There is an explanation of the matter in layman terms.
http://www.airmar.com/uploads/brochures/understanding_xducer_specifications.pdfRMS Power vs Peak-To-Peak Power
All Airmar transducers are measured in RMS power as opposed
to peak-to-peak power ratings. Peak-To-Peak power ratings
are eight times higher than RMS power, which can trick the
consumer into thinking their echosounder and transducer are
more powerful than they really are. For example, if transducer
manufacturer L advertises 4,000 Watts peak-to-peak power, this
is only 500 Watts RMS power. See the chart below for typical
Airmar transducers and their power ratings in both RMS and
Peak-To-Peak.
RMS Power Peak-To-Peak Power
250 W RMS = 2,000 W Peak-to-Peak
600 W RMS = 4,800 W Peak-to-Peak
1,000 W RMS = 8,000 W Peak-to-Peak
2,000 W RMS = 16,000 W Peak-to-Peak