DESIGN CALCULATION FOR EQUIPMENT AND COMPONENTS SPECIFICATION OF LUBRICATING OIL SYSTEM OF A TUG BOAT

The lubricating oil system is primarily used to lubricate wear surfaces to minimize friction losses, it cools internal engine parts which cannot be directly cooled by the engines' water cooling system and it cleans the engine by flushing away wear particles amongst others. Adequate lubrications require lubricant (oil) with sufficient film strength to withstand bearing pressure and viscosity index low enough to allow adequate flow when subjected to heat. The system consist of the tanks (storage, settling, sump and head), lube-oil pumps, strainers, oil coolers, piping, valves, and fittings, lubricating oil purifier, sub system and condition monitoring devices amongst others. The lubricating oil system for a tug boat whose transmitting power is about 955KW was calculated mathematically to obtain the flow rate of the shaft line bearing cooling oil, stern tube bearing cooling oil, main engine camshaft bearing cooling oil and main engine camshaft bearing cooling oil. Modelled equations were employed to obtain the camshaft lube-oil pump capacity, surface area and storage tank. The cylinder lube-oil storage and density tanks were estimated to be 1m3 while the transfer pump is calculated to be approximately 0.4m3/hr. The various suction and discharge diameters and velocities of pumps in the lubricating oil system were determined; it was observed the suction pipe diameter is always bigger than the discharge pipe diameter while the discharge velocity is higher than the suction velocity for all the pumps including the camshaft lube-oil pump, cylinder oil transfer pump and main lube-oil transfer pump. This is a clear indication that the said design process met the international standard for the design of such a tug boat. Similarly the shaft line bearing cooling oil pipe, piston bearing cooling oil pipe and main engine lube-oil pipe discharge velocities were seen to be at the acceptable limits obeying the classification rules. All designs were done in accordance to the Lloyd's specification rules and regulations for a sea going tug boat.