Act like your boat is a pickup and the river your backroad: Travel and look for tracks or the elk themselves. If you spot elk the boat WILL spook them from a good distance but that's fine. Shore up a little ways away and put a stock on and set up if you feel you're within 150 yards (or whatever your style/ preference is). Don't over complicate this, keep it simple: Spot and cut the distance. I don't call from the boat, but I have also not tried either. If you're not comfortable boating at night then bring camping gear and pre-scout for a camping spot for base camp. Your base camp could be a starting point where you just need your boat to get there and then do the rest of your hunting on foot, as the best thing about a river boat is that it can get you to extremely remote areas of the backcountry. If you can't get back to base, prepare for a night out, whether in the boat or pitch a tent on shore. River boat hunting is a special way to hunt that gets you into areas others can't, good luck!