What Sound signal that is required of a power boat that has run aground during periods of restricted visibility?

A power boat that has run aground during periods of restricted visibility is required to sound a prolonged blast on its horn for about four to six seconds at intervals of at least one minute. This signal alerts other vessels to its presence and indicates that it is not able to maneuver. Additionally, the boat may also display the appropriate day shapes, such as a ball shape, to signal its situation.