Just as lights play a significant role in understanding what other boats are doing, so do sounds. Understanding what you hear is another step towards being a "complete mariner". Virtually every boat is required to have some sound producing device. There is a great deal of latitude in what type of sound making device you choose, but loud is good!
Equipment for Sound Signals is based on the length of your boat as follows.
- Boats less than 39.4 feet in length - must carry an efficient sound producing device. In general, this may be a bell, whistle, or air horn. Though guns--even pots and pans--can make a suitable sound signal useful in getting attention in an emergency, you should always carry the appropriate equipment.
- Boats at least 39.4 feet to less than 65.6 feet in length - Must carry a whistle and a bell. The whistle must be audible for 1/2 nautical mile. The mouth of the bell must be at least 7.87 inches in diameter.
When and How to Sound Off
Sound signals are to be used only when vessels are in sight of each other and are meeting or crossing at a distance within half a mile of each other. These signals must never be used in fog or other conditions of reduced visibility, where the vessels are not visible to each other by eye. Only the fog signals listed under the Inland Rules, Rule 35 may be sounded at such time.
Sound signals are called "blasts". There are two different blasts used for warning and steering signals.
- Short Blast - Lasts about one second.
- Prolonged Blast - Lasts from four to six seconds.
There are different blasts combinations for various movements on the water that may use both short and prolonged blasts. When power-driven vessels are in sight of one another and meeting or crossing at a distance within half a mile of each other, each vessel underway, when maneuvering as authorized or required by the Inland rules must use the following sound signals.
- One Short Blast - This means that you "intend to leave you on my port side" if you are meeting or crossing another vessel. In other words, when you pass the other boat, the left side of your boat will be next to the other boat. If you are behind another boat and about to pass it, one short blast means that you "intend to pass on your starboard side."
- One Prolonged Blast - This means you are leaving a dock or departing your slip. It signals to others a change in status and that you are getting underway. A prolonged blast is also sounded when a vessel is approaching a bend in a river where vessels coming from another direction cannot be seen. It is sometimes referred to as the “blind bend signal".
- Two Short Blasts - This means that you "intend to leave you on my starboard side in a meeting or crossing situation." In other words, when you pass the other boat, the right side of your boat will be next to the other boat. If you are behind another boat and about to pass it, two short blasts means that you "Intend to overtake on your port side."
- Three Short Blasts - This means that you are backing up, or using "astern propulsion."
- One Prolonged Blast + Three Short Blasts – This is technically two different signals in succession. One prolonged blast indicates you are getting under way, and three short blasts indicate you are backing up. This is what is sounded when you are departing a dock in reverse.
- Five Short Blasts - This is the DANGER signal. Remember, that when you approach another vessel and hear either one or two short blasts, and you both understand their signal and can safely let them do it, then you are required to respond with the same signal in response. However, if you don't understand their intentions, or feel that their proposed maneuver is dangerous to either vessel, then you are required to sound the DANGER signal.
Note: Inland Rules regarding sound signals are occasionally different from International Rules. Inland Rules signal intended action and International Rules signal what you are actually doing. The following information reflects Inland Rules. If you travel overseas, you must learn the International Rules.
Proper Sound Signals
Passing Port to Port
When you meet an oncoming vessel, and wish to pass port to port, you are required to sound one short blast with your horn. If the other boat is in agreement, they should respond with a similar blast.
Passing Starboard to Starboard
If you approach another vessel head on, and wish to pass it on its starboard side, you are required to sound two short blasts with your horn. If the other vessel is in agreement, they should sound the same signal in response.
Overtaking on Portside
When you are planning on passing another vessel from behind, there are several things you must do. Any vessel that is overtaking another must keep out of the way of the vessel being overtaken. This means that you can't expect them to move, slow down, or change their course. If you plan on passing them on THEIR starboard side, you must sound one short blast. If they understand your signal and agree, they will sound one short blast in response. The vessel being overtaken has a responsibility to maintain course and speed in order to minimize the potential for collision.
Overtaking on Starboard
When you are planning on passing another vessel from behind, there are several things you must do. Any vessel that is overtaking another must keep out of the way of the vessel being overtaken. This means that you can't expect them to move, slow down, or change their course. If you plan on passing them on THEIR PORT side, you must sound two short blasts. If they understand your signal and agree, they will sound two short blasts in response. The vessel being overtaken has a responsibility to maintain course and speed in order to minimize the potential for collision.
Note: These are not the only rules concerning sound signals in restricted visibility; there are additional rules concerning sound signals that may be found in the Rules of the Road or in Chapman's Piloting.