Ben Lecomte, a 50-year-old Frenchman turned Texan, will slip into the water Sunday off the coast of Choshi, Japan, and start swimming. If all goes as planned, he won’t set foot on land for six months. In that time, he plans to swim through the largest collection of trash on the planet, great white shark migration areas, jellyfish and storms and isolation and monotony.

By November, Lecomte hopes to paddle and kick all the way to San Francisco, becoming the first person to swim across the Pacific Ocean, an extraordinary transcontinental quest that’s equal parts adventure and science experiment.

“For me, swimming is a passion,” Lecomte explained in a recent interview. “But if it’s just swimming for pleasure, that’s limited. I need to have greater purpose and a bigger vision.”

It doesn’t get much bigger than the Pacific, the world’s largest pool and something Lecomte has been targeting for nearly 20 years. In 1998, he successfully crossed the Atlantic, which earned him a bit of fame. He appeared on the “Oprah Winfrey Show” and told her, “When I arrived after swimming the Atlantic, my first words were, ‘Never again.’ Then a few months after, I said, ‘No, I need to go back.’ It’s something that I need. It’s within me. I need to find another challenge and to push myself.”

It took nearly two decades to reach this point, with plenty of false starts and funding hiccups along the way. The scale and ambition of this crossing is much different from the Atlantic. The Japan-San Francisco trek will measure 5,500 miles, a staged attempt that will take 180 or so days. Swimming from Cape Cod to France in 1998 measured 3,700 miles over 73 days. That swim was never verified by Guinness World Records because Lecomte drifted off course in a boat and didn’t necessarily resume his swims at the exact point he stopped them.

His new undertaking is a lot more involved, with financial backing from companies like Seeker, the science-focused digital publisher, and Discovery. He’ll have an eight-person crew that will be collecting and studying data on both the ocean and Lecomte throughout the journey, picking up 1,000 or so water samples along the way. Lecomte will be accompanied by a 67-foot sailboat and each day, a smaller inflatable motorboat or kayak will lead him in the water, keeping him on course.

Lecomte is aiming to swim eight hours each day, covering 40 miles of choppy waters, and then spending his nights recuperating on the sailboat.

The risks are different from the challenges. Lecomte and his crew will closely monitor changing conditions, and he’ll wear a thick wet suit to help him navigate waters that could reach 50 degrees. In addition, they’ll use magnetic and electric fields to ward off sharks.

“But an adventure like this is really mind over matter,” he said. “I’m not trying to swim faster than anybody else. I’m just trying to log my time and my hours per day. What is important is knowing what you’re going to do with your mind.”