Published: Oct 03, 2011 9:47 PM EDT

NAPLES, Fla.- Sunday night around 7 p.m., Capt. Dan Mercier, Jr. of Sea Tow Naples and his brother and Mate Chris Mercier were returning from patrolling the Gulf Coast waters north of Marco Island, Florida, when a distress call came over the VHF radio.

“The caller was screaming, ‘We need help; we’re sinking; we’re off Keewaydin Beach,’” Capt. Dan Mercier, Jr. said. “Then we lost contact.”

The Sea Tow Captain immediately relayed the distress call to the U.S. Coast Guard; then used his knowledge of the local waters to search for the sinking vessel. He and his brother quickly located the chaotic scene, a 22-foot deckboat was submerged to the gunwales in the Gulf of Mexico about a mile and a half off Keewaydin Island in Naples. A family party of 21 people, ranging in age from toddlers to grandparents, some without life jackets, was in the water around the sinking boat. The seas were rough; about two- to four-feet in height, and the sun was setting.

“I have been on cases with people in the water before,” said Capt. Mercier, 25, “But with this many people in these kind of seas, it was mayhem.”

The Sea Tow boat was the first responder to arrive on scene. Capt. Mercier and his brother were ready with spare life jackets, which Chris, 23, tossed to survivors in the water. As Capt. Mercier maneuvered the Sea Tow Naples towboat, a 26-foot Goldline with twin 150-hp Mercury Verado outboards, the mate began pulling children and women out of the water to safety.

“We were just picking them up out of the water like apples,” Capt. Mercier said. “At the time, I didn’t know how many there were. Then I counted heads and saw I already had 17 people in my boat.”

In danger of overloading his own vessel, he ran over to the Marco Island Princess, a 90-foot dinner- cruise boat that also had responded to the emergency. Unable to get into the six- to eight-foot-deep area where the sinking boat was located, the Marco Island Princess stayed on station about 300 yards away. Capt. Mercier and his brother transferred the 17 survivors to the waiting vessel, then raced back to the scene.

Four people were left in the water clinging onto the submerged deckboat, including an elderly grandfather, apparently unable to swim, who was in danger of drowning. By that time, a Good Samaritan boat also had arrived at the stricken vessel. Chris, a firefighter-in-training, jumped into the water and with the help of Capt. Mercier and the Good Samaritans, managed to get the grandfather safely into the Sea Tow boat. After that, it was only a matter of minutes to rescue the remaining survivors, including deckboat’s owner—whom they learned had recently purchased the vessel.