Logboarding is a sport that Humphrey made up when he was still a pup or a "preteen wolf".
In the movie he rides with Shakey, Salty and Mooch the first time, but it does not end well. Shakey, Salty and Mooch fall off. Humphrey doesn't even notice and flies into the air and sees Kate. Humphrey jumps and catches Kate. They hold hands and spin around in the air. They eventually land and Kate goes off to Alpha School.
The second time goes pretty well at first. The boys looked like they'd been practicing alot. "Take a left 30 degrees" and other quotes were made by Humphrey. They didn't know how to use the brakes so they hit a rock and fly to a patch of grass where they watch Kate's first hunt.
The final time logboarding is seen in the movie is when Kate and Humphrey logboard at the caribou stampede scene to save Winston and Tony. They succeed but Kate gets knocked out by a caribou. Kate awakes and Kate and Humphrey become mates along with Lilly and Garth.