close video Titanic submarine depth makes rescue mission ‘very complex’: Bob Pizzini

Retired U.S. Navy Mixed Gas Diving Officer Bob Pizzini discusses whether ‘underwater noises’ in the area of the missing sub indicate signs of life on ‘Cavuto: Coast to Coast.’

A co-founder of OceanGate Expeditions spoke out and gave reason to hope the five-man crew of the missing Titan submersible can still be rescued, including CEO Stockton Rush. 

Guillermo Söhnlein founded OceanGate with Rush in 2009 to offer pricey deep-sea tours to the extremely wealthy in manned submersibles capable of diving up to 13,123 feet. Söhnlein left the company in 2013, turning it over to Rush and reducing his role to a minority shareholder, but the two have kept in touch and last spoke a couple of weeks before the ill-fated Titanic expedition. 

In a statement posted on Facebook, Söhnlein broke his silence about the missing crew and encouraged the public and the media to remain hopeful for the crew's rescue and avoid speculation about what happened.

"For the past three days, I have watched from afar as hundreds of dedicated professionals worked tirelessly to find and rescue the crew of the research submersible, Titan, with which communication was lost during its science expedition to the wreck of the Titanic. The pilot is my co-founder and friend, Stockton Rush," Söhnlein wrote.

OCEANGATE TITANIC SUB SEARCH: MISSING VESSEL NEARS DEADLINE WHEN OXYGEN PROJECTED TO RUN OUT

The five-man crew aboard the missing OceanGate submersible has just hours before they’ll run out of breathable air. (L-R) OceanGate CEO Stockton Rush, Pakistani Businessman Shahzada Dawood, Sulaiman Dawood (no photo available), French mariner Paul-He

"Today will be a critical day in this search and rescue mission, as the sub's life support supplies are starting to run low. I'm certain that Stockton and the rest of the crew realized days ago that the best thing they can do to ensure their rescue is to extend the limits of those supplies by relaxing as much as possible. I firmly believe that the time window available for their rescue is longer than what most people think," he said.

An international search and rescue effort has continued for days since the Titan was reported missing on Sunday night. Critically, the crew is sealed inside the submersible and has a limited supply of breathable air. 

WHO IS ON THE OCEANGATE TITANIC SUB?

The Titan submersible, operated by OceanGate Expeditions to explore the wreckage of the sunken Titanic off the coast of Newfoundland, dives in an undated photograph. (OceanGate Expeditions via Reuters / Reuters Photos)

In a statement issued Wednesday night, the U.S. Coast Guard said the sub "was launched at 8 a.m. EDT [Sunday] and expected to resurface at 3 p.m., but one hour and 45 minutes into their dive, they lost contact with the Polar Prince."

On OceanGate's website, it lists the Titan sub as having 96 hours of life support for a crew of five passengers. Authorities have estimated the submersible will run out of oxygen sometime Thursday morning. 

DEEP-SEA EXPERT WORRIES ‘BANGING’ COULD BE ‘OVERLY OPTIMISTIC’ AS TITANIC SUB MAY HAVE ALREADY RUN OUT OF AIR

Equipment that was flown in by U.S. Air Force transport planes is loaded onto the offshore vessel Horizon Arctic, before its deployment to the search area of a missing OceanGate Expeditions submersible which had been carrying five people to explore t (REUTERS/David Hiscock / Reuters Photos)

The five-member crew onboard the Titan includes Rush, French mariner Paul-Henry Nargeolet, British businessman and explorer Hamish Harding, Pakistani businessman Shahzada Dawood and his son Sulaiman Dawood.

Söhnlein said there is reason to hope the crew can be rescued after the estimated deadline. 

"I would encourage everyone to remain hopeful for getting the crew back safely. In 1972, a similar rescue operation was able to retrieve two pilots trapped in a downed submersible with only 72 hours of life support. I continue to hold out hope for my friend and the rest of the crew," he wrote.

He continued, "While I completely understand the public's interest in this situation and the media's need to cover it as a notable story, I ask that we wait until after the crew returns and conducts a proper debrief to speculate on what happened. We need to give those involved with the rescue enough room to focus on their work, and we need to give the crew's families privacy to deal with their emotions in their own personal way. 

MISSING TITANIC SUB ‘DID NOT PERFORM WELL,’ SAYS VETERAN EXPLORER WHO NIXED DOCUMENTARY OVER SAFETY CONCERNS

This file image provided by OceanGate shows the Titan submersible docked in the Bahamas. (OceanGate Expeditions / Fox News)

"For myself, I have been overwhelmed by the outpouring of support I have received from friends and colleagues all over the world. It has been impossible to respond, but please know that your messages are truly appreciated, so … thank you!"

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Though Söhnlein and others have expressed optimism, there are still many hurdles for rescuers to overcome: from pinpointing the vessel's location, to reaching it with rescue equipment, to bringing it to the surface — assuming it's still intact. And all that needs to happen before the crew runs out of breathable air. 

Fox News' Bradford Betz, Greg Norman, Michael Ruiz and the Associated Press contributed to this report.