Special sonar equipment helps divers search for boy - Winnipeg Free Press

Mark Atherton (right) with Darwin Monita of Aquatics Environmental Services.

(Picture by Wayne Glowacki)

Special sonar equipment helps divers search for boy


By Paul "Willy" Williamson


IN the diving world, zero visibility is known as “black water” and it gets no blacker than the depths of the ice-covered Red River, where divers are again looking for the body of six-year-old Nathaniel Thorassie. Divers from the Winnipeg Police Service, the Winnipeg Fire Department and the Canadian Amphibious Search Team (CAST), searched the river in tandem Sunday and Monday. The city says it will postpone preparations for the Disraeli Bridge reconstruction until the search is over.

Ken Lugg, team co-ordinator for CAST and a retired Winnipeg police diver, said visibility is zero.

To add to the hazard, divers must also search through debris that includes shopping carts, barbed wire, rock piles and fallen trees.

But they have help — a specialized piece of sonar equipment on loan from Kongsberg Mesotech, a world leader in high-resolution sonar systems. The sonar equipment was brought to Winnipeg by a volunteer crew from Vancouver that includes a pair of sonar specialists. Mark Atherton, one of the specialists, said the sonar is similar to the ultrasound technology used to view an unborn child. The sonar head unit is immersed in the water through holes like the ones ice fishers drill. It sends images back to the specialists’ computer screens. The image is vivid enough a tire was easily viewed on the bottom of the muddy Red.

The divers are tethered by an umbilical cord that lets them communicate with the crew on the ice surface. Divers can search as far as 40 metres from the hole in the ice. “That doesn’t seem like much, but when you are under ice, it’s a long way home,” said Lugg.

The biggest problem is keeping the equipment warm as it does not function well in the cold. “We have our communications and our dive-control systems in heated tents to keep them warm until just prior to the dive.”

The search is being conducted beneath the Disraeli Bridge, where Nathaniel and his 10-year-old brother, Ralph Chartrand Jr., were playing with hockey sticks and breaking chunks of ice by the open water on Dec. 4 when the water’s edge broke away. Both boys fell into the river but Ralph was pulled to safety by a passerby who threw him a rope.

Republished from On7 and the Winnipeg Free Press print edition January 4, 2011 A6

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