The Ryan Hydrophone was a moored hydrophone intended for use in coastal and harbour waters.
Ryan's findings of his invention were recorded in a memorandum, some of which was excerpted in The Annual Report of the Torpedo School for 1915:
- ability to distinguish between engine sounds was the most important requirement
- the horsepower of a given craft determined the range at which it could be detected
- vessels with a deep draught were easier to hear at long ranges than shall draught types
- iron ships could be heard at longer ranges than wooden ones
- a submerged submarine was easier to hear than a surfaced one at the same H.P.
- paddle steamers were pretty quiet
- the easiest signal to pick up were engine vibrations transmitted to water through propellers and hull
- ships were 400% as noisy from the quarter as from ahead
- ships were 125% as noisy from the quarter as from dead astern
- rough seas and thunderstorms caused a "slight but continuous roar" which reduced effective ranges by 50%
- submarines running electric motors were quieter than surface craft, but when submerged they transmitted better than surface craft at the same power
- turbine boats at one or two miles could be mistaken for a submarine at a half mile
- turbine destroyers at full speed could be heard at seven to eight miles under favourable conditions
- shoals cast a "sound shadow" if they lay between a sound source and a hydrophone
- insulating the mooring cable was essential to avoid great scraping and bumping noise that overwhelms all others
- flat diaphragms picked up sounds at any angle, even when parallel to the line of transmission
- positioning the hydrophone on the same pressure plane as the sound source was ideal
- diaphragms could bear direct sea pressure up to 15 fathoms. Beyond this depth, they needed to be sealed in a watertight drum
- three fathoms from the bottom was the best depth, when overall depths allowed
- experiments to create machines able to differentiate different engine noises were not successful. A trained human ear was best
- people with a "musical ear" were ideal operators
- an operator required five minutes listening before his ears became attuned to the ambient sounds and useful detection could begin
After testing, Vernon reported that it found the hydrophone very useful for use in narrow channels. It had proven that a hydrophone in the Forth had proven able to detect submarines running on batteries at 1.5 miles and almost always at one mile if there were no unusual interference. This level of sensitivity was seen as not only sufficient, but the highest level desireable.
Deployment and Service
Fixed installations were in service in 1916. By war's end, eighteen installations were in place around England.
- Annual Report of the Torpedo School, 1915. pp. 178-9, Plates 92-5.
- Find and Destroy. p. 113.