292 Bulletin, Scripps Institution of Oceanography 
which rests on another mass of steel. The rupturing of the glass ball causes a 
violent implosion that is audible at the surface through the echo sounder. This 
hammer-and-anvil principle gives a much more satisfactory signal than did earlier 
bottom-detecting devices that did not employ the fixed steel mass as a pedestal 
for the glass ball. 
When desirable, because of bottom topography or other conditions, anchor 
flukes are welded to the bottom-detecting device, so that the device, after having 
served its purpose as a bottom detector, becomes a drag anchor. 
SYSTEM DESIGN 
The design of the mooring must stem from a knowledge of the physical forces of 
the environment acting upon the components in a geometry determined by the 
same interaction. Hence the design cannot be uniquely expressed as any simple 
function of the parameters. Rather, the various components may be provisionally 
selected by simplified criteria, the geometry of the assemblage examined, and 
adjustments made. A workable method for doing this is outlined below and is 
discussed in more detail in the Appendix. The design is carried out step by step 
as follows. 
1) The mean or modal surface current, vertical current profile, wind velocity, 
and depth of water are measured or estimated. Estimates are also made of ex- 
tremes of surface current, wind, and wave height. The magnitudes of all these 
phenomena may depend on the season and on the length of time that the mooring 
will be in place. 
2) The wind drag and the water drag on the surface unit are calculated. 
The wind drag on the vessel or skiff may be computed for any impact angle 
once the drag area has been determined. The wind drag area of the hull, the 
superstructure, the masts, and so forth, above the water line may be taken from 
the vessel’s prints, or perhaps estimated. A convenient formula for computing 
the wind drag is 
F=KAV? (12) 
where 
F = force in pounds 
K = constant = 0.0025 (a value as high as 0.004 is often used for 
more complicated shapes such as that of a large ship) 
A = wind drag area of vessel in square feet 
V =speed of wind in miles per hour 
Conversion factors for velocity in different units are given in table 2. 
TABLE 2 
VeELociry CONVERSION Factors 
Velocity St. mi/hr Knots Ft/sec Ft/min 
1 statute mile/hour............ 1 0.868 1.47 88.0 
AMOS sqrt cra ace aa eeeate 1.15 1 1.69 101 
Vit/SeCh te iicceo see. Seero eee 0.682 0.592 1 60 
