When I was doing my time with the coastal surveillance the coast guard got new inflatable speedboats. They had suspensioned seats etc. When they took the boats to test drive, on a normal weather with light waves one of the coastguards lost grip on his seat and returned with a broken leg.
Those things are nasty at high speed. I took a couple rides with the finnish army transport 'meriuisko' which is a waterjet propelled troop transport capable of doing 40-50 knots.
Only the driver had a seat with suspension and every time we travelled, we were looking at that seat with great envy, getting bruised up in the ride.

It was even worse in the front where you had to go to open space if a full team was aboard. It was fun like a roller coaster for a few seconds, but after a while you wanted to leave.