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.

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

So, IF you knew the relationship of Drag (In Pounds) VS Speed for YOUR
boat, you could create a graph of Horsepower VS Speed. (This would
be for "Perfect Horsepower" which certainly will not happen with real-
word trolling motors and propellers, OR real-world pumps and
hoses.. )

But you'd have SOME idea...

If you had a 25 pound fish scale and 100 feet of line, and someone to
paddle the boat OUT so you could pull it IN, you might start to get
some numbers...

Other Related Idea: I have thought about running a medium-large (??)
pump from my inboard boat engine to bow ports for "Bow Thruster".
Anyone seen something like this?? A pump could be engaged with an Air
Conditioner Clutch....

So let's keep thinking about this????


Generally speaking a figure of about 50% overall efficiency (prop +
motor) seems to be appropriate for my 30 and 50 lb motors if you believe
the factory-stated thrust and current, based on the speeds I've
measured. Current draw is 30 and 42 amps respectively. There are a few
(very expensive) motors that do better. Motors are available the run on
12, 24, 36 and 48 volts. Generally trolling motors are rated in static
thrust while "electric outboards" are quoted in hp. It is difficult to
directly compare electric hp with gas because the gas motor hp differs
tremendously with rpm. That having been said, volts x amps is still true
input power, and 550 ft-lb/sec is hp regardless of how it is generated.

BS