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Dry Dock - Rudder Work

Rudders are generally of framework and sheet metal construction and therefore they have to be checked for corrosion, wear and cracks. The rudder wear down is a measured to indicate excessive wear in the steering gear system particularly the rudder carrier. The significance of this is that for ram systems excessive wear can lead to bending moments on the rams. The readings taken are offered for recording by the classification society.

Trammel
This takes the form of an 'L' shape bar of suitable construction. When the vessel is built a distinct centre punch mark is placed onto the ruder stock and onto a suitable location on the vessels structure, here given as a girder which is typical. The trammel is manufactured to suit these marks As the carrier wears the upper pointer will fall below the centre punch mark by an amount equal to the wear down.

Rudder clearance
Pads are welded to the hull and rudder. A clearance is given ( sometimes referred to as the jumping clearance). As the carrier wears this clearance will increase.

 

Process of removing a rudder (step by step):

The access panels in the rudder are cut out after the ship is in dry dock. The rudder is held in place with chain falls and the rudder stock is then removed along with the mechanical connections inside the ship. The rudder stock is then lifted out through holes in the ships decks. The rudder is then lowered and tilted until the pintle pin is free of its bearing surface in the rudder horn. The rudder is then removed and set up vertically in a work bay. The pintle pin nut access panel is removed and the pintle pin nut is removed. The pintle pin is then removed. Usually the pintle pin is very loose in the pintle pin bore and that is usually the reason the rudder is being removed. Clearances of up to 1/4 inch have been found where metal-to-metal interference fit should exist.

Shown below are some drawings indicating the components and the step by step process of disassembling of the rudder:


Figure1. Supporting the rudder with chainfalls.


Figure 2. Removing the rudder stock nut.


Figure 3. Moving the rudder and pintle pin assembly away from the ships hull.


Figure 4. Removing the pintle pin and nut from the rudder.


Figure 5. Using a tight wire arrangement to determine the center of the tapered bores.

 


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