On Tue, 16 Sep 2003 17:56:16 -0700, "John R Weiss"
wrote:

"Jim Woodward" ...
Since one HP is 550 ft-lbs per second, that suggests that one hp is
5.5 pounds thrust at 100 feet per second or 6.25 pounds at 60mph
(statute miles, here).
//
Brian Whatcott wrote...

Yes, ignoring scaling constants:

Horse power = thrust X speed

It appears there are a few means of conversion...

My MinnKota EX42 is advertised to put out 42 lb thrust at 12V and 36 amps. What
is that in electrical power consumption, converted to HP?

It also pushes my 21' boat at about 2.5 - 3 knots at full thrust on flat water.
What is that in power output or work done?

I don't have my calculator and conversion constants handy, but at first glance
the electrical power draw appears considerably higher than mechanical power
output or work. OTOH, maybe it isn't pulling all 36 amps when pushing the boat
at max speed (I assume the prop RPM is electronically governed).

12 V X 36 A = 432 W
432 W X 1HP/746W = 0.58 HP

IF notice IF 0.58 HP is the electrical rate for 2.5 kt ( = 2.5kt X
1NM/hr / 6080ft/hr X 1hr/60min) = 253.3 ft/min
\so the required HP at 100% efficiency is 253.3/550 HP = 0.46HP

So the efficiency might be 0.46/0.58 (power out/power in) = 79%
which is rather high.....

Alternatively,

42 lb thrust from 0.58 HP would give at most 7.6 ft/min
which is 0.075 kt. Hence, unsurprizingly, the maker is quoting
quasi-stationary testing.

Brian Whatcott Altus OK