I just talked to one of the factory reps at the local boat show and he said with a full keel you will need two transducers with a "Y" cable. They have plastic or bronze transducers. I think a pair of bronze was $1200. A few of my friends have them and the pictures are great but they are on a planning hull boat without the full keel and using one transducer. I have heard too that they are best for less than 100 ft depths and work ok up to 200 but not much beyond. We are mostly recreational bottom fishing and diving so we definitely concentrate on the bottom and not too much on the top and in between. I not an expert by any means so check them out for yourself.