Is there a common protocol for helicopter ditchings? What I mean is -- when there is enough time to know the ditching is inevitable during an auto, is it common practice to tell pax to unlatch seatbelts and brace? Maybe even open the doors (if possible)?
If the pax unlatch seatbelts then, unless the impact is anything but gossamer-light, they will be thrown around the cabin (or even out of it) injuring themselves and possibly you and then risk being swept away from an open door and trapped in the cabin as the aircraft rolls upside down and fills with water.
Stay strapped in and wait for the violent movement to cease before releasing your seatbelt and escaping (if you have kept a hand holding on to something that will help you find your exit).