Hot Topics : Ice Breaking
By Lonny Lippsett, photos by Chris Linder

ice breaking

Unlike icebreakers with traditional wedge-shaped bows that try to crack ice by ramming it, Oden has a square bow. It has 12 thrusters that spray jets of water onto ice floes, lubricating the ice to allow Oden move up and onto it more easily.

ice breaking

The ship’s weight cracks the ice floes into smaller pieces.

ice breaking

When the ice gets tough, Oden’s best weapon is its heeling tanks. These are pairs of tanks on the port and starboard sides that each can be filled with up to 400 tons of water that add weight. Water can be shifted from one side of the ship to the other through the large-diameter pipe above—in about 15 seconds. That causes Oden to list from one side then to the other, which helps break ice.

ice breaking

Because overcast weather conditions usually prevent Oden’s crew from seeing very far ahead of the ship, the icebreaker relies heavily on its helicopter to scout ahead for openings in the ice.

ice breaking

Oden also has features on the sides of its bow called reamers. The bow ramps down to the waterline. When the ship goes backward, it scoops up loose ice chunks and pushes them off to the sides and out of the ship’s way.

ice breaking

The biggest problem for icebreakers are ice ridges, which form when the sides of ice floes smash against each or are squeezed together. They can pile up to 30 to 40 feet high.

The sea ice in the Arctic Ocean is, on average, 3 to 4 meters (10 to 13 feet) thick. You’d think that would create a barrier that no ship could get through, but icebreakers do it.

Most icebreakers have traditional pointy, wedge-shaped bows that try to crack the ice by ramming it. Our icebreaker, Oden, looks very different. It has a square bow, and it works in a different way. The bow has 12 thrusters that spray jets of water onto ice floes. The water lubricates the ice so that Oden, with its square bow and relatively flat bottom, can ride up and on top of the ice more easily.

Most people would think of snow as slippery,” said Thomas Strömsnäs, Oden’s second officer. “But with 13,000 (metric) tons of pressure on it (from the ship), you do get friction.”

The water from the jets reduces the friction, and the 13,000 tons of pressure from the ship’s weight cracks the ice floes into smaller pieces. It’s fascinating to watch a network of cracks appear and spread through large ice floes—just the way (on a much smaller scale) cracks spread across the surface of a frozen puddle when you step on it.

But once you break the ice, you have to clear it out of the way. That is often the harder part, Strömsnäs said. What’s the use of changing a sheet of ice into a jumble of smaller (though still massive) ice chunks, if those ice chunks are still in your way? When the rest of the ice pack is pressing hard against the ship from all directions, it can be hard to find a place to shove the ice.

So Oden’s officers are always on the lookout for open patches of water, or thin cracks in the ice, called leads. Sometimes, when the leads are large enough, they can sail Oden down the middle of them without breaking ice at all. But when they are smaller, they will sail Oden to one side of the lead, breaking ice on one side of the ship and pushing broken ice into open water on the other, Strömsnäs said.

Because leads are so important, and because the overcast weather conditions usually prevent Oden’s crew from seeing very far ahead of the ship, the icebreaker relies heavily on its helicopter.

Several times a day, a pilot and ship’s officer will fly up to 20 nautical miles ahead of the ship, looking for leads. The pilots will follow one lead or another, finding some that are dead-ends and others that connect to other leads to create a long, easier passageway for Oden. The pilot and officer will decide to take the northern lead around a floe, rather than the southern lead, for example, or steer the ship to avoid a particularly large floe entirely.

When they have settled on the best route, the pilot will fly along it from its end back to the ship. Transponders on the helicopter will log the route directly into the ship’s navigation system.

On a monitor in Oden’s bridge, you can watch the icebreaker moving along the helicopter’s track—at first. But then the two tracks will diverge. Over time, the ice pack moves. Ice floes surge and spin. Cracks open and close. The path that existed four hours ago, no longer does, and the helicopter goes aloft again to scout out the present situation.

Icebreaking is usually routine, but “when the ice gets tough, the best weapon we have is the ship’s heeling tanks,” Strömsnäs said. These are two pairs of tanks on the port and starboard sides that each can be filled with up to 400 tons of water.

“You have the full weight of the ship and the added weight of the water on the ice,” he said. The water can be shifted from one side of the ship to the other through a pipe as tall and wide as a person—in about 15 seconds. That causes Oden to list back and forth, from one side to the other, which helps break ice. The ship can be set to do this automatically, something the crew calls the “duck walk.”

“You can hear the hum of the water going through the heeling system,” Strömsnäs said, “so you can keep track of what’s happening outside and know there is tough ice, even when you’re in bed.”

Oden also has interesting features on the sides of its bow called reamers. The bow ramps down to the waterline. When the ship goes backward, it scoops and scrapes up loose ice chunks and pushes them off to the sides and out of the ship’s way.

“Level ice is normally not a problem,” Strömsnäs said. “The problem is the ridges, and we really don’t want to go into those.” Ridges form when the sides of ice floes smash against each or are squeezed together. They can pile up to 30 to 40 feet high, said WHOI engineer John Kemp, a veteran of many Arctic Ocean research cruises. “Sometimes there just isn’t room, and we end up smack boom in the middle of a ridge,” Strömsnäs said. “So we back up and get lined up better, and ram.”

“Sometimes, we just get stuck,” Strömsnäs said. “We wiggle from side to side or back and forth, just to move a few decimeters. Sooner or later, you will get loose. Or you wait for the tide and the weather to change and loosen the ice. I think the record
(for being stuck) is about 24 hours.”

“The worse thing is to go between (a lead in) two big floes. It looks very tempting,” he said. But the floes can exert tremendous pressure on each side of the icebreaker and wedge it in. That’s what happened to us on July 5.

Oden uses about twice as much fuel breaking ice as it does sailing through open water, Strömsnäs said. Normally, the icebreaker averages about 72 nautical miles per day through ice. But over the past few days, Oden has gone more than 100 nautical miles per day, and we reached our target site at midday Sunday, several hours earlier than expected.

“We’ve been unusually lucky with openings,” Strömsnäs said. “Normally, it’s more closed.”

 

[Back to top]