Depending on how low on the river there can be 9ft tide swings, both low and high tides can be good it's all spot-dependent, what does that water level give the birds access to? A deeper-sided boat would be my preference if spending time on the lower river, we run a 20ft boat with 34" sides, 88" beam for reference. We hunted in a 15ft Alaskan for a long time, can be done safely but need to really watch the weather and be ready to call it a short day when needed to make a quick run for the ramp.
Big water and weather can turn fast, lots of old pilings and logs barely out of the water. 95% of our hunting is from the boat, dog or boat for retrieving birds. Get a good tide app and charts like Navionics, go in the daylight in good weather through a full tide cycle both low and high, what has water at what tide/where can you go. Don't walk too far from your boat if hunting from shore, getting back across a now flooded island not knowing where the drop offs are isn't fun. lots of guys tow a marsh rat for bird and boat retrieval/substitute for a dog. The further upriver you go the less tide influence for water level changes until you get above the dams as mentioned.