Search for 3 missing American sailors off coast of Mexico has been suspended: US Coast Guard

The search for three Americans missing off the coast of Mexico has been suspended, the U.S. Coast Guard said Wednesday.

"An exhaustive search was conducted by our international search and rescue partner, Mexico, with the U.S. Coast Guard and Canada providing additional search assets," Coast Guard Cmdr. Gregory Higgins said in a statement. "SEMAR [The Mexican Navy] and U.S. Coast Guard assets worked hand-in-hand for all aspects of the case. Unfortunately, we found no evidence of the three Americans' whereabouts or what might have happened. Our deepest sympathies go out to the families and friends of William Gross, Kerry O'Brien and Frank O'Brien."

The Mexican Navy and Coast Guard spent "281 cumulative search hours covering approximately 200,057 square nautical miles, an area larger than the state of California, off Mexico's northern Pacific coast with no sign of the missing sailing vessel nor its passengers," the Coast Guard said.

Kerry O'Brien, Frank O'Brien and Gross had not contacted friends, family, or maritime authorities since April 4.

The trio likely encountered "significant" weather and waves as they attempted to sail their 41-foot sailboat from Mazatlán to San Diego.

"When it started to reach into five, six, seven days and we started to get a little more concerned," Kerry's brother Mark Argall told ABC News.

Higgins had expressed concern that the weather in that region worsened around April 6, with swells and wind creating waves potentially over 20 feet high. The three were sailing a capable 41-foot fiberglass boat, with similar sailboats successfully circumnavigating the planet. However, the lack of clear information about the sailors' location, partially attributable to the lack of GPS tracking and poor cellular service near the Baja peninsula, has left the families of the missing Americans uncertain about their loved ones' whereabouts.

"We have all been spinning our wheels about the different scenarios that could have happened," Gross' daughter Melissa Spicuzza said.

Kerry and Frank O'Brien, a married couple, initially decided to travel to Mexico to sail a 41-foot LaFitte sailboat named "Ocean Bound" to San Diego after the boat underwent repairs near Mazatlán, Mexico, according to Argall.

The couple decided to hire Gross, a mechanic by trade and sailor with more than 50 years of experience, to help navigate the boat from Mazatlán to San Diego. Spicuzza recounted that friends of Gross would compare him to the 1980s fictional television character and improvisational savant MacGyver based on his ability to repair boats.

"Whatever it takes, he'll get it rigged up. He'll get it working," Spicuzza described.

The Coast Guard believed the sailors left their slip (the equivalent of a parking spot for boats) on April 2. They eventually departed Mazatlán on April 4, based on Facebook posts and cellphone usage.

The sailors expected the trip across the Gulf of California to Cabo San Lucas, where they planned to pick up provisions, would take two days. However, the Coast Guard does not believe the sailors ever stopped in Cabo San Lucas. Since April 4, marinas throughout the Baja Peninsula have not contacted the vessel, nor have any search and rescue crews spotted it.

According to Higgins, the weather worsened around April 6, with winds of 30 knots, strong swells, and waves making navigation more challenging. Spicuzza added that the sail from Mexico to California is inherently tricky since sailors need to navigate against the wind and current.

"From the tip of Baja all the way back up to Alaska, you're going against wind and current, so it's a more difficult, exhausting sail, but of course, doable with the experience that's on board," Spicuzza.

Spicuzza added that the group's initially planned 10-day journey was likely unrealistic. Sailing against the wind and current would require the sailors to tack frequently, essentially zig-zag to make progress despite sailing into the wind, which could extend the journey to two and half weeks.

Moreover, according to the Coast Guard, the boat lacks trackable GPS navigation, such as a satellite phone or a tracking beacon. The limited cellular service in that region of Mexico also makes triangulating the cell position difficult.

Robert H. Perry, the designer of the 41-foot sailboat, noted that their boat was likely manufactured in Taiwan 35 years ago. Despite its age, the fiberglass sailboat itself was a time-tested, ocean-navigating boat.

The travel circumstances have left family members uncertain about the status of their loved ones. Based on the timing, it appears possible they are "just going to roll into San Diego like nothing happened in maybe about a week," Spicuzza suggested, with the radio silence attributable to some electronic issue. Alternatively, the Coast Guard has worked on plotting where their life raft might have drifted under current weather conditions.

"It's just been a roller coaster of emotions the last several days; I want my dad home, I want him safe, [and] I want the O'Brien's home safe," Spicuzza said. "I'm very much looking forward to sitting around a table with all of them and joking about the time they got lost at sea – that is the hope."

ABC News' Elisha Asif, Helena Skinner, Zohreen Shah, Amantha Chery and Marilyn Heck contributed to this report.