Tusunamis can and have capsized vessels before. All tsunamis are different and it all depends on whether you are riding the wave (like a surfer) or crashing into it.
True, but the physics of water is the same.
Now, what is 100 times more likely than a Tsunami striking the sailboat is a ROGUE WAVE.
Tsuanmis in the open ocean are harmless and barely detectable waves. The difference is that unlike shallow surface waves, includiing the 50 footers that can happen in severe storms, a tsunami consists of bulk motion of the entire ocean, going down to the bottom. When the wave travels into shallow water, because of conservation of mass, it becomes an enormous wave that can reck havoc along the coast.