Jumping clearance and its purpose

Abstract

Navigation is considered to be priority among all the operation on board a ship. The Steering system is one of the most crucial component in a vessel which assists the mentioned operation when the vessels are underway. Therefore, several safety features are installed in the steering system to protect the system from any type of failure during the voyage as the breakdown of the latter would prove to be a major blow to the authorities. One such safety feature, known as Jumping Clearance, is being discussed in the following study.

Introduction

The steering gear system generates a torsional force using the Tiller at a certain scale known as the sliding arm, which is then, in turn, is transmitted to the rudder stock, supported by the rudder carrier bearing, that turns the rudder. The intermediate steering systems of a modern day ship have many more components consisting the whole system, each of which have their own respective functions. The steering system works in the following sequence:

Figure 1 : The flow of the sequence of steering operation.

Rudder drop

Rudder drop is defined as the wear down of the rudder carrier bearing as a result of the mechanical forces acting on it, namely buoyancy force( with which the rudder stock would ascend and damage the steering gear components), friction etc. The rudder drop would nullify the purpose of using the rudder carrier bearing which are supposed to reduce the friction during the rotation of the rudder stock during navigation. The rudder drop is measured using the trammel gauge.

Measures to reduce the rudder drop

  • More frequent greasing of the bearing
  • Proving jumping clearance
  • Regular care & maintenance of bearing

Jumping Clearance

Jumping Clearance is defined as the clearance or the distance between the tip of the rudder and the jumping or stopper bar. The jumping bar or the stopping bar is nothing but a rigid slab of metal which is being welded to the ship’s hull. Since, the bar needs to withstand heavy buoyancy force, acting on the rudder, it has to be made of high strength materials which has to be corrosion resistant and should be having a ductile nature.

Now, whenever the rudder ascends due to bad or heavy weather, the rudder stock also ascends as they are keyed to each other. The jumping bar limits ascend of the rudder along with the rudder stock. How much the rudder would ascend depends upon the value of jumping clearance before it hits the jumping bar. The maximum jumping clearance should always be less than the clearance between steering gear (the sliding ram) and the tiller arm. If the jumping clearance was not provided then it is very probable that the rudder would hit the hull with unimaginable force resulting to the damage of hull. Further, because of the ascend, the rudder stock would hit the lower tiller which in turn strikes the sliding ram causing the ram to bend. In a nutshell, the entire steering system would break down. To prevent such undesirable situations to take place, jumping clearance is provided.  

Purpose of providing jumping clearance:

  • Prevents bending of the sliding ram.
  • Rudder drop can be reduced.
  • Protection of hull from the impact of rudder during heavy weather.
  • Tiller arm can be prevented from hitting the sliding ram or the steering gear.
jumping clearance
Figure 2 : A simplified view of the jumping clearance.

Conclusion

The technological advancements are at its peak. Every now and then a new safety feature with the latest technology in being introduced in the market not only in maritime industry but also in the other industries involving the entwined twins of computers and humans.  Jumping clearance being the simplest and the most beautiful example of the knowledge of humans along with the use of technology of welding which makes the ship much more safer place to work on.

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