A Hybrid Future
The EU Hybrid Marine (HYMAR) project is an ICOMIA led collaborative research project funded under the EU’s Seventh Framework Research Programme (FP7)
Bruntons with INSEAN as the research partner and ESP for data collection

  1. Using the test boat, to test objectively the effect of the high torque, low rpm characteristics of electric propulsion motors versus the high speed, peaked torque curve of a diesel engine, in terms of the ability to drive larger diameter, higher pitched and more efficient propellers.
  2. To research, develop and test a load following propeller with tuneable characteristics which can be matched to the characteristics of an electric drive motor
  3. To carry out the research needed to produce a parametric mathematical model of the propeller which can simulate real operational conditions, not just steady state
  4. To carry out the research needed to improve the propeller efficiency by 5% compared with the current state of the art
  5. To produce a range of self pitching propellers in different materials to use in a concept marine hybrid drive system
  6. To explore the feasibility and efficiency of a novel rim drive, self pitching propeller using stackable, counter-rotating PMDC motors
  7. To explore the feasibility and efficiency of a keel mounted drive system – integrated keel, motor, propeller and battery storage
  8. To optimise the regenerative characteristics of the self pitching propeller

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Apart from these basic principles, little is known about the detailed operation of these propellers, despite the fact that they are more efficient than conventional propellers and automatically adjust their pitch to suit the applied load.  In other situations where load following is required such as naval ships and fishing boats, much more complex controllable pitch propellers are currently used.

Work carried out in the 1980’s and early 1990’s demonstrated the efficiency advantages and showed that the torque characteristic of the propeller is flatter than a conventional prop due to its self pitching nature[1],[2].  A more profound knowledge of the dynamics of the mechanism will allow the characteristics to be tuned to match the motor more closely, to improve the efficiency further, and to improve the regenerative capabilities.

This knowledge will also be used to produce a design program for non hybrid shaft installations so propellers can be correctly matched to the power available. This will significantly improve the propeller optimisation for current installations, retrofits, and new boat designs

Autoprop Modes
[1] Coxon J, Claughton A; “Self pitching propellers”; RINA Nov 1982
[2] Miles A et al; “ The technical and commercial development of self pitching propellers”; RINA Nov 1992


There are two separate lines of investigation in this work project, one involving conventional fixed, folding and feathering propellers, the other Brunton’s “Autoprop”.

The first is an empirical investigation of the effect of the differing torque and propeller shaft speed characteristics of the HYMAR electric propulsion motors and conventional diesel engines in terms of their ability to swing different diameter and pitch propellers, and the impact of this on efficiency. This will be done by using the conventional and parallel electric installation (in serial diesel-electric mode) on the test boat with a large range of fixed pitch, folding and feathering propellers, collecting fuel consumption and performance data. Existing Autoprop propellers will also be tested to collect benchmark data.

The technical starting point for the second part of this work package will be an existing propeller known as the “Autoprop”.  This is a unique device, originally conceived in the 1970s, in which the blades are free to rotate about an axis orthogonal to the shaft.  When the shaft itself rotates, centrifugal force causes the blades to swing outwards, whilst hydrodynamic forces tend to push them inwards.  The blades take up an equilibrium position at the point where centrifugal and hydrodynamic forces balance.

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