Sec. 76.12 



DESIGN OF SPECIAL-PURPOSE CRAFf 



771 



(8) Sufficient submergence of the propeller and 

 rudder, under wavegoing conditions, to give them 

 a hold on the water and to render the vessel fully 

 manageable 



(9) Minimum of drifting when broadside or 

 nearly so to the wind and sea, as when hauling in 

 gear and nets from abeam. The effect of drift- 

 resisting keels is discussed in Sec. 36.15; some 

 design rules for them are included in Sec. 73.19. 

 The drift-resisting effect of a deep hull, like that 

 of the pilot boat New York illustrated in Fig. 

 36.K, is appreciable. 



(10) Positive stability of route under all load 

 conditions; this is discussed in detail in Part 5 of 

 Volume III 



(11) Ample speed for running to and from the 

 fishing grounds. This feature is rather closely 

 related to the provision of a reasonably high 

 free-running speed for tugs. It is one reason why 

 fishing vessels, like tugs, are invariably over- 

 powered for their size. 



While nothing is said in the foregoing about 

 minimum resistance and shaft power to meet the 

 several requirements, there is no more excuse for 

 unnecessary resistance and Uttle more excuse for 

 unneeded power in a fishing vessel than in a 

 craft of any other type. 



With respect to fishing vessels as a class, 

 Jan-Olof Traung has come to the following con- 

 clusions concerning the effect of form parameters 

 on resistance, based upon analyses of tests on a 

 considerable number of models [Int. Fishing Boat 

 Congr., Paris and Miami, Oct-Nov, 1953, "Outline 

 to a Catalog of Fishing Boat Tank Tests"]: 



(a) The displacement-length ratio is of little 

 importance. In other words, it can be as high as 

 required for other reasons. 



(b) Enlarging the beam does not increase resist- 

 ance 



(c) The center of buoyancy should be well aft. 

 It is possible that the position of the maximum- 

 area section should also be abaft midlength. 



(d) Differences in the block coefficient Cb , below 

 0.55, have little or no influence 



(e) The prismatic coefficient Cp is of great im- 

 portance, with an optimum value of about 0.575 



(f ) Transom sterns act to reduce resistance 



(g) The half-angle of entrance, or the waterline 

 .slope is in this region, should be low 



(h) Parallel middlebody and sharp shoulders are 

 to be avoided. Fig. 76. G illustrates the lines of one 

 of Traung's models. 



J.O.Trauncj Model 540 q IV 

 Ship Lcnqlh - 19.51 m -o- 6401 ft 

 beam-bZ7m-o 2057_ft 

 Meon Drofl- 2.354rTr*T72 ft 



■3.11 -H-'2.56 

 Ax" 10.347 m^ o IN. 32 ft 

 Cx = O.TOI 



Fig 76.G Body Plan, European Fishing Boat, 

 J.-O. Traung's Model 340a 



Data from the Japanese fishing-vessel standard 

 series are referenced and summarized in Sec. 56.4. 



The multiplicity of longitudinal fender bars 

 fitted on some steel trawlers to prevent damage 

 to the shell plating by heavy fishing gear banging 

 along the side is probably more objectionable 

 from a maintenance standpoint than for the added 

 resistance which they cause. A construction much 

 to be preferred from all points of view is described 

 and illustrated in Sec. 73.22 and Figs. 73.Q and 

 76.r. It embodies heavier shell plating and a 

 complete absence of all applied appendages in the 

 form of fender bars, fender shapes, and fender 

 strips. 



A combination of controllable propeller and 

 swinging tubular rudder or Kort nozzle, designed 

 for astern as well as ahead propulsion, is an 

 excellent combination for a fishing craft. Such 

 a combination, designed by the Swedish naval 

 architect Jan-Olof Traung, is illustrated and 

 described in Motorship, New York, Jun 1950, 

 pages 42 through 44. 



76.12 Partial Modem Bibliography on Fishing 

 Vessels. The modern literature on the design 

 and construction of fishing vessels, say for the 

 period following the year 1930, is very extensive. 

 This is not surprising because, although the aver- 

 age fishing vessel is less than 100 or 125 ft in 

 length, the number of t3T)es and kinds is incredibly 

 large. 



An insight into the great breadth of this field 

 and the variety in it is afforded by a reading of 

 the excellent recent book entitled "Illustrations 



