Four unauthorized modifications caused a mast aboard a tour catamaran off Waikiki in December 2006 to buckle, killing a 13-year-old California boy and injuring three other passengers, according to a Coast Guard report released yesterday.

The Coast Guard also released the results of an investigation into a separate catamaran incident in 2007 off Maui, saying a microscopic crack "on the base of the step" that holds the mast caused that mast to fall, killing a 48-year-old Illinois man when it struck him on the head.

The two catamaran incidents, just four months apart, were investigated together so the Coast Guard could examine its standards for inspecting commercial catamarans. Even before the investigations were completed, the Coast Guard in Honolulu decided to beef up its annual inspection standards, which now include a more thorough examination of catamaran masts.

"We've implemented the procedures here ... (and) there is discussion as to whether these" standards will be adopted nationally, Honolulu Coast Guard Capt. Barry Compagnoni said yesterday.

He added that sightseeing catamarans are "a safe industry."

The first catamaran death happened Dec. 1, 2006, on the Na Hoku II as it returned to Waikiki about 4:30 p.m. after a trip to Mamala Bay. The mast buckled in three places, the Coast Guard report says, because of unauthorized modifications made as far back as 2000.

Those modifications were not detected in Coast Guard inspections as late as April 2006.

When it fell, the mast struck Jordan Loser of Riverside, Calif., pinning the teenager face-down on the cabin top and killing him. A second passenger standing on the front left side of the vessel was struck on the head by falling rigging and knocked out. Two other passengers, in the front of the vessel near the cabin, also suffered injuries: one had a broken foot and pelvis, the other cuts to her shoulder and hand.

There were 23 passengers and three crew members aboard.

In addition to the unauthorized modifications, the Coast Guard report says, the master of the catamaran and one of its crew members tested positive for marijuana immediately after the incident.

The Coast Guard report said it is unclear whether marijuana use affected the crew members' abilities "to respond to changing conditions on-scene in a manner that might have prevented the casualty." Passengers on board the vessel said the two crew members did not appear to be impaired.

The Coast Guard said it plans to pursue fines against the Na Hoku II for its unauthorized modifications, but will likely not pursue fines for the drug use as the master has stepped down and the crew member no longer works for the company. The maximum fine for failing to report a modification to the Coast Guard is $6,500 per modification, a spokesman said yesterday.

In the Maui incident, the Coast Guard said, a microscopic stress crack spurred "catastrophic mast failure" aboard the Kiele V on March 25, 2007, as it was about 10 minutes from Ka'anapali Beach.

Hal Pulfer, 48, of Highland Park, Ill., was hit by the mast and rigging and was later pronounced dead. Two other passengers required medical care, the report said.

The vessel had 47 passengers and five crew members on board. After the mast fell, the catamaran started taking on water. It was abandoned and broke apart in rough seas overnight.

The Kiele V had last been inspected in September 2006 and no problems were found.