What does the signal of three long blasts indicate?

The signal of three long blasts is specifically used to signify that a vessel is restricted in its ability to maneuver. This signal is part of the International Regulations for Preventing Collisions at Sea (COLREGs) and serves to alert other vessels in the vicinity that the signaling vessel is unable to change its course or speed due to constraints, such as being towing another vessel or conducting underwater operations.

When this signal is emitted, it communicates to nearby vessels that caution is needed, as the vessel emitting the signal may not be able to respond to potential collision situations like a vessel with full maneuverability. This is crucial for maintaining safety and preventing accidents in busy waterways where vessels with different operating capabilities are navigating.

Other signals, such as those indicating course changes or requests for assistance, have distinct sounds or patterns recognized under the COLREGs, thus differentiating them from the three long blasts used specifically for indicating restricted maneuverability.