CHAPTER 72 



Design Features Applicable to Shallow and 

 Restricted Waters 



72.1 General 659 



72.2 Reference Data on River, Canal, and Chan- 



nel Slopes and Currents 660 



72.3 Economical and Practical Speeds in Shallow 



and Restricted Waters 660 



72.4 Design for Reduction of Confined- Water 



Drag, Sinkage, and Squat 661 



72.5 Transverse Dimensions and Section Shapes 



for Shallow- Water Running 662 



72.6 Typical Shallow- Water Vessels 663 



72 . 7 Length, Longitudinal Curvature, and Wetted 



Surface 665 



72 . 8 Modifications to Normal Forms for Shallow- 



Water Operation 666 



72.9 The Adaptation of Straight-Element Design 



to Shallow- Water Vessels 666 



72 . 10 Bow Shaping 667 



72.11 Slope and Curvature of Buttocks 668 



72 . 12 Adequate Flow of Water to the Propulsion 



Devices 668 



72.13 The Design of a Tunnel Stern 669 



72.14 Hull Surfaces Abreast Screw Propellers . . 672 



72 . 15 Powering of Tunnel-Stern Craft 672 



72.16 Handling of the Vibration Problem in 



Shallow Water 673 



72 . 17 Partial Bibliography on Tunnel-Stem Vessels 673 



72.1 General. The elements of the flow average depth h. The speed V^ may always be 



about a body or ship in shallow and restricted 

 waters are discussed in Chap. 18; the behavior 

 of actual ships under the same conditions is 

 described in Chap. 35. Formulas, graphs, and 

 procedures for predicting or estimating the 

 behavior of ships in confined waters are set down 

 in Chap. 61. 



The design comments, suggestions, and rules 

 given here apply primarily and rather exclusively 

 to craft which operate more or less continually 

 in water that is shallow with reference to the 

 linear dimensions of the vessel. One rule of thumb 

 for all speed ranges is that a shallow depth is 

 one which is less than the beam of the vessel. 

 Perhaps a better one is that a shallow depth is 

 less than twice the draft. Another rule, for the 

 subcritical range only, is that the depth is less 

 than the so-called square draft; in other words, 

 less than the square root of the maximum-section 

 area, or VAx. To be sure, many such shallow- 

 water vessels are required to traverse deep spots 

 now and then but at some sacrifice in performance, 

 if need be, to insure the best shallow-water 

 behavior. 



For design and operational purposes, craft 

 intended to run in shallow and restricted waters 

 are divided into four categories: 



(1) Self-propelled, fine-lined craft having a shal- 

 low-water speed V^ that is close to but always 

 less than the critical speed Cc for the nominal or 



less than the critical speed Cc for the shallowest 

 part of the route. These craft usually carry 

 passengers and moderate amounts of freight. 



(2) Self-propelled, full-bodied craft of moderate 

 speed, where V^ does not exceed about 0.7c ^ , 

 for the carrying of the maximum amount of 

 cargo on a given set of limiting dimensions 



(3) Non-self-propelled barges, lighters, and scows 



(4) Self-propelled pushboats and towboats, for 

 which the free-running shallow-water speed V^ 

 may exceed the critical speed Cc . 



Design notes and rules for the latter two groups 

 are given in Part 5 of Volume III. For the second 

 group, carrying capacity is usually of far greater 

 importance than efficiency of propulsion or 

 hydrodynamic performance. Bottoms are flat and 

 of large area, lying at the limiting-draft level. 

 Waterlines are full and sides are vertical or nearly 

 so, except perhaps in way of the inflow jets to 

 screw propellers. The hydrodynamic design fea- 

 tures in this chapter are therefore limited generally 

 to vessels in the first category preceding. 



Design notes previously published for particular 

 types and for shallow-water vessels as a class 

 may be found in the following references: 



(a) Ward, C, "Shallow-Draught River Steamers," 



SNAME, 1909, Vol. 17, pp. 79-108 



(b) Wilson, R. C, "Construction and Operation of 



Western River Steamers," SNAME, 1913, Vol. 21, 

 pp. 59-65 



659 



