Kongsberg Simrad SN90 Reference Manual page 289

A hull unit may be provided as an option. It allows you to lower and hoist the transducer.
All information and tasks related to the hull unit may be disregarded and omitted if the
SN90 system is installed without this unit.
Procedure
1 Inspect the hull unit for water intrusion.
2 Consider whether it is necessary to add grease to the transducer shaft sleeve.
Adding grease to the transducer shaft sleeve is only required if the shaft is dry, or if
water forces its way up along the shaft.
3 Open the pressure relief plug.
You do not need to remove the pressure
relief plug completely. It has a groove that
allows excess lubricant to drain out.
4 Connect a grease gun to the nipple and add
grease.
Note
Do not use excessive amounts of lubricant.
If you add too much grease you may damage the internal bearings. Such damage
may result in a large water leak, and it may cause the hull unit to malfunction.
5 Stop applying lubrication when excess grease leaks out of the pressure relief plug.
6 Close the pressure release plug firmly.
381294/E
Maintenance procedures
287