R Swarts wrote:
wrote:

Should also have mentioned that my 30 lb Endura pushes a 14' Hobie at
about 3.5 mph in still water.


I think this general theme (Using inboard pumps for propulsion) is
worth pursuing. One interesting aspect is being able to use the same
pump(s) for forward propulsion and bow-thruster/steering.


I would tend to doubt that, but...

Can we start with a decent idea of the efficiency of the trolling
motors?

How much current do some typical units draw (all 12Volts?) ??

Are they rated only in static thrust? Or also Horsepower? Horsepower
can be converted to Force VS Distance VS Time. (1.0 Horsepower == 550
Foot-Pounds per second, right??) HighSchool Physics was, um, 50 years
ago :-) Yes, I just see "1 horsepower [electric] = 550.221 382 975
foot pound-force/second" at
http://www.onlineconversion.com/power.htm

Well, yes, but HP is really irrelevant other than as a comparison
between similarly configured devices. What you're really concerned with
is *Force*, calculated as F=ma (i.e. force = mass x acceleration). No
matter what system you employ for propulsion, it boils down to the mass
of water displaced per unit time.

To do a meaningful comparison, you'd need to know a lot of information.
You need to have a force chart for the outboard (i.e. mass flow rate
generated by the propeller over the operational range, versus amp draw
for the motor). Then you could compare the amp draw of your pump versus
mass flow rate. I think you'll find that the pump idea is *far* less
effcient than an outboard. The propeller has no frictional losses
associated with supplying water to, or discharging water from, the
'pumping' device. The frictional loss at the propeller surface is
offset by the surface frictional losses at the pump impeller.

Keith Hughes