Furuno FSV-84 - Manual (Page 12)

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1.1.3 Remarks for installation of retraction tank
1. Install, if possible, the tank on the keel where the tank can be most firmly fixed.
2. Install the reinforcement ribs as near as possible to the top of the retraction tank, allowing
space for tightening of nuts and bolts.
Retraction tank
250-300 mm
Reinforcement rib
Minimum quantity: 4
Thickness: at least 12 mm
How to install reinforcement ribs
3. Add a doubling plate (a plate added to another to give extra strength or stiffness) at the
location where the retraction tank is welded to the hull bottom. The size of the doubling
plate is such that it may lie across two bottom frames.