Paul,
We had a hand held DF before and thought it was somewhat cumbersome to use when you were by yourself.
We glued in a
thru hull type
transducer for a humminbird in to our hard nesting
dinghy and find it to be much easier to use. Either rowing or w/the
outboard we see continuous
depth data which show contours better, etc. A stern mounted
transducer would
work similarly.
There are some newer apps (Navionics?) that allows one to collect data, then transfer it to your chart plotter to essentially make
charts.
Haven't fully researched this to see how feasible it would be to collect data in poorly charted areas, but would think this could be very helpful info for fellow cruisers.