Enjoyed mr. robert’s posts but would mention:
There’s a huge difference in righting arm from form stability v. ballast. Multis and beamy boats may have huge righting arms but low AVS.
Beyond issues of “stiffness” gyradius is equally if not more important in quality of the ride and performance in a seaway. Particularly for small (<100’) recreational trawlers wher facing a wave train is a common tactic.
Rapid drainage of green water is a huge concern effecting stability and often not adequately considered when judging boats. Newer designs which have eliminated bulwarks are one solution. Center cockpit boats like the Seapiper raise concern imho. Even Portuguese bridges maybe an issue depending upon design.
It’s generally considered that an AVS of 120 is the lower limit for a blue water mono hull sailboat and significant area under null in the Gz curve is of great concern. However given different storm tactics for small power and somewhat better ability to slide down a wave face down flooding would seem a greater real world risk in event of a knockdown. Hence although a AVS of ~90 would seem reasonable there’s so much more to consider. Of particular concern is the construction of the house and details of any and all hatches, ports, glass and doors. One notes after a knock down it’s not the grp on the side that hits the water but rather the side that wasn’t immersed that more commonly fails. Forces are communicated across the house and its non immersed side that more commonly cracks and fails. The salons of recreational trawlers are so wonderful but also present great potential vulnerability to a knockdown or even boarding waves.
Every time I read or talk with a NA, particularly one of Tads stature, I learn something. I know it’s more important to know what you don’t know than what you do. I know I don’t know enough about stability beyond the most basic terminology and concepts but I do know that there’s a huge difference between a safe BWB and coastal vessel. I also know sooner or later your interpretation of weather data will be wrong and even your professional weather routing service will let you down. One of the few times I was ever knocked down was as crew on a pleasant 10-15k day with 3-5’ waves. I was off watch ( came up L.I. Sound through the night) and sleeping. Either a rogue wave or amplified wave from the two wave trains running or a microburst put us right down with half the house submerged. That happened between Block and Point Judith. This is not just a voyagers concern
