What is Rudder Drop or Rudder wear down and how to measure it ?

What is Rudder Drop ?

Rudder Drop is simply the wear down of the bearing of rudder carrier.

How Rudder Drop measured in ship ?

It is measured by an instrument called a Trammel gauge.

Must Read :- Propeller Drop

How Rudder Drop measured ?

As We know that the drop is measured by a trammel gauge.

The Trammel gage is an L-shaped instrument.

Generally, a point marked on the rudder stock and another point is marked on the hull within the steering gear room (Here it is on the Deck head girder).

The distance between these points shall be measured and recorded at the time of construction.

The difference between the original and the measured points shall be referred to as the rudder drop


the rudder wear down as shown in the fig.

Rudder drop

Rudder Clearance

The pads are welded to the rudder and the hull. The clearance is given sometimes referred to as the jumping clearance . This clearance will increase as the carrier wears increase.

Why Jumping clearance required ?

The jumping clearance is required for preventing damage to the steering gear,regardless of type of rudder.

Therefore the maximum jumping clearance should always be less than the clearance between steering gear and the tiller arm.

Increasing jumping clearance can mean that the wear of the bearing is excessive.

Steering clearance

The measurement can be taken directly from the steering gear assembly. One example is shown below, here the clearance will be seen to reduce as the carrier wears and impact on the system can be directly judged.

The below figure is of Rudder:-


You can read

1.How is rudder supported ?

Rudder is supported on rudder carrier

2.What is pintle in rudder ?

Pintle on which rudder turn.

3.Which of the following instruments is used to measure rudder carrier bearing wear down?

1.Feeler gauge

2.Trammel Gauge

3.Vernier callipers

4.None of these

4.How is propeller drop measured ?

5.What is propeller clearance ?

The distance from the blade to the different part of the hull is called propeller clearance.

It must be kept above certain minimum limits to avoid transferring vibrations to the hull.

The distance from the propeller to the hull has a linear influence on the pressure impulses. 

As this distance decrease cause increase pressure impulse on hull ,so to avoid transferring vibrations to the hull this us kept up to certain limit.