In 1957 at the Madrid Conference, the ITTC agreed upon a new "model-ship correlation 

 line" for use in all published work, which would give ship results differing somewhat from 

 those based either on Froude or the ATTC line. However, pending agreement on the appropri- 

 ate correlation allowances to use with the new line, it has not come into common usage as 

 yet. When such agreement is reached, a chart similar to that in Reference 47 can easily be 

 constructed. 



In comparing a number of closely allied forms, all suitable to fulfill certain design 

 conditions, this © - ® presentation has the advantage that for a given displacement and 

 speed, ® is the same for all models. An ordinate erected at this value of @ will indicate 

 the relative merits of the forms since (?) also involves only the speed and displacement. 

 The other differences in the various hulls can then be considered to determine which features 

 are responsible for the differences in resistance and power. 



Before proceeding with the methodical variations in LCB position and hull proportions, 

 the results of the actual ship models and the Series 60 equivalents v/ere compared. For this 

 purpose, the same five designs as before were used as the control models, and equivalent 

 Series 60 models having the same dimensions, displacement, and LCB position were made 

 and tested. The exception was for the MARINER design where the Series 60, 0.60 Cg 

 parent was used in the comparison. 



Such comparisons must be made at speeds appropriate to the individual designs, and 

 for this purpose, service and trial speeds have been c^iosen based on two suggested relations 

 between fullness and speed-length ratio. 



The first of these is an old formula first given by F.H. Alexander, but using coeffi- 

 cients suggested by Sir Amos Ayre as being more appropriate to modern ships: 



V 

 -r=r =2(1.08 - Co) for trial speed 



V^sp [1] 



V 

 — =- = 2(1.05 - C g) for service speed 



These formulae give reasonable speeds for the fuller ships, but for the fine ships, 

 such as that of 0.60 Cg, they give speeds which are too high from the standpoint of economic 

 performance. 



In 1955, Troost proposed a new formula to define the "sustained sea speed." Based 

 on a survey of many single-screw models run in the Netherlands Ship Model Basin (NSMB) 

 over some 20 years, the formula generally gives speeds higher than the Alexander service 

 speed for full ships and lower for fine ships, a result in conformity with modern practice. 

 For all forms, the Troost sea speed lies at that point where the (?) curve first begins rising 

 steeply, and for some range above it the resistance is varying approximately as the cube of 

 the speed, or the power is varying as V^. Troost therefore assumed a trial speed Y j some 

 6 percent above the sea speed F^, so that the power on trial at speed V j \s approximately 



V-14 



