DNV rules – shaft alignment
The DNV rules for classification are tailored to address the industry’s needs for proper shaft alignment and the safe, competitive operation of vessels.
These rules have been developed as part of a continuous process using results from thorough research projects, field experience and evolving design trends – in discussion with key stakeholders in the industry.
In line with the main DNV class rules for shaft alignment, a highly diligent hydrodynamic oil film criterion is applied to verify that the propeller shaft aft bearing performs satisfactorily in all relevant continuous operating conditions. The criterion ensures that sufficient contact area is available to initiate and maintain an oil film of acceptable thickness under these conditions – also considering the viscosity and type of oil used.
This supplements the traditional industry requirements focusing generally on the acceptable loading of all propulsion shaft bearings and on a standard limitation on the maximum angular misalignment of the propeller shaft in way of the aft bearing (relative slope).
Recent main class rule revisions Pt.4 Ch.2 Sec 4 include:
- Mandatory double-slope aft bearing for single stern tube bearing installations in 2018
- Introduction of a compensating influence factor for use of environmentally acceptable lubricants (EAL) in 2019. DNV research project findings showed that EALs exhibited inferior load bearing capabilities in some extreme conditions.
Shaft alignment class notations
New class notation TMON(Oil lubricated, +) is now offered to vessels with Shaft align and TMON(Oil lubricated) class notations.
We also introduced the optional class notations Shaft align(1) and Shaft align(2) in 2018 with the prescriptive design, installation and monitoring requirements.
Shaft alignment for fleet in service
DNV customers can contact us through DATE (Direct Access to Technical Experts) via email or via the customer portal.
Otherwise, our advisory experts are there for you.
Approval of service suppliers – shaft alignment verification
We offer approval of service suppliers (AoSS) CP-0484 (14) engaged in the verification of shaft alignment on-site – to assist the industry in improving and standardizing the process.