tential as an inexpensive offshore oil pros- 
pecting tool. 
II. SONAR THUMPER 
A. General Description 
The standard thumper unit consists of 
a power supply cabinet, capacitor bank cabinet, 
and transducer, The power supply converts ship's 
power or electrical generator power (110 or 220 
volts A.C.) to high voltage D.C. which is fed 
to the capacitor bank cabinet. When the trigger 
circuit is activated by a recorder contact, the 
capacitors discharge into the transducer, The 
epoxy encapsulated flat coil has an aluminum 
plate which is spring loaded against the face 
of the coil. The aluminum plate is violently 
repelled from the coil when the strong pulse of 
current flows through the coil. 
A precisely repeatable positive 
pressure pulse is produced by the repulsion of 
the plate in the water. The standard 1,000 watt 
second thumper gives a pulse duration of 0.5 
milliseconds and a peak pressure of approximately 
1 X 10° dynes/em? at one yard. The 5,000 watt- 
second unit gives a pulse duration of 2 milli- 
seconds and somewhat higher peak pressure. 
B. Large Thumper Units 
The unique désign of the thumper 
transducer makes it inherently a non-saturable 
type of device. Therefore very high power 
thumpers can be built using the basic trans- 
ducer design. The first 5,000 watt-second 
Figure 2. 
installation on board the R.V. Chain duriug 
5,000 watt-second Sonar Thumper 
the June, 1961 cruise to the Puerto Rico Trench 
284 
transducer was a scaled up version of the stan- 
dard model, Several double coil transducers 
were then designed to eliminate the bulkiness 
of the scaled up version and produce a greater 
concentration of energy, However, the energy 
concentration of the double coil transducers was 
so great, the back pressure of the coils caused 
the eposy encapsulation to shatter, To eliminate 
this difficulty, a symmetrical transducer was 
designed with two coils arranged back to back 
and an aluminum plate mounted against each coil. 
Thus the backward pressure of one coil counter- 
balances the pressure of the opposing coil. 
Initial tests of this transducer design at 
powers up to 14,000 watt-seconds have been very 
encouraging, 
+\ 5 
Figure 3. 13,000 watt-second Sonar Thumper 
system. 
The larger thumper units are com- 
pletely modular in design to give great flexi- 
bility. The standard thumper components can be 
used along with more capacitor bank cabinets for 
greater power storage. The firing rate can be 
stepped up by simply adding more power supply 
cabinets, Figure 2 shows a photo of a 5,000 
watt-second unit consisting of two 2,000 joule 
capacitor banks, the standard triggered capaci- 
tor bank, and two power supply cabinets. This 
particular system was used on a June, 1961 
cruise by Woods Hole Oceanographic Institution 
on the ship R.V. Chain. to the Puerto Rico Trench 
area. Figure 3 illustrates a schematic diagram 
of the 13,000 watt-second Sonar Thumper unit. 
Installation and Operation of the Thumper 
The installation and preliminary check 
of the Sonar Thumper components can be done in 
a short time. The components are designed to 
be portable by two men. The power supply and 
capacitor bank cabinets are ordinarily placed 
in a cabin or sheltered area to avoid salt 
water exposure. 
C. 
