Oilers/Plant Tenders (HHC) Civil Service Practice Exam

Stern-tube lignum-vitae bearings are known for what feature?

1. They are cast iron

2. They contain synthetic materials

3. They are made with strips of lignum-vitae

4. They require frequent replacement

The correct answer is: They are made with strips of lignum-vitae

Stern-tube lignum-vitae bearings are particularly distinguished by being constructed with strips of lignum-vitae, a dense and durable wood known for its excellent water resistance and low friction properties. This natural material has been traditionally used in marine applications due to its superior performance under harsh conditions, such as exposure to water and heavy loads. The use of lignum-vitae in these bearings allows for effective lubrication through the water surrounding the bearing, contributing to smoother operation and longevity. In contrast to synthetic materials or cast iron, which would not provide the same natural lubricating qualities, lignum-vitae bearings maintain effective functionality without the frequent replacement that other types of bearings might require. Thus, the correct identification of this feature highlights the unique benefits of using lignum-vitae in marine engineering applications.