11.5.1 Clearances of sea water—lubricated bearings
Similar to measuring the clearance of the rudder pintle, remove the guard ring, insert the feeler gauge or the measuring wedge from the stern tube side and measure the clearance. Before the lignumvitae dries out after the ship is drydocked, measure the clearance of the upper surface and record the results of the measure-ments in the Inspection Record Form M-1. For
a ship with twin shafts, item 1. in the form is for the propeller on starboard side, and item 2. is for the port side. If a twin—shaft ship has shaft
brackets, enter the measurements in the lower Dart of the form
Fig.11-6 Measurement of Clrarance
Table 11-2 Results of mesurement (1)
The allowable maximum clearances according to shaft diameter are given below. If the values below are exceeded, the stern tube bearing material should be replaced or repaired.
Table 11-3 Allowable max. clarance
12.5.2 Weardown of oil—lubricated bearings
Unlike lignumvitae used in water—lubricated bearings, metal can be used in oil—lubricated bearings, and the clearance between shaft and bearing can be reduced. Wear is also small, and most modern ships use oil—lubricated bearings.
Clearances should be measured at the same shaft positions as the previous measurement. To specify the shaft position, use the position of
the propeller blade or the position of the main engine piston. Generally, this position is specified according to the position of the propeller blade; for example, measure clearance with blade A at the top. If no hole for measuring sinkage is provided in the guard ring, the guard ring should be
removed, the screwed cap of the measuring hole removed, and a measuring instrument such as Vernier calipers, so—called wear down gauge, inserted and distances from the bearing to the upper and lower surface of the shaft measured. The measued records is to be entered in the survey report showing the position of measured point sucha sa the Key Top or No. 6 Crank Top.; however, unless the bonnet is removed, the key position cannot be judged; therefore, it is convenient to take a specific blade (cylinder) as the reference for sinkage measurement. In large ships today, propellers are generally keyless. Sinkage is the difference in measurement at the time of inspection and measurement when the ship was built. The standard limit for sinkage is 0.3 mm irrespective of the shaft
diameter. Sinkage should be determined by studying the properties of lubricating oil, and the history of temperatures of the lubricating oil and bearing material. An example of the Inspection Record is shown below.
Photo.11-6 Measuring clearnce
Example of position propeller shaft
Fig.11-7 Position of propeller blade
Table 11-4 Results of measurement (2)
(1) Example of measuring clearance in a oil-lubricated bearing
Similar to measuring the clearance of the rudder pintle, remove the guard ring, insert the feeler gauge or the measuring wedge from the stern tube side and measure the clearance. Before the lignumvitae dries out after the ship is drydocked, measure the clearance of the upper surface and record the results of the measure-ments in the Inspection Record Form M-1. For
a ship with twin shafts, item 1. in the form is for the propeller on starboard side, and item 2. is for the port side. If a twin—shaft ship has shaft
brackets, enter the measurements in the lower Dart of the form
Fig.11-6 Measurement of Clrarance
Table 11-2 Results of mesurement (1)
The allowable maximum clearances according to shaft diameter are given below. If the values below are exceeded, the stern tube bearing material should be replaced or repaired.
Table 11-3 Allowable max. clarance
12.5.2 Weardown of oil—lubricated bearings
Unlike lignumvitae used in water—lubricated bearings, metal can be used in oil—lubricated bearings, and the clearance between shaft and bearing can be reduced. Wear is also small, and most modern ships use oil—lubricated bearings.
Clearances should be measured at the same shaft positions as the previous measurement. To specify the shaft position, use the position of
the propeller blade or the position of the main engine piston. Generally, this position is specified according to the position of the propeller blade; for example, measure clearance with blade A at the top. If no hole for measuring sinkage is provided in the guard ring, the guard ring should be
removed, the screwed cap of the measuring hole removed, and a measuring instrument such as Vernier calipers, so—called wear down gauge, inserted and distances from the bearing to the upper and lower surface of the shaft measured. The measued records is to be entered in the survey report showing the position of measured point sucha sa the Key Top or No. 6 Crank Top.; however, unless the bonnet is removed, the key position cannot be judged; therefore, it is convenient to take a specific blade (cylinder) as the reference for sinkage measurement. In large ships today, propellers are generally keyless. Sinkage is the difference in measurement at the time of inspection and measurement when the ship was built. The standard limit for sinkage is 0.3 mm irrespective of the shaft
diameter. Sinkage should be determined by studying the properties of lubricating oil, and the history of temperatures of the lubricating oil and bearing material. An example of the Inspection Record is shown below.
Photo.11-6 Measuring clearnce
Example of position propeller shaft
Fig.11-7 Position of propeller blade
Table 11-4 Results of measurement (2)
(1) Example of measuring clearance in a oil-lubricated bearing
| (1) Original |
| (3) Inserting the gauge |
| (4) Measurenent |
Fig. 11-5 Measuring of propeller shaft clearance
(2) Example of measurement results for sinkage
Measurement results for two ships and their graphs are provided below for reference.
The part above the kinked line shows the top, and the part below the kinked line shows the bottom measurement values. The position of the blade does not conform to the key top position but the No. 8 piston top
position.
Ship (1) : Tanker, 72,368G/T,built in 1975
(2) Example of measurement results for sinkage
Measurement results for two ships and their graphs are provided below for reference.
The part above the kinked line shows the top, and the part below the kinked line shows the bottom measurement values. The position of the blade does not conform to the key top position but the No. 8 piston top
position.
Ship (1) : Tanker, 72,368G/T,built in 1975
| Month | Measurement | Month | Measurement |
| 4/1977 | 114.30114.85 | 6/1978 | 115.40/114.75 |
| 9/1979 | 115.50/114.80 | 11/1980 | 115.50/114.80 |
| 5/1982 | 115.60/114.80 | 9/1983 | 115.30/114.70 |
| 5/1985 | 114.90/114.70 | 11/1986 | 114.90/114.60 |
| 10/1988 | 114.90/114.60 | 10/1990 | 115.10/114.90 |
| 9/1992 | 115.40/115.00 |
Ship (2) : Tanker, 43,444G/T, built in 1975
| Month | Measurement | Month | Measurement |
| 12/1981 | 72.7/73.1 | 4/1984 | 72.6/73.2 |
| 5/1986 | 72.9/73.1 | 6/1988 | 73.3/73.3 |
| 4/1990 | 73.4/73.3 | 5/1992 | 73.3/73.4 |
Fig.11-6 Results of measurement (3)
11.6 Inspection of Stern Tube Seal
Oil leaks from the propeller boss in the stern frame of an oil—lubricated system can sometimes be detected during a bottom inspection. This is probably due to a defective seal, therefore, a detailed examination of the
seal is necessary.
Fig.11-7 Oil leakage from propeller boss
11.7 Bow Thruster and Side Thruster
These items are shipowner's options, therefore, they need not be inspected under class requirements. However, if these items are
installed on the ship, they should be inspected at the docking survey. Frequently observed damage includes damage to guards at sea water ports due to impact with submerged or floating objects, and bent propeller blades. If the shaft seal is defective, water entersin to the ship; however, such incidents are not reported. Inspection results should be entered in the Survey Report.
When the stainless plate is used in the surface of the nozzle, the corrosion of
adjusent steel plate suould be carafully inspected.
Fig.11-8 Damage of side thruster guard
Fig.11-9 Damage to side thruster
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