40 knots is already nasty on cruise ship. In this size boat you'd be praying to get home alive, let alone undamaged.

Yeah, you are right, I was mainly thinking about swell, which can sometimes be quite important, while local wind isn't particularly strong. Beaufort scale is more a wind scale than a swell scale, my apologies for using it. I don't think big waves are that problematic to navigate with a speedboat if the period between two waves is long enough, but I don't think foiling would work with that kind of sea. Since I used to live in an area where such conditions were relatively frequent, I was wondering how well the Candela could handle them.

My boating skills aren't that fresh anymore, despite living on one during my childhood, and spending a good chunk of my youth close to the sea. I might thus misremember or exaggerate things, but I am fairly confident of the above.

You're not wrong, but also the minimum foiling speed for this particular boat is listed at 17 knots. If you're navigating a speed boat through rough seas at 17 knots you're a braver person than I am for sure. :o)

Below that it seems to me like it behaves more or less like a regular boat. Regardless, I'd probably avoid speeds above 10 knots if I found myself in relatively high seas, and I'd just avoid going out in that kind of boat altogether if I had the option. If you do find yourself in that kind of sea though my experience is that most swells tend to come from one direction so you can find a good bearing surf the waves, zig-zagging if need be. Adjusting speed as need be is crucial in rough seas for sure.

It does have a reasonable draft without the foils extended it seems, 1 meter, and at 2.4 meters wide it seems like it could be pretty stable actually. It'll be interesting to see once my buddy gets his delivered.