Recent news items and an everyday question asked by Florida residents to law enforcement regards the carrying of self-defense weapons, specifically firearms, on sailboats, yachts and other seaworthy craft capable of entering international waters. Legal authorities are regularly asked what the legal implications are and what laws and accepted rules are in place for this.
The answer? Well, it's complicated. Legally, it's far easier not to have a firearm on your boat. That's just how it is. Sadly, many legal issues we might take for granted as Floridians and Americans are nonexistent or so confused as to be generally ignored once a vessel enters international waters.
To understand the legalities surrounding firearms carriage on seagoing vessels, we have to first look at maritime law. Then we have to look at international law. Then national laws. Then state-specific law. Like I said, it's complicated.
Maritime Law
We begin with the overarching law of the ocean referred to as Maritime Law (also called Admiralty Law, the Law of the Sea, etc). Our modern international maritime law is rooted in United Nations agreements, which themselves are largely made up of generally accepted rules of the sea that were created by tradition over time. Specifically we're talking about the United National Convention on the Law of the Sea.
On the open ocean, in international waters (defined as anything beyond 12 miles from the nearest coastal point of a nation, but more clearly as anything beyond 24 miles of the nearest coast) the law to be enforced on the boat is the law of the boat's flag of origin. In other words, a vessel flying a United States flag of stars and stripes or other recognized U.S. maritime flag (e.g. the Yacht ensign) are subject to the laws of the United States. Legally this means that the ship is registered to the country whose flag it flies and carries paperwork to that effect. So merely flying the flag of a nation on a boat is not necessarily indicative of that ship's true nation of origin or registration (if any).
Thus a vessel flying the American flag (legally) in international waters may carry any firearm allowed by U.S. federal law as well as legal ammunition to go with it. This, however, is only true in international waters. Obviously, a ship must go to port sometime.
International Law
The short of it is that a vessel entering the protected waters (coast) of a nation becomes subject to the laws of that nation once it does so. By law, the protected (or "owned") coastline of the nation begins at 12 miles from the nearest coastal point. In practice, it can extend as far as 24 miles from that nearest land point, with the interim 12 miles being a sort of contended zone that may or may not be upheld by international court. Most captains operate on the 24-mile rule of thumb.
So for an American vessel entering the coastal waters of Mexico, the vessel, despite the U.S. flag, is now subject to the laws of Mexico. Currently, those laws prohibit firearms except by special permit and with some exemptions (such as the ship's emergency flare gun).
National Law
At this point, obviously, knowledge of the laws of the areas you'll be sailing to and from as well as all points between is important and is what makes things so very complex. A firearm may be legal in one area, but you may pass through other areas where it's illegal in order to get there. A good example is on our other coast up north, where travelers from the U.S. mainland to Alaska pass through Canadian jurisdiction and thus must declare weapons on board or face harsh consequences if caught.
In some places, all that is required is a registry of the firearms and ammunition on board and certification (subject to inspection) that those weapons are safely locked away. In other places, no provision is given for the carriage of firearms at all. In still others, only specific types of arms are allowed.
State-Specific Law
Even just sailing along the U.S. coasts, whether from Florida to New York or to Texas, territorial law changes as you leave and enter each states' jurisdiction. The firearms laws here in Florida, for example, are far more lax than are the laws in New York. While enforcement may be more or less lax along the way as well, the law is the only thing that can be truly counted on when moving from one jurisdiction to the next.
Conclusions
So putting all of this together, we can see that the laws surrounding firearms on seaworthy vessels are very complex. There are some ways around some of them and no way around others. This is why, for the most part, yachts plying international ports often carry no weapons beyond their flare guns or employ non-lethal, accepted weapons such as water cannons or the like as these are generally accepted without restriction in most parts of the world.