What sound signal is indicated for an aground vessel?

The sound signal for a vessel that is aground is three bell claps followed by a whistle. This specific signal is intended to indicate a situation where a vessel is stuck on the bottom and may require assistance. The use of the bells and whistle is a means of communicating to other vessels that the aground vessel is in a vulnerable position and alerting them to navigate with caution in the area to avoid potential collisions. Sound signals like this are crucial for ensuring maritime safety and awareness among vessels in close proximity.

Other options do not correspond to the correct signal for an aground vessel. For instance, five short blasts are used to indicate doubt or to signal the intention to reach a closer area with caution. Firing a cannon is not a recognized sound signal within the COLREGs framework and does not serve the purpose of communicating the status of an aground vessel. Two long blasts typically indicate an intention to leave a dock or a similar maneuver, which is irrelevant to the context of a vessel being aground. Understanding these specific sound signals is essential for mariners to communicate effectively and maintain safety on the water.