Updated

Investigators were focusing on excess weight as a possible cause of the boat accident that killed 20 elderly people on a calm, clear day during a sightseeing tour on an Adirondack lake.

Just days before the boat overturned, the Coast Guard began rethinking its per-passenger weight limits to take into account Americans' expanding waistlines.

The current standard, set 25 years ago, assumes a 140-pound average for each man, woman and child.

At the time it flipped over Sunday, the 38-foot Ethan Allen was just under its capacity of 50 people — a figure that was arrived at by using a New York standard that assumes a 150-pound average, authorities said.

On Wednesday, the National Transportation Safety Board (search) was to perform tests to see how the vessel operated by Shoreline Cruises would have handled at various speeds while carrying its maximum load at an average of 160 pounds per passenger.

The tests aim to show what might happen if such weight suddenly shifted to one side, a possible cause of Sunday's accident on Lake George.

Investigators also were to look at excess weight from recent changes made to the boat, such as the addition of a larger engine and replacing a canvas canopy with a wood-Fiberglas design.

"We're going to learn a lot," acting NTSB Chairman Mark Rosenker (search) said Tuesday.

Finally, Rosenker said, a "human factor" test would study the actions of the boat's 74-year-old captain, the only crew member aboard, in the 72 hours leading up to the accident.

The NTSB was to perform Wednesday's tests on the Ethan Allen's twin sister boat — the de Champlain — in what Rosenker called "a very scientific road test."

The 47 passengers were senior citizens from Michigan and Ohio who had come to see the changing fall colors. Of the 27 people brought to Glens Falls Hospital (search), four remained hospitalized Tuesday.

It's not just the Coast Guard that's changing standards to adapt to heavier Americans. After a 2003 commuter plane crash that killed 21 people in North Carolina, the Federal Aviation Administration raised its summertime weight average from 160 pounds per person to 174, including carry-on baggage.

The Coast Guard awarded a contract a few weeks ago to a research firm to determine how increasing the average weight per passenger would affect vessels around the country, spokeswoman Angela McArdle said.

McArdle said the Coast Guard knew the weight requirement has been outdated for some time, but it did not move on the issue until the NTSB warned about the problem after five people were killed when a water taxi sank in Baltimore.

Asked why the Coast Guard did not move more quickly, McArdle said: "It has such wide-ranging implications. You need to address the economic impact on the industry, looking at the scope. It's not something where we can just say, 'Now passenger ferries must carry 20 fewer people.'"

McArdle said it was too early to say when a new regulation would be drawn up or what the new weight standard might be.

James Quirk, owner of Shoreline Cruises (search), said Tuesday he was "shocked and saddened" by the sinking. He refused to answer questions beyond a statement in which said: "This company's been in the passenger boat business for 27 years and until this event we have had a perfect record."