Need to be able to type on a computer and not have your coke on your desk tip over. Some small smooth motion is tolerable. The level of Acceptable Motion depends on your application, but should generally be based upon or exceeding the standards for Off-shore Accommodations established for industries such as oil rigs and deep sea drilling.
Another factor is Whole-body Vibration
Working and/or living onboard offshore installations imposes a series of generally low-frequency mechanical vibrations, as well as single-impulse shock loads on the human body. Low-frequency vibrations are also imposed by installation motions, which are produced by the various sea states. These motions can result in motion sickness, body instability, fatigue and increased health risk aggravated by shock loads. Some shock loads may be produced by wave “slamming”. Floating installations with unusual hull forms may be particularly susceptible to certain wave frequency motions. Higher-frequency vibration influencing comfort is often associated with rotating machinery. The imposition of higher frequency vibrations (about 1 to 80 Hz) induces corresponding motions and forces within the human body, creating discomfort and possibly resulting in degraded performance and health (ABS GUIDE FOR CREW HABITABILITY ON OFFSHORE INSTALLATIONS FEBRUARY 2016)