I've never seen one that big, but we fished in 20-30 foot waves as a matter of course, and there would be big ones in the group(swells, and us in small boat, so no worries). Even in the gulf, with seas running a moderate 6-8 with a cross chop, we would get 15 to 20 footers rogues, mixed in pretty often They have to be wind or confluence waves, though, there is just not enough energy in them to pile up that high in deep water..