GRAND RAPIDS, Mich. (AP) _ A federal investigation continues in the disappearance of a West German captain from his freighter in Lake Michigan, and one marine superintendent says it was unlikely he slipped overboard.

''Falling off a ship is not that easy,'' said Peter Hahn, who met Capt. Frederich Helling when the freighter Sirius made its first stop in Cleveland after leaving Antwerp, Belgium, nearly two weeks ago.

''The ship is surrounded with the high rails that go at least to your belly button,'' Hahn said. ''Someone would have to lift him over ...''

Hugh Goldie, vice president of World Shipping, the Sirius shipping agent in Cleveland, said Helling didn't appear to be preoccupied or bothered by anything.

''There was nothing out of the ordinary that I could see,'' Goldie said. ''He didn't complain about the ship. He didn't complain about the crew. He was basically no different from any other skipper I meet.''

U.S. Attorney John Smietanka in Grand Rapids said Sunday that nothing has been ruled out - accident, suicide or homicide - in the skipper's disappearance.

''It appeared he was a fairly well-liked captain - there was no apparent unhappiness with his crew members,'' Smietanka said.

Helling, 48, a resident of Buxtehude, West Germany, was reported missing early Wednesday as the ship moved through northern Lake Michigan from Chicago en route to Duluth, Minn.

The Sirius and U.S. Coast Guard boats searched until dark Wednesday.

The freighter continued on to Sault St. Marie, Mich., where FBI and state police searched the ship and interviewed 10 of the 35 crew members Thursday and Friday, Smietanka said.

The FBI boarded the ship shortly after it entered the Duluth Harbor about Saturday to interview the rest of the crew. The FBI joined the investigation because in some cases it has jurisdiction over crimes on the Great Lakes.