Question 64 QMED05 - Machinist-Pump Technician

The Correct Answer is A **Explanation for A (Lithium-based grease):** Lithium-based grease (specifically Lithium 12-hydroxystearate) is overwhelmingly the most commonly used type of grease aboard ship, as well as in general industry. It is often referred to as 'multipurpose' or 'general-purpose' grease. Its popularity stems from its excellent overall performance characteristics, which include: 1. **High Shear Stability:** It maintains its structure under mechanical stress (vibration and movement), crucial for shipboard machinery. 2. **Good High-Temperature Performance:** It handles operational heat well. 3. **Excellent Water Resistance/Washout Protection:** While not as good as some specialty marine greases (like calcium sulfonate), its water resistance is sufficient for general machinery located outside the most extreme wet environments, making it a reliable general-use option across the vessel. 4. **Corrosion Protection:** It offers satisfactory defense against rust and corrosion. Due to this versatility, ship engineers standardize on lithium grease to simplify inventory and prevent the accidental mixing of incompatible grease types. **Explanation for B (Aluminum-based grease):** Aluminum-based greases (such as Aluminum Complex) offer excellent water resistance and are often used in specialized applications where continuous water exposure is expected (like deck machinery or stern tube applications). However, they are generally much more expensive and do not offer the same universal mechanical stability and temperature range as multipurpose lithium greases, preventing them from being the *most commonly* used general grease on the vessel. **Explanation for C (Calcium-based grease):** Traditional calcium-based greases (like Calcium Sulfonate) provide superb water resistance and anti-corrosion properties, making them excellent choices for specific marine environments, such as propeller shaft bearings or deck equipment heavily exposed to seawater. While their usage is growing in niche marine applications, they have historically had limitations regarding maximum operating temperature and shear stability compared to lithium greases, meaning they have not replaced the general-purpose lithium grease as the fleet standard. **Explanation for D (Lime-based grease):** Lime-based grease is an antiquated term often referring to traditional calcium (lime) soaps. These greases have very poor heat resistance and are easily washed out by water compared to modern alternatives. They are rarely used in modern shipboard machinery and certainly are not the most commonly used type.