Series of data for ships with U-type aft frame line indicate that form factor which represents the viscous pressure resistance is increased as aft fullness is increased. On the other hand, it is obvious that ships with V-type frame shape give a considerably lower form factor value although aft body is very full.

 Figs. 5 and 6 show an effective wake factor and thrust deduction factor on a basis of run coefficient. Effective wake factor (1-wE) is larger in case of V-type aft frame line shape than that for U-type because bilge vortex is weakened and thus, velocity at propeller plane position is higher. Thrust deduction factor is decreased as aft fullness is increased due to the interaction between hull and propeller. Although this factor for a ship with V-type aft frame shape seems to be smaller than that for a ship with U-type aft frame shape, no obvious difference is found between two ships when run coefficient is largest (marked with ※).

　

　

　

 Consequently, V-type aft frame lines have an advantage to decrease viscous resistance although wake factor is increased by its nature. In case of ship with largest run coefficient shown with mark ※, effective horsepower for V-type aft frame line shape is 8% lower than U-type aft frame line shape. Although total efficiency is 3% lower in this case according to the change of effective wake factor, applying V-type aft frame line shape can attain energy saving effect of 5% on break horsepower.

　

2-3 Maneuverability and aft fullness/frame line shape

　

 Fig.7 shows directional stability factors on a basis of run coefficient, which is derived from a circular motion test with different aft fullness and frame line shape.

　

　

　

 As is shown in this figure, no obvious relationship

between directional stability factor and aft fullness was found. These data are re-plotted in Fig.8 on a basis of σa which represents the tendency of aft frame line shape between V-type and U-type.

　

　

Where,