What's the difference between the Garmin Marine GT56 and GT51 transducers? It all comes down to frequencies and power. The GT56, it's 2D element, has 350W of power, and it is a high, wide beam. This means it has a fair coverage, so it spreads the power out a long way. Being a high frequency, it doesn't quite go as far as mediums and lows. The GT51's 2D element is 600W, not 350W, and a medium frequency which drives a lot further out than a high frequency does. Take a look at the video to compare