Chartplotters are often combined with fishfinders to offer a visualization of what’s waiting below. For this purpose, power and transducer size determine just how deep you’ll be able to look. For shallower depths (up to 200’), units with 100-300 watts should prove adequate. Boat in deeper waters, however, and you’ll need more power to truly see what’s waiting below. You’ll also benefit from a transducer with a more focused beam. Look for the size of the transducer crystal; the larger it is, the more focused the beam…and the deeper it will penetrate.