Understanding the boundaries of waterways is important when it comes to what laws apply to the specific area. If you have an incident, you must know which government has jurisdiction over it.
While there is a general rule, it does not always apply. So, you will also need to understand the different exemptions as well as the basic law.
The basic boundary line of US waters is 12 nautical miles off the coast of US-owned land. Anything beyond that is international waters. But that rule does not always apply as there are some exemptions.
Exceptions to the rule
The main exception to the international water boundary line is that jurisdiction for legal matters extends beyond that. Countries can impose their laws 24 nautical miles from their coastline.
Another important exception is that each country maintains control over its own vessels. So, a US ship would remain under US law no matter where it goes.
Because of these exceptions, the line of where international law starts becomes blurred. There is not always a cut-and-dry answer when inquiring which laws would apply in a given situation. Sometimes, it requires ironing out the details in court. In the US, there are even situations where state and federal laws collide, which also require some legal work to figure out.
Maritime legal situations can be difficult. To avoid issues, US vessels should focus on following US law, which usually will keep them out of trouble, even if they are in international waters. When all else fails, the matter usually goes to court where skilled professionals will figure out the jurisdiction.