SI may be a nuisance to some folks - but it shines here, because there
is NO scaling constant in this relation:
power (watts) = force (newtons) X speed (meter/sec)

Now let's put in all the scaling constants to US customary units
(Can't say British, or Imperial, any more...)

1 watt X 1HP/746watts =
1 newton X 1kg/9.81newtons X 2.2 lb/kg X
1 meter/sec X 39.37 inch/meter X 1ft/12 inches X
1 mile/5280ft / (1min/60 sec X 1hr/60 min)

And this boils down to
0.00134 HP = .2243 lb X 2.237 mph
or even more succinctly:
1HP = 374 lb X mph
(Your solution gives 6.25 X 60 = 375 lb X mph - close enough)

As James Watt defined the HP as a horse capable of exerting a force of
550 pounds at a speed of one foot per second (which is about 50% more
than a good horse can do for a shift, without then falling down dead)
your figure of 5.5 lbs at 100 ft/sec is *exact*

Brian Whatcott Altus OK

On 16 Sep 2003 11:22:30 -0700, (Jim Woodward)
wrote:

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).

That feel OK, but my college days are in the distant past -- any
comments?

Jim Woodward
www.mvfintry.com
Brian Whatcott wrote in message . ..
On Tue, 16 Sep 2003 22:51:57 +1200, "Paul Squire"
wrote:

Is there a simple equation between lbs thrust (as specified in electric
outboard motors) and Horsepower?


Yes, ignoring scaling constants:

Horse power = thrust X speed

Brian Whatcott Altus OK