One can still fish the Gulf beach and get in closer on good days in a flat bottom hull. Tunnels Tunnels come in all sizes and shapes from short pockets to full hull lengths, short to tall, and round to square. This is not a hard and fast rule. A full hull length tunnel seems to trap more air causing cavitation. A short tall tunnel is hard to prime and keep primed when running at lower speeds.
Square tunnels cause turbulence and drag.
Hull Helpers Key slots or boxes help in two ways. First, they help when jumping up as they keep the propeller closer to the hull causing less bow rise. Second, when the engine is put on a jack plate the balance point moves aft on the hull. The key slot helps to offset this by adding displacement beyond the engine. Also a key slot that is designed properly will help keep the water trapped around the propeller.