Trolling motor question

[Oteam76]

Hi everyone,
My name is David. I just got a used 9' Starcraft row boat. It came with a 3hp min kota trolling motor. I'm looking to see what size battery I should get, but all the sites have the trolling motors in pounds of torque. So does anyone know how many pounds of torque a 3hp electric trolling motor has, or what size battery would be best?
Thanks,
David

 

[Silvertip]

Re: Trolling motor question

Trolling motors are not rated in pounds of torque. They are typically rated in pounds of "thrust" (the "push"). Minnkota only lists a 2 HP trolling motor and its current draw is rated at 40 amps at 48 volts. Now think about that. You don't need one battery, you need four of them wired in series. 12+12+12+12=48. Since a 2 HP draws 40 amps one can extrapolate that a 3 HP requires about 50% more current so the maximum current draw is in the neighborhood of 60 amps. Since you have a 9 foot boat, I suggest that this 3 HP trolling motor is not really 3 HP or else this boat is going to be full of batteries. For the cost of four batteries you would be better served selling what you have and buying a 30# thrust 12 volt motor and a group size 27 deep cycle battery. The money saved would be used for beer and bait. I suggest you check the motor again to make sure what it is you actually have.

 

[cjjjdeck]

Re: Trolling motor question

David's probably right on the model name.

I have the same model MinnKota (3hp.... yes, that's the actual model name that MinnKota gave it, they even had a 2hp model and 4hp model at 24 volt..... the names didn't last long for obvious reasons) that I use with my square stern canoe. It is a 12 volt motor. Since your boat is on the smaller size, I would suggest using as big a size battery that you and your boat can comfortably handle (I have always used a size 27 Deep Cycle in a portable battery box). I've had the motor since the early/mid '90's and I haven't killed it yet. My experience with that motor lead me to buy a Terrova for my new boat.

 

[Silvertip]

Re: Trolling motor question

3 HP on 12 volts?????? 3HP = 2237 watts. 2237W/12V = 186 amps. The average group 27 deep cycle has a reserve minutes capacity of about 175 minutes at 25 amp draw. 186/25 =7.45 which means the discharge rate is 7.45 times the spec on the battery. Therefore 175 minutes/7.45=23.48 minutes run time at maximum current draw. All I can say is don't get far from the dock. Granted, one does not typically see maximum current draw but at even half speed that would put run time at 45 minutes at half the full current draw. If Minnkota was advertising the motor as "equivalent performance" to a 3 HP outboard where the motor was not actually producing 3 HP then all of this is rather moot.

 

[gm280]

Re: Trolling motor question

3 HP on 12 volts?????? 3HP = 2237 watts. 2237W/12V = 186 amps. The average group 27 deep cycle has a reserve minutes capacity of about 175 minutes at 25 amp draw. 186/25 =7.45 which means the discharge rate is 7.45 times the spec on the battery. Therefore 175 minutes/7.45=23.48 minutes run time at maximum current draw. All I can say is don't get far from the dock. Granted, one does not typically see maximum current draw but at even half speed that would put run time at 45 minutes at half the full current draw. If Minnkota was advertising the motor as "equivalent performance" to a 3 HP outboard where the motor was not actually producing 3 HP then all of this is rather moot.

Silvertip, I believe what is actually going on here is nothing more than some clever marketing ploy. It is obvious that they didn't sell true 2HP, 3HP and 4HP trolling motors that ran on 12 volts per say. It is like calling a trolling motor a "Brute" or “Magnum” or even “Big Foot” and in this case they used “2HP” and “3HP” names, nothing more... The only way to truly know the current draw is to install a current meter in-line and run it at top speed in the water under max load. Then and only then will you know for sure the max current draw and the correct size battery for that setup... 3HP SMH!!! ound:

 

[Silvertip]

Re: Trolling motor question

Silvertip, I believe what is actually going on here is nothing more than some clever marketing ploy. It is obvious that they didn't sell true 2HP, 3HP and 4HP trolling motors that ran on 12 volts per say. It is like calling a trolling motor a "Brute" or “Magnum” or even “Big Foot” and in this case they used “2HP” and “3HP” names, nothing more... The only way to truly know the current draw is to install a current meter in-line and run it at top speed in the water under max load. Then and only then will you know for sure the max current draw and the correct size battery for that setup... 3HP SMH!!! ound:

And that's why I said all is moot if this was not a true 2, 3, or 4 HP motor. They do currently offer a 2 HP motor running on 48 volts and that I believe is a true 2 HP motor as it's maximum current draw is 40 amps.

 

[cjjjdeck]

Re: Trolling motor question

Silvertip, as usual, you are correct in your technical assessment comments and gm280 , what you stated is also correct in that Minn Kota marketing (back when they made these motors) threw logic a curve ball. Your comment about having a performance "like a 3 hp" was probably their strategy. It was a strategy obviously short lived. Regardless of their questionable marketing, the product had solid and reliable performance.

The 3 hp was the largest size 12 volt model at the time. Although I haven't seen data comparing the 3hp model to actual thrust in lbs, I would think it would probably be pretty close to a 55 lb thrust model of today. It still moves my Coleman Scanoe pretty well. Of course the current Minn Kota technology (with features like their Digital Maximizer) would probably make a newer model more efficient.