Gary wrote:
Evan Gatehouse wrote:

Gary wrote:

I think the stability curves are wrong. If you plug the numbers into
the formulas at US sailing you get a much higher AVS. 110 degrees
just doesn't make sense. Not only that but the 460's keel, although
seemingly a little light, is bulbous with the weight quite low.
Something is wrong with that graph.

Gaz



I didn't find the formula at US Sailing's site but...How do you find
AVS without using a sophisticated stability program that knows the
shape of the hull?

The US Sailing formula may give an indication of ultimate stability
(the capsize screening formula) but that is a very simple rule of thumb.

The inclining experiment data, which does determine the VCG of the
real boat, is plugged into a stability program (GHS/Autohydro etc.)
that gives the stability curve.

Robert has retired fairly recently but he should be able to help you
with your questions.

Evan Gatehouse

Try he http://www.sailingusa.info/keelboat.htm
Under sailing calculators in the right find angle of vanishing stability.

The problem with the inclining data is that it only takes hull shape and
weight distribution into account. It doesn't allow for things like
pilothouses or foam filled masts. I still think the curve is wrong and
Tayanas claim of an AVS of 0 is probably correct.

O.k. I'm a polite guy on usenet but you sir are totally
wrong and beginning to **** me off. I'm a naval architect.
I do this stuff for a living.

The stupid calculator only is used to give an ESTIMATE of
the AVS.

An inclining experiment establishes the VCG of the boat in a
real world test. It does NOT calculate the AVS. For that
you need software that does take into account the shape of
the hull and the pilothouse. GHS and Autohydro DO that!
You could model a foam filled mast as part of the model if
you wished. They are far more trustworthy and are accepted
by USCG for stability calculations of commercail vessels

Here's the formula from US Sailings site. Note that in the
last line, the formula says the AVS = 110 + .....

This says that the AVS is ALWAYS going to be = 110. There
are lots of boats that are 110!

From US Sailings web site:
" This formula gives an estimate of the angle of vanishing
stability or the angle the boat can heel and still right
itself. This formula does not fully take into account the
vertical position of the center of gravity (VCG)."

Screening Stability Value ( SSV ) = ( Beam 2 ) / ( BR * HD
* DV 1/3 )

BR: Ballast Ratio ( Keel Weight / Total Weight )

HD: Hull Draft

DV: The Displacement Volume in cubic meters. DV is
entered as pounds of displacement on the webpage and
converted to cubic meters by the formula:

Displacement Volume in Cubic Meters = ( Weight in
Pounds / 64 )*0.0283168

The Beam and Hull Draft in this formula are in meters.
These values are entered in feet on the webpage and are
converted to meters before SSV calculation.

Angle of Vanishing Stability approximately equals
110 + ( 400 / (SSV-10) )