Oilers/Plant Tenders (HHC) Civil Service Practice Exam

Where is lignum vitae usually found in marine applications?

1. Propeller shafts

2. Stern tubes

3. Engine mounts

4. Hull sections

The correct answer is: Stern tubes

Lignum vitae is a dense, oily hardwood that is often used in marine applications due to its remarkable durability and resistance to water. In the context of marine machinery, including propellers and shafts, lignum vitae is particularly effective in stern tubes. The stern tube is the part of the vessel that houses the propeller shaft and connects it to the hull, and it requires materials that can withstand high stress and water exposure while maintaining structural integrity. The natural oils present in lignum vitae help inhibit water absorption, making it less susceptible to rot and deterioration in a harsh marine environment. Additionally, the hardness and self-lubricating properties of lignum vitae allow it to reduce friction and wear in the stern tube bearings, which is crucial for longevity and performance. In contrast, while other parts like propeller shafts and engine mounts may involve the use of specialized materials, they are not primarily constructed from lignum vitae. Hull sections also do not typically include this wood as it is neither practical nor necessary for the construction of the vessel's primary structure. Thus, its main application in marine contexts usually centers around stern tubes, highlighting its importance in maintaining efficient and durable vessel operations.