Sec. 60.7 



SHIP-POWERING DATA 



363 



of the water flowing through the disc position. 

 Using the techniques available as of the date of 

 writing (1955), the propulsion device is not work- 

 ing when the wake measurements are made, so 

 there are no inflow and outflow jets and there is 

 no race contraction. 



The presence of what might be termed "inter- 

 secting" vector projections, of which there are 

 both horizontal and vertical rows in the torpedo 

 wake diagram of Fig. 60. K, means that the 

 flowlines are converging at the base points of the 

 vectors. The stream tubes meeting abaft the 

 fins obviously can not cross each other, as do the 

 vectors, although there may be some mixing due 

 to flow irregularities. Rows of "intersecting" 

 vectors of this kind are found abaft skeg and 

 bossing terminations on ship models, and some- 

 times abaft shaft struts, if the measurements are 

 sufficiently numerous. 



Visual inspection of the wake-fraction numerals, 



Fig. 60.G Wakb-Survet Diagram for TMB Model 



4358W-3, Representing a Variation op the Mariner 



Class Hull 



Fig. 60.H Wake-Survey Diagram for a Model 



Representing a Variation of the Mariner Class 



Hull 



or the sketching of contours of equal wake 

 fraction, indicates whether or not these values 

 change in a reasonably uniform manner in all 

 directions across the disc. It is to be expected that 

 the numerical values of the wake fractions will 

 increase progressively toward the adjacent hull, 

 because of the retarded flow due to viscous wake 

 within the boundary layer. Large or sudden 

 changes in a transverse direction across the wake- 

 survey plane are indications of longitudinal 

 discontinuities in the flow; possibly also of partial 

 separation or incipient eddies. 



On rare occasions there are indications of 

 longitudinal vortexes in a pattern of so-called 

 "pinwheel" vector projections, appearing to have 

 rotational components about a common center. 

 This center may lie within or without the wake- 

 survey field. A wake survey for the wall-sided 

 ship of Fig. 25.F of Volume I would show such a 



