smaller struts (fig. 1A). The temperature sensors were placed 
2-1/2 feet apart, starting 4 inches from the top. The shoulder of 
the sleeve of the sensor element was flush with the leading edge, 
and the thermistor bead extended about 1/8 inch into the fluid 
stream. 
The strut currently in use (fig. 1B) is made of three sections, 
each 10 feet long, of a commercial antenna tower. Each section is 
triangular in cross-section, having three 1-inch tubular vertical 
pipes braced by flat straps. The tower is suitably guyed laterally, 
as well as fore and aft. At 6 knots, the coefficient of drag for the 
circular tubes was 1.2 and for the straps it was estimated to be 
1.5; thus the estimated total drag on the strut was 1675 pounds at 
6 knots. There are 34 thermistor beads in the vertical array. 
Of these, 26 are used with the digital data system; they are spaced 
at 1-foot intervals. Five are used as in the original array, except 
that they are spaced at 6-foot intervals. The remaining three 
beads all have fast thermal response, and are used for continuous 
temperature measurements. Two of these beads are located near 
the middle of the tower while the third is located at the top. In 
addition, there is a fixed resistor which is mounted at the foot of 
the tower. 
It is clear that the motion of the platform through the water 
causes an essentially time-independent distortion of the stream- 
lines about the bow. This leads to a distortion of the time- 
dependent vertical temperature structure, and the shape of the in- 
ternal wave is modified. Since the distortion is most severe near 
the hull, the lowest beads are mounted some distance above the hull, 
and of the several isotherm signals obtained, the ones intercepted 
by the upper part of the strut are preferred. 
TEMPERATURE INDICATING SYSTEM 
Thermistors were chosen as temperature sensor elements 
because of their high sensitivity and simplicity. Thermistors have 
a large negative temperature coefficient of resistance, and the re- 
sistance is an exponential function of temperature. Commercially 
available thermistors do not have the same resistance vs. 
