GZ curve and AVS for a Centaur

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François Le Goaziou
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GZ curve and AVS for a Centaur

Post by François Le Goaziou » Fri Nov 10, 2006 10:51 am

Just as a matter of comparison with modern yachts, does anybody know about the GZ curve and AVS for a Centaur ?

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RogerLloyd
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Re: GZ curve and AVS for a Centaur

Post by RogerLloyd » Tue May 22, 2012 12:31 pm

Has anybody now got any GZ curve or AVS for Centaur or Konsort?
Thanks
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Nigel Birch
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Re: GZ curve and AVS for a Centaur

Post by Nigel Birch » Tue May 22, 2012 12:57 pm

There's an interesting thread here but I think the calculation is quite complex and relies on all sorts of parameters we don't have ready access to....

http://www.boatdesign.net/forums/stabil ... 69-25.html

There is a rough calculation here http://www.sailingusa.info/cal__avs.htm

which gives 131.15 degrees for the Centaur and 131.8 degrees for the Konsort.
Last edited by Nigel Birch on Tue May 22, 2012 7:48 pm, edited 1 time in total.
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Re: GZ curve and AVS for a Centaur

Post by RogerLloyd » Tue May 22, 2012 6:07 pm

I thought that AVS (Angle of Vanishing Stability) was an angle between 90 and 180 degrees defined as the angle (in still water) at which a heeled boat showed no desire to return to being upright. It is a little disappointing if this angle is <90 degrees! I don't think it makes sense to talk about angles greater than 180 degrees, because 190 degrees heel to port is 170 degrees to starboard.

Therefore I do not understand "which gives 131.15% for the Centaur and 131.8% for the Konsort". A %age of what are we talking about?
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Re: GZ curve and AVS for a Centaur

Post by Nigel Birch » Tue May 22, 2012 7:49 pm

Yes, that should have been a degree symbol.
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Re: GZ curve and AVS for a Centaur

Post by RogerLloyd » Tue May 22, 2012 10:14 pm

Yes, indeed, Nigel. I realised after I posted that I had not been very clever!

Do I gather that these AVS angles are all derived from approx values of weights distributed about the boat and the (very approx?) shape of the hull? They would not of course take into account the additional weights of stores and equipment in a cruising boat (which in any case might not be "fixed" enough, and might contribute negatively to the angle!)

I obviously expect a centaur to have done the test practically, but of course I am not offering my own boat!
However if all AVS's are theoretical, then I would have thought there would be a little more information about what they are for popular boats. I looked on a list at the RYA website and could not find Centaur or Konsort there. Where did you get these values from?
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Re: GZ curve and AVS for a Centaur

Post by Nigel Birch » Tue May 22, 2012 10:38 pm

There are several formulae on the Sailing USA website I mentioned in my post. The AVS is very much a rough and ready calculation based upon beam, displacement, keel weight etc etc and has to be taken with a pinch of salt.

There's a bit more on the calculation here:

http://dan.pfeiffer.net/10m/avs_calculation.htm
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Re: GZ curve and AVS for a Centaur

Post by RogerLloyd » Sat Dec 21, 2013 2:31 am

Hi Nigel,
A very belated thank you for your information.
Roger
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Re: GZ curve and AVS for a Centaur

Post by GTom12 » Fri Feb 09, 2018 12:20 pm

Very interesting topic, I was wondering if anyone has professionally assessed/measured Westerly boats from the '80s for STIX? I would be interested how the values look like for bilge-keel models (Centaur, Fulmar, 33, Falcon, Discus).

There are literally thousands of these boats still on water, racing, etc. no professional marine architect looked into at least one specimen?

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Re: GZ curve and AVS for a Centaur

Post by Jolly Roger » Fri Feb 09, 2018 7:27 pm

You could contact Laurent Giles, the designer, as the business is still trading. They may have to calculate the numbers and they may make a small charge. Personally these numbers are unnecessary as we know they are stable from a historical point of view and the designs pre-date the EU classifications. These numbers are more essential for classification for modern designs which more of the stability coming from beam, rather than their keel.
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