Re: [electricboats] Outboard Sizing Help Needed

One thing you should know is trolling motors are designed, not for primary propulsion, but to control the boat at slow speeds. 

Their props are pitched for slower speeds and more torque, not higher speeds you might be able to achieve with the same motor.

The stock props that come from the motor manufacturer are usually low pitch, like 3 - 4".
https://www.jdpower.com/boats/shopping-guides/understanding-propeller-pitch

You might consider changing the prop on your existing electric motor to gain additional speed.

Identifying which pitch/diameter of prop you would use depends on how much power you are consuming now when your motor is at wide open throttle.

You would need an in-line or clamp on amp meter to take these measurements.

Specific motors have an upper limit to how many amps they are designed for. 
That specification should be in the motor's documentation. 

The gap between your current power consumption and the rating of the motor will give you how much power you have to play with trying new props.

I use model airplane props to "dial in" the pitch/diameter choice, paying close attention to how they affect speed and power consumption.
https://www.apcprop.com/product-category/marine/

You may need to make minor modifications to the prop hubs or use nylon spacers to get them to fit on your motor's prop spindle and match your shear pin.

Don't expect miracles with this approach.  You might gain a 0.5 mph increase in speed, or, perhaps some additional efficiency because the model airplane props are thinner and slice through the water with less resistance.

Physics is a tough taskmaster.  There is an exponential relationship between additional speed and power consumption.

With my 26 foot, 4000 pound cruiser, I can go 2.5 miles per hour on 400 watts, 3 miles per hour on 700 watts and 4 miles per hour on 1200 watts (zero wind, no current, no chop)  I literally have to triple my power consumption for that extra 1.5 mph.  6 mph is possible, (My hull speed is 6.4 mph) but would consume over 3kw.

Your mileage/speed/power consumption will vary depending on your boat hull design and water/wind/current conditions.

I vote for using your existing motor, adjusting your props to use all its power, and be happy with 3.5 mph and invest in better batteries.  New LiFePO ones are an interesting option if you can get the right charge controller for them and keep them reasonably dry.

Ken Cooke

Solar Six

If you

On Sat, Oct 7, 2023 at 12:17 PM Kelly R. <kelly@skraye.com> wrote:

My max range requirement would be 10 miles total one way in a rescue situation and that range would be more than enough for the electric lakes.  The speed is not a big concern, reliability and range is the driving factor so if that 6MPH number is pushing me over a line I would be happy with 4 or 5 MPH, I just want to know I can get home. I can always fish along the way ;). 

The golden EZ-x10 is about $3500 with no additional controllers needed.
The Navy 6 would be $3500 plus an additional $350 for the basic controller. 

Option 2:
Stick with 36 volts and put the money into batteries. I already have the 36-volt trolling motor up front with autopilot for steering and when needed I could add a second 36-volt motor to the rear. Would a second motor on the rear of the boat work? This gives me even more redundancy.  

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