SubscribeRailko Limited supply over 30 Navies around the World with bearings for propeller shaft and rudder, for both surface vessels and submarines.
Our latest 'New Customer' surface ship successes are the Spanish and Norwegian Navies, where we were able to provide a 'performance package' that convinced them that Railko and NF material are superior to other bearing materials under consideration (rubber types, elastomer and other composite materials).
We are successfully converting both surface ships and submarines originally employing lignum vitae, cotton and rubber staved systems, to Railko 'NF' material and we are also converting 'Elastomeric' shell bearing material to NF. NF is also specified for water lubricated Ferries and Ro-Ro vessels’ propulsion systems.
Spanish Navy F100 Frigate
Photo Property of Navantia
Railko NF is used because of its:
- Low wear rate
- Extremely low/nil noise signature
- Ability to run hydro dynamically at very low RPM's - with low/no stick-slip
- Higher thermal capability than rubber or elastomeric material
- Proven shock resistance
- Higher load carrying capacity
- Low thermal expansion - better stability (less reduction of running clearance) if there is a reduction of coolant flow, causing over-heating of the system
- Low swell characteristic
- Creep resistance - does not allow the shaft to 'sink-in' to the bearing (squeezing the water out from the bearing/shaft interface), leading to a 'dry' (usually noisy) start
- Kindness to shafts - does not tend to allow abrasive particles to embed in it's surface (like rubber and elastomeric materials can), therefore causes less scoring of the shaft
- Consistency of quality (not variable like Lignum Vitae)
- Ease of replacing rubber or other bearing materials/systems
- Ease of machining/fitting and.............
- Our knowledge/technical support/track record of supplying materials to the industry - Railko, in conjunction with the UK Ministry of Defence, have developed the 3rd generation of shell bearing design from the original stave (lignum vitae, thence to rubber) concept; this gives much better hydro-dynamic performance of the propeller shaft bearing system and control of the shaft. The length of a Railko bearing is much shorter (half) than the traditional design of rubber bearing, resulting in fewer shaft : bearing misalignment issues.
- Only one material needed to cover all bearing sizes/vessel type - 'NF'
- NF material can currently be manufactured to suit shaft diameters of 25mm up to around 840mm. We can expand tooling availability to produce 900mm I/D material - when required !
- The design and properties of our material enables very low speeds to be achieved - quietly; high speeds are not an issue, assuming sufficient water flow.
- Shaft counterface: traditionally Gunmetal has proven an excellent counterface, but stainless steels have also been used successfully.
- Operating environment - our reference list covers theatres of operation around the whole World.
- Service time - our UK Navy has furnished us with data of a series of measurements from several Frigates which concludes that the life of a set of Railko NF propeller shaft bearings can be 97 years - obviously, they are changed earlier than that, at key docking periods - but they have the confidence to know that NF will last to the next planned docking.
- Independent tests completed some years ago which gives the performance of NF over an increasing/decreasing speed range in seawater with added abrasive particulate:
The first test observed that there was no significant deterioration of the counterface on conclusion of the test. It does however, also state that there was some 'smearing' of the bearing surface on this aggressive test - albeit of minimal detriment to the overall performance during the test.
Test 2 compared a rubber make of bearing, concluding that NF had 1/5 th the wear, with less deterioration to the surface of the shaft sleeve and friction levels generally lower than rubber.
UND Ro-Ro
Photo courtesy of Flensburger Schiffbau Gesellschaft mbH & Co KG
We would like add at this time that our knowledge of the performance of rubber bearings, in terms of friction and wear, is good - initially. We know that rubber can initially prove to exhibit low friction and wear, however in time, the bearing surface deteriorates, with corresponding increases in friction and wear. The major difference in performance between Railko NF material and materials such as rubber or elastomeric, is the ability of NF to resist embedding of abrasive particles in it's surface - due to it's relative increased hardness compared to the other types of materials. Over time, the particles embedding in the relatively softer rubber scratch the shaft (as indicated in the test reports) such that hydro-dynamic lift of the shaft is impaired. Friction levels increase and wear accelerates.
Through-life-costs of using Railko, particularly with the long life prediction stated by the UK Royal Navy and the reduction in damage to the shaft sleeve, are therefore reduced by using NF. Confidence in the knowledge that Railko is fitted is also greater - particularly in the low/no noise signature, when used in submarines.
We hold ISO 9001 (2000), ISO 14001 and material approvals from all the major Classification Societies.
Phil Cumberlidge.
Head of Business Development.
