Good thread Pelagic. Really making me think. I don't think there can be a definitive answer as it all depends on one's mood and everything as much as what one thinks their crew/boat can take. My rule
of thumb, would be to chicken out if the wave height was more than half the boats w/l length, but when you add a 1.5 period/moment thats throws my thinking way back to an earlier turnaround or smaller wave.
As a "cruise for plesasure" kinda guy now, I ticked the 2m box. I would go for the turn around perhaps earlier than most, because I am not in a hurry (eg: restricted by holidays from work for example), and am a bit "risk averse" and don't particularly want the challenge anymore. Comfort is good. My acrylic
wrap-around high-vis pilot house negates against taking chances, which also suits my general persona today.
Different boat types, traditional long keel
, flat bottom daggerboard, and different crews: young and fit, or old and infirm, different AVS, and all sorts of factors would bring different decisions. I would accept the moment and roll more on a boat that I had just re-rigged, than on one where I hadn't changed the stainless in a while. There are so many factors.
1.5 period and big waves isnt that uncommon in inshore parts
here sometimes, where the estuary narrows, when the wind
is easterly it brings them in and the bottom contour steepens them up with a little help from a wind
against tide situation. We'd bash through them in a Pilot boat without much thought, as they are momentary and not continuous. However, I can't remember ever experiencing quite that relationship out at sea. Probably because I had bottled-out early.
From looking at your video, the waves do not appear steep sided. It would appear that the parametric roll is induced directly by the combination of moment and height (which is interesting and educational) as theoretically one could make a graph for every boat showing what it would be? In the same manner as AVS? Can one presume that the Metacentre and CG have pronounced affects on how this would differ from one boat to the next?
Not sure if I am making sense here, but do we ever measure the seas accurately anyway? It's usually gut feel based on experience. We form "an impression" of the waves. Or is that just me? I must admit I am not experienced in Ocean crossings, I have never done one. But in the North Sea here, most of our decisions, while based upon our techincal knowledge (or, as in my case: complete lack of it), are based upon the traditional seat of the pants instinctive feel, gained from all our receptors rather than mathematical formulae.
Sorry, I am rambling here, more thinking out loud (or on the keyboard).