🔍 Key Concepts

• Stern tube bearings on older ships often used lignum vitae (a very hard wood) as the bearing material • Think about what fluid is naturally available around the stern tube area on most ships • Consider which lubricant would best protect wood while also carrying away heat and not contaminating the cargo or machinery spaces

💭 Think About

• Which lubricant on the list is most compatible with a wooden bearing material continuously exposed to the sea? • If there is a leak at the stern tube, which of these substances would be least harmful to the marine environment and easiest to manage? • Which lubricant can flow easily in and out of the bearing area without complex pumps or seals on a traditional shaft system?

✅ Before You Answer

• Be sure you know what lignum vitae is and why it was chosen as a bearing material • Consider where the stern tube is located and what fluid is already present there • Eliminate any lubricants that would be too thick, messy, or hard to circulate through a long, enclosed tube around a spinning shaft