Introduction ESA Notation Requirements of this Guide are optional for classification purposes. However@ where assignment of the optional notation ESA ?C Enhanced Shaft Alignment is being requested@ provisions of this Guide are compulsory. This Guide provides criteria for additional calculation requirements@ such as design optimization@ as well as more detailed requirements regarding the shaft alignment procedures in support of the optional notation ESA - Enhanced Shaft Alignment. Objective The objective of this Guide is to identify additional requirements and procedures beyond the minimum requirements currently specified in the ABS Rules for Building and Classing Steel Vessels so as to further enhance the shaft alignment. Vessels designed@ constructed and operated in compliance with the requirements of this Guide may be assigned the Class Notation ESA.