In order to be rolled, a boat’s righting moment has to be overcome. Obviously, different boats will be more susceptible to rolling than others based on length, beam, displacement
, roll inertia, and center of gravity. Generally, the starting point for a wave to be dangerous to rolling a boat
, is one that is only 30 percent high as the boat
is long. Your 35 Ft boat might
be in danger
of capsise in about 10 ft. beam
seas, if breaking, and almost certainly in 21 footers.
Your boat may be more or less susceptible to rolling than other boats based on its design, but the aspects to remember are that although your boat may be severely heeled over by the wave front, the wave will have to be:
- over 30 percent  of the boat’s length
- be breaking on the boat 
the boat will have to be orientated obliquely (beam on is the worse) to the wave, to knock the boat down, or completely roll the boat over.
Unless the wave is so large that it pitch-poles the boat, a boat that is bow or stern onto the wave should not be rolled.
 Andrew Claughton (who co-authored the University of Southampton
, Department of Ship Science’s report) writes in Adlard Coles’ Heavy Weather
Sailing by Peter Bruce, “During the model tests that were carried out to investigate the problem, when the breaking wave was 30 percent of the hull
length high, from trough to crest, it could capsize
some yachts, while waves to a height of 60 percent of the hull
length comfortably overwhelm all of the boats we tested.”
 Generally, when the wave height exceeds the wave length at a 1:7 ratio, it may begin to collapse. (a non-breaking wave cannot throw the boat down into the trough);