The propulsion system in the "G.O. Sars" is designed to reduce noise.
Fish hearing thresholds (Mitson, 1995)
Fish have different hearing thresholds, but most fish are adversely affected by conventional engine noise. They respond to engine noise by diving and swimming away.
Disturbed fish tend to dive. They thus send back fewer signals. Echo sounders cannot take into account body angle, and so schools of diving fish will give off fewer and signals showing smaller fish. Also, by diving, they may move out of the field of measurement and thus, miss being counted.
Noisy boats, therefore, cause errors to be introduced into the data.
A combination engine using both diesel and electric power produces less noise and disrupts normal fish behaviour less giving more accurate data on school sizes.
The engines on the new "G.O. Sars" are combinations engines, and will thus generate much less noise than convention ships' engines, thus reducing the level of error in the data collection.
This graph shows typical vessel noise signatures. The red box indicates the normal fish reaction region to noise.
According to Per W. Nieuwejaar, director of the Research Vessel Department at the Institute of Marine Research, the engine will not be heard on board the "G.O. Sars" unless you are in the engine room. The special motor was made in Austin, Texas. There is also extensive insolation to reduce the vibrations from the engine that can be transmitted along the ship's hull.