Work boat propulsion system

This type of propulsion system is particularly suited to working vessels (tow-boats, fishing boats, river bargers and pusher tugs) in the sea and on rivers. The nozzles can be of two types: “Fixed” or “Rotating” (Steering Nozzles). The main geometric parameters are the following: L/D ratio D = Internal diameter of the nozzles, where the propeller is positioned L = Nozzle length Contraction ratio This is the ratio between the point of water entry at the aft and the exit point at the stern Section geometry The advantages gained are the following: Reduction of propeller diameter; Reduction of propeller shaft and stern tube diameter Reduction in vibrations, expecially in the wider stern as the nozzle regulates the water flow Reduction in ship’s pitching when in rough waters Increase in the propeller thrust to the tow and to the Bollard-Pull Possible increase of ship speed by approx. 15% Better performance from heavily loaded propellers, especially in shallow water At the same conditions of speed, trawler work, Bollard-Pull, need 30% less power engine The smaller engine cost, the reduction of fuel consuption, the high-performance of trasmission allow to recover the investiment within one or two years.