The OP asked for strategies for steering a sloop
in chop and wind, when conditions become uncomfortable.
The 30% rule is for the full height
of breaking waves, beam on
. Narrower boats the limit is higher around 50% with all boats being rolled at 60%. I agree that it is related to beam, hull
shape and harmonics i.e. a boat recovering from a heel one way on one face of a wave may accentuate the opposite heel on the other face of the next wave.
I think the point with breaking waves is to avoid them. Waves are more likely to break in shallower water and when the wave height is < 7 x the wave length. In short when the waves are close and big. The odd ones are twice as big but the chances of breaking on the boat less in open water.
The tactic for breaking waves is to try and meet them head
on, thus presenting as small a profile to the wave as possible. This is shown simply by standing side on versus head
on in surf, or watching surf boat races. The difficulty with sailing is that if the wind and waves are in the same direction as they usually but not always are, you can’t sail directly into the wind or breaking waves.
Running before them if one could get the speed to stay ahead of the break one might surf ahead of it, but that is unlikely consistently. The waves will be faster than most boats. More likely one can surf with crest of a non breaking wave. The danger with a breaking wave is that it breaks on top of you, filling the cockpit
or if one is not dead square the wave tosses the stern around giving a broach or even a roll.
In lesser conditions namely an uncomfortable chop the general rule of taking the wave at an angle is less of a problem for a sail boat as you are tacking. You might handle the wind by reefing or by heading a bit higher.
If the waves are say four m, close and very steep or square, say with wind against tide ( a situation best avoided) it is more tricky because the bow can be thrown off and there is less change in gradient from being at an angle. I prefer to motor
head on then.
Downwind. A modest chop is no issue. When the waves are bigger if you are not square to them the stern can be thrown around and that is very difficult to correct. For most boats the waves will be faster than the boat but you can pick up a ride for a while. It seems to me that when at the crest you can steer easily to ride it square but the trick is that it can respond at the crest to the rudder
in the opposite way because there is a point where the water flow is reversed over the rudder
. The trick is in the timing because the usual rudder movement will make it worse ie putting the wave on the quarter so you broadside down..
On a power boat
I have been able to get good rides in effect riding as much as possible largely lengthwise along a crest and matching speed rather than wallowing. It would be harder in a sail boat because of the speed difference.
In any significant chop relative to boat size I prefer not to be beam on because the motion is less comfortable, and as the waves become higher and steeper the rolling becomes greater with loss of wind and speed. Otherwise a beam reach is the fastest and most pleasant sailing.
Most of us won’t hopefully be out in extreme conditions. Then one gets into drogues and parachutes but I don’t think that is what the OP was asking about.