clculating AVS

[shaile]

The US Sailing AVS calculator ( http://www.sailingusa.info/cal__avs.htm ) requires:
"4. Enter Hull (not including the keel) Draft in Feet: "
This data is usually not available but the whole draft is likely to be available.
I thought about some go around proceadure:
I try to find a side view of the boat out of the water.
In the picture, I measure the height from the tip of the keel to the waterline, this should be the whole draft. Now I measure the the height from the bottom of the hull to the waterline and calculate the Hull Draft.
The problem with this method is that it is not accurate.

Is ther another method of calculating the AVS of a boat ?

thanks.

 

[Paul Kotzebue]

The only way to estimate the AVS is to develop a righting arm curve with an accurate displacement and center of gravity. The US Sailing method is misleading at best.

 

[shaile]

Thanks.
What order of error does the US Sailing's method makes.
Is it in the order of few degrees or tens of degrees.
Is there any site that contains comprehensive stability data of boats ?

 

[TeddyDiver]

What order of error does the US Sailing's method makes.Depends
Is it in the order of few degrees or tens of degrees.btw them in most occasions
Is there any site that contains comprehensive stability data of boats ?No

 

[Guillermo]

shaile,
The formula used by US sailing to get a rough value for AVS is a pretty well known one and produces reasonable AVS figures for boats with a flush or small volumes over deck most of the times. Obtained AVS figures for boats with wheelhouses/big overdeck volumes and/or big cockpits or unsusual freeboard are the less acurate.

I have used it widely to analyze many dozens of boats of all types, using precisely the same method you use to estimate hull (body) draught, and when able to compare it with known data, I have found the usual deviation (80% of times?) is less than 5º and the maximum deviation is in the range of 15-20º.

Of course there are many other uncertainties when trying to figure out the necessary data from the information provided in magazines, marketing material, etc, when analyzing boats with simple formulas. One of them is stated displacement, as usually the load condition considered is not revealed or doubtful.

I fully agree with Paul Kotzebue: the only way to precisely stablish AVS is to know hull hydrostatics and KN curves, perform a detailed inclining experiment in a known loading condition and then do the CoG and GZ curve calculations.

But, as said, the formula to approximate AVS -as the one US Sailing calculator uses- is pretty useful to get an idea of how things are most of times.

Cheers.