PORTLAND – The owner of a bulk cargo ship suspected of illegally discharging its waste oil and bilges while at sea was found guilty in U.S. District Court of failing to maintain records of overboard discharges it made without required pollution control equipment.

The jury verdict against Petraia Maritime Ltd. of Sweden, owner and operator of M/V Kent Navigator, was returned late Thursday.

Two chief engineers of the Kent Navigator had previously pleaded guilty to making false statements to the Coast Guard in an attempt to conceal the oily waste discharges. The two were each sentenced in January 2005 to two years of probation and a $3,000 fine.

The case against Petraia Maritime was continued for sentencing. The maximum penalty for the offense is $500,000 per count, the U.S. Justice Department said.

The investigation began in August 2004 in response to an anonymous tip that the Kent Navigator was discharging wastes at sea in violation of a treaty that limits their oil content to no more than 15 parts per million.

U.S. law implementing the treaty requires use of an oil water separator, a pollution control device intended to prevent oil discharges in excess of that limit.

A Coast Guard inspection of the Kent Navigator when it arrived in Portland found oily residue in piping that led to overboard discharge valves and inoperable pollution control equipment, the Justice Department said.

Investigators found that while at sea, the crew discharged waste oil tanks and bilge tanks directly overboard, and discharged its bilges in a way that circumvented the oil water separator.

The Coast Guard determined that there were 13 discharges over an eight-month period, usually in excess of 5,000 gallons each, resulting in the discharge of “significant” quantities of oil.

To conceal the illegal activity, Petraia employees falsified records to make it seem that the required pollution control equipment was used when the waste was discharged.

Officials said Thursday’s verdict should put members of the shipping industry on notice that they must abide by environmental laws if they intend to enter U.S. ports.

“Vessel operators and mariners should take note that deliberately dumping waste at sea and concealing it from our inspectors is a serious crime, and it simply will not be tolerated by the U.S. Coast Guard,” said Capt. Stephen Garrity, commander of the Coast Guard’s northern New England sector.