Use an Ax: If you're worried about the thickness of the ice at any time, give it one hard chop with your ax. If you see water, get out of there. If your ax can't get through with a good chop, it can support a human. Sometimes, the ice will be strong enough to cross but abrupt jagged ice is sticking up like a knife blades means you can't get across. Use your ax to chop a path wide enough for your snowmobile to get through.