I have no idea of the size of your boat, but I have used the Mtronics sound board (choices of engine type) together with a pair of Dayton Exciters/transducers ( EX25VT 4 Ohms) which are 2” in diameter.

My boat is a Tug only 21” long with 8” beam. Volume is fine and exciters easy to accommodate.
All the best.
NPJ

I’ve fitted the mtroniks sound board and speaker in my Solent class with twin Napier Diesel engine sound, I am very pleased with it