THE PROBLEM OF THE HULL AND ITS SCREW PROPELLER. 
Ship steaming with one idle propeller on each side:— 
197 
Tigevis ies asi e ales irae Fh 10 eG) 15 
= Me UR Tes/ Sho NES CaM 292 .4172 . 5632 6258 
Sis ee ras Beane 1,760 4,443 9,263 11,586 
Z, (curve I, Fig. 6). 1.44 1.0 .62 -49 
§ oid SG Gee e ERROR -3995 . 3661 .3182 -295 
PGMA few evornice ie, ta aka 77.87 105.4 a2Ee 142.1 
PAC UNE IR eS vu 75.9 101.9 132.1 143.85 
RN EO ete Sa acca 15,760 15,760 15,760 15,760 
TOS SEO EB ao I I I I 
a es for > areal .06 122 a3) ~545 
Bie OS NO Ae ER a 1.25 .94 5 Bea 
ESSE EN Se EES 1.101 745 -365 202 
eu. p) Biel 105 .192 .442 .635 
Os TRS Oa ete eae Rane 1,166 2a 4,910 7,050 
In the above calculations— 
2Z,=Log 8. H. P.—Log S$. H. P..+Z,. 
It has been stated that with vessels of types 1 and 3 the transposition of Zs; 
from curve I to curve 2, Fig. 6, does not occur. This statement requires modifica- 
tion because it does happen when what may be called “induced cavitation”’ occurs. 
By this term is meant cavitation which is produced by means other than the con- 
ditions normally governing the performance of the propeller. It is frequently 
encountered with vessels of the destroyer type when propeller struts have been so 
constructed and fitted as to increase the squat of the hull and to produce areas of 
reduced pressure in the wake of the struts, the propellers working in these areas. 
In such cases the value of Z, gradually passes over from curve I to curve 2, the 
departure from curve 1 for vessels of 310 feet L. W. L. length occurring approxi- 
mately at a speed v=1.42 VL. L. W. L. and arriving on curve 2 when v=1.92 
SYA, Ey WO 
To illustrate this phenomenon, the case of a destroyer is given in which the 
shafts were carried by two struts each, the axis of the lower arm of each forward 
strut being parallel to the base line of the vessel, while the axes of the lower arms of 
the after struts were inclined downward at the forward edge, 41% degrees. 
