Mounting the installation trunk extender
If you are replacing an older sonar with a new SU90 system, you may not need to install a new installation trunk. A dedicated trunk extender can be provided to increase the height of your existing trunk.
Prerequisites
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The shipyard must provide all necessary tools and manpower.
The item is heavy. Always use appropriate lifting equipment to minimize risk of personnel injury or equipment damages. Only certified equipment must be used.
Procedure
1 Make sure that the upper surface of the installation trunk is level, undamaged and clean.
2 Clean the trunk extension properly.
3 Place the gasket (O-ring) in its thread at the top of the existing trunk.
4 Apply a thin film of silicon grease on the O-ring.
5 Place the trunk extender carefully on top of the existing trunk, and mount it with the bolts.
Use the correct torque:  470 Nm
6 Brace the installation trunk to the hull plating and the surrounding hull frames by adding several strengthening plates.
The minimum plate thickness is 10 mm, but the classification society can specify other dimensions.