[onewhippedpuppy]

For cooling, most boats have a raw water pump that sucks lake water out of the lake, which then feeds the engine cooling system water pump just like a car would have. After the lake water is circulated through the engine it dumps overboard. So basically the lake is your radiator. But as you expected this gets really corrosive in salt water, most boats have a hose connection so you can flush out the salt water with fresh water when you’re done. There are also boats that have a closed cooling system and radiator like a car, but they aren’t as common.