JRC JLN-900 Installation And Instruction Manual page 42

Transducer "Bottom View" from hull underside Transducer "Profile"
Bottom Parts
The two versions of Bottom Parts of the system are shown in Fig. 1.1 and Fig. 2.1.
A steel flange is welded to a cut-out in the ship's bottom hull plating. The Bottom Flange,
including the Guide Ring, positions the Transducer flush with the underside of the hull.
With the SeaValve arrangement the intention is to provide retraction/removal for
service/maintenance or replacement of the Transducer while the ship is still afloat, thus dry
docking is not needed.
The Connecting Tube with a Tube Bracket assembly holds the Transducer fixed in its position
and has a watertight Cable Gland at its top end.
Sea Valve arrangement (MSSBSV H as example)
4-4