Aside the main propulsion for a vessel, supporting systems for navigating, steering and stabilising the vessel are of equal importance.
Steering systems are in constant use and form a key element of any maintenance and inspection programme – they literally keep the vessel on track. When it comes to ensuring the comfort of passengers or stability of a warship platform – stabilisers maintain minimum vessel movement while making way in heavier seas.
Tunnel thrusters come into their own when entering or leaving port – time is saved in not waiting for tug support and fine manoeuvrability in confined quarters and heavier weather are of great benefit.
Forming an essential part of ship operation, comfort and safety – these systems are of particular importance during vessel maintenance.

STEERING

The forces generated around the rudder are proportional to the size and speed of the vessel – with enormous loads being supported through bearings to the ship structure in the case of large container of cruise vessels. Effort to maintain a steering course in heavy seas or rotate the vessel while moving is large and the majority of rudder systems are hydraulically actuated and controlled. Rudderstock diameters can vary from only a few centimetres on a leisure vessel up to well in in excess of 1.5m in the case of larger ships.

Rudder systems need routine maintenance and a proactive approach can help to identify small issues before they become a risk to operations.

A typical steering gear survey would include:
  • A review of performance to date
  • Review of manufacturer recommended maintenance and part upgrade schedules
  • Visual inspection of the installations for damage, noise, leaks and wear
  • Measurement of operating range and any bearing wear
  • Control and monitoring system checks
  • Checking of system oil and condition

The above can normally be carrier out during service, with the resulting recommendations leading to a repair plan for the next dry dock.

THRUSTERS

Tunnel thruster operating time is generally low compared to the running time of the main propulsion system. They are mostly used for manoeuvring the vessel in dock, or to help maintain position alongside in high winds in case of a mooring line failure.

They are not propulsion critical equipment, but should they be damaged – significant vibration and noise can degrade passenger experience, as well as causing water leakage into the vessel or of lubricant into the sea.

A limited system survey can be carried out in service, sometimes including dive inspections from underwater noting and leaks and damage. During dock, a more thorough survey can be undertaken by removing outer covers to check bearing condition, gear clearances and seals.

STABILISERS

Stabilisers are expected to have an almost opposite operating profile to thrusters, in that they are in almost constant operating during transit and inactive during manoeuvring and docking.

Again, while not considered an essential propulsion item – they are instrumental to the comfort aboard passenger and cruise vessels in transit.

Full in-service survey can only be undertaken in certain conditions owing to the limited extension on at least one side of the vessel while moored alongside.

This would include:
  • A review of performance to date
  • Review of manufacturer recommended maintenance and part upgrade schedules
  • Visual inspection of the installations and hydraulics for damage, noise, leaks and wear
  • Measurement of operating range, cylinder extension and retraction and any bearing wear
  • Control and monitoring system checks
  • Checking of system oil and condition

FAQ’s

There is an unusual whistling from a thruster in operation following a rebuild – Is this a problem?

It could be but could have a simple fix.
Assuming the overhaul was completed correctly, it is possible the hydraulic system still has some residual air. Bleeding the system again may help. If the issue persists further investigation is recommended.

We want to change to an EAL oil – is this a straight swap?

No – each part of the system needs to be considered for compatibility first. A system flush may be required and some seals and other equipment might need to be changed for a compatible material.
AtZ can review your system and advise any required steps for upgrade.

Our vessel is getting old and we are no longer able to source parts for the stabiliser control system. We cannot justify a new system – what are our options?

We have experience in retrofitting controls to legacy systems. Assuming the mechanical and hydraulic elements of the system can be returned to serviceable condition, we could propose a retrofit of controls.
Please get in touch and we can arrange a consultation with one of our controls team.

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