A floating object that appeared to be a 5-foot-long, barnacle-encrusted torpedo was spotted by a Maui dive boat before it drifted away somewhere inside the Hawaiian Islands Humpback Whale National Marine Sanctuary.

"It was obviously a navigational hazard," said Jeff Strahn, general manager of Maui Dive Shop. "We've never seen anything like this."

The Navy, in a brief statement yesterday, said that "based on the photograph provided by the Coast Guard, this item is nonexplosive and poses no hazard to the public or marine mammals. The device is a mobile target that is used for training purposes. Should the Coast Guard locate the item, the Navy is ready to support efforts to recover it."

The crew of the 48-foot Maka Koa dive boat nearly hit the object Thursday morning in calm water about six miles offshore, said a visitor onboard, John Ness, an experienced scuba diver from Seattle.

Ness first spotted the object while the Maka Koa was about halfway toward its first Lahaina dive site and alerted the captain.

"I hollered at the captain to turn the boat," Ness said. "I didn't want him to hit it. We missed the torpedo by 10 feet. ... The disconcerting thing is (the Coast Guard) didn't find it."

The crew of the Maka Koa tossed a bodyboard into the water to mark the object's location, Strahn said. The captain radioed the Coast Guard around 8:15 a.m. and gave the boat's global positioning system coordinates, Strahn said.

A Coast Guard helicopter and a 110-foot cutter searched the waters in the Olowalu region for 2 1/2 hours without finding the object, Petty Officer 3rd Class Angela Henderson said.

The Coast Guard then passed its information to the Navy.

"It's the first I've ever heard of an actual torpedo being seen in the sanctuary," said Jeff Walters, co-manager of the 1,400-square-mile Hawaiian Islands Humpback Whale National Marine Sanctuary.

"If it's just floating like that, whales don't typically just blindly run into things. They typically have good sight."

But juvenile whales and calves like to play with new things in the water, Walters said.

If the object should turn out to be live ordnance, Walters said, "there is a remote possibility that something bad could happen if they go up and touch it to see what it is."

The captain of the Maka Koa told Strahn that the crew and passengers saw a "torpedo-shaped object with a blunt nose and a halo ring around the tail, where you would have a prop on it," Strahn said. "It had a plate on it but they were unable to read it. They didn't want to put someone in the water next to live ordnance."

The Maka Koa had left Ma'alaea Harbor around 7 a.m. with a captain, three divemasters and 21 customers on board for a two-tank dive off Lanai, Strahn said.

Reach Dan Nakaso at dnakaso@honoluluadvertiser.com.