Sec. 54.14 



AIR AND WIND RESISTANCE OE SHIPS 



285 



0,50 

 0.45 

 0.40 

 0.55 

 0,30 

 0,25 

 020 

 0.15 

 0.10 



5 -1 



r 



Data Token from 



EMB Rep.- 276 for 



EMB Rep. 512 for 



EMB Rep. 334 for 



EMB Rep 345 for 



EMB Rep 562 for 



FENSACOLA 

 HAMILTON 

 CLAIRTON 

 5AL1NA5 - 

 3ANTA ROSA 



Each Report Contains a Photoqroph 

 of the Model Tested I 



10 20 30 40 50 60 70 80 90 

 Anqle6 of Relative Wind from Centerline of Ship Aheod,decj 



Fig. 54. G Centee-of-Wind-Pkessure Data fob 



Five Typical Ships 



Theoretically, all graph values should be zero when = 



models of the five ships listed in the graphs of 

 Figs. 54. C, 54.D, and 54. E. Schematic wind-drag 

 force vectors for a few representative relative- 

 wind directions are indicated on diagram 2 of 

 Fig. 54. F. G. Hughes gives center-of -pressure data 

 for three aboveAvater models tested m a Avind 

 tunnel [INA, 1930, p. 321 and Fig. 2 on PI. XXXV; 

 INA, 1933, PL VIII, Fig. 4], for values' of d 

 from to 180 deg. 



54.13 Lateral Wind Drag. Ships underway 

 are often subjected to strong relative \vinds from 

 abeam, at an angle d of approximately 90 deg, 

 measured from ahead. Vessels anchored and at 

 moorings, lying to the tide or moored at both 

 ends in assigned positions, are subject to cross 

 winds. Moreover, vessels often have to be berthed 

 and unberthed when the true wind is about at 

 right angles to their axes. The wind resistance 

 under these conditions is nearly zero, but the 

 wind drag may be very large. 



The most extensive and probably the most 

 rehable data as to lateral wind drag appear to 

 be those of T. Thorpe and K. P. Farrell [INA, 

 1948, pp. 116-117]. These list transverse wind- 

 drag loads for a wind velocity of 60 kt as ranging 

 from 37.5 long tons for a large battleship to 7.85 

 long tons for a frigate or escort vessel. W. W. 

 Smith, in reference (4) of Sec. 54.6, mentions a 



wind-resistance load of 22.6 long tons for a large 

 collier with multiple derricks. 



The value of the dimensional drag coefficient for 

 a broadside relative wind is very nearly as large 

 as for an end-on wind or for a flat plate having a 

 length ecjual to that of the ship and a depth of 

 twice the ship height (including the mirror image 

 below the water surface). However, tests on 

 models indicate a somewhat smaller drag co- 

 efficient for the broadside presentation. 



For a dimensional expression of the form 



D, 



ksA,,W^ 



(54.viia) 



the dimensional coefficient ks for 6 = 90 deg has 

 values ranging from 0.003 to 0.0042. In their 

 analysis, and for practice, Thorpe and Farrell 

 recommend a kg of 0.004. 



It is interesting to make an estimate of the 

 mnd drag exerted on the ABC ship of diagram 3 

 m Fig. 54. F when lying beam-to in a 60-kt storm 

 mnd. The silhouette area for 6 = 90 deg and for 

 the ship at designed draft, estimated from Fig. 

 68.M and from diagram 3 of Fig. 54.F, is 20,167 

 ft^ For a /c-value of 0.0042, the maximum quoted 

 by T. Thorpe and K. P. Farrell in Sec. 54.13, the 

 lateral wind drag is 



Dw = keA^Wi = 0.0042(20, 167)(60)' 



= 304,925 lb. 



This is almost twice the ahead hydrodynamic 

 resistance at the designed speed, as predicted by 

 the model test. Under this lateral force the ship 

 would, if left to itself, heel and drift downward, 

 as described in subsequent sections. 



54.14 Lateral Wind Moments and Angle of 

 Heel. It is unfortunately possible for certain 

 craft, especially when m a light or nearly light 

 condition, with the relative wind about abeam, 

 to be subjected to a wind-drag moment which 

 exceeds the righting moment. The craft then 

 capsizes. This can happen in areas of relatively 

 smooth water, if a vessel is struck by a sudden 

 high-velocity squall. In areas where waves 

 already exist, the menace is obviously greater if 

 the ship is perched broadside on a high wave 

 crest, Avith a diminished metacentric stability, 

 at the instant that it experiences the maximum 

 force of the squall. 



The heeling moment due to beam winds on 

 full-scale vessels, about an axis in the waterplane, 

 may be estimated by using a 0-diml formula 



