Propeller and Nozzles
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.
Calculation Parameters
In order to define the most suitable propeller for a vessel, it is necessary to provide all data regarding the boat’s dimensions, displacement, motorization and reduction ratio. In fact the customer is given a technical questionary to complete in order for us to have as clear as possible data.
After making our calculations, and according to each requirement, we are able to provide the following data:
Fishing Boat
1. Propeller and thrust calculation at maximum speed
2. Propeller thrust calculation at 73% and 90% RPM engine with a speed of 4 knots (or other)
3. Propeller Bollard-Pull calculation with a speed 0 knots and absorbed engine power.
Tug Boat
1. Propeller calculation with free speed and thrust
2. Bollard-Pull calculation (with speed =0 knots) and absorbed engine power.
- Tail Shaft with Steering Nozzle 19A Type
LINEA D’ASSE CON MANTELLO TIMONE 19A - Propeller and Nozzle Position – Fixed nozzle 19A type
POSIZIONE ELICA E MANTELLLO - Mantello fisso Tipo 19A - Which nozzle?
QUALE MANTELLO ? - Fixed Nozzle 19A type dimensions
DIMENSIONI MANTELLO FISSO 19A