Furuno CH-270 Installation Manual page 22

Installing the retraction tank
Install the retraction tank referring to outline drawing for
the retraction tank.
Note 1: The seam of the tank should be positioned either
at the port or starboard side, otherwise the tank
guide on the soundome will contact the welded
portion of the retraction tank, preventing smooth
retraction.
Note 2: When the retraction tank is locally made, it is
recommended that the seamless pipe
STPG38-S-C (carbon steel pipe, for pressure
release) or equivalent be used.
Installation on an FRP vessel
The retraction tank is usually installed vertical to the ship's draft line. For a small FRP vessel
tilt it 2°. However, since this method increases water pressure in the tank because of
resistance at the rear of the tank well, install a fin at the location shown below to provide
smooth water flow.
The fin creates a rise of 1-1.5 cm at the front side of the retraction tank. This allows water to
flow smoothly along the ship's hull, eliminating swirls.
Retraction dome
Hull
Fin
Water flow
10
Tank Guide
BOW
Welding
Seam
BOW