The Tisbury harbor master’s fire patrol boat sank at its Owen Park slip during an early October storm because a deck hatch was left unsecured, according to a loss and damage survey by Marine Safety Consultants of Fairhaven.

“The cause of the sinking appears to be from bilge pump failure after water intrusion into the bilge through [an] unsecured deck access plate,” the report said in part.

The report was released by Tisbury selectmen this week.

The boat, named Rock Salt, is equipped with a self-bailing cockpit, but its watertight integrity was compromised when a deck access plate was left unsecured, the surveyors found.

“On the evening of 10/2/19, this deck hatch was just left sitting in place, with no gasket or fasteners, allowing any water on deck to down flood into the bilge,” they wrote.

Rock Salt was found on the harbor bottom the morning of Oct. 3 by assistant harbor master Will White. According to the report, Mr. White was the last to use the vessel Oct. 2, tying it up at the end of the day.

In a letter to town insurers dated Dec. 5, town administrator Jay Grande wrote that based on preliminary bids, repairs to the boat and its firefighting equipment may add up to more than the vessel’s insured value of $255,000.

“Once repairs commence, it could be determined to be more expensive than what we forecast here,” he wrote.

Depending on what is uncovered during repair work, Mr. Grande said, the town may take the insurance payment of $255,000, plus about $11,326 for salvage work on the vessel, a total of $266,326, and either bid on the boat as salvage or turn it over to the insurance company.