Fig. 1 The ship propulsive system
1-propeller shaft
2-Outer stern tube seal (oil)
3-Outer propeller shaft bearing (water)
4-inner propeller shaft bearing (water)
5-inner stern tube seal (oil)
6-propeller
7-inner propeller shaft bearing (oil)
8-Outer propeller shaft bearing (water)
Fig. 2 The diagram of SPS elements failure rate (%)
It is possible to declare confidently, that the given data are justly also for vessels built under supervision of other Classification societies - of the members of the International Association of Classification Societies (IACS).
The scale of a problem can be estimated rather evidently in money as the damage to shipowners deal by failures of SPS elements. It is enough to specify that the rent of a dock charges call for 1000 and more US dollars per day, cost of the repair works reaches the same sums, cost of replacement of any SPS components reaches tens thousand US dollars lump sum, the loss of profit is estimated by the sums in tens of thousands US dollars per day. The common sum of the losses only for the examined vessels is estimated approximately by 1 billion US dollars per 5 years without the cost of ecological damage and penalties. It is indisputable, that both widespread technical decisions basically are not capable to solve an SPS reliability problem. So in case of using the outer water for lubricating and cooling of propeller shaft bearings the probability of the propeller shaft damage, and also of the propeller shaft bearings damage is great. The total expenses of the shipowner are increased because of a complicated design of the propeller shaft, at which antifriction bronze facings and special coverings for protection against corrosion (fiberglass, rubber) are present. Besides that an unmetal antifriction material (exotic wood, rubber, textolite, nylon, carbonplastic etc.), which is usually placed in the brass body, is used for water lubricated bearings. At the same time there are no ecological problems if the water lubricating is used.
The alternative technical decision provides using of mineral oil for lubricating and cooling of the propeller shaft bearings, It also has both advantage, and weakness. It is possible to attribute to advantages a primitive design of the propeller shaft and of the propeller shaft bearings, the maximum high reliability of last. The main weakness of this technical decision consists in ecological danger. The oil leakages from SPS pollute coastal water areas, are pernicious for flora and fauna.
