When can a passenger stand or walk on a moving vessel?

Passengers can typically stand or walk on a moving vessel when it is safe to do so, usually during calm weather and when the vessel is operating under normal conditions. However, they should always follow the crew's instructions, especially during rough seas or in situations where the vessel is maneuvering. It's important to be cautious and use handrails when available to maintain balance and safety. Always be aware of your surroundings and the vessel's movement.