Introduction of specially developed propeller for GREEN-MOTION system
AFRICAN CATS finalized the propeller type and sizes for her 10, 20 and 30 kW motogen* in the GREEN-MOTION retractable motor set up.
To realize a good balance between propulsion and generation with the retractable underwater electric motogens* used with the GREEN-MOTION system, African Cats has experimented with different sizes, types and materials of propellers during 2010.
4-bladed prop – DAR 71%
For the 10 kW motogen this resulted in a 4-bladed propeller made of an aluminium / titanium alloy with a size of 17’ x 7, 5’. This propeller has a displacement area ratio of 71% and is of the tractor type.
Speed vs. generation
Although there is a small loss of top speed under power, (7, 9 knots against 8, 1 knots), the gain is over 30% in regeneration. Electric generation now starts at 6 knots instead of 7 knots.
Power efficiency in propulsion mode at cruising speed has improved by 10% with this 4-bladed prop with lower pitch settings.
Because the motogen* and propeller can be retracted when the batteries are full, we are able to use a larger diameter then with electric motors that cannot retract their prop. This gives the advantage of better generation.
The other significant advantage is less resistance when sailing retracted so both speed and pointing has improved (6 to 12 %). The aluminium/titanium alloy reduces the weight of the propeller.
Further the aluminium anode used has been developed for this type of motogen*, being shaped to decrease drag.
Weight 34 kilo
The motogen, anode and propeller have a total weight of 34 kilo’s.
* Retractable electric underwater motor/generator