Most ski boats have fixed shafts, so they're hopelessly inefficient compared to stern-drive boats. And I've never seen a single-engine ski boat that could top 65 mph... 90 mph is pure fantasy for those boats.

More to the point, skiing at 90 mph is utterly insane. A fall at that speed would involve serious injury.

I've fallen a couple times at 42 to 45 mph, and even wearing a 3/8 inch wetsuit, it felt like my arms were being ripped off my torso. My neck was sore, my chest was sore (both from the impact with the water and the tearing sensation in my shoulders), and my legs were bruised. (What I learned from that was that you need to be going nearly 50 mph to have any chance at all of barefoot skiing, and even if you do manage to plant a foot and it sticks, you're going to fall sooner or later...) I don't even try to ski that fast anymore.

A kneeboard, on the other hand, has a much longer running surface than a waterski does. Most people can kneeboard comfortably at 18 mph. Even someone as heavy as me (240 lbs) only needs to be going around 22 mph to be comfortable. With a lightweight rider, a kneeboard will start to porpoise at around 25 mph. When I was on it I could get up to around 28 mph or so, but any faster and I was flirting with a crash. 90 mph on a kneeboard would be suicide...

So yeah... Your co-worker was full of shit.

Adam