CHAPTER 71 



The Design of Miscellaneous Propulsion Devices 



71 . 1 General Considerations 638 



71.2 Design Features of Paddletrack Propulsion . 038 



71 . 3 Notes on the Hydrodjoiamies of Paddlewheel 



Design •. . 038 



71.4 Calculating the Blade and Wheel Propor- 



tions and Dimensions 641 



71 . 5 Alternative IMethods of Determining Paddle- 



wheel Blade Area 642 



71 . 6 Relation of Paddlewheel Diameter and Pro- 



pulsion to Ship Hull Design 643 



71.7 Design Notes on Paddlewheel Details and 



Mechanism 645 



71.8 Variations from Normal Paddlewheel Design 648 



71.9 Design Notes for Hydraulic-Jet and Pump- 



Jet Propulsion 648 



71 . 10 The Design of Surface Propellers 050 



71.11 Asymmetric Propulsion 051 



71.12 Feathering and Folding Propellers .... 651 



71.13 Auxiliary Propulsion for Sailing Yachts . . 652 

 71 . 14 Vertical Drive for Screw Propellers; Under- 



the-Bottom Propellers 053 



71 . 15 Design of Devices to Produce Transverse and 



Vertical Thrust 654 



71.16 Design Features of Tandem and Contra- 



Rotating Propellers 655 



71.17 Design Notes Relative to Rotating-Blade 



Propellers 656 



71.18 Airscrew Propulsion 658 



71.1 General Considerations. The screw pro- 

 peller is now so widely employed for propulsion 

 in water that ahnost any other type of device 

 is unusual by comparison. Likewise, in a pro- 

 gram of research, experiment, and development 

 that is in keeping with the total number of 

 propulsion devices employed, a very large pro- 

 portion has been devoted to screw propellers. 

 As a result, the design of other types has suffered 

 rather severely. In fact, in most books of this 

 kind the discussions of other propulsion devices 

 aire hmited to brief mentions only. Design notes 

 and rules for these miscellaneous devices are 

 notable by their absence. This situation is not 

 easily nor quickly remedied, hence the notes and 

 comments for these devices, in this chapter, are 

 by no means as comprehensive, definite, and 

 helpful as they should be. 



Although the title does not so indicate it, this 

 chapter treats also of certain design aspects when 

 screw propellers and other propulsion devices are 

 intended to work in unusual positions. Examples 

 of this are under-the-bottom screw propellers, 

 tandem propellers, and contra-rotating propellers. 



The order of subjects in this chapter follows 

 in general those of Chaps. 15 and 32 in Volume I. 



Data for predicting the performance of pro- 

 pulsion devices of all types, or references to those 

 data in the literature, are given in Chap. 59. 

 I 71.2 Design Features of Paddletrack Propul- 

 sion. Paddletrack propulsion is mentioned 

 briefly in Sec. 15.4, described in Sec. 32.2, and 

 illustrated in Fig. 32. A. 



Very little analytic work has been done on 

 paddletracks and there has been only a moderate 

 amount of systematic experimentation on model 

 and full scale. Correlation of the large number of 

 specific tests, on both self-propelled models and 

 full-scale craft, made in the United States during 

 the period 1940-1955, is difficult and time 

 consuming, so much so that it may not be under- 

 taken or completed for an indefinite period. 



The hydrodynamic design requirements for 

 reasonably efficient paddletrack propulsion in the 

 water have been pushed rather far in the back- 

 ground by the need for closely spaced cleats which 

 will insure adequate traction and support on the 

 ground. It so happens that almost any kind of 

 deep cleat gives some measure of propulsion in 

 the water (or in liquid mud) but only certain 

 cleat designs provide substantial support and 

 withstand severe usage over any type of ground, 

 including submerged rocks, reefs, and concrete 

 roads. 



For the reasons given, no attempt is made here 

 to furnish design notes or criteria for paddletrack 

 propulsion. 



71.3 Notes on the Hydrodynamics of Paddle- 

 wheel Design. It is reported that S. W. Barnabj', 

 in his treatise on propeller design of 1885, stated 

 that "As a propelling instrument the paddle is 

 not inferior to the screw and some of the best 

 recorded performances have been obtained with 

 it." Screw-propeller performances have improved 

 since then but so have those of the paddlewheel, 

 especially of the feathering type. 



638 



