Nippon Kaiji Kyokai (ClassNK) has joined the most important classification societies to amend its guidelines referring to the inspection of seawater-lubricated propeller shaft programs.
The modification implies that ships with open seawater-lubricated propeller shafts which can be constructed to ClassNK guidelines are topic to the identical 15-year shaft withdrawal inspection intervals as oil-lubricated shafts and sterntubes, topic to monitoring standards.
The announcement brings ClassNK’s necessities in step with these of different massive class societies, together with Lloyds Register (LR), the American Bureau of Shipping (ABS), Det Norske Veritas (DNV), Bureau Veritas (BV) and the China Classification Society (CCS), which have already stipulated 15-year or longer intervals between inspections, a few of them since 2016.
In its amendments to the Rules and Guidance for the Survey and Construction of Steel Ships, printed on 30 June 2023, Class NK clarified its causes for the change: “In recent years, the development of mechanical type sealing devices, and bearings with lower wear properties as well as improvements in corrosion prevention technology, have led to fewer wear and corrosion defects in both shafts and bearings. In addition, interest in seawater-lubricated bearings, which do not use lubricating oil, and their effectiveness has increased among relevant industry members due to concerns for the environment.”
ClassNK additionally famous that the modification follows requests obtained from {industry} stakeholders referring to the developments made in superior seawater-lubrication system expertise.
Thordon Bearings is among the corporations that has supported requires industry-wide standardization of prolonged shaft withdrawals for seawater-based lubrication options that are actually corresponding to sealed oil lubricated programs.
Craig Carter, Vice President of Business Development, Thordon Bearings, mentioned, “We are delighted that ClassNK has now joined the other major classification societies in dispensing with the wholly unnecessary and costly need to withdraw a seawater-lubricated propeller shaft for inspection every five years. Technology has come a long way since the first-generation seawater-lubricated lignum vitae bearings of the 1950s.”
While the danger of shaft corrosion in open seawater-based programs was traditionally a priority with first-generation bearings, main some classification societies to proceed demanding enhanced inspection regimes, new supplies and applied sciences imply seawater-based programs can exceed the efficiency and reliability of their oil-based counterparts.
Elena Corin, Senior Manager, Special Marine Projects, Thordon Bearings, mentioned, “Aside from our pioneering polymer bearing technology, Thordon has enabled the development of Thor-Coat – a toughened, modified epoxy coating, which is applied to exposed steel areas of the shaft between the liners to eliminate the need for shaft withdrawal. In the event of damage, seawater cannot wick under the coating along the shaft and the epoxy coating is spot repairable.”
In addition to the modification concerning the inspection of seawater-based propulsion programs, Class NK has additionally up to date a number of different necessities. These embody new formulae for sloshing masses and new necessities for the upkeep and administration of offshore wind turbine installations. Other modifications embody clarification of scope for cover in opposition to fireplace when transferring cargo to different vessels on liquefied fuel carriers, clarification of the NOx emission requirements for biofuel, new necessities for forged and solid metal merchandise, and amendments to security necessities for reciprocating inside combustion engines.