Oyster Dredge Tunnel Design

I am looking for information or a reference source that can give us some options for designing a prop tunnel for a 60' shallow draft oyster vessel. Can anyone guide me to a book that can give me some basics to consider when looking at tunnel design? Our current boat has twin tunnels, but the hull is different than the new boat and I don't know if we can use the same concept. Has anyone ever heard of a tunnel design with squre sides and a tapered lead into the tunnel? I don't need specifics at this point, just some general information so we can make some decesions on cost of the project. I think if I could find decent design book/article/guide/? I could get enough info to at least determine if we should move ahead on this type of hull design.

Thanks, Brian