The vessel sank during a fishing trip in 2016, leaving Carmen's mother, Linda Carman, missing and presumed dead. Carman has denied doing anything to intentionally make the boat unseaworthy. He told the Coast Guard that when the boat filled quickly with water, he swam to the life raft and called for his mother but never saw her again.
The judge found, among other things, that shortly before the fishing trip, Carman, of Vernon, Vermont, made improper repairs to the boat. Witnesses testified that he removed two stabilizing trim tabs from the stern, near the vessel's waterline, leaving holes that he tried to seal with an epoxy stick.
"The removal of the trim tabs and the faulty repairs rendered the boat unseaworthy and in poor condition," the judge wrote. "Having four holes in the back of a boat lends itself to taking water on. It is more likely than not that this improper repair at least indirectly caused water to fill up the bilge, causing the boat to sink."
Messages seeking comment were left Monday with Nathan Carman's attorneys. The younger Carman was found floating in the raft off the coast of Martha's Vineyard, a Massachusetts island, by the crew of a freighter eight days after the boat was reported missing.
During the civil trial, witnesses presented evidence calling into question where and when the boat went down. Charts showed the raft would not have floated to Martha's Vineyard from the spot Carman claimed the boat sank, an expert on tidal patterns said.
Carman's attorneys argued that this was the first time he had used sea charts and that he was confused about its exact location. Relatives have accused Nathan Carman of killing his mother and his grandfather, John Chakalos, a wealthy real estate developer who was shot in 2013, in a scheme to inherit $7 million that Chakalos had left to Linda Carman.
Nathan Carman has been named by police as a "person of interest" in the killing of Chakalos, who was shot in the head at his Windsor, Connecticut, home. No criminal charges have been filed, and both deaths remain under investigation.
Attorneys for three of Nathan Carman's aunts have said bullet fragments from the shooting could have been fired from a missing Sig Sauer rifle that Nathan Carman bought weeks before his grandfather's death.
A lawsuit the family filed in New Hampshire, where Chakalos also had a home, was dismissed this year on jurisdictional grounds. That case is now before New Hampshire's Supreme Court.