In a narrow channel an overtaking vessel which intends to PASS on the other vessel's port side would sound..?

In a narrow channel, an overtaking vessel intending to pass on the other vessel's port side would sound one short blast of its horn. This signal indicates the intention to overtake on the left side. The vessel being overtaken should then respond with a signal to indicate it has acknowledged the maneuver, typically by sounding one short blast in return. Proper communication is crucial to ensure safe navigation in confined waters.