Zhang Wuyi, a 37-year-old former boilermaker, waves to onlookers before taking his self-made submarine under water in Wuhan, Hubei province, on Tuesday. PROVIDED TO CHINA DAILY

Crawling out of a small silver submarine after a 20-minute dive, Zhang was ready to show off his new gizmo on Tuesday.

"It's like an automatically-controlled undersea harvesting machine, and absorbs aquatic products like a vacuum cleaner," said Zhang, 37, who hopes to put the craft into large-scale production.

The civilian sub is 6 meters long, 2 meters in circumference and can hold two people. The 9-ton craft can stay underwater for up to 20 hours. It is equipped with a camera, radar, positioning system and harvesting equipment.

Since his first dive last August, he has received several orders and numerous calls from home and abroad.

More than 20 people work in his boat company, located in a shabby bungalow in a suburban area, and they share a workshop with another factory.

He has already invested 4 million yuan ($635,000) and is building a 10,000-square-meter plant. About 500,000 yuan was out of his own pocket, while the rest came from friends and other investors.

It takes nearly two months to finish one submarine, catering to customers' different requirements.

In October, Cong Zhijie, who runs a sea cucumber farm in Dalian, Liaoning province, became Zhang's first and, so far, only buyer with a payment of 150,000 yuan.

According to Cong, the submarine works well and saves him 10,000 yuan a day in divers' pay.

In late March, Zhang started to cooperate with a boat factory in Wuhan, which has more than 300 workers.

"They make hulls out of ship plate for me, so I can go into mass production in the future," said Zhang, who used to be a boilermaker in a textile machinery plant.

Since being laid off in 1996, Zhang has done various jobs such as driving a tricycle taxi and running a grocery. He became obsessed with submarines the first time he saw one in 2008.

"How wonderful the invention of the submarine is," Zhang said.

"It could give human beings so much power and save us so much trouble," he said.

In 2009, Zhang decided to make a submarine on his own, eying its huge potential market.

"I thought he had a fever," Zhang's friend Bao Laijiang recalled when Zhang approached him to invest in the submarine business.

Bao was then owner of a clothes-making plant.

"But he got me eventually, being such a good marketer," said Bao, who sold his plant and joined Bao half a year later.

Making a submarine, however, was not as easy as they imagined.

"Our first submarine leaked like a sprinkler," Bao recalled.

"Our second one looked functional, but it was stolen."

Zhang's wife was strongly against his "stupid submarine business", but finally gave her tacit consent and support, especially after Zhang injured his left leg in an accident.

"He is crazy about submarines," his wife said.

Zhang reads and surfs the Internet to study. Whenever he has questions, he turns to experts.

"Learning is a lifetime thing. I learn as I make the submarine," said Zhang, who only has a high school education.

He also hired several engineers to help design the submarine, and more are joining his team.

"It's like how Thomas Edison invented the electric light bulb. I have to do various experiments before succeeding," said Zhang.

xulin@chinadaily.com.cn