Judge JC Jagdale convicted them of conspiracy, attempt to murder and kidnapping under relevant sections of the Indian Penal Code, and those of Unlawful Activities Prevention Act and Arms Act.
The court also imposed a fine of Rs 17,000 each on them, special public prosecutor Ranjeet Sangle said.
It directed the government to deport the convicts to Somalia after they have served their sentence.
The judge, however, acquitted them of charges of kidnapping for ransom where the maximum punishment is death.
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According to the prosecution, Indian Coast Guard Ship (ICGS) Samar was on patrolling duty near Lakshadweep islands where on February 5, 2011 it got a message from its headquarters that a Greece flagged ship MV Chois had come under attack in the Exclusive Economic Zone of India.
Officials saw a small vessel in the area and suspected it could be a pirate ship as it had no lights on and was not moving.
The prosecution said when the Coast Guard saw a skiff coming towards Samar they opened fire at it. The tiny boat moved towards the mother vessel later identified as Prantalaya-11.
Coast Guard officials also directed the Dornier aircraft to carry out search and identify the vessel.
In the meanwhile, the pirates opened fire at Samar, prompting the Coast Guard to fire two rounds from rocket launchers.
Soon the pirates started waving a white flag as a gesture of surrender and threw their weapons into the sea.
The Coast Guard detained the vessel and took custody of 52 persons present of whom 28 were Somali pirates and 24 Thai nationals. One of the Somali pirates died during the trial.
The Navy and Coast Guard had nabbed a total of 120 pirates between January and March 2011.
Till now the court has convicted 57 pirates in three cases, while it is likely to deliver its judgment in the last case next week.
All 119 captured pirates, including the one who died during the trial, had pleaded guilty to charges.