For example, to avoid damage to the 
Inverted Sounder and velocimeter a lightweight 
aluminum tubular frame is constructed around 
the principal components (Fig. 4 at C) and 
mounted to the internal structure by neoprene 
and plastic shock absorbers (Fig. 4 at D and 
E , for example). The support points of the 
whole assembly are located on the internal 
structure itself, not the frame. Therefore, 
damage to the frame is not apt to affect op- 
eration of the instrument. 
During bottom survey work a possible 
cause of loss is snagging the instrument on 
the bottom. To guard against this, the rub- 
ber and plastic shock material present weak 
links which will part before the supporting 
steel cable. 
An additional way of retrieving snagged 
gear is provided in a safety cable. One end 
is fastened at the lower end of the instrument 
(Fig. 4 at F) the other to the steel support 
above the clamp (Fig. 4 at G). All external 
aluminum metal surfaces are coated with an 
epoxy type paint to resist surface corrosion. 
Teflon bearing material was used on the bail 
pivot to reduce noise. 
D. Watertight Electronic Chambers 
The two watertight compartments contain - 
ing the transmitter and receiver respectively 
consist of two 7075-T6 aluminum tubes, 
(Fig. 5) and end caps of the same material. 
These compartments will withstand 10, 000 
P.S.I. and are sealed with double O-rings 
mounted on the caps. (Fig. 6 at A and B). 
One O-ring is located as near as possible to 
the perimeter of the cap to prevent corrosion 
from developing between cap and tube surfa- 
ces. Such corrosion would cause considerable 
difficulty in removing the end caps. Each cap 
is held to its tube by four quick acting stain- 
less steel drawhook latches. Eight standard 
Joy plugs provide electrical connections 
through the caps. 
The earlier models of the instrument 
employed a standard model airplane engine 
spark plug as the high voltage feed-through 
which conducts the 15, 000 volt pulse through 
the end cap. These plugs are capable of 
withstanding the 14, 000 P.S.I. required for 
deep submergence. Because these plugs are 
266 
no longer manufactured, a special feed through 
designed for the purpose is used on the current 
model. 
After considerable investigation it was 
found that a certain commercial weather- 
stripping putty had excellent insulating quali- 
ties for high voltage even when subjected to 
high pressure in salt water. This material 
was therefore used directly to insulate the 
high voltage terminal described above. The 
entire high voltage assembly is protected by 
an external aluminum housing (Fig. 6 at C). 
An internal bulkhead incorporating an O- 
ring seal is placed within the transmitting 
tube to separate the battery compartment 
from the high voltage transmitter (Fig. 6 at D). 
This precaution was taken because silver zinc 
batteries, when defective or subjected to heavy 
drain, have been known to emit enough hydroga 
to cause an explosion when mixed with air and 
ignited by a spark such as might accidentally 
be generated by a defect in the high voltage 
system. 
E. Internal Construction 
Stainless steel was used for chassis con- 
struction where possible to prevent salt air 
corrosion. The transmitter and receiver 
chassis are mounted on the end caps, thus 
eliminating several connectors. The receiver 
battery is contained in a plug-in chassis, on 
which is also mounted the velocimeter mixer- 
amplifier (Figs. 7 and 8). A fibreglass cover 
protects the components from salt spray when 
the battery chassis is removed from the tube 
on deck. To reduce acoustic noise, the timing 
motor is suspended by neoprene strips and 
entirely encased in a sound absorbing plastic 
foam. 
F. Velocimeter 
AN.B.S. velocimeter may be attached 
below the internal assembly, where it is pro- 
tected by a tubular structure and shock mounts 
(Fig. 4 at H). This instrument is designed 
for 20,000 P.S.I. If it becomes desirable to 
also operate the sounder under such pressure, 
this can be accomplished by a slight increase 
in the wall thickness of the aluminum tubes 
