The St. Clair is not quite a "thousand footer", but still pretty big: 770' x 92'. Earlier the same day, the waves were going well over that wall, as you've seen pictures of. Those people standing in the foreground would've had waves pouring over them at head-level and above had they been standing there earlier. The waves calmed considerably (from 4-6m to 3-5m) just a few minutes before the St. Clair departed.