Many bigger boats, including the fleet operated by the Washington State Ferries here, have avoided real practical change by simply revising their vessels’ capacity downward. For example, the ferry boat Wenatchee, previously capable of holding 2,000 people, is now said to hold about 1,700. But while the Wenatchee’s vehicle hold sometimes fills, its passenger decks virtually never reach capacity. It is one of the largest ferries in the world. So the chance that the lowered capacity will ever mean turning away passengers is very low.

(“Some fine examples of what we’re talking about just went down the stairs,” said William H. Matchett, a retired English professor at the University of Washington, lifting an eye from Henry James’s “The Golden Bowl” to nod toward some formidable passengers on the Wenatchee recently. “But this is a big boat.”)

Some larger private boats have also avoided real impact. In Savannah, Ga., ferries that cross the Savannah River had to reduce capacity on paper but expect no real impact because they rarely are full. In New York, the World Yacht and Circle Line cruises, which depart from Piers 81 and 83 in Midtown Manhattan, deliberately operate at about 50 percent of capacity, about 300 people, to make for a roomier, more pleasant experience, said Jason Hackett, a spokesman.

The same has been true for the popular Argosy Cruises that operate in the many waterways around Seattle. Argosy had to reduce capacity on four of its boats, said Maureen Black, a spokeswoman for the company, but still had plenty of room to accommodate its usual customer base. Ms. Black also noted that some other details of Argosy boats would allow for bigger bodies.

“Chairs are armless,” she said.

Not every boat can handle extra pounds so easily. The Coast Guard inspects about 6,000 passenger vessels across the country, and many owners of smaller boats have been scrambling to comply. Rather than concede any capacity, many have chosen to undergo new stability tests to try to prove that they can meet the new weight rules and still maintain the same number of passengers.