Able Bodied Seaman - Rules of the Road Practice Test

Inland sound signals for overtaking are about clearly communicating your passing side. A single short blast is the signal you give to indicate you intend to pass the other vessel on its starboard side (your right). This lets the other vessel know which side you plan to pass on so you can avoid a collision. If you intended to pass on the port side, you would use two short blasts. The other described actions, like changing course to starboard or leaving berth, aren’t conveyed by a single short blast in this overtaking context.