I took a jet boat from Hong Kong to Macau during my first and only trip to Hong Kong in the 1970's. There was considerable vibration and it was noisy, but not particularly rough. I remember there was a plaque in the cabin showing who built it and it was an American aircraft company.

Here is a pic of one of the jet boats used today, this one by Boeing. It's possible that it has some similarity to the one I was on 40 years ago . No gambling on the ferry in those days, and probably still not since China doesn't allow.