by looking at it’s AVS and mass,
• recovery from knockdown by overcoming water in the sails,
• displacement-length factor giving credit for a heavy displacement for a given length,
• beam-displacement factor recognizing problems associated with topside flare and excessive beam,
• wind moment representing the risk of flooding due to a gust and
• the risk of downflooding in a broach or knockdown.
STIX is arguably the most sophisticated stability screening tool yet available. The required RCD* STIX limits which are applied in addition to the above limits on mass and AVS are:-

Category A equal to or greater than 32"


http://europa.eu.int/smartapi/cgi/sga_doc?smartapi!celexapi!prod!CELEXnumdoc&lg=en&n umdoc=31994L0025&model=guichett

http://www.rya.org.uk/images/uploaded/3352ce73-ea82-4eb8-a0a6-865dfa94e88a/Stability_Intro.pdf


32 is not a big figure for Stix and it is very close to the figures that those light displacement 36ft(Benetau, Bavaria, Jeanneau) have, with normally an AVS that goes from 115 to 125 .

For instance a Malo 41 has 55,4 with an AVS of 132; a Southerly 135 has a Stix of 59,7 and an AVS of 150; the Regina de Vindo 38 has a Stix of 46 and an AVS of 134.

I would not call the first ones Bluewaterboats, but I think everybody would say that the last ones are (and they are referred as that by the specialized press) and they don''t have full keels.




Paulo
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