188 THE PROBLEM OF THE HULL AND ITS SCREW PROPELLER. 
These two types and type 2 of first order of apparent slips having K =1, pass on 
v 
V 
Thrust Column,” with consequent loss in efficiency, is encountered. These curves, 
C, have been determined from the performances of a four-shaft vessel when steaming 
with only one propeller in use on each side of the ship, the idle propellers dragging, 
a slight correction having been allowed in the e. h. p. curve of the vessel for the 
increase in resistance due to these idle screws. The actual increase occurring is 
one that should be solved by the Model Tank. 
Turning now to hulls of type 2 with basic apparent slips of the second order, 
only one change occurs in the slip conditions, and that is the change from slips of 
the second order to those of cavitation. These latter are augmented (similar to 
down to values shown by curves C, Fig. 7, before genuine “Dispersal of the 
those of types I, 3, and of 2 when original slips are of the first order, when 7 is 
less than those of curves C (Fig. 7), on entering cavitation due to the increase in 
power demanded by the cavitating condition. 
As the curve B is the change limit for slips given by the slip curve D, it is 
assumed that a corresponding change from slips of the second order to those of cavi- 
1—S of B curve d 
1—Sof 2d order * 
by assuming different values of these slips of the second order, curves of cavi- 
tation limits varying from S=.27 down to curve B have been laid down. 
For hulls of type 2, curve B has been checked by the performances of subma- 
rines of the Holland type, while the curves for slips of the second order have been 
checked by submarines of the Lake type. These two types usually are radically 
different in the forms of hulls and in the arrangement of their propellers. Vessels 
of the Holland type require the use of the surface draught in obtaining the 5. B. C., 
while only one-half diameter of the hull is used in determining the ratio 2L.A.B.+H, 
and those of the Lake boats, while obtaining the S. B. C. in the same manner 
as for the former, use a much greater value than one-half diameter of hull in 
obtaining the after-body length ratio; in fact, for both types the H in the ratio 
2L. A. B.+H equals the height of the point of the stern above the base line. 
This results in a much greater value for the after-body ratio of the Hollands 
than for the Lakes, with a corresponding reduction in the basic slip values. Due 
to the position of the propellers in relation to the hull and also to the peculiar form of 
hull, the Lake boats have a shifting value of K depending upon the length of the 
vessels until this length equals or exceeds 230 feet, when K becomes unity for all 
surface conditions of speed. For all lengths of vessels of the Holland type operating 
on the surface, K has a constant value of unity. 
When vessels of either type are running submerged it becomes necessary to 
bring the diving rudders into operation in order to maintain proper balance, and 
the additional resistances introduced by the resistances of the diving rudders 
appear to vary with the speeds, disappearing entirely at 10 knots with boats of the 
tation will occur at values of = varying inversely as the ratios 
