The outside sheath consists of two layers of 
galvanized steel strands in opposed lays to 
prevent twisting and kinking. The overall 
diameter of the cable is slightly less than 
1/4" and it has a breaking strength of 4, 265 
pounds. 
This cable was selected because it is 
strong, small in diameter,relatively cheap 
(17 cents/foot in 30,000 foot lengths), and 
readily available. Although its attenuation 
is high at the higher frequencies, the trans- 
istorized Class B cable driving stages in the 
receiver and velocimeter amplifiers have 
more than sufficient power to overcome the 
losses in a six mile line at the expense of an 
average battery drain of only a few mili- 
amperes. 
D. Accuracy 
The accuracy of the depth measurement 
depends, of course, upon the velocity of 
sound in the water at the place where the 
lowering is being made. This velocity in 
turn depends on the temperature, density, 
and salinity of the water through which the 
sound travels. The more accurately these 
factors are known, the more precise the 
measurement since the resolving power of 
the gear is sufficient to indicate vertical 
changes of a few feet regardless of the depth 
of the instrument. 
When an accurate velocimeter is lowered 
with the sounder so that the sound velocity is 
known throughout the transmission path, it 
is certainly safe to assume that a deep 
measurement is good to a fathom and perhaps 
better. Expressed in the usual way, as per 
cent accuracy of full scale, this would cor- 
respond to an accuracy of at least 0.04%, if 
full scale were considered to be 15, 000 
feet for example. 
265 
PART #2 - Stephen L. Stillman 
STRUCTURAL DESIGN 
A. Orientation 
In order to obtain the strongest signal 
return from the water surface, it is neces- 
sary to hold the axis of the main lobe of the 
transducer perpendicular to the surface. This 
requirement dictates a self-aligning hydro- 
dynamic design containing components so 
located as to produce balanced drag effects 
and to properly locate the center of buoyancy. 
B. Vertical Stabilization 
Static stabilization of the gear is achieved 
by pivoting a towing support bail (Fig. 4 at A) 
at a point just below the center of buoyancy. 
A strong righting moment is thereby produced 
about this towing-pivot point thus providing 
the primary vertical aligning force. When 
towing, the hydrodynamic drag developed a- 
bove the towing pivot point must be balanced 
by the drag below this point. This is accom- 
plished by adding a vane at the top (Fig. 4 at 
B). It was found necessary to add a second 
vane to provide a moment of force about the 
vertical axis. This orients the instrument in 
the direction of tow allowing the upper vane to 
position the entire instrument and develop the 
proper drag for balance. Since the gear will 
remain vertical regardless of cable angle, 
towing speeds up to 4 knots even in rough seas 
are permissable. 
C. External Frame 
Damage to instruments while handling on 
deck and over the side has often in the past 
been disastrous especially when the ship is 
rolling severely. Mildly rough seas average 
a good part of ship time at sea, and productive 
use of this time is obviously advantageous. 
The instrument described has been developed 
for use under these conditions. 
