Which of your systems need an environmentally acceptable lubricant
The oil-to-sea interface rule in plain terms: which shipboard systems it captures, what actually qualifies as an EAL, and what the technical infeasibility exemption requires you to document.
The environmentally acceptable lubricant requirement is one of the few regulations in this field with a genuinely simple test at its centre. If oil in a system can reach the sea in normal operation, that system needs an EAL. Everything else is detail about what qualifies and what to do when it is not possible.
The requirement entered force through the US Vessel General Permit, which applies to commercial vessels of 79 feet and above operating in United States waters. Under the Vessel Incidental Discharge Act the framework is moving to a new set of federal standards implemented through the Coast Guard, but the oil-to-sea interface obligation carries across. Confirm the currently effective instrument before relying on any date-specific detail — the technical requirement below is the part that has been stable.
What counts as an oil-to-sea interface
The phrase means what it says: any point where lubricant and seawater are separated only by a seal, or not separated at all. In practice that captures more systems than most operators expect on first reading.
- Stern tube bearings — the obvious one, and usually the largest oil volume involved.
- Controllable pitch propeller hubs and their hydraulic systems.
- Thruster bearings and propulsion pod lubrication, including azimuth thrusters.
- Rudder bearings, rudder stock seals and steering gear where it interfaces with the sea.
- Stabiliser fins and their hydraulic actuation.
- Wire ropes and mechanical equipment that is immersed in operation.
- Deck machinery hydraulics where a leak or a seal failure discharges over the side.
The test is whether oil can reach the sea in normal operation, not whether it usually does. A sealed stern tube that has never leaked is still an oil-to-sea interface — the seal is the only thing between the oil and the water, and the regulation is written around what happens when that seal does what seals eventually do.
What actually qualifies as an EAL
This is where a supplier's word is worth very little, because "biodegradable" is not a regulated term on its own. Three properties have to hold together:
- Biodegradable — it breaks down in the marine environment within a defined period, tested to a recognised method such as OECD 301.
- Minimally toxic — it passes aquatic toxicity thresholds against standard test species.
- Not bioaccumulative — it does not concentrate up the food chain.
The practical route to demonstrating all three is a recognised eco-label. Products carrying Blue Angel, the EU Ecolabel, Nordic Swan, EPA Safer Choice or an OSPAR listing have been assessed against criteria that satisfy the requirement. A data sheet stating a biodegradation percentage without naming the test method and the label is not the same thing, and it is not what an inspector is looking for.
Base chemistry is a reasonable first filter but not a qualification in itself. Saturated synthetic esters are the common choice for stern tube and hydraulic duty because they combine the environmental profile with the load-carrying and hydrolytic stability those systems need. Vegetable oils biodegrade readily but oxidise and hydrolyse in service, which is why they have largely fallen out of use in sealed systems. Polyalkylene glycols qualify but are not miscible with mineral oil, which makes a conversion considerably more involved.
The technical infeasibility exemption
The requirement is not absolute. Where using an EAL is technically infeasible, a mineral product may remain in service — but the exemption has to be earned and documented, not simply asserted.
Genuine grounds are narrow. An EAL meeting the equipment manufacturer's specification may not exist for that application. The equipment maker may explicitly decline to warrant EAL use. Or no product may be available at the ports on the vessel's trading pattern. Cost is not a ground, and neither is preference.
Where the exemption applies, the reasoning goes in the vessel's recordkeeping documentation, and it has to be specific to the system and the vessel. A generic statement will not survive an inspection.
Converting an existing system
A conversion is not a drain and refill. Two points cause most of the trouble.
Residual mineral oil in a system compromises the environmental profile of what replaces it, and beyond a few percent it can also affect the seal compatibility that the EAL was selected for. Flushing procedure and acceptable residual level should come from the equipment manufacturer, not from a rule of thumb.
Seal compatibility is the second. Ester-based fluids interact differently with elastomers than mineral oil does, and stern tube seal makers publish their own compatibility positions for exactly this reason. Check the seal manufacturer's guidance for your specific seal type before selecting the fluid, not after.
Water ingress behaves differently in an ester-based stern tube oil than in a mineral one, and the condition monitoring limits are not the same. Carry the EAL's own limits forward into your monitoring programme rather than continuing with the mineral oil figures.
Working through it
For most vessels the exercise is short: walk the systems list above, mark which ones exist on board, and for each one establish what is currently in it and whether that product carries a recognised label. The systems that fail that check are the conversion list.
Our own EAL range covers hydraulic, gearing and stern tube duty across the common viscosity grades, with the full technical data published rather than sent on request. If you want the systems list worked through against what is actually on your vessel, send the equipment details and we will go through it with you.
Related
Need this confirmed for your engine?
Send us the engine make and model and the fuel you are burning. We will confirm the grade in writing, with the approval evidence attached.
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