Sec. 58.6 



RUNNING-ATTITUDE DIAGRAMS 



329 



OZ 04 0.6 0.8 1.0 I.E 1.4 16 18 20 



Toylor Quotient Tu'V/Vt 



Fig. 58.D Non-Dimensional Change-of-Thim Data 

 FOR High-Speed Scout Cruiser op D. W. Taylor 



reference (4) of Sec. 61.22. Other data are listed 

 in Sec. 58.7. 



It is obvious from the short-dash graphs for 

 h/H = 2.38 in Fig. 58.D that the sinkage and 

 change of level are greatly affected by the position 

 of the vessel on the solitary wave which travels 

 through the shallow water at the speed Cc = \gh. 

 This critical speed can change rapidly with depth, 

 as can the normal sinkage due to the Bernoulli 

 contour system and the ship's Velox-wave 

 system, so it must be remembered that a pre- 

 diction of sinkage and trim for a nominal constant 

 depth is that and no more. 



For the prediction of the sinkage and change of 

 trim in the cargo-vessel category, W. H. Norley 

 has published rather complete data on the be- 

 havior of the models of four vessels in three 

 depths of shallow water as well as in deep water 

 [TMB Rep. 640, Feb 1948]. The graphs of Fig. 

 58. E give the 0-diml sinkage of both bow and 

 stern for the four ship designs whose character- 

 istics are listed in Table 58. a. The data represent 

 self-propelled conditions for both models and 

 ships. 



An example of the use of these graphs, involving 

 extrapolation to lower h/H values than those 

 given, is worked out for the ABC ship of Part 4 

 in Sec. 72.8. 



The data derived by Norley for full-bodied 

 and blunt-ended vessels, as well as those derived 



by D. G. Davies in reference (12) of Sec. 58.7 for 

 lake freighters having very high Cp values, reveal 

 that at the low speed-length quotients customary 

 in confined waters the ship trims by the bow, just 

 as in deep water. This means that, if the initial 

 keel or bottom slope is zero, and if the speed is 

 too high, the ship touches the channel bed at its 

 forward end. 



58.5 Changes of Attitude and Trim of Ships 

 with Fat Hulls. In former years, excessively fat 

 and full forms like large scows, barges, and pon- 

 toons, could rarely be towed or propelled at 

 speeds through the water high enough to change 

 their attitude and trim, even in shallow and 

 restricted areas. Sinkage and squat was therefore 

 not much of a problem. With the advent of higher 

 speeds and more powerful tugs and pushboats, the 

 marine architect is left with little or no model 

 data or full-scale observations for predicting the 

 changes in normal bed clearance likely to be 

 encountered by these craft in given areas. This 

 situation is aggravated by the possibility of 

 towing blunt-ended and full forms through 

 regions where the water is shoaler than expected, 

 and where the position of a craft upon a solitary 

 wave will have a large effect upon the actual bed 

 clearance. 



In ETT, Stevens, Report 279 of January 1945 

 there are given on page 15 the change-of -level 

 data for the two groups of models having dis- 

 placement-length quotients A/(0.010L)^ of 300 

 and 400, and Cp values of 0.50, 0.60, and 0.70. 

 The characteristics of these models are listed in 

 the referenced report and in SNAME RD sheets 

 105-110. 



58.6 Variation of Attitude and Position of 

 Planing Craft with Speed and Other Factors. 

 The matter of bodily rise of a planing craft above 

 its position at rest, together with the changes in 

 trim which occur throughout the whole speed 

 range, are described and illustrated in Sees. 

 29.4 and 30.2 of Volume I. In fact, the sinkage and 

 trim are related to the whole planing behavior. 

 This, in turn, as brought out in Chap. 77, is a 

 most important function of both weight and 

 power. 



Unfortunately, there are no known data by 

 which the trim and vertical position of a planing 

 craft may be estimated or predicted directly, 

 corresponding to those in Fig. 58.A. Possibly 

 there will never be a simple procedure for deter- 

 mining these values, because of the considerable 

 number of parameters that are intimately 



