While Calvin drowned, Santhia, Aruldass, Sinnasi and Devoss in the boat were rescued by fishermen of another boat in the sea, they said.
The boat broke into two pieces under the impact of the collision.
The rescued fishermen alleged that their motor-fitted boat was hit by an Indian Coast Guard ship, which was patrolling in the sea. The ICG ship did not stop after the incident and continued its patrolling, they told the police.
However, Coast Guard Commander Harish Morre disputed the allegation of the fishermen. "Our ship is not involved in the mishap", he said.
A search was on to trace Calvin's body, police said.
Meanwhile, a large number of people here blocked traffic on the Pamban bridge demanding action against those who were in the ship at the time of the incident.
Two fishermen were killed when a ship collided with their boat off Kerala's Alappuzha coast on March one.