What sound signal is used by a power vessel that is stopped?

Answer: C — Five short blasts

A power vessel that is stopped and not making way is required to signal its status through sound. According to the COLREGs, when a vessel is at anchor or not under command, certain sound signals are specified to ensure safety and communication with other vessels. For a power vessel that is stopped and not making way, the appropriate signal is five short blasts. This signal indicates uncertainty or warning when the vessel is stationary and alerts other vessels to its presence. In contrast, one prolonged blast is typically used to indicate that a vessel intends to leave a harbor or is alerting its presence in restricted visibility. Three bell claps followed by a whistle is associated with vessels at anchor, signaling their presence rather than their motion status. Lastly, while there are situations where no sound signal might be necessary, specifically in cases where a vessel is at anchor, the specific signal for a stopped power vessel relies on the five short blasts to convey clear communication to other mariners in the vicinity.