a.

Survey of the running gear and components of a marine diesel engine for main propulsion is every 5 years (apart from the economiser which is every 2 years). So that there is not one huge overhaul and survey every five years, classification societies have agreed to the items to be surveyed over a five year rolling programme where 20% of items are surveyed each year.

b.

The crankshaft, main bearings, bottom end bearings, and thrust bearings must be surveyed by the classification society surveyor. However if the Chief Engineer has held  his certificate of competency for more than 3 years and has sailed in the capacity of Chief Engineer for 1 year with the company the classification society may agree to him surveying other items such as crossheads, pistons, cylinder liners etc.

c.

Some Classification Societies will, if the planned maintenance scheme is of an approved type, allow the planned maintenance records of the condition of an item to negate the need to open an item for survey when it falls due. Full records of the condition of the item together with any measurements, clearances etc. must be recorded on the PM report together with the running hours.

Alternatively if an item is due for opening up under the planned maintenance scheme, it may be surveyed at the same time, even if the survey may not be due, thus saving on down time.

d.

VIBRATION ANALYSIS

A change in vibration amplitude and characteristics can be an indication of excessive wear or that the item under consideration is not performing within the design criteria. Modern methods of vibration analysis involve holding a probe against nominated marked places on the engine. The engine must be running at a predetermined constant load (usually 85% MCR). The vibration amplitude, frequency and other characteristics are recorded onto a hand held computer. The information recorded is analysed and compared to previous readings. A report detailing the trend in the change in any vibration at any point will give an indication as to whether the component under consideration is in need of overhaul.

LUB OIL ANALYSIS

A representative sample of crankcase lubricating oil is drawn from the same point on the engine at regular intervals and sent away for spectrograph analysis. As well as monitoring the trend in the deterioration of the oil (decrease in alkalinity, increase in acidity, decrease in antidispersants, decrease in antifoaming additives and antioxidants, which if seen to be happening more rapidly than usual points to malfunctions such as blowby), the analysis will also show the amount and type of metal particles present in the oil. This can be an indication of excessive wear in a bearing or between rings and liner. Because bearing materials within the engine are of different specification, it can point to whether the white metal is from main, bottom end or crosshead bearings.

It should be noted that the two above methods of condition monitoring are often used in conjunction with each other and with an approved planned maintenance scheme.