304 Bulletin, Scripps Institution of Oceanography 
may be desirable.* An embedment-type explosively propelled anchor has been 
designed by the Cleveland Pneumatic Company, Advanced Systems Division, El 
Segundo, California, and is in use for depths such as those with which we are 
dealing. 
It should be kept in mind that in installing the anchor, the only exact measure 
of depth is made with the wire. If the anchor is very light or has high drag, this 
measurement will be inaccurate. This inaccuracy also obtains with an anchor in 
free or nearly free fall. 
RETRIEVABILITY OF SUBMERGED FLOAT 
Generally, it will not be worth while, because of the relatively low cost of the 
anchor and the mooring wire as compared with the value of ship’s time, to try to 
recover a complete mooring. Also, depending on the length of time the mooring 
has been in and the stresses that have been applied to the wire during installation, 
use, and recovery, it may not be wise to use it again. Above all, the potential 
hazard to personnel involved in recovery has made us hesitate to recommend 
recovery of the moorings as a general practice, although we have recovered the 
upper sections, including the submerged float, for purposes of inspection. 
One of the hazardous points involved in recovery is that the wire may part 
beneath the submerged float, permitting it to “free balloon” to the surface with 
enough force to cause damage to the ship’s propellor, rudder, or hull. If a 3-foot- 
diameter steel sphere, of a type used on deep moorings, is released while sub- 
merged, it will reach a terminal upward velocity of 8 feet per second in 3 seconds. 
On reaching the surface with this velocity it will partly or wholly emerge. If 
inflated rubber drums are used for the submerged float, the hazard is diminished. 
CORRECTIONS TO HCHO-SOUNDER READINGS FOR SOUND VELOCITY 
The velocity of sound in water varies as a function of depth, temperature, and 
salinity. Most sonic depth-finding instruments are adjusted for a constant sound- 
ing velocity, usually 800 to 820 fathoms (1,460 to 1,500 meters) per second. In 
certain eases it is desirable to correct the readings to true depths. This can be done 
if the distributions of temperature and salinity are known. For different areas of 
the oceans and for different depths, the British Admiralty Tables (Mathews, 
1927) contain mean sounding velocities, that is, mean velocities from the surface 
to the stated depth. In general, these first decrease somewhat with depth, because 
the effect of decreasing temperature predominates, but at greater depths they 
increase again as the pressure effect becomes dominant. Figure 11 indicates the 
magnitude of the correction to the indicated echo soundings for one area of the 
ocean. 
When an accurate depth determination is essential, a deep hydrographic east 
is in order to measure temperature and salinity at intervals from the surface to the 
bottom. 
* This places extreme requirements on the handling of the winch, because the wire is capable 
of sinking faster than the “floated” anchor. 
