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[Page 39]
this. The propellers of a turbine driven vessel revolve at such an excessive rate even at comparatively slow speeds (180 at 10 knots in the case of the "Torrens" and her class) and the consequent water-born noises of such intensity thus created, were registered by the "fish" to the total elimination of the very sounds it was desirous of picking up.
[The following paragraph crossed through.]
By stopping the engines it was thought that perhaps these noises might be reduced to a minimum, and an expert operator in the silence chamber able to ignore them in much the same way as a wireless operator, while cognisant of several aerial waves, can keep concentrated on the particular one he is listening to. But even this proved little better as although it was possible to stop the two wing propellers from revolving by putting astern steam on them the centre shaft continued to trail owing to the way of the ship through the water. N.B. In Parson's turbines, the centre shaft cannot be driven astern.
In addition to this, vessels of the "Torrens" clas have so much auxiliary machinery, feed pumps, dynamos, etc. all of which create their own separate noises whilst in motion, and must be kept going if you are to keep way in the ship - and once way is lost the "fish" gets out of the fore and aft line and does not register correctly - that it was found that, as far as turbine driven T.B.D's were concerned, the Nash "fish" was a totally impracticable proposition.
Naturally we on the Barrage were sorely disappointed as we had hoped great things of the "fish", so many glowing accounts had we heard of its prowess in English waters. [The following crossed through] and it was with sad hearts that we had to acknowledge defeat, yet we had this consolation, that as soon as it could be fitted in vessels suited to its peculiarities we might see similar results here in the Adriatic as those obtained round the coasts of Britain.
Two other Types
However, the "Torrens" arrived with three different types of hydrophones, there were still two other kinds on which to rely. These were the shark fin hydrophones and the bi-directional. Of the former little need be said, they were originally intended to be used in conjunctionwith the "fish" and were fitted on either bow, oval shaped plates being cut out of the ship's hull to receive them,