Marine

Marine lubrication is not chosen by viscosity. In a marine diesel engine the base number (BN) of the cylinder or crankcase oil has to be matched to the sulphur content of the fuel being burned, and getting it wrong is damaging in both directions:

BN too low for the fuel — sulphuric acid formed during combustion is not neutralised, and the result is cold corrosion of the liner and ring pack.
BN too high for the fuel — the unused alkaline reserve leaves calcium-based deposits on the piston crown and in the ring grooves, which can lead to bore polishing and scuffing.

Since the IMO 2020 sulphur cap, many vessels switch between fuels, and the lubricant has to follow the fuel rather than the calendar.

Two-stroke crosshead engines

These need two separate products: a cylinder oil fed to the liner, and a system oil for the crankcase, bearings and cooling.

Fuel	Cylinder oil
High-sulphur residual fuel, severe duty	NAUTILUS HEAVY XT 140 (BN 140) — strong cold-corrosion protection and liner cleanliness
Residual fuel, ultra low-speed engines	NAUTILUS HEAVY XT (BN 100)
Residual fuel, low-speed crosshead	NAUTILUS HEAVY (BN 70) — exceeds MDT and WARTSILA (SULZER) requirements
Low-sulphur HFO up to 1.5%	NAUTILUS LS (SAE 50, BN 40)
Low-sulphur distillate or HFO, up to 2–2.5%	NAUTILUS LS II (SAE 50, BN 40)
Ultra-low sulphur distillate in ECAs, LNG, methanol, ethane, LPG	NAUTILUS VLS/25 — for fuel at or below 0.1% sulphur

For the crankcase, ARMOR MEDIUM SAE 30 is the system oil: alkalinity to neutralise acids reaching the crankcase, with enhanced load-carrying ability to reduce bearing wear, suitable for high-output crosshead engines.

Four-stroke medium and high-speed engines (trunk piston)

A trunk piston engine oil (TPEO) does both jobs from one product, so the BN choice carries even more weight.

POSEIDON HT — high-detergency crankcase lubricants for highly rated medium-speed engines running on heavy fuels, with excellent cleanliness and efficient contaminant separation in centrifugal purifiers. Available across SAE 30 and 40 with a range of base numbers; the designation combines the two, so HT 3040 is SAE 30 at BN 40.
POSEIDON HT/20 — for medium-speed engines on 0.10–0.50% sulphur fuels, LNG and IMO-compliant blends, including dual-fuel units.
POSEIDON DT, SX and TN — for medium and high-speed trunk piston engines on distillate fuels, in SAE 30 and 40. DT also serves as a cylinder and bearing lubricant on medium and high-speed engines.
PWR SUPER LM 40 — high-alkalinity, low-ash, phosphorus-free, zinc- and chlorine-free, for medium-speed engines on distillate fuels, biodiesel or LNG in heavy-duty shore and offshore environments.

Stern tubes and environmentally acceptable lubricants

CYBIO-STETUB (ISO VG 100 and 150) is an environmentally acceptable lubricant on selected ester basestocks, for stern tube and stabiliser applications in both neat and emulsion form. Vessels calling at United States ports fall under the EPA Vessel General Permit, which requires an environmentally acceptable lubricant at all oil-to-sea interfaces — stern tube, thruster, stabiliser, controllable pitch propeller. CYBIO-HFE covers hydraulic systems in the same role.

Practical points

Feed rate matters as much as BN. Cylinder oil feed rate should follow the engine builder's guidance for the fuel in use, and piston underside drain analysis is how the setting is verified rather than guessed.
Keep purifiers working. A TPEO's ability to release contaminants in a centrifugal purifier is part of what you are buying; a bypassed or poorly maintained purifier removes that benefit entirely.
Switching fuel means reviewing the lubricant. A vessel moving between residual fuel and ECA distillate is not running one lubrication regime, and the cylinder oil should be reviewed at the same time as the fuel changeover procedure.

Frequently asked questions

How do I choose the base number of a marine cylinder oil?

Match it to the sulphur content of the fuel actually being burned. Too low a base number leaves combustion acid unneutralised and causes cold corrosion of the liner and ring pack; too high leaves calcium deposits on the piston crown and in the ring grooves, which can lead to bore polishing and scuffing. For high-sulphur residual fuel Cyclon NAUTILUS HEAVY XT 140 (BN 140) and NAUTILUS HEAVY XT (BN 100) apply, NAUTILUS HEAVY (BN 70) for low-speed crosshead engines on residual fuel, NAUTILUS LS and LS II (BN 40) for low-sulphur fuels, and NAUTILUS VLS/25 for ultra-low sulphur distillate at or below 0.1% as well as LNG, methanol, ethane and LPG.

What changes when a vessel switches between residual fuel and ECA distillate?

The lubricant has to follow the fuel, not the calendar. A vessel moving between high-sulphur residual fuel and compliant low-sulphur distillate is not running one lubrication regime, and the cylinder oil should be reviewed as part of the fuel changeover procedure. Feed rate matters as much as base number: follow the engine builder's guidance for the fuel in use, and verify the setting with piston underside drain analysis rather than assumption.

What is the difference between a cylinder oil and a system oil?

A two-stroke crosshead engine needs both. The cylinder oil is fed to the liner to lubricate the ring pack and neutralise combustion acid, and is selected by fuel sulphur. The system oil lubricates the crankcase, bearings and cooling circuit, and Cyclon ARMOR MEDIUM SAE 30 serves that role with alkalinity to handle acids reaching the crankcase and enhanced load-carrying ability to reduce bearing wear. Four-stroke trunk piston engines use a single oil for both duties, which is why base number selection matters even more on those.

Which lubricants are needed for US Vessel General Permit compliance?

Vessels calling at United States ports must use an environmentally acceptable lubricant at all oil-to-sea interfaces, including stern tube, thruster, stabiliser and controllable pitch propeller. Cyclon CYBIO-STETUB (ISO VG 100 and 150) is formulated for stern tube and stabiliser applications in both neat and emulsion form, and Cyclon CYBIO-HFE covers hydraulic systems in the same role.

Not sure which product a vehicle, machine or fleet needs? Try the Cyclon oil selector, or send us the details and we will specify it in writing.