Per two statutes, 14 U.S.C. § 89(a)2 and 19 U.S.C. §1581(a), the US Coast Guard has virtually unlimited authority to stop, board, and search vessels without any suspicion of wrongdoing. No warrant required. tl/dr:

Sorry, but when it comes to Coast Guard boardings, you don’t have any rights.

I’m surprised how many boaters don’t know this. The US Coast Guard can board your boat any time they want, and look anywhere they want, without probable cause or a warrant. They can do this on the open sea, or while you’re asleep aboard in your marina at midnight. They can look through your bedsheets, in your lockers, in your bilges, in your jewelry box, or in your pockets. They can do it carrying just their sidearms, or they can do it carrying assault rifles. They can be polite about it or they can be rude, but mostly they’re polite.

If you’re an avid boater you can expect to be boarded every year or two.

I explain this to my guests aboard Condesa, some of whom are lawyers, and I’m met with disbelief: “But that’s a blatant violation of your constitutional rights! They need probable cause, or a warrant from a judge!”

“Not on a boat, my friend, not on a boat.”

The U.S. Coast Guard Boarding Policy:

Title 14 section 89 of the United States Code authorizes the U.S. Coast Guard to board vessels subject to the jurisdiction of the United States, anytime, any place upon the high seas and upon any waterway over which the United States has jurisdiction, to make inquires, examinations, inspections, searches, seizures, and arrests. The U.S. Coast Guard does not require a warrant to conduct search, seizures, arrests over any United States Waterway or high seas. The U.S. Coast Guard also have full legal law enforcement power on any land under the control of the United States, as needed to complete any mission.

Sweeping powers. In a paper in the William and Mary Law Review, law scholar Greg Shelton says, “In terms of enforcement power, Coast Guard boarding officers are clearly America's "supercops."”  Another law scholar, Megan Jaye Kight, says, "As such, these provisions comprise what has been accurately characterized as 'one of the most sweeping grants of police authority ever to be written into U.S.  law.'"

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Why can the Coast Guard search our boats without a warrant or probable cause, when the police can’t search our homes, cars, offices, motorhomes etc.?

It’s always been this way. The same congress that passed the Bill of Rights passed the Revenue Service Act of 1790, which gave revenue cutters the right to search any vessel anywhere in US waters, and any US-flagged vessel anywhere in the world.

Our fledgling nation was strapped for cash, and tariffs were the way to solvency. This was controversial even back in 1790, since many of our gripes against the British, as stated in our Declaration of Independence, had to do with tariffs (see Boston Tea Party). The crews of revenue cutters were allowed to board vessels to make sure they’d paid the tariffs on their cargoes.

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Various parties have challenged Coast Guard boardings and suspicionless searches in the highest courts, but the courts have consistently upheld the Coast Guard’s right to board vessels under the Revenue Cutter Act of 1790, and its subsequent variations.

Part 1: Coast Guard Boardings and Your Fourth Amendment Rights, Part 1

Part 2: Coast Guard Boardings and Your Fourth Amendment Rights, Part 2

Part 3: Coast Guard Boardings and Your Fourth Amendment Rights, Part 3

Part 4: Coast Guard Boardings and Your Fourth Amendment Rights, Part 4: Longer and Legaler

Constitutional analysis: Constitutional Barriers to Smooth Sailing: 14 U.S.C. § 89(a) and the Fourth Amendment