LAKE GEORGE, N.Y. — Federal investigators raised new concerns yesterday about modifications that added weight to a tour boat that capsized and sank Sunday, killing 20 people.

In 1997, the boat's canvas top and vinyl windows were replaced with a wood and Fiberglas top and Plexiglas windows, said Mark Rosenker, acting chairman of the National Transportation Safety Board (NTSB). A larger engine was installed about five years ago, and investigators found seven lead bricks in the boat's bow to help keep its balance, he said.

"Definitely if you increase the overhead weight you are going to affect" the boat's ability to right itself, said David Smith, an expert in maritime safety and retired U.S. Coast Guard commander from Ann Arbor, Mich.

Today, using the twin of the boat that capsized, federal investigators will simulate the accident. Investigators will conduct a "very scientific road test" that examines speed, weight distribution and stability of the Ethan Allen boat using its twin sister, the de Champlain, Rosenker said.

Both boats, owned by Shoreline Cruises of Lake George, are 38 feet long and rated to carry 50 people. For the simulation, investigators will put the equivalent weight of 50 passengers weighing 160 pounds each aboard the de Champlain.

"We're going to learn a lot by using this vessel," Rosenker said. "The top of the vessel is virtually identical, and the hull is identical. That will be enough to give us what we need to know."

In other developments yesterday, state officials said the boat's owner faces a fine of up to $250 and 15 days in jail for not having a crew member aboard the Ethan Allen, in addition to its captain, when the accident occurred. State regulations require the boat to have at least two crew members aboard when it is operated with more than 20 people.

Rosenker said the NTSB also was studying whether to increase the average weight that older vessels use in calculating how many passengers to allow. When the Ethan Allen was built in 1966, the formula was based on an average weight of 140 pounds. "Clearly people are a bit heavier today," Rosenker said.

Material from Newsday is included in this report.