Re: Saginaw river marine growth...
I use a mixture of muriatic acid and water- 50/50. My boat is fiberglass, but I also use it on my outdrive, etc....... Works like magic- the stuff just sizzles off. And it's very inexpensive. But you have to rinse very thoroughly, and take other precautions.
Try googling muriatic acid hull cleaner, or simliar to get full information.