T-Pain Is On A Boat: Re: [Electric Boats] Power Consumption for Minn Kota Riptide 50 & MotorGuide 54

Friday, September 25, 2009

Re: [Electric Boats] Power Consumption for Minn Kota Riptide 50 & MotorGuide 54

I bet your motorguide 54 is really a 34. There aren't 12v trolling motors that produce 54# thrust.

If these have discrete speeds, like position 1 to 5 (max) forward and 3 for reverse like my MK endura 36, you waste a lot of power running at anything less than full throttle. They cut speed by diverting part of the power to heat a resistor instead of turning the prop. You will pay 2-3x for a trolling motor with an efficient PWM speed control.

I'm doing a lot of tests on an Endura 36 and can tell you mine draws 38 amps with the boat tied to the dock and 32 amps moving at 4.5 mph pushing a canoe.

The published amp hour ratings are for a slow draw that discharges the battery in 20 hours [ C20 ]. You will be discharging much faster than that so must derate the battery. Without getting into peukert exponent calculations, all you need to do is use the Reserve Capacity figure - that is how many minutes it will give up 25 amps. Figure on at most using 75% of this time as you are pulling more than 25 amps and the voltage drops off toward the end so you will slow down.

Denny Wolfe
www.wolfEboats.com

----- Original Message -----
From: cal29brad
To: electricboats@yahoogroups.com
Sent: Friday, September 25, 2009 5:12 PM
Subject: [Electric Boats] Power Consumption for Minn Kota Riptide 50 & MotorGuide 54

Hello to All,

I have a MotorGuide 54 that has these specifications:

12 Volts 0.34 Kwatts

I also have a Minn Kota Riptide 30 with these recommendations & specification:

12 Volts
105 Ampere/Hour Battery
"... your 12 volt motor with draw 1.0 ampere/hour ... for each pound of thrust produced when the motor is running on high."

By my calculations these work out to:

MotorGuide 54: (0.34 * 1000) / 12 = 28.33 ampere / hour

Minn Kota 50: 1.0 * 50 = 50.0 ampere / hour

Do those numbers look correct to all of you? The units and the pounds of thrust they produce are pretty similar, which makes me suspect the somewhat significant difference in the ampere/hour ratings.

All enlightening efforts are greatly appreciated. I plan to use these two units to move a Cal29 sailboat about six to ten miles across (or down) Boca Ciega Bay to downtown St. Petersburg Florida early next week, and need to calculate what size batteries I should get. The boat is not refitted yet, so I need to jury-rig all of this, including battery locations, cabling, breakers, and so on.

I have found a local firm that has what appear to be 85 amp/hr (they "rate" them thus: 205 minutes at 25 Amps each) 12 Volt deep cycle marine batteries currently on sale for about $60.00 each. Again, according to my calculations, three of those should give me either 2.5 hours (using the Minn Kota) to 4.5 hours (with the MotorGuide) of full speed motor use with about 50% battery consumption. Does that look correct?

Thanks much in advance,

Brad Bates
Play Mate
St. Petersburg, FL
(I am dangerous with a calculator)

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