I've been on the ferry across Bolivar Roads (Galveston to Bolivar) When the wind was 40 knots outa the north and the tide was running in hard. The waves were tall and square. The traffic across trhe Houston ship channell was normal (read:lots of really big ships all the time) My truck, an F550 crew cab, was TOTALLY inundated several times. The deckhands said "wernt no big deal" folks gotta get home. I estimate 15 foot waves, but then again, I was in the middle of it. Coulda been 25 foot waves, or `10 footers. I just remember seeing green water over the hood of my truck.