Got a sniff of these Furuno 1kw transducers a little while back and they look the goods
A good combo would be the wide angled for 200khz (4xtimes beam width)
and the narrow angled for deep water readings to 900mts for the 50hkhz
Wide Beam
http://airmartechnology.com/airmar20...uno&PageNo=512
Narrow Beam
http://airmartechnology.com/airmar20...uno&PageNo=513
regards Frank