They are indicating dangerous
From the USCG Navigational Rules of the Road (International and Inland.)Rule 34Maneuvering and Warning Signals(d) When vessels in sight of one another are approaching each other and from any cause one fails to understand the intentions or actions of another, or is in doubt whether sufficient action is being taken by the other to avoid collision, the vessel in doubt shall immediately indicate such doubt by giving at least 5 short and rapid blasts of the ships whistle.
When vessels in sight of one another are approaching each other and from any cause either vessel fails to understand the intentions or actions of the other, or is in doubt whether sufficient action is being taken by the other to avoid collision, the vessel in doubt shall immediately indicate such doubt by giving at least five short and rapid blasts on the whistle
One prolonged blast followed by two short blasts every two minutes is a sound signal used by vessels in fog or low visibility conditions. This signal indicates that the boat is under way and making way through the water. It serves to alert other vessels in the area of its presence and movement to help prevent collisions.
there is a dangerous situation
A short blast on the whistle to indicate intention to alter course to starboard (right) or two short blasts to alter course to port (left). This is commonly used by vessels when navigating in a narrow channel to communicate their intentions to other vessels in the vicinity.
Sailboat
Two short horn blast from a vessel means that she is turning port and one short horn blast that she is turning starboard
they are indicating a dangerous situation exist
on short blast
Five short blasts from another vessel's horn typically signal danger or an uncertain maneuver. It serves as a warning to nearby vessels that the signaling vessel is unsure of the other vessel's intentions or is indicating a potential collision risk. In maritime communication, this signal emphasizes the need for caution and awareness in navigating close quarters.
A. Three prolonged blast of the ships whistle or general alarm at an interval of three means a man overboard. This is dismissed by three short whistle blast.B. Three Short blast can also be Rule 34 "Maneuvering and Warning Signals."Three short blast means "I am operating astern propulsion."