T-Pain Is On A Boat: Re: [Electric Boats] torgeedo motors

Tuesday, August 4, 2009

Re: [Electric Boats] torgeedo motors

Hi again

A week or two back I promised to return with some results of speed
tests on my Torqeedo powered trimaran. (Torqeedo Cruise 4 powered by
200 ah LiFePO4 bank)

At the time of the test there was an incoming tidal stream of maybe
about half a knot and a light variable wind (about 5 knots). The
combination of the two has produced such variable results that its
simply not clear how much each of the motor, the wind and the tide
are contributing to the speed effects.

I'll show you what I mean by listing some of the data here for you.

The test was done in the Caboolture River where it snakes around in
the flood plain, and so its direction changes radically. As well
some parts of the river are well shielded by mangroves lining the
banks, and other parts are open grass right to the river's edge.
Even though light, the wind clearly has a marked effect on these
results.

To begin with here's some figures going with the current and
generally with the wind. But the wind effect is variable because it
swung from aft to abeam during this run.

Watts Knots
2600 6.5
2700 6.6
2600 6.7
2600 6.4

Then we turned the boat and returned down river. wind and current
against.

2600 4.5
2600 4.5
2650 4.3
2800 3.7
2800 3.9
2800 3.6
2880 3.4
2900 3.3
2730 3.8
2700 4.0
2760 4.2

Now upstream again

680 4.6
700 4.4
840 2.8
850 2.4
820 2.9

And we continued like this for two hours and the results followed the
same pattern of variability.

By the way, the voltage during these tests was generally around 50 to
52 volts, so you can deduce the amperage.

Notice some of the extreme values such as 6.7 knots at 2600 watts and
3.3 knots at 2800 watts. This may give you a sense of the
variability of these readings. It seems unlikely to ever get achieve
reliably repeatable data when we consider the vagaries of wind and
tide that will challenge us almost every time. Assuming of course
you're like me and don't have access to a very large under cover test
tank!

Perhaps as I collect more data there'll be enough to get a reasonable
line of best fit.

These results are after fitting flaps to the outboard well, and
positioning the prop as best I knew how. Because of the wind effect
I can't judge whether there has been any improvement in speed. Top
speed was 7.2 knots aided by current and perhaps a little wind.

Cheers

Chris

http://www.currentsunshine.com