Rudder - Swing test

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Rudder

Purpose

To check the rudder swing in port and starboard directions, its maximum movement. Also the jumping stopper clearance, pintle bush clearance, and neck bush clearance is checked for three conditions: center, port swing, and starboard swing.

Procedure

Rudder swing inspection is done after the rudder assembly is fitted in the ship, and in the dry-dock (in case of the ships constructed in the dock).

Tests
Illustration Description
Thickness gauge
Clearance measurement

The first step is to keep the rudder at the center position. The rudder centering is done earlier so that the ship center, shaft center, and the rudder stock center meet at a point. From this point, along the centerline of the ship, a ling is drawn which is the zero degree of the rudder movement.

Once that is established, the various measurements are taken. The clearances are all measured using a thickness gauge. The photo on the left shows a Hando (Germany make) gauge with a range of 0.03 to 1 mm.

Rudder swing-nut inspection.jpg
Nut Inspection

Pintle nut inspection plug: Usually in the port side. A rod is connected to the pintle nut and it extends towards the plug. Through the plug the position of the rod will show if the nut has moved (loosened). The tip of the rod is orange in colour. In the snap on the right the central orange color is the tip of the rod whose other end is the pintle nut. The circular opening is the plug.

Rudder stock nut inspection plug

Similar to the pintle nut inspection plug there is also the rudder stock inspection plug. Here we see if the rudder stock nut has loosened by noting if the orange tipped rod has moved position.

Rudder swing-jumping stopper.jpg
Jumping stopper

Jumping stopper bar clearance: The jumping stopper bar is attached to the rudder horn lower side on the port and starboard side. As the name suggests it prevents the rudder from jumping up while the ship is in motion.

The normal clearance between the stopper and the rudder is 2-3 mm and this is measured using the thickness gauge.

Rudder swing-pintle bush clearance.jpg
Pintle bush clearance

Pintle bush clearance: The clearance between the pintle and the bush (rudder stock lower side) is measured using the thickness gauge. The clearance is taken in four sides: forward, aft, port, and starboard. The measurements are taken through the inspection cover, usually on the port side.

The normal clearance is about 1 to 2 mm.

Rudder swing-neck bush clearance.jpg
Neck bush clearance

Neck bush clearance: The clearance between the rudder stock and the neck bush (rudder stock upper side) is measured using the thickness gauge. The clearance is taken in four sides: forward, aft, port, and starboard. The measurements are taken from top of the rudder.

The normal clearance is about 1 to 2 mm.

Rudder swing check

Rudder swing to port side: Now the rudder is swung to port 35 degrees and the above clearances are measured.

Rudder swing to starboard side: After that the rudder is swung to starboard 35 degrees and the above clearances are measured.

Rudder maximum swing check: The maximum swing value of the rudder, 37.5 degrees is verified. This is usually the maximum angle mechanically possible.

Rudder sealing

Once these inspections are finished the rudder is filled with VCI (Volatile Corrosion Inhibitors) powder, a white crystalline powder, one kg of it is sprayed inside the rudder through the plug on the top of the rudder. After that the rudder is sealed and vacuum test is done to confirm the water-tightness.

Conclusion

The outcome of the test has to be noted down and any suggestion has to be mentioned in the inspection report.