5. CONSIDERATIONS
It is noticed that the redundant system should not be evaluated from only one view-point of reliability (failure rate λ) or maintainability (average man-hour mh) but should be done from two viewpoints of dependablity (manning index MI) which can combine by two senses of reliability and maintainability due to the equation (4-1) and Fig.4-1 (MVC). Especially it is the best evaluation index for crew on board to take care of the minimum man-power for any kind of redundant system.
Although the average numbers of redundant system for generating power station were obtained to be between 2.5 and 2.9 [sets/vessel], it should be not forgot that there has been installed a tubo-generator and/or shaft-driven one added to diesel engine sets of the lower redundant system, whose numbers meight be the higher.
It is already mentioned that some special ships have a redundant propulsive power system, there were only 19 vessels installed parallel engines themselves among 224 vessels from the Data Base of JSRIC. This was very low value of about 9 [%], so that there occurred lots of emergency failures whose occurring failures was about 1,700 [ooc.] occupied about 25 [%] of the total failures (6,800 [occurrences]). However on the other hand there occurred few emergency failure on the generating power stations (more than 500 engines) due to their rdundant systems whose emergency ones was 86 [ooc.] occupied less than 2 [%] of total failures (4,900 [occurrences]). This fact could depend upon the redundant system because all the generaing engine sets have anyone of redundant system but main propulsive engine system have not always redundant one.
In this paper some statistical values of both the numbers of engine sets and their cylinders were studied, but the details of numbers of cylinders and their influences on reliability, maintainability and dependability will be analysed and presented for further discussion. With respect to maintainability crew used to say to author that they do not like and hesitate not only many engines set but also lots of cylinders because they have to repair and manage MES. Therefoe there may be some optimum points and some policies on trade-off problems (R6 〜 R10) between the levels of redundancy and man-power of crew on board.
6. CONCLUSIONS
This paper describes the models of redundant system and dependability (reliability and maintainability with supportability) of power systems which are propulisive primemover and power generating station of ships, and their running data (more than 11 million propelling hours) during 15 years 1982 〜 1997 and designing and manufacturing data during 2 years 1997 〜 1999.
From two kinds of surveyed data by the 3rd. Technical Committee of Machinery of MESJ and by JSRIC (Ship Reliabailty Investigation Committee in Japan) the average number of genegating sets per vessel has been range 2.5 〜 3.5 [sets/vessel] during the past 33 years 1964 〜 1997, in which their ranges of set number have increased from 2 〜 3 [sets/vessel] to 2 〜 5 [sets/vessel] shown in Table 2-1B.
Their models are redundant powering systems which have some number of cylinders driven by diesel engines, and the two kinds of investigated data are more than 6500 field data (Database of JSRIC; Ship Reliability Investigation Committee in Japan) submitted by 224 ships and the 661 ones done by 13 shipyards in west part of Japan.
As the some results of analyses it was obtained that the more safety degree due to the more paralell redundancy of systems could be demonstrated by both the theoretical models and some statistical values as four kinds of evaluation indices and on other hand the harder man-power degree due to the more redundant systems could be also confirmed by both of them.
According to the surveyed the above data and 661 generating diesel engine sets it was cleared that the avarage number of generating sets was estimated to be 2.90 [sets/ship] with the range between 2 and 5 [sets/vessel], and that the range of the number of cylinders per a generating set is 3, 5, 6, 8 [cyl/set] shown in Table 2-1A.
Analysing more than ten thousands fielddata from the JSIC Database during more than 11 millions propelling hours the four kinds of evaluation indices (failure rate λ, average man-hour mh, manning index MI and average delayed time Td) were obtained on 573 main diesel engines for propulsive powering sets and 528 diesel ones for generating ones with respect to all the failures and emergency ones which were about 11,700 and 1,700 occurrences respectively.
According to the above facts the more redundant model of main-engine could increase the more safety of reliabilty, where the average delay time could decreased from Td1 =0.664 [Hr/occ,] (of total delayed time=2,700 [Hr]/ total emergency nunmber Nd1=3,500 [occ.]) of single engine set M1 to Td2=0.374 [Hr/occ.] (of total delayed time=502 [Hr]/ total emergency number Nd2=1,340 [occ.]) of parallel ones M2 for the main propulsive power system, for the generating power system from Td1, Td2=1,58, 2.79 [Hr/occ.] of single of single one G1, parallel ones G2 to Td3, Td4=0.355, 0.61 [Hr/occ.] (of total delayed time=12.8, 1.83 [Hr]/ total emergency number Nd2=36,3 [occ.]) of triple one G3, quadruple one G4 respectively shown in Table 4-1A and 1B and Fig..4-1.
