That 2 waves can overlap one and another

Good evening Physicists! I am a bloke from Norway(Please excuse my writing, aint that good on the english language.). And my question to you, is if you can tell me how waves evolve into what most people would call Monster waves, and How high they can get. I have always asked this question when it seemed fit to the right person. I'm a fisherman, and last week I got hit by one of those, of course, not the real large ones. But there was about 2-3 meter swells, and then suddently i couldnt see ANYTHINg but a large wall of sea heading towards me, but somehow it just collapsed a few seconds before it would hit. My guess would be that the 'monster wave' was about 5-6 meters high. So I guess you can figure out how my face looked at that point. It did ofcourse hurt my boat (wich is a 35 fot 'Sjark', its smaller fishing vessels fit for us that doesnt want to spend months on the sea. ) the impact didnt damage the baug, but everything that was nailed to it from the inside, got ripped right off on the impact, don't know how though. But who cares about that, the real question is HOW, and WHEN? My theory is, that 2 waves can overlap one and another, and evolve into one huge wave. I don't know if this is correct though, hope you can help me with this.

Thanks in advance!