This giant tug was built in 1972 by Star Shipyard as the Mary B. VI for Federal Commerce & Navigation. Her name was shortened in 1981 to Mary B., then changed back to Mary B. VI the following year. In 1983 she was sold to the Arctic Transportation Company and renamed Arctic Tuktu. McKeil Marine of Hamilton, ON purchased the Arctic Tuktu in 1993. The following year she was renamed John Spence and went to work on the Great Lakes pushing the asphalt barge McAsphalt 401. After her charter to McAsphalt expired, she began working with the multipurpose deck barge Niagara Spirit for McKeil.
The John Spence was retired in late 2013, and is currently laid up in Port Maitland, ON.
- Type: Twin Screw Tugboat
- Year Built: 1972
- Builder: Star Shipyard, New Westminster, BC
- Hull No.: 404
- Engines: 2 EMD 16-567C
- Horsepower: 3,280 bhp
- Length: 171′ 00″
- Breadth: 38′ 00″
- Depth: 15′ 01″
- Port of Registry: Hamilton, ON