GZ curve and AVS for a Centaur

[François Le Goaziou]

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

best regards

François
CR1134 (Brittany)

[RogerLloyd]

Has anybody now got any GZ curve or AVS for Centaur or Konsort?
Thanks

[Nigel Birch]

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.

[RogerLloyd]

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?

[Nigel Birch]

Yes, that should have been a degree symbol.

[RogerLloyd]

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?

[Nigel Birch]

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

[RogerLloyd]

Hi Nigel,
A very belated thank you for your information.
Roger

[GTom12]

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?

[Jolly Roger]

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.