Cottonmouths have the visual acuity of about 12". They don't know what boats are, have terrible vision, and have no ears to hear talking (or screaming). They recognize an object floating in the water, and they like to bask on floating objects. They also associate those things as places fish and frogs like to hang out around. They have very strong senses of smell and could possibly investigate smells of bait or fish you've caught.
They're also inquisitive, so they'll investigate objects they don't recognize. I've stood on a bank and watched one swim directly towards me. Most would conclude that snake was "after" them. When it got close enough to make out what I was it bolted away and hid under a matte of grass.
It's all about perception and having a better understanding of these very misunderstood animals. They're never after you. But instinctual fear and lack of knowledge drives perception.