I recently purchased a Newport NT300 electric outboard rated input 1300W (3HP). It uses 4.5feet of 8AWG wire to go to a LiTime 36V 50Ah Trolling Motor Bluetooth Low-Temp Protection LiFePO4 Battery Buit in 50A BMS, Deep Cycle Group31 Lithium Iron Phosphate Battery. I would like to add about another 6 to 8 feet Maybe as much as 10 feet of wire to reach the battery. Should the added wire to go to the battery in a more weight forward position go to 6AWG or is more 8AWG OK?
link to the motor
https://tbnation.net/products/newport-nt300-3hp-electric-outboard-motor
Doug, Figures don't Lie, but Liars'll Figure! >:(
Knowing that 746 watts of energy is equivalent to 1 hp and then reading the Newport folk rate their motor as 3hp at 1300 watts, my skepticism hackles immediately rose up; since 746 (watts) times 3 (hp) = 2238 watts, NOT 1300!
I was mildly mollified, when their literature a little further down claimed: "3HP equivalent".
This is a common tactic among the electric motor set, dealing with the torque equivalencies of ICE, vs electric motors. Still and all, 1300/746 = 1¾ hp not 3hp the way I learned it, back in the last millennium. :-X
My oft-quoted saying: "God does not repeal the Laws of Physics for anyone."
Is both working for you and against you.
Higher voltages let you get away with smaller gauges.
But! Current is a loop thing that has to go from the battery to the motor and then from the motor back to the battery, in order to get current flow.
Quote from: Doug SC on Feb 11, 2026, 05:53 PMMaybe as much as 10 feet of wire to reach the battery.
That's really 20 feet, not 10 feet, since the current has to go out and back, to the battery.
Another "gotcha" in ABYC wiring tables is the difference in wire gauge calculations between 3% vs 10% allowable voltage drop. In Ye Olde Analogue Dayes, 10% drop was permissible for analog loads, like incandescent lamps and old-style trolling motors, but only 3% drop was allowed for life safety equipment and electronics.
In your Newport motor, there is a TON of electronics under the cowl, helping make that 3 hp ::) claim, even remotely achievable.
So Good News: Higher voltage = Smaller required AWG wire gauge.
Bad News: 20 feet of cabling and only 3% permissible drop.
Here's an on-line calculator to help you get there.
https://www.inchcalculator.com/wire-size-calculator/
Since I did it already, I'll just cut to the chase:
No problems, using #8 AWG wire in your described application. ;D
There's still lotsa ways to screw yourself up, however.
Primarily, having enough copper mass on your terminals to prevent overheating during periods of high current draw.
(You know, like every second the motor is running.) :o
Check the pic below:
20260205_160809 1024X768.jpg
The terminals at the extreme right of the pic are available in #8 gauge sizes, but that lug does not have sufficient current-carrying mass, for a trolling motor. Not too worried about it, since it is only carrying about a 5 Amp load from the switch panel.
The two pairs of #8 gauge leads at the bottom of the pic are the kind that have sufficient current carrying capacity, to run a trolling motor, like I'm going to do.
Quote from: Doug SC on Feb 11, 2026, 05:53 PMI would like to add about another 6 to 8 feet Maybe as much as 10 feet of wire to reach the battery.
Your other caveat, will be getting in-line butt splicers with sufficient current-carrying mass.
Get as much information as you can, as to the size of the butt splices.
BTW, my total trolling motor wire length was 22 feet and in my case, was very close to the figures you cite.
Your calculated voltage drop will be 2½%, vs my calculated voltage drop of 2¾%.
Hope this helps,
Charles Brennan
I always learn something I didn't know when consulting with you. It's nice to know that I ca stay with 8AWG wire, Thanks. Yes, I plan to butt join the wires. I saw you mentioned ones that when you heat shrink, they solder themselves as well. Could you point me to a source with specifics.
From my observations of gas and electric outboards, an approx 1KW electric is functionally equivalent to a 3hp gas outboard. In comparison with 17 Mariners motoring at full throttle in close proximity, I had a 1KW Spirit electric outboard. The others had 4-6hp gas outboards, and I had previously had a 5hp Honda.
The Spirit couldn't quite make full hull speed like the gas outboards did (5.7kts). I could only get 5.5kts at full throttle (confirmed with speed runs in my creek).
Mariner sailors who use the 2-3hp gas auxiliaries report similar.
But it doesn't matter - if you run an electric outboard at any wake dragging speed, you are eating battery needlessly. My range more than doubles if I slow down to 400 watts, 4.1 kts. 300 watts, 3.5 kts is even better. If you want to do more than enter/exit the dock area with an electric outboard, you have to change your perspective.
The fact is and remains that gasoline can store a lot more energy in a given volume than the best batteries available (LiFePO4 is good compared to most batteries but horrible compared to gas).
But my shoulders and back and ears thank me for having an electric outboard. Motoring with an electric puts a big smile on my face. I have a 12nm+ range without recharge if I keep my speed down to 4kts.
Ya pays your money, ya makes your choices.
Fred W
ODay (Stuart) Mariner #4133 Sweet P