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Old 15-12-2014, 19:13   #931
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Re: The Yard Guys

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Originally Posted by neilpride View Post
Easy Pol, chill, im just posting what some NA are explaining in the net, they are not my words, so , you see, if you want i bring you the links to see with your own eyes that im not saying nothing weird, its in fact NA words. Now go ahead, where is the SD 50 avs, mr i know all!!!
Can you explain me what has to do the Jeanneau 50DS AVS has to do with the overall stability of the boat (the energy needed to capsize it)? I can tell you: almost nothing. it seems that you think that a boat is harder or easier to capsize due to a higher AVS. Well, you are wrong the AVS plays only a small part regarding that.

No, I am not saying those STIX are not correct. what I am saying is that the STIX is not a measure of the energy needed to capsize a boat. As I had already said that energy is equivalent to the area under the positive part of the RM curve.

You should understand, at least intuitively, that even if the Island Packet 380 has a STIX of 55 and an AVS of 136º that, obviously, a Island Packet 440 even with a much smaller STIX (48) and a slightly slower AVS (133) will have a much bigger overall stability and will need a lot more energy to be capsized.

I think this should be intuitive to all, including you.

It is clear that you don't know why a boat that obviously has more stability can have a much lower STIX. That's why I said that you should look at the STIX formula to understand of what you are talking about and what that formula (the STIX) represents. It is not an easy or small formula, like the one of the capsize ratio and as you can see by those results on the Island Packet, can give weird results.
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Old 15-12-2014, 19:35   #932
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Re: The Yard Guys

I don't why I keep doing this to myself, but exactly how does the stability of a 37' boat vs. one that's 50' have anything to do with this thread? Isn't it more about the noob who is wondering whether to buy the heavy bluewater boat vs. the newer lightweight production boat? If so, don't we want to compare, say, the stability of an approx. 40' IP, for example, to perhaps Smack's 40' Hunter??

Just thinkin' out loud here . . . .
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Old 15-12-2014, 20:11   #933
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Re: The Yard Guys

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Originally Posted by Exile View Post
I don't why I keep doing this to myself, but exactly how does the stability of a 37' boat vs. one that's 50' have anything to do with this thread? Isn't it more about the noob who is wondering whether to buy the heavy bluewater boat vs. the newer lightweight production boat? If so, don't we want to compare, say, the stability of an approx. 40' IP, for example, to perhaps Smack's 40' Hunter??

Just thinkin' out loud here . . . .


Not to mention the whole argument is ridiculous, ie the 37 costs as much as the 50, therefore buy the 50. That assumes that the initial outlay will be the only expense associated with either boat. Obviously the 50 will cost a great deal more over the years to maintain, insure, and berth.
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Old 15-12-2014, 21:08   #934
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Re: The Yard Guys

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Can you explain me what has to do the Jeanneau 50DS AVS has to do with the overall stability of the boat (the energy needed to capsize it)? I can tell you: almost nothing. it seems that you think that a boat is harder or easier to capsize due to a higher AVS. Well, you are wrong the AVS plays only a small part regarding that.

No, I am not saying those STIX are not correct. what I am saying is that the STIX is not a measure of the energy needed to capsize a boat. As I had already said that energy is equivalent to the area under the positive part of the RM curve.

You should understand, at least intuitively, that even if the Island Packet 380 has a STIX of 55 and an AVS of 136º that, obviously, a Island Packet 440 even with a much smaller STIX (48) and a slightly slower AVS (133) will have a much bigger overall stability and will need a lot more energy to be capsized.

I think this should be intuitive to all, including you.

It is clear that you don't know why a boat that obviously has more stability can have a much lower STIX. That's why I said that you should look at the STIX formula to understand of what you are talking about and what that formula (the STIX) represents. It is not an easy or small formula, like the one of the capsize ratio and as you can see by those results on the Island Packet, can give weird results.

Take a break, breath deep, read again my post...

Originally Posted by neilpride
STIX is a stability index, the higher the number the better, AVS is the angle of vanishing stability.



To get the STIX of a certain model they need the overall measures of the boat, beam , lenght, etc..and the righting arm curve GZ.


Im sure Contessas Owners keep teir rudders in good condition, after all is kind of a cult boat, but yes why not , check your rudders!!!!
Im just checking Contessas in the net, overall they are well maintained..

BTW Exile, im not a expert in this matter, but what you say about how quickly a boat will right itself after being knocked down to 90 degs enter in the STIX equation to.

Easy Pol, chill, im just posting what some NA are explaining in the net, they are not my words, so , you see, if you want i bring you the links to see with your own eyes that im not saying nothing weird, its in fact NA words. Now go ahead, where is the SD 50 avs, mr i know all!!!


Lets see if you get it, what im posting are NA words, not my!! i dont give a **** the STIX or the other calculations, its Obviously that what i try to bring here is some light regards STIX and AVS in a wide comparison boat list, since you compare a Ip 38 to DS 50, if you try next time to bring some real veracity to your arguments , use links or real NA data , so we can see actually some veracity in your posts, i dont take for granted a wanabe NA in a fórum banging my head over and over with the same argument, please...

From what i understand the STIX is a magic formula created for the ISO to categorized boats in the EU.
Again not my words, NA words...

Obviously i believe you can even argue with a real NA in this matter..
Nevermind.. If a boat no matter the size weight have a hig stix plus a hig AVS is ok to say it have a good stability curve and seaworthy properties...and to be honest a breaking freaking 20 ft wave can knock down easy a Ds 50 same as a Ip 38..

So if i understand, ft by ft, keel by keel, pound by pound a hig AVS boat is harder to roll than a low AVS boat, this part is what i keep it to me...
Back to the Yard guys.
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Old 15-12-2014, 21:20   #935
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Re: The Yard Guys

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Thanks Neil!



As for rudders, this thread has me paranoid! All I (think I) know is that a solid bronze rudder stock won't be subject to crevice corrosion but may be susceptible to friction & wear if the bearings/bushings go bad (like steering pulley pins). Hopefully this would result in noticeable play when inspecting on the hard. But a SS stock could be subject to crevice corrosion & may not be detectable w/o dropping the rudder. Is any of this correct?

And then there are the couple of hollow SS stocks I've seen at the yard on inexpensive boats that have busted, probably after hitting something but who knows? Of course, this is not because hollowed-out SS is cheaper to produce, right? Must be to make the boat lighter & thus enhance performance.

I'm off to check out Contessa's . . . .

Actually no, if they are well designed, my rudder stock is naval bronze, original stock, the lower part rest in a delrin pad inside of the lower bronze rudder shoe, at the top there is enough clearance between the bronze bushing and the stock and then the stock just made friction at a packing gland , very similar to a prop stufing box.. overall the bronze stock dont made any friction with bronze or metal.

And for hollow SS stocks, no comment, he he. Lighter yes, ...
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Old 15-12-2014, 21:26   #936
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Re: The Yard Guys

I'm only an ex-architect (not nautical), so, though I have a pretty good understanding of how design and engineering work together successfully, I don't know the intricacies of these particular numbers - STIX, etc..

That said, Charlie Doane wrote a pretty good article that explains a good deal of this stuff:

MODERN SAILBOAT DESIGN: Quantifying Stability

And the section specific to STIX...

Quote:
A STIX number is the result of many complex calculations accounting for a boat's length, displacement, beam, ability to shed water after a knockdown, angle of vanishing stability, downflooding, cabin superstructure, and freeboard in breaking seas, among others. STIX values range from the low single digits to about 50. A minimum of 38 is required by the European Union for Category A boats, which are certified for use on extended passages more than 500 miles offshore where waves with a maximum height of 46 feet may be encountered. A value of at least 23 is required for Category B boats, which are certified for coastal use within 500 miles of shore where maximum wave heights of 26 feet may be encountered, and the minimum values for categories C and D (inshore and sheltered waters, respectively) are 14 and 5. These standards do not restrict an owner's use of his boat, but merely dictate how boats may be marketed to the public.

As useful as they may or may not be, STIX numbers are generally unavailable for boats that predate the EU's adoption of the STIX standard in 1998. Even if you can find a number for a boat you are interested in, bear in mind that STIX numbers do not account for large, potentially vulnerable windows and ports in cabin superstructures, nor do they take into account a boat's negative stability. In other words, boats that are nearly as stable upside down as right side up may still receive high STIX numbers.
The bottom line when evaluating stability is that no single factor or rating should be considered to the exclusion of all others. It is probably best, as the STIX critics suggest, to gather as much information from as many sources as you can, and to bear in mind all we have discussed here when pondering it.
Judging by your arguments, I think some of you guys could definitely stand to read it.
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Old 15-12-2014, 21:29   #937
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Re: The Yard Guys

Thx Smack, i read it, there is a couple of very iteresting topics in sailboatdsign. net, to.
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Old 15-12-2014, 21:33   #938
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Re: The Yard Guys

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Originally Posted by neilpride View Post
Take a break, breath deep, read again my post...



So if i understand, ft by ft, keel by keel, pound by pound a hig AVS boat is harder to roll than a low AVS boat, this part is what i keep it to me.. Back to the Yard guys.[/I]



Now that's a "magic formula"! Especially if you add, " harder to roll and keep rolled".
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Old 15-12-2014, 21:33   #939
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Re: The Yard Guys

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Thx Smack, i read it, there is a couple of very iteresting topics in sailboatdsign. net, to.
Good. Then you'll realize that what Polux is saying is largely true. And we can move on. Because you guys are starting to look a little silly here.
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Old 15-12-2014, 21:59   #940
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Re: The Yard Guys

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Now that's a "magic formula"! Especially if you add, " harder to roll and keep rolled".
Muhaa, we can open a can of worms here, nahhh....
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Old 16-12-2014, 05:50   #941
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Re: The Yard Guys

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OK, I'm sure there are others who don't know what the stix & avs values mean, but I'm willing to reveal my ignorance for the sake of learning something.
Forget about stix and avs - what the heck does "doublé Wheel polipop" mean????

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Old 16-12-2014, 06:06   #942
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Re: The Yard Guys

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Heavier boats can have a better overall stability then slightly bigger lighter boats...but when a boat is substantially bigger and is also heavier, if it is well designed, no way it will have lesser overall stability than the smaller boat, meaning by overall stability the energy required to capsize the boat. It is impossible.
avb3, run the numbers for this through your famous equation, compare the results to your Flicka 20 (they will be very unfavorable, with the Flicka far more "stable") - then ask yourself which do you REALLY think will be more stable in 50kt winds and 30' seas?

Like Polux is trying to educate you - energy is the key, and your equations are only good for comparing very similar boats.

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Old 16-12-2014, 06:22   #943
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Re: The Yard Guys

A lot of this stuff is making my head spin. One of the posters threw out the old bigger will cost you more. So my take on this is relative. Yes haul out will be a bit extra as will hard stand and a few extra gallons of paint you will pay more for dockedge. But the difference between a 40 and a 50 is not a lot considering the extra comfort and room.


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Old 16-12-2014, 07:00   #944
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Re: The Yard Guys

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avb3, run the numbers for this through your famous equation, compare the results to your Flicka 20 (they will be very unfavorable, with the Flicka far more "stable") - then ask yourself which do you REALLY think will be more stable in 50kt winds and 30' seas?

Like Polux is trying to educate you - energy is the key, and your equations are only good for comparing very similar boats.

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He'll never believe you. He's got calculators.
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Old 16-12-2014, 07:06   #945
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Re: The Yard Guys

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He'll never believe you. He's got calculators.

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