Measurement station Roeleveense Plas at Nootdorp (1953 – 1961)
During the development of sonar transducers, the measurement station in the Waalhaven, Rotterdam no longer met the requirements in the early 50’s:
- the water was not deep enough on the spot,
- the background noise was too high due to the proximity of ship traffic and ports, and
- the distance between the laboratory in The Hague and the port in Rotterdam was impractically large.
In 1953, a new raft was constructed in the Roeleveense Plas using the pontoons from the earlier sonar measurement facilities in the Rotterdam Waalhaven. The Roeleveense Plas is a triangular artificial freshwater lake with sides of 300 and 400 metres located near Nootdorp next to the highway A12.
The pontoons originally were the doors which protected the German Schnellboot bunker in the Waalhaven during the Second World war. The compartmentalised pontoons were made of half inch steel plate and sized approximately (lbh) 4 x 3 x 2 metres. There was therefore headroom in the pontoon. Both pontoons were connected to each other with a gap of one meter in between. A hoisting device was installed. On each pontoon there was a hut: on one pontoon a hut for taking measurements and on the other a hut with a diesel engine and dynamo for the power supply.
The raft was stationed with four anchors near the narrow part of the lake above the deepest point (-18.5 m). For measurements, the employees had to row with a rowing boat from a jetty to the raft. This was a bit easier than in the Waalhaven with the high quay of the old Schnellbooten bunker.
The turning mechanism for the hydrophones and transducers under test originally came from the Hr.Ms. Paets Van Troostwijk. The mechanism could be tilted in a way that the bottom side came above water to ease the mounting of a hydrophone or transducer. This mechanism is still in use in the laboratory’s underwater acoustic basin.
A new raft
The quiet environment and the large depth (18.5 metres) benefited the quality of measurements, especially for frequencies below 500 Hz. This raft was also made suitable for measurements on sonar domes (a “dome” is a streamlined envelope of the transducer that serves to reduce the noise of the water flow). Although this measuring station initially met all the requirements, after a number of years it turned out that a replacement was needed.
The development of the sonar technique led from the searchlight sonar with a single beam to the panoramic sonar with a combination of a number of fixed beams in a single transducer as described above. The second element in development was the use of lower frequencies. Both factors combined resulted in transducers and domes becoming considerably larger and heavier. Transporting it to the raft could therefore no longer be done per rowing boat as before.
Around 1960 it was decided to construct a larger raft (6 x 14 metres) with a fixed fifty meters long pontoon bridge connected to the bank. The new setup was designed to be able to test objects with maximum dimensions of 2 x 2 x 4 metres and a weight of 5 tonnes. To this end, a rail system was installed on the bridge and the bank. The bottom of the pontoon had a 2 x 4 metre hole. A 13-metre high lifting column above the hole could lift objects up to 1.80 m high from the trolley and could lower them up to 6 meters below the water surface. This raft was put into use in 1961.
TNO has used these facilities for experiments until the mid-1990s.
The old, Second World War-based pontoon raft was transferred to the Navy Electronic and Optical Company (MEOB), which used the raft for a number of years at the side of the lake. The raft was connected to the lake shore with a bridge. The pontoons were later re-used as a base for a house at the other side of the lake.