Tunnel vision

Knut Andresen, Technical Director for Brunvoll A/S explains the need for and the measures to reduce noise from tunnel thrusters.

With increasing environmental pressures and restrictions on anchoring at some of the popular destinations for cruise ships, Royal Caribbean Cruise Lines (RCCL) wanted its Millenium Class series at Chantiers de L`Atlantique to be able to hold position without resorting to anchors. The theory of dynamic positioning (DP) is not a problem: podded drive does most of the work and bow thrusters take care of the rest.

However, tunnel thrusters are a powerful source of vibration and noise, especially with larger installations seen in the cruise industry in recent years. Indeed for cruise ships wanting to adopt DP, this posed a problem as the areas above, or close to, the thruster are often used for accommodation for the vessel`s entertainers. Because of the nature of their work the entertainers often sleep during the day while passengers go ashore – the very time the vessel will be using the thrusters to hold station. In order to overcome these problems RCCL worked with Brunvoll on a noise reduction programme. This culminated in the adoption of resiliently mounted thrusters for its newbuildings.