The only time I ever actually had a boat fall off a wave and hit really hard was during the early nineties Perfect Storm. The waves were probably not 30 feet but somewhere between 18-25. The wave heights would have been nothing too bad in a gradually building storm but in this storm the wave periods were shorter than I've ever seen or experienced since. It was literally; wave peak, one one thousand, two one thousand, three one.. peak!
We fell of three wave faces, really hard, during that storm in a very well build Shannon but let me tell you it felt like we hit a brick wall. Stuff broke! We were not even in the bad parts
of that storm so I can't imagine the waves bigger than they were and any shorter wave periods. The waves were cresting and the faces nearly vertical so we went through them more than over them, or that's what it physically felt like, but every now and then the bow would get knocked off just before the crest and we'd fall into the trough and then get pummeled by the next wave. We were rolled to close to 90 two or three times.
Unfortunately for us we were beating off a lee shore so we had it a lot rougher than we otherwise would have had we been able to trail a warp and fall off the wind
or heave to.
This however was and is not a typical storm so I would not worry to much about being caught in one especially with today's weather forecasting. The seas and waves built so fast I've never seen anything like it, and I've sailed in a hurricane
and with higher wind speeds but never with waves that short & steep. I honestly did not think it was possible to go from 20-30 knots & 5-6 footers to 45-55 knots and waves over twenty in a very short time frame but it is..
This storm would have been fine in this vessel had we had the sea room but we did not as we were delivering this boat up the New England
coast from RI to NH.
I can assure you that if you ever experience short steep seas like this you want a STRONG boat. None of mass production boats I've owned could have survived this without some serious structural damage. Hell I had stitches and broken bones myself. I actually had a solid brass cabinet latch snap in half. In fact I feel quite comfortable saying I may not be here today had it not been for the robust construction of the vessel we were on. One hard trough smash on a production boat maybe but two or more is doubtful.
We were young and dumb and this storm snuck up on everybody but it still could have been avoided.
The conditions are all about wave period! I've sailed in some very heavy winds, 50+, with no problems (relatively speaking of course) and then some in the 35-50 knot
range with massively short steep seas.
I'll take forty foot seas even cresting swells with long wave periods over 18-20 foot seas with short wave periods any day of the week.. In my experience height is not the only determining factor it is the period between wave peaks..
Of course these days I chose NOT to put myself in those situations..