Thrusters are very crucial machines for each vessel. It is very important to have them in good technical condition. Maintenance of thrusters is done based on running hours or actual condition indicated by CM techniques. Condition Monitoring (CM) compared to PMS based on running hours has the following benefits:
- the maintenance is done only when there are signs of wear down of particular elements
- the maintenance (that needs to be done according to running hours) can be postponed if condition of elements is good (there are no abnormalities indicated by implemented CM techniques)
- the quality of maintenance is checked by implemented CM techniques
- abnormal readings after maintenance can be used as a proof for claim for performed service
The best system of Condition Monitoring for thrusters is an online system which gives information about thruster in real time. The online system uses two CM techniques:
- oil analysis of lubrication system
- vibration measurements
Info Marine provides an online system that has the following scheme:
For this thruster below sensors are used:
- one vibration sensors on Non drive end bearing of electric motor
- one vibration sensor on Drive end bearing of electric motor
- two vibration sensors on upper gear part bearing
- one revolution speed sensor installed near coupling
- one oil sensor that indicates quality of lubrication system.
Whole data from sensors is going to electrical module that processes all the signals and uploads information in digital form to the server installed on board. Information from server can be seen on every screen on board via browser or also on shore in client’s office if the vessel has good internet connection.
The online system gives in real time:
- RMS values and FFT charts of Velocity
- Peak values and FFT charts of Bearing envelope
- Trend and history of RMS Velocity and Peak Bearings envelope
- Information about oil cleanliness and particle size according to ISO 4406:99 or SAE AS 4059E
The online system has defined limits for warnings and alarms for each mentioned parameter so the Crew will know exactly what the condition of the thruster is.
RMS velocity can indicate:
- misalignment and coupling defect
- looseness and a problem with structure stiffness
- problem with propeller blades
- gearbox defect
- bearings defect (late stage)
The peak envelope indicates every stage of the bearing wear down process. We can see the wear down process from an early stage that can last up to six months. It gives enough time to plan maintenance.
Oil cleanliness according to ISO 4406:99 gives information about the number of particles greater than 4 microns, greater than 6 microns, greater than 14 microns and greater than 21 microns. With reference to the above information we know if in present time we have more and bigger particles that in future can affect the seals or bearings. Many producers have their own standards of oil cleanliness that ensure long life of bearings and seals.
When any parameters exceed the limit the Crew should send measurements for analysis and then Info Marine will precisely advise the reason of abnormal readings and what action needs to be performed.
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