Log 2014-11-10 : Dusk sailing and more data

With the days getting shorter and daylight-saving time helping, I decided to sail later in the afternoon to be able to capture some dusk/night footage of the Sequana.

I had switched props and was running the Raboesch #174 45mm 4-blade propeller. With its larger diameter and much wider blade surface it makes for a perfect towing prop. An increase of current draw was expected.

Using the same Turnigy 2-in-1 Power meter/Servo meter, I decided to measure the actual power draw with this prop.

It's not an "apple to apple" comparison as the prop diameter is not the same (45m vs 40mm) but final pitch is close tough (39mm vs 41mm).

Looks like the motor itself and the loss in the powershaft account for around 1 amp. This isn't unexpected.

At 40% amp draw is a bit over 2 amps (2.60 - 0.55) with this prop compared to 1.50A with the #147 prop.

At full throttle (which happens only during heavy towing) there's a significant increase: 10.60A vs 6.6A.

As expected the battery performed well. SLA batteries have low internal resistance and can withstand significant amp draw. At 11A run time would obviously suffer. 15-20 minutes according to the spec sheet of my cheap 6V/7.2Ah battery. But this would be an extreme usage pattern.

Next up: measuring thrust/bollard pull. I ordered an electronic fish scale/luggage scale on eBay ...