Some time later, one of them made a frantic 911 call on his cell phone and said the boat was taking on water - but the call went dead within seconds, before rescuers could pinpoint it.
The boys have not been heard from since.
On Monday, as a helicopter-and-boat search for the boys entered its third, fruitless day, hopes dwindled on City Island, the modest maritime neighborhood of quaint storefronts and seafood houses where the boys were last seen.
"I keep looking out the window - just hoping, I guess," landscaper Jack Harris said, looking out across icy Long Island Sound at Hart Island, where authorities believe the boys were headed.
The boys, who had gone to a party Friday night on City Island, were last seen toting a guitar and boat oars. Family members said the four New York City friends - Charles Wertenbaker, 16; Andrew Melnikov, 16; Max Guarino, 17; and Henry Badillo, 17 - planned to form a band.
On Saturday, Wertenbaker's family found the guitar in a cemetery on City Island, and police search dogs traced their scent to a City Island marina, where an 8-foot dinghy was reported missing. The find led police to believe the teenagers tried to row to neighboring Hart Island.
Their apparent destination, less than a mile across the sound, is a colorful place. Some 800,000 bodies are buried there in a potter's field, and abandoned missile silos are scattered around.
"This is all very sad," said Kathy Devlin, who was walking her dog on City Island on Monday. "Kids do silly things, but I never heard of anyone taking a boat like that out on a winter night like Friday."
The temperature was in the teens Friday night on City Island, which is joined by a bridge to the rest of the Bronx. The water was 33 degrees.
The 911 call came through about 10 p.m., but went dead after 12 seconds. Police Commissioner Ray Kelly said that was only long enough for the caller to say the boat was taking on water in Long Island Sound - off of "City I."
The dispatcher entered the call into a log, but did not have specific enough information to send rescue crews to the scene, Kelly said. Still, he said, police procedures say the operator should have notified the police harbor unit anyway.
"Obviously, this is distressing news to the family members," said Kelly, noting that internal affairs investigators are reviewing the case.
The nearest boat or helicopter could have arrived in about 20 minutes, Kelly said. Still, department officials said an immediate response might not have been enough; without lifejackets, they said, the boys would have slipped below the water in less than 20 minutes.
However, Coast Guard Petty Officer Michelle Krupa of the New York Search and Rescue team said people of average build wearing street clothes in roughly 30-degree water should have been able to survive at least 30 minutes and perhaps as long as two hours.
Krupa said it was possible the boys' bodies were trapped beneath ice or deep below the surface because corpses typically sink in cold water.
City Island is lively in the summer, when it is full of tourists who dine at crab shanties and browse its nautical museum. In the winter, it is a still, tight-knit community of tidy bungalows.
Since Saturday, though, the island has been alive with rescue activity - police boats bearing scuba teams, helicopters, Coast Guard crews and scores of concerned City Island residents.
"We're trying to keep hope," said Paul Wesley, a Transportation Department worker regularly stationed on the island who is helping the search. "It's been a long time."