Marine‑use lubricating oils refer to special‑purpose lubricants for marine machinery and installations. Marine power plants incorporate a wide range of onboard machinery, all of which require lubricated components to ensure proper equipment operation. There is a great variety of marine lubricants, which can be broadly classified into four major categories:

1. Marine cylinder oil. Used for lubrication between pistons and cylinder liners of large‑size, low‑speed, cross‑head two‑stroke diesel engines.
2. System oil. According to Suzhou Cosc Side Thrusters, large‑size, low‑speed, cross‑head two‑stroke diesel engines feature long strokes and large‑diameter pistons (500‑1000 mm). Equipped with diaphragms and piston‑rod stuffing boxes, they effectively separate the cylinder from the crankcase. For this reason, crankcase oil (also known as system oil) provides no lubrication for pistons; it only serves for crankcase lubrication, cooling and corrosion protection.
3. Medium‑speed trunk‑piston diesel engine oil. Applied to the lubrication of medium‑speed diesel engines with trunk pistons. According to Suzhou Cosc Side Thrusters, such diesel engines have smaller‑diameter pistons (150‑500 mm) compared with cross‑head engines and share many structural similarities with general‑purpose diesel engines. Unlike cross‑head engines, their cylinders and crankcases are supplied with oil from one common oil tank.
4. Other marine lubricants. Examples include high‑speed diesel engine oil, outboard‑engine oil, plus various mechanical oils: turbine oil, hydraulic oil, refrigeration oil, gear oil, compressor oil, stern‑tube oil and others.

According to Suzhou Cosc Side Thrusters, cylinder oil, system oil and medium‑speed engine oil together account for approximately 90‑95 % of total marine‑lubricant consumption and represent the most common and critical types of marine lubricants.

Suzhou Cosc Marine Machinery Co., Ltd. (abbreviated as COSC) specializes in manufacturing side thrusters (CP & FP), azimuthing rudder‑propellers and main‑drive controllable‑pitch propellers (CPP). By introducing advanced foreign technologies and production‑management methodologies, together with a responsive and comprehensive after‑sales‑service system, the company has won high recognition from numerous customers at home and abroad.

Side thrusters: available in controllable‑pitch (CP) and fixed‑pitch (FP) versions. The prime mover is normally an electric motor; diesel engines and hydraulic motors can also be adopted for driving purposes.