Govt. report: Shiretoko tour boat sinking caused by partially open hatch

The Japanese government's Transport Safety Board has issued a report on the cause of the fatal sightseeing boat accident off the northern main island of Hokkaido in April. It says that the boat sank because it was flooded with seawater that had entered from a hatch which had not been closed completely.

The "KAZU I" with 26 people on board sank off Shiretoko Peninsula. Twenty people have been confirmed dead and six others remain unaccounted for.

The report says damage on the boat's bottom had not extended to the interior.

It points out that the latch of the hatch cover on the forward deck had worn away. It also says there was testimony that the hatch couldn't be fully shut during training two days before the accident.

Investigators believe the hatch opened as the boat swayed, allowing a huge amount of seawater to flow in.

They say the entire vessel was flooded because there were holes in three bulkheads, which separated the two below-deck holds from the engine room. If the bulkheads had been intact, the sinking could have been prevented.

Investigators also believe the hatch cover flew off and shattered the front window of the cabin, letting in more seawater and speeding up the sinking.

Phone conversations between the boat's captain and his office, as well as between passengers and their families, reveal the boat was flooded in about 20 minutes.

The board suggested that the transport ministry consider inspecting hatches of tour boats and making bulkheads watertight.