Re: Electric Trolling Motors (was: Good Girl For Sale)



Displacement can be deceiving when thinking about moving a hull through the water.  It's not so much the "weight" as it is hull shape which determines the size of the bow wake.  The the bow wake is created by pushing the boat through the water and pushing it requires power.  Complicating this, it's somewhat exponential so that as you increase speed the power required goes up a lot, especially as you approach hull speed (top end of displacement motion).  The electric boat community has worked this out well, and as I recall the rule of thumb is doubling the power for an increase of a knot approaching hull speed.  So moderate speeds, in the realm of half hull speed, can be fairly efficient, like your "leisurely, rate of progress".

Regarding 12 vs 24 volts.  From your examples, 5 amps x 24 V = 120 watts  &  30 amps x 12 V = 360 watts;  lower watts = less losses to heating in all components.  If you are using lead acid batteries, either flooded or AGM, higher amperage cause losses due to the peukert effect which can be quite significant at the higher amperage.

John A

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