The death of a 71-year-old boater while the U.S. Coast Guard was trying to rescue him off Maui in 2015 was probably caused by the boater’s decision to launch and operate a “poorly maintained vessel,” the National Transportation Safety Board has concluded.

An NTSB report of the incident, which was released last month, also described the owner’s last attempts to get his degrading boat into the water off Hawaii island to cross the Alenuihaha Channel and sell his boat on Molokai when he ran into trouble.

Lance Alexander of Hawaii island was being towed by the Coast Guard cutter Kiska in the Alenuihaha Channel between Maui and Hawaii island at about 11 p.m. Nov. 5, 2015. Alexander called the Coast Guard for help because the tiller on his 30-foot recreational boat, Kolina, had broken, and he was adrift during a small-craft advisory with increasing wind and seas of 8 to 10 feet.

The NTSB report said Alenuihaha Channel is known for having strong winds that funnel between the islands and rough seas.

The Coast Guard responded and was towing Alexander, who stayed on his boat because he wanted to monitor a pump since his boat was taking on water.

The tow began at about 10:50 p.m. with 325 feet between the two vessels. The report said the Kiska crew did not have sight of the vessel during the tow because of darkness, the rough seas and the length of the towline.

Trouble began between 10:58 and 11:05 p.m. when the Kiska crew lost radio contact with Alexander. The crew shortened the towline to 100 feet and was able to see that the mast had snapped and was floating in the water.

A helicopter crew lowered a rescue swimmer, who confirmed Alexander was no longer aboard, and the Coast Guard continued searching.

The next morning, the Coast Guard launched another helicopter, a C-130H Hercules aircraft, a boat and the cutter Galveston Island to help search. At 9:17 a.m. the response boat crew found Alexander under the boat, entangled in the mast and rigging. He was about ­ 15 feet below the surface and didn’t have a life jacket on.

The Kolina sank about 10 hours later, in about 10,000 feet of water, swamped by large seas.

An autopsy determined Alexander died of a head injury that occurred before he went overboard, the NTSB report said.

Alexander was an experienced mariner with more than 35 years of sailing but could not swim, family members told investigators.

A Coast Guard report of the incident released in September said Alexander had tethered himself to the jury-­rigged mast while his vessel was under tow, and the mast snapped, causing the fatal injury.

Coast Guard investigators did, however, also fault the rescue vessels, including the commander of the Kiska, for failing to fully assess the situation, including the condition of the Kolina and problems that could arise during the tow.

The NTSB report outlined the dilapidated condition of the Kolina, built in Thailand in 1952.

In the three years before the incident, the Kolina was in dry storage, uncovered, at Kawaihae Boat Park. The manager told Alexander his lease would not be renewed because of the boat’s condition and that the boat would be removed from the park Sept. 30, 2015.

He launched the boat in October and anchored it near the harbor entrance, but the anchorage didn’t hold and he drifted into the channel Nov. 3.