How many Engineer's Bell Books are required if a ship has two shafts?

The correct answer is two because each shaft on the ship requires its own Engineer's Bell Book. The Engineer's Bell Book is a log that records the operational status, performance, and any issues related to the propulsion system. With two shafts, it is essential to maintain separate records for each, allowing for accurate tracking of their individual performance, maintenance history, and any necessary adjustments. This distinction is vital for safe and efficient vessel operation, as each shaft may have different operating conditions or requirements based on its service.