Don't have any idea how common they are. They do exist, I've experienced two, one seen clearly, the other unseen and just experienced.
The seen wave was mid channel between Catalina
and San Clemente Islands, that is about 40 miles offshore
. By the local coast guard weather
station it had been blowing a steady 45, gusting 55 the previous night. We left the next morning, wind
was down to about 25. The seas were 10-12', short wave length and steep like you see right after a storm. It was very clear, maybe 10:00 AM when we spotted the wave. We could see it a long way off, it looked like the horizon but was too close for that. It was a long grey line. From the time we first spotted it until it reached us was several minutes. When it got close enough to see clearly these things could be observed: it was moving in train with the other waves, it was not a product of cross seas impacting each other because there were no cross seas, and its face was really, really steep, more like a breaker forming up on a beach than a deep ocean wave. As it got close to us it was starting to go concave and I could see that it was going to break. It did break, just in front of our bow, and we hit this huge wall of falling white water
. I can tell you that we had solid water
at least 20' high over the top of the boat judging by a short mast
17' above the waterline which had a 3' length of bronze rod for lightning
protection mounted at its head
. We later found the rod bent straight back by the force of the water. I did my best to estimate the wave height later by estimating angles and distance and came up with a height of 45'.
The second wave I never saw, just experienced. I was on board the USS San Jose, an approx. 560' Navy
ship in the South China
Sea. It was rough, we were taking a good sized sea on the port beam. Sometime after midnight, I was in my rack, the ship took a very heavy roll to starboard and just kept rolling. Guys were falling out of their racks, a set of lockers tore off the bulkhead and fell across the compartment. She kept rolling, slowed, finally paused, and just lay there for several seconds before slowly starting to recover. Next morning I checked with a buddy who had been on watch on the bridge. We had a recording inclinometer. According to it the roll stopped 3 degrees short of the point of vanishing stability for our state of loading at that time. She was obviously very close to going over, judging from the sluggishness of her roll recovery.
My conclusions? There are waves out there can roll any boat. The second one damn near rolled a good sized ship. The one I saw, because it was daytime and clear, I was able to take head
on. If it had been night I don't think I'd be here writing this. That wave, taken broadside, would roll anything small enough to be called a boat.
I've decided that I want a boat strong enough to take this kind of a hit and stay together. And I want a boat that will right itself after capsize
. At the time of the wave I saw I was designing a cat for long distance cruising. This experience converted me to monohulls.