The shaft alignment class notations put additional focus on the impact of transient hydrodynamic propeller forces and moments, induced during extreme turning conditions in the upper speed range, on the aftmost propeller shaft bearing. This is aided by a mandatory requirement for a multi-sloped aft bearing, coupled with an additional aft bearing lubrication evaluation criteria, with an increased propeller bending moment acting downwards on the bearing.
Shaft align(1) is a basic option intended for propulsion systems installed on vessels with conventional hull forms and facilitates enhanced aft bearing performance during normal and turning operating conditions. The following key requirements for the Shaft align(1) class notation apply:
- Multi-sloped aft bearing is mandatory
- Increased propeller bending moment ranging from –30 to +30% MCR torque in the aft bearing loading criteria
- State-of-the-art measurement techniques for installation sighting (laser or equivalent)
- Means of warning for propeller immersion
Shaft align(2) is intended for propulsion systems requiring additional calculations to estimate hydrodynamic propeller loads during turning conditions. Typical installations are vessels with non-conventional hull forms such as asymmetric stern and twin skeg.
The following key requirements for the Shaft align(2) class notation apply:
- Design-specific hydrodynamic propeller load spectrum and transient forces (using CFD)
- FE analysis for transient bearing contact pressure and area
- Hull deflections where applicable
- Shaft align(1) requirements apply as the basic criteria
Design and follow up requirements are published in Part 6, Chapter 2, Section 10 and Part 7, Chapter 1, Section 6 (38) respectively of the DNV GL Rules for classification of ships.
Your advantages with a shaft alignment class notation from DNV GL:
- Customized design criteria beyond generic class requirements
- Enhanced design and operating margins for continuous and transient (turning) operation
- Operators are able to reflect enhanced installations (class notations) in vessel’s certificates
- Provisions for warning against typical risks, e.g. inadvertent operation with incomplete propeller immersion
- Follow-up during operation ensures acceptable lubricant quality