How do you launch a 330-ton tugboat? Very carefully.

How do you get a 660,000-pound tugboat into the water?

Slowly.

Western Towboat moved its newest tug, dubbed the Mariner, from its Ballard shipyard about 100 yards down Northwest 40th Street into Seattle’s Lake Washington Ship Canal on Wednesday, a multistep process that took the better part of the day.

The Mariner will be Western Towboat’s 23rd tug, and the 19th that it has built in Ballard.

It took two semitrucks pushing, and a guide forklift pulling, to get the 80-foot, 330-ton boat down the sloped drive to the water. The Mariner was resting on a rolling metal frame with at least six separate hydraulic dollies that had to be constantly adjusted as the frame moved to keep the ship level.

It rolled down specially prepared ramps into a dry dock, which was pulled into place Wednesday morning. Then, after Ship Canal traffic cleared, a sister tugboat towed the dry dock into the center of the shipping canal, where it was deep enough to lower the Mariner, and its 15-foot draft and twin 2,000-horsepower Caterpillar engines, into the water.

Western Towboat has been building the Mariner for more than two years, said Russell Shrewsbury, the company’s vice president and the third generation of his family to lead the business. Shrewsbury’s father remains president of Western Towboat and his brother and sister also hold executive positions in the company, which has been based in Ballard since 1948. In 1982, the company began building tugboats itself for its own operation.

Shrewsbury said the Mariner cost about $10 million to build, but, “We don’t really know yet.”

“About 75,000 man-hours went into building the boat, I bet,” Shrewsbury said. It’s not quite done yet. Several months of work remain to be done on the deck and interior.

Each of the company’s tugs is a little different, with interior specifications designed in consultation with each boat’s captain. Also still to come is the company’s iconic yellow, white and blue paint job. Company officials hope it will be finished by the end of the summer.

Most of the company’s business involves towing barges between Seattle and Southeast Alaska, where many communities aren’t accessible by road and there are no terminals big enough for a container ship to dock, so all freight arrives by tug and barge.

The boats also operate in and around Seattle, towing barges through the Ship Canal and through Elliott Bay to the industrial plants along the Duwamish Waterway. The Mariner is a harbor tug, which will operate around Seattle, handing off barges to larger ocean tugs, that will make the trip to Alaska.