This video dramatically illustrates what happens when you ignore them.
The Collision regulations started developing in 1972 to help prevent situations like this one. They have been expanded and improved over time to cover practical situations that have occurred. In collision situations, they determine what actions each vessel involved is required to do, and must be followed by everyone, regardless of vessel size or propulsion method.
In each case, one vessel, called the stand on vessel, is required to hold their course and speed and the other vessel, called the give way vessel, is required to take action to avoid collision. The reason it is structured this way is to avoid having both vessels take action and end up turning towards one another, making the situation worse. Regardless of whether you think you’re in the right, it’s everyone’s responsibility to take all actions necessary to avoid a collision!
In the video above involving the yacht Atlanta of Chester and the freighter Hanne Knutsen, obviously someone made the wrong decision. According to the collision regulations, the Atlanta of Chester is the vessel at fault in this situation. One of the many things that she did wrong was that she did not follow rule 17.
Rule 17 is an excellent place to start when learning about the collision regulations. This rule explains that if the giveaway vessel fails to act, the stand on vessel must act to avoid a collision. Even if Atlanta of Chester thought they were the stand on vessel, they still had to act to avoid a collision.
Here is a link to a newspaper article describing the incident.
Besides knowing the rules and how to apply them, there are also aids such as sound signals that are used to communicate with other vessels in this situation. The most important one here is 5 horn blasts. This signal tells other vessels in the area that you think their actions are unsafe and that a collision is likely. Here is a memory aid for this sound signal.
Here’s the text from the col-regs document for rule 17:
Rule 17 (Action by stand-on vessel)
(i) Where one of two vessels is to keep out of the way the other shall keep her course and speed.
(ii) The latter vessel may, however, take action to avoid collision by her manoeuvre alone, as soon as it becomes apparent to her that the vessel required to keep out of the way is not taking appropriate action in compliance with these Rules.
(b) When, from any cause, the vessel required to keep her course and speed finds herself so close that collision cannot be avoided by the action of the give-way vessel alone, she shall take such action as will best aid to avoid collision.
(c) A power-driven vessel which takes action in a crossing situation in accordance with subparagraph (a)(ii) of this Rule to avoid collision with another power-driven vessel shall, if the circumstances at the case admit, not alter course to port for a vessel on her own port side.
(d) This Rule does not relieve the give-way vessel of her obligation to keep out of the way.