05H36 Knockdown experience
Hal -I had an experience in my 05H36 with a downdraft from a summer thunderstorm that led me to that same conclusion.When coming back from the Isles of Shoals one summer day a couple of years ago, I saw a big, black Tstorm coming offshore to meet me. It had heavy rainfall lines descending at its sides and was a more solid yellow on my RADAR screen than the shoreline, so I 3-reefed my mainsail and partially furled the jib.As it hit, Persephone was doing rather well by my feathering her into and slightly off the wind as it passed 48kts true on my ST60 Wind in a soaking deluge that made it hard to see the jib.Then, a wild shift in wind direction and increase in velocity - most likely from a downdraft - backed the jib, rapidly spun her broadside and pinned her.My inclinometer only reads to 60 degrees, but I estimate the angle at which she was pinned to be 75-80 degrees. Based on the H36's stability curve, that's just slightly beyond the maximum righting moment peak.She just calmly lay there on her side, slightly fore-reaching in all that wind, with water only part way up the sidedeck (rail just awash)- and a dry cockpit.After letting down the arch-mounted traveler to bring her up a little, I was able to crawl forward to the cabintop winches and release the mainsheet - and she came right back up as if nothing had ever happened.The same high freeboard that is at the limit of what I can step-up to from a floating dock to pull myself aboard by the shrouds, and provides occasionally annoying windage when docking, suddenly became worth a king's ransom in my eyes.We often focus on ultimate stability when considering seaworthiness. And knowing that if inverted you can come back up again is important. However, it's initial stability or "stiffness" that provides the resistance to inversion in most conditions. And modern wide, high freeboard hulls have more form stability.The stability curve for my boat has an area above the 0-axis that's more than 3 times the area below the axis. So, obviously, it'll take less than one third the wave energy required to invert her in order to flip her back upright again. A Pacific Seacraft 40 has a more than 4-to-1 areas ratio and will come back from inversion with very little wave action.Since any boat can be inverted by a breaking wave on her beam whose height exceeds the beam of the boat, if I wanted to be able to go below and passively wait out a storm I'd be more confident in the PS40. I might get rolled, but I'd have a high probability of coming back upright more quickly.However, since I do coastal cruising in the Gulf of Maine rather than 2-3 week ocean crossings, I count on active measures in heavy weather and have a lot of faith in Persephone's ability to take care of me, as long as I don't go out in hurricanes. (I also have as much interior volume as the PS40.)That confidence is based on her inital stability - not the curve, but what I now know it means. Part of that is the ballast ratio, but that's only 36%. Much is form stability - from her wide beam and high freeboard. I'll never look enviously at a slinky sheer line and low freeboard again.(Also - to Ken's point - I'm awfully glad I was singlehanding when I learned all this .)Fair winds,Al