vor 1 Jahr

HANSA 07-2019

  • Text
  • Hansaplus
  • Maritime
  • Hansa
  • Shipping
  • Sewage
  • Hamburg
  • Ships
  • Cyber
  • Marine
  • Schifffahrt
  • Vessels
Neue Studie Offshore-Wind | Brandschutz & Lifesaving | Abwasser-Behandlung | Neuer Container-Typ | Car Carrier & Fahrzeughäfen | Piraterie und die Folgen | Cyber Security

Schiffstechnik | Ship

Schiffstechnik | Ship Technology Thordon promises reduced seal maintenance costs Compliant and economical by seawater Compliance with the ever-increasing amount of marine environmental legislation inevitably comes at a cost. But sometimes there are solutions that are not only able to satisfy the legislators, but also save money for the ship operators © Thordon Bearings Take, for example, compliance with the current United States Environmental Protection Agency (EPA) Vessel General Permit (VGP) regulations, with similar laws expected within other jurisdictions. Under the VGP, discharge of harmful lubricants and oils is very tightly controlled. This can apply to many areas of the ship – fuel spillage, grease on chains or wire ropes, lubricants for deck gear, and most of all, leakage from propeller shaft seals. For cruise companies, whose ships sail frequently in US waters, and with most cruise ships having multiple propellers or podded propulsion units, such leakage is a particular problem. The VGP demands the use of Environmentally Acceptable Lubricants – EALs. The EPA defines an EAL as one that is non-toxic, biodegradable, and exhibits low bioaccumulation, i.e. it will not build up over time within the tissues of an organism. Formulating efficient lubricants which display all these properties is something of a challenge for the manufacturers, so EALs inevitably carry a cost premium over conventional oils. Seawater as the sterntube’s lubricating medium fulfils the EAL criteria perfectly and is available in plentiful quantities at no cost. After all, for many years prior to the 1950s, ships’ shafts turned with lignum vitae (wood) bearings lubricated by seawater. However, those old wooden bearings wore out quickly, so the industry turned to conventional white metal bearing materials requiring oil lubrication, which in turn needed seals to keep the oil within the sterntube. Canadian company Thordon Bearings has specialised in reviving and updating the traditional technology, replacing the old bearings with modern polymer materials offering far superior wear characteristics. Thordon’s COMPAC bearings have been developed over more than 35 years and the company is now sufficiently confident in their durability and reliability that its seawater lubricated propeller shaft system comes with a lifetime guarantee. The previously stated lifetime was 15 years, but extensive studies of more than 550 systems installed on commercial ships show that, with the current life of the average merchant vessel given as 25 years, a Thordon COMPAC-based system is capable of exceeding that timespan. Thordon Bearings’ President and CEO Terry McGowan explains: »We found that if the bearing environment was controlled – ensuring an adequate supply of clean water consistently delivered to the shaft bearings – the COMPAC bearing wear was minimal.« The complete system comprises, in addition to the modern polymer bearings, of the ThorShield anti-corrosion shaft coating, the shaft liners, the SeaThigor forward seal, and, the Thordon Water Quality Package to remove abrasives from the seawater and pump it to the shaftline. 56 HANSA International Maritime Journal 07 | 2019

Schiffstechnik | Ship Technology © Thordon Bearings The COMPAC bearing allows for inspections without shaft withdrawal Despite the environmental and operational cost savings to be had with seawater lubricated systems, over 95% of all new commercial ships continue to be built with oil lubricated propeller shafts. This is largely due to the low capital expenditure of an oil lubricated system. The complete Thordon system may have higher up-front costs, but any financial advantage of an oil lubricated bearing disappears as soon as the vessel enters the water due to the purchase of lubricating oils plus the regular maintenance and unscheduled drydockings to repair or replace faulty seals and other components. According to Thordon’s calculation, the cost of a typical oil-lubricated system depends on oil price fluctuations, but over the ship’s 25-year life it is in the region of 606,000 $ – or more if the cost of EALs is included – against 370,000 $ for the COMPAC system. And the use of seawater completely eliminates the risk of pollution as there will never be a release of oils or other lubricants due to shaft damage or seal failure. Even EALs are regarded as pollutants where some research suggests that the impact on ecosystems is similar to mineral oil. The cruise industry has been a major user of Thordon’s system for over 20 years, with well over 30 ocean-going cruise ships operating with COMPAC seawater-lubricated bearings and many more on order. Of the first installations, in 1998, the bearings on »Grand Princess« were routinely replaced during a major refit after 18.5 years of continuous service, while those installed on »Disney Magic« are still operating reliably. However, a number of cruise ships use azimuthing propulsion pods rather than conventional propeller shafts and rudders. Although benefits advertised include increased manoeuvrability, low noise, and efficient use of space within the hull, these are disputed by some in the industry as the reported problems of podded propulsion have led to many weeks of cruise cancellations or delayed itineraries. Other disadvantages of azimuthing propulsion pods include limitations to about 30MW maximum power, high maintenance costs, and the need for correct operation in order to limit high loads and stresses that can occur during some manoeuvres. Wear resulting from such stresses adds to normal risk factors – such as seal damage resulting from fishing nets and rough seas - in making pods susceptible to oil pollution discharges. Thordon points out that use of propeller shafts, especially using seawater lubrication, eliminates those pollution risks, provides a more reliable system, reduces the risk of lost revenue from unscheduled downtime, is not subject to power limitations, is simpler to operate and is far less costly to run and maintain. And the efficiency gains often attributed to pod installations are mainly due to the electric drive systems within the pods, so can be closely matched by diesel-electric propulsion driving conventional propellers. Thordonargues that the sterntube can be eliminated altogether, reducing building and operating costs. A paper presented to SNAME in 2018 by Thordon founder George A. Thomson and Engineering Director Kenneth Ogle says that while a sterntube is an absolute necessity when oil-lubricated bearings are employed, it incurs an operating cost of around 31,000 $ p.a. Water lubrication, designed into the ship from the outset, means the sterntube is unnecessary, simplifying shaft installation and maintenance and drastically cutting operating costs. »It’s a no-brainer and saves cost for the yard and the owner,« says Thomson.ED HANSA International Maritime Journal 07 | 2019 57

HANSA Magazine

HANSA Magazine

Hansa News Headlines