To get to work, he must jump from a swaying boat to a rope ladder dangling off the side of a massive ship 15-stories high, all as rolling waves crash below him.

"When it's really rough weather, this is a very dangerous spot," Kellerman said.

He is part of a small but scrappy unit called the San Francisco Bar Pilots, a group of master mariners who for the last two centuries have been scaling some of the world's largest cargo ships, then steering them in and out of the San Francisco Bay.

They're called bar pilots for their ability to navigate through shallow channels with sand bars on either side.

"We are kind of the first line of defense for the bay," he said.

Both state and federal law require a local pilot to take over from the ships' captain to navigate through San Francisco Bay, not just to protect the cargo, but the bay itself.

"When we first started back in 1850, during the Gold Rush, we were brought on to keep the ships safe from the environment. Now we're keeping the environment safe from the ships," he said.

At San Francisco's Pier 9, Kellerman boards a small boat that will take him to the Port of Oakland. There, he'll climb a state-of-the-art cargo ship called George III -- bound for Hawaii -- and guide it into the open sea.

One of his biggest challenges is a narrow channel the ship must travel through on their way out of the port.

"It's only 50 feet deep, so we have a limited amount of space on each side, and also below us," he said.

If he's worried at all, it doesn't show. After all, this is what he's trained for.

Becoming a bar pilot is not that easy. Candidates must attend a four-year maritime academy and are expected to have 15 years of experience as captains of deep-sea ocean vessels or tugboats before they can even apply. There's also a written exam, a simulator exam and an interview. Those who pass all that are then required to spend another 18 months to three years training.

The groups' business director Capt. Anne McIntyre said the San Francisco Bar Pilots serve as the "human link in the supply chain," responsible for almost all containerized goods moving through Northern California.

They went mostly unnoticed until the pandemic when supply chain disruptions caused an epic traffic jam of ships around the Bay. The bar pilots were the ones to get it moving again.

"It really took the supply chain disruption for people to understand how critical we are to the economy," McIntyre said.

As Kellerman pulls up next to the ship, we get one final instruction: "No swimming."

It's a steep climb — no safety net or harnesses. Luckily, it's a beautiful day. But this is the Bay Area, where conditions deteriorate rapidly (more on that later).

Once onboard, you get a sense of how mammoth the ship actually is. The size of 2.5 football fields, it's carrying anywhere from $150 -$300 million worth of goods to Hawaii.

Ed Washburn -- the Senior Vice President of Fleet Operations for Pasha, the company that owns the ship -- takes CBS San Francisco to the beating heart of this vessel, a huge clean-energy engine with about 200 times the horsepower of an average car.

"The ship is built specifically for the Hawaiian trade," Washburn said. "They need their goods right away and if we're late, their stores are empty."

Which is why Kellerman wastes no time. With the help of two tugboats, he slowly pulls the 45,000-ton ship out of its spot and into the channel.

His biggest concern other than crosscurrents, boat traffic and sand bars along the ocean floor, is a thick blanket of fog forming on the horizon, the kind San Francisco is famous for.

"We will probably be completely enveloped," Kellerman said while looking through his binoculars.

Within minutes, the fog closes in. Looking forward, it's impossible to see past the bow.

For the next 20 minutes, Kellerman is flying blind, navigating the steel behemoth through one of the Bay's most dangerous areas, using radar, GPS and his instincts.

After 11 long miles of near zero visibility, the ship is safely out of the Bay. But the bar pilot is not out of the woods yet.

Kellerman hands control of the ship back to its rightful captain before rushing back to his pilot boat waiting for him below. But this time, he's in the open sea and that rickety ladder is his only way down.

"Out past the Golden Gate Bridge, you don't have any protection," he said. "It's really scary out here."

As he dangles from the side of the ship, the pilot boat gets into place so he can jump on. The surf is so rough, the waves are crashing onto the boat. As Kellerman starts his descent, he knows there is little room for error. One wrong move here could be catastrophic.

Thankfully, the transfer to the pilot boat goes off without a hitch, for him and for us. At the end of a long day, Kellerman heads back to the pier, having made it through yet another shift.

"I come home feeling like I accomplished something, and I get to have a little bit of an adventure along the way," he said.

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