Fishfinders

Where you mount your transducer depends what boat and purpose you are using
the sounder. There are pros and cons for each mounting.
Transom mount is probably the most popular among trailer boat owners
because it is quick and simple to mount. When positioned correctly the
transducer will provide excellent results at all speeds.
The down side is that it is exposed to damage when running aground and
launching and retrieving dependant on the rig. The transducer needs to be
mounted so the sending face is below water level at high speed or the air
under the transducer will prevent it reading this can cause a rooster tail
effect when poorly mounted.
Mount the transducer between the hull strakes and so the sending
face sits about 5 to 10mm below the hull as close to the centreline of the
boat as practical.
Thru hull mounting is more popular with moored displacement hull
vessels it does require putting a hole in the hull but ensures the best
possible results in most situations.
Wet box mounting is achieved by building a box filled with glycerine
and mounting the transducer in the lid with the sending face submerged in
the glycerine. The sounder is then reading through the hull and will have a
slightly reduced sensitivity at the out side ends of its capability. The
only downside of this mounting is when mounted on a fibreglass hull there
are often air bubbles within the lay-up which can prevent the transducer
from working.
to find the right spot for a wet box mounting first use a soft silicone
sealer to mount the transducer ensuring there are no air bubbles in the
silicone and test for suitability before building the wet box. I would
suggest this for a thru hull fitting as well. Hope this has been of some
help
Dave