The Columbia rule is 7x anchor rope to the depth. This is a good idea for a newbie for safety and also as you are nearing the other boats slow yours down with the motor and the bow facing upriver and then cleat off at the bow and see how well you have lined up. I would try this at least 50' above the line. Once you are settled with the current, let out line and ease on down till you have lined up transomes. Not like an O'city shad fisherman in helter skelter fashion.