A vessel’s machinery runs almost continuously for weeks or months at a time, often with no realistic option to stop and inspect a component that starts to wear. Add constant vibration from the propulsion system, salt water exposure on any exposed metal, and drydock intervals measured in years rather than months, and the margin for error on marine lubricants is much smaller than in most other sectors.
A lubrication failure on land usually means a breakdown and a repair bill. At sea, depending on what fails and where the vessel is, it can mean a much more serious problem. That’s part of why marine lubricant selection tends to be more conservative and more tightly specified than in other sectors, and why getting it right the first time matters more here than almost anywhere else.
Marine vessels typically run two separate types of diesel engine: the main propulsion engine, and one or more smaller auxiliary engines for onboard power generation. Both need engine oil, but the requirements differ depending on engine type and the fuel being burned.
Large low-speed two-stroke main engines use a cylinder oil rather than a conventional crankcase oil, and this is where fuel sulphur content becomes a major factor. Since IMO 2020 sulphur regulations came into effect, many vessels have shifted to lower sulphur fuels, which in turn requires cylinder oils formulated for lower base number (BN) operation. Shell Alexia 40 XC is one example of this: a low-BN 40 cylinder lubricant developed specifically for modern two-stroke engines running on VLSFO, ULSFO, distillate fuels, LNG and biofuels, allowing operators to avoid switching between high and low BN oils depending on the fuel in use.
Auxiliary generator engines are usually medium or high speed four-stroke units, and these tend to use a more conventional trunk piston engine oil, selected by viscosity grade and BN in line with the fuel sulphur level and the engine builder’s specification.
Reduction gearboxes and other propulsion gearing operate under sustained high torque, often for extended periods without a break, and in a permanently damp environment. Gear oils for this kind of duty need extreme pressure (EP) additives to handle the load, along with strong resistance to water contamination, since even a well-sealed gearbox will see some moisture ingress over a long voyage.
These are typically specified by ISO viscosity grade in the same way as industrial gear oils, though the specific grade and additive package should always follow the gearbox manufacturer’s documentation rather than a general assumption, since propulsion gearing varies considerably between vessel types.
Winches, davits, mooring equipment and other deck machinery are constantly exposed to spray, rain and direct water contact, which makes water washout resistance the single most important property of a marine grease. A grease that performs well in a dry industrial setting can wash out quickly in this kind of environment, leaving components under-lubricated without any obvious sign until wear sets in. Shell Naturelle S2 Grease A600P 1.5 is built for exactly this kind of exposure. It’s formulated for wire ropes, open gears and marine equipment, with strong adhesion properties designed to keep it in place on metal surfaces rather than washing off, which reduces both lubricant loss and how often deck equipment needs to be re-greased.
Marine is one of the sectors where biodegradable lubricants aren’t just a nice-to-have. Applications like stern tubes and bilge systems sit in direct contact with, or very close to, open water, so any leak from these systems has an immediate environmental impact in a way that’s much less likely on land. We’ve covered the properties of biodegradable lubricants in more detail in our guide to different types of lubricants, but the short version is that they’re formulated to break down faster than mineral oils while still providing full lubrication and protection.
Given the environmental risk profile of a stern tube or bilge leak, biodegradable options are worth considering as standard for these applications on most vessels, rather than only where a specific regulation makes it mandatory.
Manufacturer and engine builder approvals carry more weight in marine than in most other sectors. Main engine builders test and approve specific cylinder and system oils for use in their engines, and running an unapproved product can affect warranty cover as well as engine performance. This is part of why product ranges developed in direct collaboration with engine builders, rather than general-purpose oils adapted for marine use, tend to be the standard choice for main propulsion systems.
Engine oil, gear oil and grease selection all come back to the same underlying question: what does this specific component need to cope with, and what does the manufacturer actually specify for it. Our guide on how to choose the right lubricant for your equipment walks through that process in more detail.
If you’re unsure which marine lubricant is right for your fleet, our team can help. Contact Velocity Edge and a knowledgeable member of our team can assist you in selecting the correct product for your equipment.