The accused, including a minor of 14, attempted to hijack the 47,000-dwt Torm Kansas (built 2006) and Zhong Ji's 46,000-dwt chemical carrier Zhongji No. 1 (built 2008) in November, 2013.
They had been released last year by the Danish government and promised compensation of DKK 19,600 ($3,247) for delays in bringing them to court.
Judge Mohan Niranjit Burhan rejected the defence's argument that the nine accused were merely fishermen.
“There was no fishing equipment or deep freeze on board the whaler to indicate that the accused were genuine fishermen,” he said.
All three counts of piracy of which they were convicted carry a maximum prison sentence of 30 years and a fine of almost $75,000.
But Burhan sentenced the eight adults to 14 years and the juvenile to three years.
Time served would be deducted from the jail terms.
