I find it helpful to look for large pine planks 2x12, these are from larger, older trees, and usually have a clear run down at least one side that you can rip off for gunwales, then rip it in half the other way and you have .75xdepth of your gunwales, and if you've got pretty vertical grain on that slice of 2x12, you should have even bending characteristics. If you get southern yellow pine, don't rip it until you are ready to lock it into forms, it has a way of going curly when it dries.