THE PROBLEM OF THE HULL AND ITS SCREW PROPELLER. 193 
transformed to S. H. P. by dividing by the factor .746. The estimated S. H. P., is 
seen to be somewhat in excess of the actual, and this excess estimate is accompanied 
by an excess in estimated revolutions over the actual. Should the actual measured 
power at the highest submerged speed be used in the calculation of revolutions 
for that speed, the resulting estimated revolutions become 264.1 instead of 267.1. 
The vessel just discussed has an after body of such form that it is almost at 
the dividing line between vessels of type 2 and type 1, and the character and quality 
of the wake are so good that there is no augment of power, that is, K=1. 
Should the vessel be one of type 2, slips of the first order, but with the character 
and quality of the wake such that K is in excess of unity, the performance becomes 
radically different. Upon entering cavitation the value of K becomes increased 
to approximately K,=1.26 K. 
Suppose in the case of such a vessel a series of performances be taken in which 
Silais So : , 
the net load fraction aaa is constant but the speed fraction + for this load 
fraction is decreasing due to progressive loading of the vessel, then 
Log I. H. P.z=Log I. H. P.tLog K—Z,. 
Now let 
Zog=—Z,—Log K, 
that is Z,, is the gross load factor for the propeller when delivering the net 
load fraction ook with a power augment K. Call the gross load fraction 
e. h. pig 
Iedelley 
When = has decreased until it reaches the intersection of the ordinate at 5 Dis 
with the cavitating curve of the basic slip S, of the first order, cavitation ensues and 
K changes value to K,=1.26 K. 
The equation for power then becomes 
Log I. H. P.,=Log I. H. P.+Log K,—Z,. 
As the value of 7 still decreases, call the value of the load factor corresponding 
; Reis ‘ BED : 
to the point on the cavitation curve of S whose ordinate is 7a Z,, the equation for 
power becomes’ 
Log I. H. P.,=Log I. H. P.+Log K,—Z,+Z,—Z,, 
but Z,—Log K,=Z,,, therefore 
Log 1. H. P.,=Log I. H. P.—2Z,,-+-Z,. 
