Tsaacs—Faughn-Schick-Sargent: Deep-Sea Moorings 293 
The water drag or hull resistance of a vessel is broadly considered in two parts: 
(1) the surface or skin resistance and (2) the wave-making resistance. 
The surface resistance is computed by using the conventional formula, 
R,=f, A Vxi*8 (13) 
where 
R, = surface resistance in pounds 
f, =a coefficient of friction, assumed here as 0.01 
A =area in square feet of wetted surface 
Vx =current or water speed in knots 
The wave-making resistance is not normally computed, but for our purpose here 
it may be assumed to approximate 30 per cent of the total hull resistance. For 
ships of usual design at moderate speeds (as when anchored in a current) this 
approximation is frequently used. 
3) The weight and the horizontal drag of the submerged elements are calculated. 
The chief components are the mooring wire and the submerged float, which is 
selected to have a net buoyancy equal to about 60 per cent of the ultimate strength 
of the wire. 
When the current structure (vertical distribution of current) at the mooring 
site is known or assumed, the drag force on the mooring wire and components may 
be computed from the formula, 
MS Oh AWE (14) 
where 
F = drag force in pounds 
Ca=a coefficient of drag which may vary from, say, 0.3 to 1.5, but 
which, for first approximations, we assume to be 1.1. 
A =area of wire in square feet 
V =current speed in feet per second 
If instrument strings are suspended over the side, the added drag may be com- 
puted by using the above formula. If the current is not uniform from surface to 
bottom, the total force will be obtained by appropriate integration, or forces may 
be applied as a series of point loadings for several increments of depth. 
4) The angles of the wire at the submerged float and at the anchor are estimated 
from the relationships: 
y1 = wire angle from the vertical at the submerged float 
Fy, = total horizontal drag of submerged float and array above it 
B  =buoyancy of submerged float 
yi = tan” (Fy,/B) (15) 
yz =wire angle from the vertical at the anchor 
W =weight of wire in water 
Fy, = total horizontal drag on entire system below submerged float 
Then 
yo=tan* (Fu, + Fu,)/(B- W) (16) 
5) A preliminary estimate of dip and excursion may now be made by fitting 
between these two angles a circular are having a length equal to the length of 
cable between the submerged float and the anchor, as follows (fig. 10): 
