What is the liability of an experienced snowmobile passenger in a snowmobile accident?

In Hewett v. Higgins, [1993] O.J. No. 2870 both passenger and driver were thrown from a snowmobile driven at 35 mph across a pressure crack on a lake which the driver had seen from the short distance but had not reduced his speed. The female passenger was experienced with snowmobiles and was held to be 30% liable for failing to communicate her knowledge of pressure cracks and her concern to the defendant. The driver's negligence consisted of failing to keep the proper lookout and travelling at an excessive speed in the circumstances.