There are some new (and priced like new technology it expensive) transducers by Airmar which will "see" or "hear" through the hull. Since you already have a transducer, it is probably installed through a hole in the hull. You would be better off just taking it out and installing a new through-the-hull transducer in the same opening.
NOne of these companies make their own transducers. Virtually all of them buy them from Airmar. I have had good luck with products from Garmin, from Northstar (not cheap) and Furuno. Some of the newer RayMarine stuff looks pretty good but I have not used it myself. In the past Raytheon had a reputation for letting their first customers figure out all the bugs in their new equipment. Personally I would get an inexpensive LCD Garmin or Furuno. Get the best transducer you can with it, it makes a difference in how they work. A good transducer will give you better info, better pictures, and last longer. A good source for info on transducers is Gem Electronics in South Carolina. They are a small outfit but know a lot about transducers and can give you good advice as well as selling them, and the cables to hook them up.
Many of these units come with transducers or not very many choices about what you get. Furuno seems to be the exception- they often sell the units bare and let you pick the transducer that you want for your boat. That, to me, is a better approach.
