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Rudder carrier bearing,how to measure rudder drop

Rudder carrier bearing structure:
The rudder carrier bearing takes the weight of the rudder on a grease lubricated thrust face. The rudderstock is located by the journal, also grease lubricated. Support for the bearing is provided by a doublers plate and steel chock. Wedge type side chocks, welded to the deck stiffening, locate the base of the carrier bearing. The carrier is of meehanite with a gunmetal thrust ring and bush. Carrier bearing components are split as necessary for removal or replacement. Screw down lubricators is fitted, and the grease used for lubrication is of a water resistant type (calcium soap based with graphite). reasons for conshaped contouring of thrust
face:. i For lubrication .ii. Conical in order to prevent sideslip and centralize rudder iii. Projected area gives greater bearing area allowing smaller diameter bearing.
Measurements made: 
Generally two measurements are made
 rudder wear down: down refers to the measurements taken generally during a docking period to indicate excessive wear in the steering gear system particularly the rudder carrier. This wear down or rudder drop is measured using a special L shaped instrument called Tramel. 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 center punch mark by an amount equal to the wear down.
Jumping 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

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