Originally Posted by goboatingnow
Note that inverted stability is very much determined by the cabin
structure, modern yachts with significant top hamper actually exhibit better numbers then the hull
AVS suggests ( from the incline tests etc) take for example the moody 45 DS which has no negative curve. ( ie it will never stay inverted ) yet its a typical beamy boat with the beam carried right aft ( and hence twin rudders )
Dave I agree with most of your post, but we do need recognise that beamier boats rely on more form stability and less on ballast (generally) to provide the righting moment. They will have a lower AVS. The high inverted stability of a wide beam makes the whole stability curve worse leading to a more stable upside down position. These are well known yacht design principals.
AVS angles have been getting progressively less over the years.
In many ways this trend has been negated by the increase in boat size. Larger boats are less likely to capsize
and are therefore acceptable with a poorer stability curve.
Boats with a large superstructure (such as the Moody 45) will always have a higher AVS angle. A narrow beam boat will a high superstore will still have a better stability curve than its beamier cousin.
There is a price
to paid with the vulnerability of the superstructure. Many people feel such features unless very careful designed and built, detract, rather than enhance the overall seaworthiness of a vessel, despite the always positive effect on AVS.
Wide beam boats with high super structures to counter an inherit poor stability curve is not a positive move in terms of blue water
capability although such design features are great at anchor
where a cruising boat will spend most of its time.