Richard van den Berg wrote:
On Wed, 26 Jul 2006 08:43:23 -0700 Bob S
) wrote:
I have noticed that real numbers concerning electric outboards seem to
be few and far between. Therefore, I thought some of you might be
interested in some results I obtained the other day with mine.

I used two Excide 6 volt golf cart batteries in series. Open circuit
voltage at the time of the tests was 12.53 volts.

The motors were both Minnkota Enduras, one 30 lb, the other 50 lb. I
have no way of directly measuring thrust, nor did I have a calibrated
current shunt, so I assumed the factory-published values of 30 lb at 30
amps and 50 lb at 42 amps.

Voltages at the input to the motor leads were 12.14 and 11.96 with the
motors set to max. This indicates and combined internal battery and
external wiring resistance of about .013 ohm. The nominal input powers
are therefore .49 hp and .67 hp.

Again, assuming factory stated thrust is accurate, the output powers are
.28 hp and .53 hp for overall efficiencies of 57% for the 30 pounder and
80% for the 50. Incidentally, when I questioned Minnkota by phone they
would not state efficiencies but did say the 50 lb unit is their most
efficient.

These motors push a 16 ft flat-bottomed sailing skiff at 3.5 and 4.0 mph
respectively.

See the extra power needed for that 0.5 mile faster?

I would be pleased to hear from any of you who are also interested in
electric propulsion.

The Queen Mary II has electric propulsion.;-) For now I think battery
propulsed boats will be a niche product, nice for fishing or cruising
protected areas or coming home but not for holidays.

Do the math and find out yourself. My boat has also electric propulsion.
When the day comes that fuelcell or other electric generation becomes
cheaper then a diesel generator set, I'm prepared. Untill then the
diesel keeps running.

Bear in mind that many of the boats on the water today ARE used for
fishing or utilitarian functions on protected waters. No one suggested
serious cruising. But my 16-footer does have a 30 mile range at 4 mph at
the 70% discharge level which is more than adequate for its crabbing and
homecoming (sail backup) functions. The math does work in many cases,
but, as you say, picking the right niche is important.

BS