An OMI crewman who blew the whistle on dumping of oil and sludge at sea from the 47,000-dwt tanker Guadalupe (built 2000) has been handed the largest US government reward ever in a tanker case.

Former OMI third engineer Maha Patra received $2.1m of the $4.2m fine assessed against OMI Friday in US District Court in Newark, New Jersey. OMI agreed to a plea deal in response to charges that it had presented false log books that covered up illegal use of its oil-water separator equipment in 2001.

OMI general counsel Frederic London, who attended the sentencing hearing before Judge Katharine S Hayden, said it was determined during the courtroom discussion that Patra’s award amounted to four times the largest previous outlay for a whistleblower in a tanker case – around $500,000.

The 50% cut is standard under whistleblower regulations, which cut across a wide range of industries and are perhaps most prevalent in drug cases.

“While I perfectly understand the government’s reasons for doing it, you worry that it encourages people to report any future problems to the government rather than to us,” London said of the award.

OMI’s fine was as expected under a plea deal reached several months ago, as was its acceptance of three months probation. The government found a bypass hose used to frustrate the intended separation of oil from water to be discharged into the ocean. About 20 discharges took place as the tanker carried out voyages to the US, Europe, Latin America and Caribbean.

“This case should send a message that polluting our environment and lying to the government will not be tolerated,” said Tom Sansonetti, assistant attorney general for the US Justice Department.

London said a second allegation of pollution from an OMI vessel, reported to the company by a crew member while the Guadalupe plea deal was pending, had been investigated and found to be without merit. The government accepted the results of the OMI investigation and no further action is expected, he said.