When he gets really busy as a filmmaker, Joseph Van Blunk turns down shifts at the waterfront, where he's a union longshoreman.

When he needs to earn more money to pay the bills or save up for his daughter's college tuition, he puts in more hours unloading or loading giant cargo ships at docks along the Delaware River.

That makes him, depending on the day, a longshoreman/filmmaker or a filmmaker/longshoreman.

"Slashing - I didn't know what that was until you told me," laughed Van Blunk of South Philadelphia, looking over at author Marci Alboher, who wrote One Person/Multiple Careers: A New Model for Work/Life Success.

"I think psychotic would be more like it," said Van Blunk.

Sipping their glasses of wine, the ladies at Amy Nislow's book club chuckled.

Ordinarily, the book group, which meets monthly at Nislow's grand but comfy Main Line mansion, focuses on fiction. But on Monday, the topic was multiple careers - each engrossing - and Alboher and a group of people featured in her book were the guests.

These people are not ordinary moonlighters or even people with hobbies, Alboher said. They are fully committed to dual or even triple careers.

Sitting next to Alboher, besides Van Blunk, were a theater producer/filmmaker and a lawyer recruiter/work-life consultant. Nislow describes herself as a slash person, too. She's an investor/philanthropist/art dealer.

Alboher, 41, is also a slash, as she somewhat gruesomely refers to this category of workers.

These days she is a speaker/coach/New York Times online columnist, and/of course/author of her book, published in February by Warner Business Books, a division of Hachette Book Group USA.

Its subtitle: "How 'The Slash Effect' Can Work For You."

Alboher used to be slash-less, just a plain old lawyer in New York. But once she got interested in people with multiple careers, she noticed them everywhere - just the way pregnant women suddenly notice that everyone at the mall has either a belly or a buggy.

"These are people who come at things from multiple angles and multiple disciplines," Alboher said. "When I talk to people in hyper-achievement circles, they understand it."

Alboher said it was hard to get good numbers on how many people were slashing.

According to the U.S. Labor Department, 5.4 percent of the workforce, or 7.9 million people, hold multiple jobs. That is the highest number since 1999, although the percentage has remained fairly steady.

Those numbers do not figure in the 9.6 million who are self-employed (slashers are an entrepreneurial lot) and the 25.7 million people who work part time - either because they choose to or because they have no choice.

Alboher's book also does not include people like Natasha Maye, a certified nurse aide/union organizer.

"I'm not making enough at one job to take care of my four children," said Maye of North Philadelphia. Maye injured her hand and can only work five hours a day as an aide, a physically demanding job that yields $380 in take-home pay every two weeks.

Low-wage workers often work multiple jobs because they "can't make ends meet or because the pay is so low," said Philadelphia labor economist Eileen Appelbaum, an author of Low Wage America and a professor at Rutgers University (economist/author/professor).

"At the high end, you can pursue many different things in a way that's meaningful," she said.

Alboher said her interviews with dozens of "slashers" show that some, such as Deborah Epstein Henry, relied on their husbands for financial stability as they began their slash careers. Now Henry of Ardmore is a work-life consultant and recruiter of part-time lawyers. She wanted to create a slash life so she could meet her children's school bus in the afternoon.

Some, Alboher said, had one job that paid the bills and provided the benefits, while the other was more risky. Van Blunk's longshoreman job fit that category. "I try to keep my personal overhead modest, so I can take time from my job to work on my films," he said.

Alboher also found that slashers, although driven, often make a deliberate choice to get off the fast track.

"These are people who choose to do what they love to do, but to do a little less of it, so they can do something else as well," Alboher said.

Sometimes, she noticed, the two slash jobs complemented each other. Sometimes, contacts in one arena led to opportunities in another. And sometimes the jobs contrasted.

In her book, Alboher describes, for example, a Massachusetts man who works three days as a violin-maker and two days as a psychotherapist.

But even jobs that seem unrelated turn out to be connected. "When people have slashes, they pull things together in a way that nobody else can understand until they explain it," Alboher said.

Jaime Donegan, a filmmaker/theater producer from Germantown, who used to be a landscaper/theater producer, told the book group Monday that his landscaping helped his theater work and vice versa.

"In my landscaping, I use a lot of my set-designing experience," he said. "And, this is kind of Zen, but when I work with individuals [in the theater], it's really a nurturing project, and I learned that by growing things in my garden."

Contact staff writer Jane M. Von Bergen at 215-854-2769 or jvonbergen@phillynews.com.