Kevin,
The 12v will get up to 800 rpm pushing a canoe, the 36v will get to 800 pushing a 2000# sailboat, sort of. Tied to the dock (measuring thrust) the 36v will spin faster, producing more thrust.
You want to pick a prop that loads the motor to its max continuous amps on your boat. You need an ammeter to measure load and the ability to change props or gearing. Trolling motors have none of these abilities - but they are cheap. You clamp it on and get what you get.
Case in point: I have an EPIC electric outboard with a kort nozzle. With the nozzle it has enough thrust to push the boat up onto the trailer. Without the nozzle it will barely nudge it up half way. It's gotta be producing 2 or 3x the thrust with the nozzle. With the boat running free the nozzle makes no difference in speed vs. power.
Its static thrust (bollard pull) is not relevant to how fast it will push the boat. Thrust is a stupid way of comparing motors as the boats are not used tied to a stationary dock.
Denny
www.wolfEboats.
----- Original Message -----
From: Alycia & Kevin Miller-Lynch
To: electricboats@
Sent: Thursday, July 30, 2009 9:29 PM
Subject: RE: [Electric Boats] Re: Trolling Motors
àAnswer: All MinnKota and MotorGuide products (12v, 23v, 36v) are design to
spin at about 800 rpm for a max speed of around 3 mph . . . though they
claim 4 mph.
This doesn't make sense to me. If the 12, 24, and 36 all spin the same RPM,
and all use the same prop, they should all have the same thrust - so why
different voltages?
The only thing that would make sense is if the same prop on 12v makes 54lb
thrust and on 36v produces 108lb of thrust, it must be spinning a lot
faster. Thrust is somewhat like F=mv where F is force (thrust) m is mass
(amount of water moved by prop) and v is velocity (speed of the water moved
by the prop). The only way to increase F without increasing the mass (the
amount of water the prop moves, hence prop size or pitch) is to increase
velocity. Is anyone else following my logic? The only reason I'm beating
it to death, is I don't have access to a 24 or 36v motor, and I don't want
to spend the money to find out that John is right..
Anyone else care to comment?
Thanks for the tip on streamdancer
Kevin
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