I don't know if I'm going to use a reduction drive or not. My hope was to find an outboard for the suitable voltage, power requirement, and desired efficiency.
Maybe the outboard to look at would be the Aquawatt Green Force. Specs copied from http://www.aquawatt.at/downloads2/2012-Prospekt-Motor-Komp-EN.pdf :
Transom height: 20 Inch
Nominal voltage: 48/50 Volts
Current max: 190 Amp
Power output max: 8 KW
Weight: 66 Kg
Propeller size: 11, 12 or 13 inch
Thrust with standard propeller: 135 da N
Maximum speed: 8 Knots
Range of use Lakes, coast, rivers - suitable for salt water use
Looking at the pictures, it's apparent that the Green Force is built with the motor itself down in the water, in line with the prop. I haven't read anything indicating whether or not it's directly coupled or if there's an inline gearbox. I also haven't read anything indicating whether the motor is brushless or brushed, how it's wound, etc.
Single digit slip sounds great. I'm doubting I can get there with the things I have to work with though.
This whole discussion really goes hand in hand with my previous question about a chain drive electric outboard. It sure seems like that would be a simple, elegant, and efficient solution to powering pleasure craft with electric. Reduction could be built into the sprockets... 2 to 1 would be pretty easy. Even approaching 3 to 1 would still work. One would be limited by the size of the sprocket down near the prop and the (lack of) efficiency associated with small sprockets (less than 10 teeth starts to become fairly inefficient). Anyhow, I digress.
Thanks again,
-keith
--- On Sat, 5/5/12, Robert Lemke <mailto:robert-lemke%40att.net> wrote:
I'm assuming your going to be using a reduction drive? Change gearing for speed but still use as large a diameter and pitch as will fit. That way if you upgrade in the future to a more powerful motor you just need to change the reduction gears. Slow turning props are the best for minimum slip. My slip figures are single digit aboard the container ships I served on, 112 rpm direct drive from the engine.
Bob
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