I'll include some links to elec. motor info, since most boaters know
less about them than about the familiar low-hp gas engines.
Let me say right up-front that if, as you say, you wish to go
up-stream against a reasonable current, in a loaded boat, the elecs.
are at a distinct power disadvantage.
To make this clearer, you can roughly equate 750 watts with 1
hp.(this ignores efficiency losses in the unit). This would equate to
about a 62.5 amp draw with a 12v. system(1 battery) / a 31.25 amp
draw in a 24v. system(2 batteries) / a 21.8 amp draw in a 36v. system
The "lbs-thrust" rating of the trolling motors is a relatively
less-accurate method of comparing to "horsepower' in the gas-motor
sense, as so much depends on the prop, boat speed, etc., when any
attempt is made to measure thrust.
So, obtaining the full-throttle amp-draw spec. for a given motor will
give you the best approximation of the actual power of the motor, in
hp terms. Effectively applying that power to the water is a whole
'nother thing, too. (Where the prop-meets-the-water, ...discussed
You can see from this that when you even think of comparing elecs
with even small gassers, you are gonna be talking some SERIOUS
amperage (biggest motor many batteries/mucho weight), if you want
to approach the power of the gas engines.
A 1 hp elec is a very powerful one, by today's standards. Finding a
prop to match your boat/speed, etc., from the available (limited)
choices designed for these elec motors, would be sheer good fortune.
These motors/props are designed to move heavy(bass) boats,
slowly,...something in the neighborhood of 3-5 mph. A (relatively)
lighter driftboat attempting to operate at a speed great enough to
make decent progress against any real current, is a different beast
altogether. Since prop-design is very "condition
specific"(speed/load/rpm), it is not an easy match to make.
The small(4 - 9.9 hp) gassers, originally mostly used on john-boats,
etc., have much more power, and are usually propped to efficiently
apply that power at greater speeds. (And chances of finding several
props to "try" on your rig, at your speeds, with your loading, are
When you compare the weight/bulk/cost of the number of batteries
needed to power the larger elecs., add the weight of the motor
itself, and then compare the total to the weight/bulk/cost of a small
gasser + fuel Tank, ...then see how much useful power-per-lb. you are
ending up with, you may feel the gas engine is the obvious choice.
Of course the relative silence of the elec can be a plus when you are
being swept seaward or over the falls, ...people will be better able
to hear your screams! :-)
here just in case you're curious about what's going on out there in
the "electric boat" world: