As the last boats point ice-masked bows toward their respective ports of layup this weekend, the tally of active vessels set to winter in the Duluth-Superior harbor is set at six lake freighters and one tug-barge (see graphic).

The 2017-18 campaign was noticeably vibrant locally with steady boat traffic for much of the season. The numbers are starting to come out in support of the visuals too. Iron ore shipments surpassed 60 million tons and beat the five-year average by almost 5 percent, said a Lake Carriers' Association news release this week.

Until a subzero slowdown of ore loading earlier this month left as many as nine boats at a time waiting at anchor outside Duluth, the lakes offered mostly clear sailing throughout the season. Ice cover on the Great Lakes even diminished this week to less than 19 percent on Thursday, according to the National Oceanic and Atmospheric Administration's Great Lakes Environmental Research Laboratory. It followed a seasonal high of near 20-percent ice coverage. A warm-up last week, with temperatures climbing above freezing at times, was responsible for the reduction in the ice blanket.

Two of the boats laying up in the Twin Ports, the Kaye E. Barker and Lee A. Tregurtha, docked last week at Fraser Shipyards in Superior.

"Fraser crews are scheduled to do work on all seven — as well as the Arthur (M.) Anderson, which is the eighth, but never left the harbor this season," said Fraser spokesman Rob Karwath.

Monday marks the one-year anniversary of Anderson laying up on the east side of Canadian National Dock 6 in West Duluth. CN and Key Lakes Inc., which own and operate the Great Lakes Fleet, respectively, have declined to comment on the reason for the extended layup of what is a popular boat.

At the Soo Locks, the conversion from sailing to salvaging the vital infrastructure that is the locks is in full swing.

"It's our busiest time of the year," said Kevin Sprague, an area engineer with the U.S. Army Corps of Engineers based in Sault Ste. Marie, Mich. "During most of the year, we're locking boats. But in the offseason, we throw everything we have at projects and maintenance."

The Soo Locks feature two sets of locks on the St. Marys River which connect Lake Superior with the rest of the Great Lakes. Most of the iron ore from the United States and Canada makes its way through the locks to steel mills on the lower lakes. The locks handle an estimated 4,500 ship visits every year, said an Army Corps of Engineers news release.

Offseason projects at the Soo Locks range from preventative maintenance to a continued effort to refurbish both the Poe and MacArthur locks, one replacement piece or upgrade at a time.

"Some of these jobs repeat themselves, because certain things have short lives," Sprague said. "But we have an asset renewal program where we're trying to basically rebuild the facility over time. We've got almost 50 years on the Poe Lock and over 70 on the Mac Lock. We believe that if we invest in some of their components we can extend their lives another 50 years."

The biggest projects being done this offseason include embedded anchorage replacements on both locks where fatigue issues are apparent, Sprague said. Additionally, the Army Corps of Engineers said it is will conduct "lock miter and quoin block replacement" on the Poe, which is the longer lock and the only one of the two that can handle thousand-foot lakers.

"On the upstream miter gates, the main doors open and close to let the ships come in and out and forms your dam," Sprague explained. "The blocks come in contact with the wall. They're original and have wear and tear." The intensity of the work finds both contractors and government employees working side by side in winter conditions which aren't always favorable, Sprague said. But the only option is success. "There's no forgiveness for being late," Sprague said, citing the traditional March reopening of the Soo Locks. "We must open on time. In everything we do, it's always on our mind. We have to be there for the shipping industry on the 25th of March."