A South Carolina man was killed on the Beltway early yesterday when he was struck by a motorboat flung from a trailer of a car that had collided with a van halted in the middle of the highway, police reported.

Eighteen-year-old Stewart Chinn, Jr. of Greenwood S.C. was struck by the 15-foot motorboat as he stood in the northbound lane of I-495 at U.S. 50 at 6:50 a.m. He died a short time later.

Four other persons were injured in two separate accidents at that location.

Police said Chinn had pulled his car to the side of the road after a friend's car was struck by a camper.

Rachel Connor, 20, and Curtis White, 27, both of Greenwood, suffered minor injuries in that accident.

A van approaching the scene of the accident stopped in time to avoid hitting Connor's car, but a car driven by Conrad Kalkiewicz, 28, of Columbia, S.C. and towing a boat did not stop in time and slammed into the van.

The boat was thrown loose and hit Chinn and his 16-year-old sister, Ida Mae Chinn. She suffered a concussion and a broken leg. Kalkiewicz, who apparently did not know the other South Carolina travelers, suffered a broken arm in the accident.

The passengers of the van and the camper did not require hospitalization.