Almost three decades ago, we started dabbling in strange things in Tampere: We had to develop a loudspeaker that could withstand “moisture and small knocks!” In other words, an underwater sound source for sweeping acoustic influence mines.

Text: Timo Pyy Photos: Patria


Akustinen raivain

We had never even heard of influence mines before, let alone acoustic minesweeping. We “started from scratch” with very limited empirical data, yet also unburdened by history and any unnecessary constraints it may have brought. We were able to attack the task with completely open minds, with no clue as to what we would encounter during the project.  

During the specification and planning phase, we found ourselves almost losing faith from time to time, but we remembered our old motto: "Per aspera ad astra!". Even the preliminary requirements were extremely demanding, and they got even more challenging as time went on. Throughout the project, we had a very small team that was under a great deal of pressure and had to work to a tight schedule. On the other hand, the low turnover of the team staff honed the team’s personal chemistry, condensed a lot of expertise into one place, created a dedicated team of experts, and thereby helped to achieve a good result.

In order to meet the challenging system requirements, we had to develop new material and structural solutions. We had to learn new theories and working methods, and how to use new kinds of tools.  After all, the system used the latest in digital technology, hydraulics, mechanics, magnetism, hydroacoustics, measurement technology, signal analysis, just to name a few.

Akustinen raivain ja poiju
An acoustic minesweep on a Kuha-class vessel.

The prototype equipment was manufactured and installed on board a ship: the Kuha-class minesweeper was an incredibly small and cramped place compared to the wide open sea. The equipment was installed wherever we could find room for it. One funny detail worth mentioning is that we had to saw a palm-sized chunk off the radio operator’s bed so that we could get some cables and connectors to fit! Similar ingenuity was required during many other installations.

When sea trials of the prototype finally began, we also began “learning the hard way”. The float (more correctly: the sweeping gear buoy) had to be remade several times, many structures had to be reinforced, the size of the hydrodynamic control surfaces​ had to be increased, the tow cable was replaced, etcetera, etcetera. Finally, quite a few things had changed.

The system combined compactness, high performance and high shock resistance in an unprecedented way. The telemetry data generated by the system provided users with real-time information about the system’s status and operation. This, if anything, was likely to increase its usability and reliability.

The prototype was followed by the specification phase for the serial version, during which the final delivery version was finalized. The changes made to the serial version included much more than just the new colour. The acoustic output level was increased, additional features were added, the mechanical durability of the structures was improved, and particular attention was paid to the system’s usability.

We conducted several blast tests to verify that the system met the shock-resistance requirements. As a result of these tests, many structures were redesigned, materials were replaced, new solutions were modelled and new components were manufactured – and then the system was retested. As we returned to the naval base after the final successful shock test at sea, one member of the project team let out a short burst of song: “We’re all heroes, when you really look us in the eye....” A high-ranking officer, who had been following the tests, said: “That song was truly deserved.” I can only say that we all felt great at that moment.

In this article, I’ve described the early stages in the development of an acoustic minesweep – but only very briefly. There are enough stories on this topic to fill an entire book.  I have left out many phases and details of the project, as well as names all the people involved, so that anyone I may not have mentioned wouldn’t have felt as if they or their input was being underestimated. I would once again like to thank all of those who were involved in the development work. And at the same time, I would also like to remind everyone that this article is based on my own recollections and personal view of events. Through someone else’s eyes, the focus might have been different.