CHAPTER XIII 



POSSIBLE EXTENSION OF SERIES 60 

 AND FUTURE RESEARCH 



Although at the time the original series was planned, the numerical ranges adopted 

 for the variables seemed adequate for future designs of single-screw ships, developments 

 over the last 15 years have already overtaken the choice made in 1948. 



The single-screw arrangement is preferred by most ship owners because it results in 

 higher propulsive coefficients, cheaper machinery installations and lower running costs than 

 equivalent twin-screw machinery, and in recent years single-screw ships have been built of 

 greater and greater size, with more and more power, higher speeds, and larger propellers. 

 For the dry-cargo or refrigerated ship there has been a demand for increasing speed which, 

 with these other factors, has resulted in many single-screw ships having block coefficients 

 less than the smallest one of 0.60 used in Series 60. Coefficients of 0.55 have been used, 

 and to take care of the future and have adequate design information, it would be useful to 

 extend the series down to a block coefficient of at least 0.55 and perhaps 0.50. 



At the other end of the scale, the economics of carrying bulk cargoes, whether oil, 



ore or grain, have resulted in the mammoth supertankers of today with block coefficients in 



the neighborhood of 0.825 to 0.85. An extension of Series 60 to 0.85 block coefficient would 



therefore be of great. interest to designers in this field. 



B . , , • , 



The range of — for the Series is from 2.5 to 3.5. The former figure is rather too high 



H D 



(many cargo ships have ratios around 2.25), and an extension to a value of — equal to 2.0 



H 



would be of interest. The upper limit of 3.5 is probably adequate for most ships in fully 



loaded condition, but with draft restrictions in many ports and canals, it is reasonable 



to suppose that supertankers and similar ships may well spend appreciable time in a 



p> 

 partially loaded condition when — may quite likely exceed 3.5. As a first step, a few 



B ^ 



models having — values of 2.0 and 4.0 could be run to see how reliable anextrapolation 



H 

 outside the present limits might prove to be before embarking on an extensive program. 



• Studies of seakeeping characteristics have shown the advantages of longer ships in 



maintaining sea speed, and an extension of the series at the finer block coefficients to 



higher values of — would be of interest in this respect; at the full end, a similar increase 



. L ^ 



in -— would cover ships designed for the Great Lakes trade. 



The extension of Series 60 to cover any or all of these areas would be a worthwhile 

 research project. In addition, there remain the planning and running of additional series to 

 cover twin-screw ships, trawlers, tugs, and high displacement-length craft of all kinds. In 



XIII-1 



