AVS of 1978 Reliance 44 - SailNet Community
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AVS of 1978 Reliance 44

I'm hoping someone can help me determine the angle of vanishing stability (AVS) of a Reliance 44.

Here's the formulas I've found. AVS = 110+(400/(SSV-10)), with SSV (Screening Stability Value) = Beam^2/((Ballast/Displ)*Hull Draft*Volume^.33). All values are in Meters or Kg.

From sailboatdata.com I've found:

Beam: 3.56
Ballast: 5080
Displ: 12701
Hull Draft: 0.88 (I'm guessing from the drawing)
Volume: 12.36 (calculated from the displacement)

This gives me an AVS of 180.14 degrees... which is, well, a little optimistic. If my formulas are right, then I suspect I'm simply wrong about the Hull Draft, but I don't know where I can find this.

Any help would be appreciated. Thanks.
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Old 06-18-2015
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Re: AVS of 1978 Reliance 44

At 180.14 degs you have capsized and most probably be coming back up on the other side. I have some experience with stability studies and By now I have well tuned seat of the pants feel for a boat's limit of positive stability. Looking at the Reliance I'd guess it would be between 128 degs and 134 degs. That's fine, similar to a Valiant 40.

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Re: AVS of 1978 Reliance 44

Thanks Bob. Just about every boat I've researched (Downeaster 45, Westsail 42, Fuji 45, etc.) have AVS numbers in that range, if not on the high end. From all the factors going into the calculation (and just gut feel) it seems that the Reliance should have the highest AVS of any of these "bluewater" boats. I was just trying to confirm that and see just how "good" it was for high latitude ocean passages.

Thanks,
Dan
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Re: AVS of 1978 Reliance 44

dc:
The Reliance is not heavy enough to get really high AVS numbers. To get the number up you need displacement so you can have a high B/D, draft, so you can have a low VCG and the deadrise that you most often get with heavier displ. For a boat with the 44's numbers to have a AVS over 135 would be very rare. My 62' DE FRANCIS LEE has an AVS of 158 degs. But that is with a very narrow boat and 7,500 bulb down 10'. It's not your normal cruiser.

My newest project, the four carbon fiber 43' cutters will have an AVS close to 140 degs. But we have plenty of displ and a very low VCG due to the carbon fiber construction. I have not done a stability study yet but I'm counting on at least 140 degs. To me the number is not so important. It's fun to look at though.

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Last edited by bobperry; 06-18-2015 at 05:16 PM.
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Re: AVS of 1978 Reliance 44

DC, Bob, What would be the values for the constants 110, 400, 10 if I want to calculate in feet and pounds? How would I calculate the volume of my Catalina 34? We "Tupperware" owners want to play along too!

George B
2000 Catalina 34 MkII
Alameda, Ca.
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Re: AVS of 1978 Reliance 44

George:
I'm not sure what you are asking. I'm a bit slow. I have no idea what those "constants" are. Be very careful when you work with overly simplified stability estimations.

The volume of your boat below the waterline would be the displ divided by 64. So a 7,400 lb boat would have a volume of 115.6 cu.ft. below the DWL.

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Re: AVS of 1978 Reliance 44

DL's formula uses those numbers as multipliers and factors and I was wondering if they are metric specific or if I can just plug in my feet and pounds and crunch the formula? Heh, heh, I wish I had a displacement of only 7,000 pounds. I own a Catalina after-all.

George B
2000 Catalina 34 MkII
Alameda, Ca.
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Re: AVS of 1978 Reliance 44

George:
Given the answer he got, I'd stay away from that formula. It looks funky to me. It throws ballast and hull depth in but there is no place for VCG. VCG is the king of the stability study.

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