Many of the passengers would suffer extreme injuries from the changes of velocity (up to 230 mph based on a loop radius of 3 x ship length) and rotation (unlike rollercoasters, or even airplanes during simple take-off and landing, passengers aren’t normally strapped down).
Next try to calculate what it would actually mean to make that much water follow a path like that. My guess is, it’s going to get very spicy.
The xkcd explained brushes near it.
Can’t you just tell them to hold on to something?