CHAPTER 55 



The Calculation of Appendage Resistance 



55.1 General 288 



55.2 Scale-Effect Problems 288 



55 . 3 Customary Values and Proportions for Over- 



all Ship Appendage Resistance 288 



55 . 4 Classification of Appendages by Predominant 



Type of Drag 290 



55.5 Lift, Drag, and Other Data for Typical 



Bodies Representing Appendages .... 291 



55.6 Allowances for Wake Velocities on Ap- 



pendage Drag 292 



55.7 Shadowing AUowanoes for Appendages in 



Tandem 292 



55.8 Modifications in Drag for Appendages 



Abreast 293 



55 . 9 The Drag of Exposed Rotating Shafts ... 293 



55. 10 Drag Data for Holes, Slots, and Gaps . . ' . 294 



55 . 1 1 Estimated Resistance of Discontinuities . . 294 



55.12 The Resistance of Large Appendages Con- 



sidered as Parts of the Ship 295 



55 . 13 The Calculation of Appendage Resistance for 



Submerged Vessels " 295 



55.14 The Displacement of Appendages . . . . . 295 



55.1 GeneraL Chaps. 36 and 37 list and 

 describe the use and effect of a considerable num- 

 ber of fixed and movable appendages, respectively, 

 found on many types of surface vessels of normal 

 form. Within the space available, this chapter 

 endeavors to furnish data by which the resistances 

 of the most common of these appendages are 

 estimated or calculated. This is possible from 

 several sources of information: 



(a) Drag coefficients of submerged geometric 

 bodies and shapes approximating those of the 

 appendages 



(b) Observed drag data for various ship append- 

 ages, generally from model tests 



(c) Ranges of percentage of bare-hull resistance 

 for appendages of normal size and form. 



The drags listed in (b) are determined separately 

 by towing a model and removing the appendages 

 one by one. This involves some experience and 

 knowledge as to just how much of each type of 

 appendage to reproduce to small scale. This is 

 especially true of representations of comphcated 

 objects such as handrails, antennas, and fittings 

 on submarine models. 



Screw propellers which are prevented from 

 turning by casualty, or which are locked within 

 the ship for other reasons, constitute a special 

 kind of appendage, at least as far as drag is 

 concerned. They represent a special case of the 

 situation where the propeller rotates at other 

 than a thrust-producing rate, and as such are 

 discussed in Part 5 of Volume III. 



There is a second engineering reason for calcu- 

 lating or predicting the resistance of appendages. 



This is to determine the hydrodynamic loads on 

 the various parts of the appendage, so that these 

 parts may be made sufficiently strong and rigid 

 to meet all service requirements. 



55.2 Scale-Effect Problems. A great deal has 

 been written in the technical literature about the 

 problems of assessing or determining the Correct 

 resistance of appendages when added to a towed 

 or self-propelled model. An excellent resum^ 

 covering all aspects of this situation in which the 

 ship designer is interested is presented by P. 

 Mandel [SNAME, 1953, pp. 493-495]. Despite 

 their efforts to solve the model-prediction problem, 

 the techniques and prediction procedures of 

 various model-testing estabhshments still vary 

 rather widely. 



The difficulty here is that almost all ship 

 appendages are completely submerged, they do 

 not make gravity waves, and hence dynamic 

 similarity of flow is gauged by the Reynolds 

 rather than by the Froude number. Only in 

 exceptional cases, in model basins, can dynamic 

 similarity on the i2„ basis be achieved while the 

 test of the model as a whole is being conducted on 

 a Froude-number basis. 



It may be assumed by the marine architect 

 that, until these problems are resolved by the 

 model-testing establishments, each one has good 

 engineering reasons for its own procedure. Its 

 predictions of appendage resistance \vill, in its 

 own opinion, meet the needs of the ship designer, 

 the shipbuilder, and the ship owner. 



55.3 Customary Values and Proportions for 

 Overall Ship Appendage Resistance. It is often 

 necessary, as indicated in the latter part of Sec. 



288 



