how to figure limit of positive stability....... - SailNet Community

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Old 06-03-2011
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how to figure limit of positive stability.......

Ok, so at the dock party after the race last night, one fellow was trying to figure out what his LPS for lack of better way to put it was. He as told there were two ways, if you did it one way, his boat came out to about 115* or there abouts, another in the 130's. To get a cat 1 PIYA cert, you need to be over 120. so he was trying to figure out what formula to use. I have seen this one at USSailing, puts me at about 117 or so. Not sure where this guys boat is, ie a Farr 1020.

Google searching gets me lots of articles, but only the following ussailing link. I did find an excel program using some STIX figures, but not sure I can find ALL the numbers they want and need.
Angle of Vanishing Stability

So in the end, is there another BETTER formula program online that might do a better job estimating ones LPS?

Marty
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Old 06-03-2011
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My understanding is that's the best calc available. If you want any better you need to have the boat measured, which I think involves an inclination test, and majority of people only do that for racing certification.

I believe most yacht designers would be able to come up with measurements, assuming they have sonme fancy software. However, as you normally only see this info on new yachts (and not always) my guess it that it is a difficult process / fair amount of work.

Ilenart
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Old 06-03-2011
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Yes, those simple formulas are only good for very approximative results. Stay away from them. You can have the boat fully measured and weighted and get the results to someone that has a very expensive program (Naval cabinet) that makes the calculations for you (you have to ask what they need) or you make the easiest way that is through an inclining test following ORC instructions. Contact ORC for instructions.

http://www.orc.org/rules/Stability%2...ion%202010.pdf

2010_Stability


http://www.gidb.itu.edu.tr/staff/aky...ing%20test.doc


About the differences you can get on stability curves using different programs you may want to have a look here:

Misleading stability - Yachting and Boating World Forums

Regards

Paulo

Last edited by PCP; 06-03-2011 at 07:04 AM.
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Old 06-03-2011
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As always Good Links Paulo.
Yes both of you are correct. emailed with the other person earlier today, he is at 124 with the ussailing link. so he is happy, The other option to get the number, is to measure at many what sounded like thousands of dollars. IIRC getting an IRC cert is about 500-1000 USD.

In the end, he is happy, as he can now do some of the local more open water to ocean catagory races, like Swiftsure, southern straights to name two. My boat turns out to be 121 or 122 depending upon if I use the stock 1.4" hull measure, or 1'5" that I measured when out of the water last Feb, going with seaweed line.

Do either of you know the difference between the old CE number certs and the newer Letter certs? ala is my CE2 equal to or there abouts to a current CE B? this would be my guess.......CE 1 would be equal to an A. Not sure about a CE5, as there is no CE E, only a-d.......

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