Fully-loaded, the Mackinaw displaces 5,252 tons. She’s 290-feet long, 74-feet wide and capable of making 18.7 knots. Her power plant consists of six diesels with electric drive and three propeller shafts (one forward, two aft) delivering a total of 10,000 horsepower. She can move through three feet of ice at three knots continuously and is capable of cutting a channel wide enough to assist the largest of the Great Lakes ore carriers.
The bow propeller is useful for occasions when the Mackinaw is forced to back out of surrounding ice, or for creating a wash that forces broken ice from around the sides of the vessel, thus keeping the sea chests (water intakes) clear. Contrary to popular belief, the bow propeller is not used the suck water from underneath the ice in front of the vessel, in theory making it easier to break, however it is sometimes used “as a poor-man’s bowthruster” when maneuvering from a dock.
Other unique features are the Mackinaw’s heeling and trim tanks. Connected by 24-inch piping, the tanks allow more than 100,000 gallons of water to be shifted fore and aft, or side to side, in less than two minutes. This shifting gives the Mackinaw a rocking motion, allowing it to break free of heavy ice. Additionally, the Mackinaw boasts strengthened steering gear and a padded notch at the stern in which to nestle the bow of a vessel being towed through the ice, allowing the two vessels to operate as one. Over time, the size and power of the vessels the Mackinaw escorts have grown, making this feature little-used today, although occasionally it has been employed to pull low-powered tug-barge combinations through heavy ice. When she was built, the Mackinaw also carried a helicopter on her aft deck, but the chopper was eliminated many years ago when it was decided shore-based aircraft were more efficient at conducting ice patrols. A towing winch at the stern also sees little use.
One common misconception about the Mackinaw is that, because of her size, she’s a prisoner of the Great Lakes. That was true when the vessel was built, but the opening of the modern St. Lawrence Seaway in 1959 removed that limitation. The Mackinaw has spent her entire career on the lakes mainly because her icebreaking hull – shaped like a football cut in half – offers poor stability in heavy seas. Additionally, the water piping systems were designed to operate in freshwater and offer no protection against salt. This one drawback alone makes her eventual sale to a friendly foreign government for future service unlikely.
“She’s not a good sea keeping vessel for the open ocean and she was designed specifically to operate on the Great Lakes,” Nickerson confirms.
The Mackinaw’s engine rooms are impressive – and noisy. There is no soundproof booth from which to operate the machinery. Those on duty pay close attention to their equipment so potential problems can be spotted before they lead to major mechanical “casualties.” When operating in heavy ice, casualties can be a frequent occurrence.
Given the age of the equipment, keeping it all operating is a challenge, acknowledges Nickerson. It comes as no surprise to find that nearly half of the Mackinaw’s crew is in the engineering department, in Nickerson’s words “willing to do whatever it takes to keep the ship running. They know it is vital to commerce and they see it when they see ships behind us as we’re escorting them.”
The power behind the Mackinaw’s brute strength consists of six, 10-cylinder, Fairbanks-Morse diesel engines, divided into pairs in three different engine rooms. Each engine turns an electric generator that powers the motors that move the propellers. Twin propellers at the stern and one in the bow push the Mackinaw through even the most difficult ice conditions. The diesel-electric configuration offers flexibility when dealing with different running and ice conditions. When sailing in open water, one engine room is on-line with the power sent to the rear propellers. As ice conditions worsen, additional pairs of engines are brought on-line and, in the worst conditions, all six engines are running, with power from four engines heading to the stern propellers and two engines powering the bow propeller.