selecting a bow mount trolling motor.

[osok]

OK people,

I have an '89 Crestliner Viking, good beam, high gunnels,nice V hull. I'm looking @ bow mount trolling motors and have talked w/ a few salesmen w/ conflicting replies. some say a 55# will be just fine even in windy rough water. Others say minimum of 70#, and one said nothing less than 80#. and I've heard shaft lengths from 48" to 60".

Other than $$(which is huge), The only other advantage a 55# has is it's a 12v system and I wouldn't have to go 24v. I have a 54# 12v on the stern and run dual batteries for it, and have a 3rd reserved exclusively for cranking.

So if I have to go to 24v what do you do about charging the 24v system? Or being able to run existing 12v accessories?

Sorry for all the questions but I grew up in the NW and all trolling was done in saltwater with outboards.

If I do end up going the 24v system I will have a Motorguide 54# transom mount for sale and I also have a Mercury bow mounted trolling motor for sale, all it will need is steering and battery cables.

[Esox_Magnum]

Go with the biggest longest you can afford, you can always raise it or turn it down but cant make it longer or get more power later. Batteries you should always run just the trolling motor off a battery or set and nothing else, all accs should be to your cranking battery.

Personaly I wouldn't go back to a 12 volt system you get so muck more run time from a 24 volt. My last ride I ran a 3 bank onboard chraging system the current one just has a 2 bank for the trolling batteries but that will get changed out to a 3 bank in time.

A 55# 12 volt will pull more amps per hour than a 70# 24 volt, hence the 24 will give you more power and longer run times. My old rig came with a 42# and I ran 2 batteries and would get 5-6 hours tops, swapped to a 74# 24 and couldnt run it dead in a day.

I currently run an 80# on a 17' Skeeter deep V and considering going to a 36 volt 101 when I move to a terrova. I only pull 2.6 mph with the 80# my old 17'6" Alumacraft deep v walk thru with a 74# would pull 3.4mph.

[Get'n Jiggy]

My first trollmotor was a Minn Kota 55 12v, lasted one season. Sold it,took

my beating bought a Motor Guide 24v never looked back, that was 33 years ago. As far as shaft length you can always raise it up you can't make it longer. Better to wait and save up for a good one IMHO, GOOD LUCK! BTW I still have a Motor Guide 24v but it's not the same one.

[walleyemaniac]

I've got 24v 62# 48in shaft on an '89 crestliner 17'. It has the power for my boat and the batteries last all day with no worries, the only thing is I wish I would have gone with the longer shaft. It works fine on my boat but the lock collar is up right under the head in rough conditions.

I'd at least go with the 70# 60in shaft.

Like everyone says, get as big as you can afford.

[PerchJerker]

A 55lb motor will probably get you by in most situations, a 70 or 80 lb motor would likely get you by in every situation. Of course it depends on how you're going to use the motor --- bouncing around in big rollers on Mille Lacs or something like that is one thing and you'd want all the power and length you can get ---- slipping along and casting to a quiet shore is something else and a 55 lb motor would be plenty almost every time.

Even so, I'd go with a 24 volt motor if the 2nd battery is not a problem.

[Palerider77]

Yep 24v all the way. I got a 80 lb minnkota power drive V2. Pulls hard with good control and battery life. I just installed the I Pilot system, worth every penny. Power is good.

[kdawg]

I would agree with the 24V system, and personally would go with the biggest motor for all the reasons listed above. If you were only going fishing a few times a year, maybe you would be better served by being budget-minded, but if you plan on fishing a lot over the next few years or more, then a 80# 24V is well worth the money. My last system was a 84# Minnkota that I sold with my 04 Alumacraft. My new Minnkota is a 80# Terrova - it pulls way better than my old one. I have fished with it all weekend during various conditions with my 1850 WX Skeeter and wasn't even half way down on the batteries. The way I look at these purchases is like this: If the trolling motor costs 1,000.00 and I use it for 5 years, then it cost me 200 bucks/year. Not too steep a price to pay for something you use almost every time you're on the water. If you use it for 10 years, well then it's almost like they're giving the thing away! Good luck.

[osok]

Thank you everyone for the responses, 24v longer shaft wins hands down.

So moving on to charging a 24v system....am I wrong to assume that using a 12v charger will work it will just take 2x the time?

[Esox_Magnum]

Best way is an onboard charger, go fishing come home plug it in and forget it till you fish again, helps maintain your batteries and helps them last another year or 2.

It is a pain trying to charge 2 batteries with 1 12 volt charger overnight.

[PerchJerker]

Correct. Best way to go is with an on-board charger, get 1 bank for each battery you have in the boat. Plug it in when you get home with your boat, unplug it when it's time to leave with the boat.

[BobT]

Personaly I wouldn't go back to a 12 volt system you get so muck more run time from a 24 volt. My last ride I ran a 3 bank onboard chraging system the current one just has a 2 bank for the trolling batteries but that will get changed out to a 3 bank in time.

A 55# 12 volt will pull more amps per hour than a 70# 24 volt, hence the 24 will give you more power and longer run times. My old rig came with a 42# and I ran 2 batteries and would get 5-6 hours tops, swapped to a 74# 24 and couldnt run it dead in a day.

I'm sorry but I can't let this one go by. This information is absolutely false. The battery life is not based on amps, it is based on power over time. A 12v 55# motor will consume very close to the same power over time as a 24v 55# motor. A 55# motor might be just a tiny bit more efficient than the 12v but it will be minimal at best. Not enough to really matter in the grand scheme of things.

I would opt for the 24v system for a couple reasons.

* As I've already mentioned, the 24v motor might be a bit more efficient and so you will maybe get a small amount of added life.

* A 24v motor draws lower current so you can get by using smaller wires and this is less costly.

* Batteries wired in series are not subject to parallel destruction. What I mean is that when wired in series for 24 volt, if one battery develops an internal short-circuit it will only result in losing half your voltage and so you'll be running on 12v. but it won't hurt the other battery. When wired in parallel to provide 12v output, if one battery developes an internal short-circuit there is a very good chance that it will destroy the other battery as well because it will load the other battery to the max.

[rmb]

Have to disagree. Within electric motors generally as voltage increases your required amperage decreases. With a given battery with a finite amount of amp hours to give you have so much run time based on the amperage draw per hour. so if you are drawing less amps per hour for the same thrust over the same time period you will have a greater run time with a 24 volt system.

but don't take my word for it. the following is directly from page 6 on the 2010 minn kota pd owners manual

"As a general on the water estimate your 12 volt motor will draw one ampere and your 24 volt will draw .75 ampere per hour for each pound of thrust produced"

so for our 55lb motor the 12 volt would draw 55 ampere in an hour and the 24 volt would draw 41.25 ampere. that is 25 percent less amperage or 25 percent more run time take your pick. might be enough of a difference to sway a buying decision to some.

i prefer the 24v systems but for reasons than run time but thought people would be interested in what minn kota is saying directly regarding run time vs voltage. i would assume that going to 36 volt would be a similar step up but didn't bother to find info on it.

[BobT]

Ahhh, fell for that one didn't you? As you increase motor voltage you'll burn up the motor unless you rewire the windings for the new voltage. Try it. Take your 12v bow mount and connect 24 volts to it and see what happens. I can all but guarantee that you'll be buying a new motor as the current draw through that motor doubles and the wires fry.

Motors will demand current based on the horsepower (wattage) rating. In the example from Minn Kota you're forgetting something. In order to run at 24 volts you will need two batteries. Those same two batteries connected in parallel to deliver 12 volts will also be capable of delivering twice as much amperage over the same time period.

Two 105AH 12v batteries connected in series can deliver 1 amp of current for 105 hours at 24vdc within spec. The same two 105AH 12v batteries connected in parallel can deliver 1 amp of current for 210 hours at 12vdc.

A 12vdc motor rated at XHP will demand the same power as a 24vdc motor rated at the same horsepower.

Here's the catch. A 55# motor wired for 12vdc will use roughly twice the current of a 55# motor wired for 24vdc. But since the batteries for the 12v motor are wired in series they also have twice the capacity supply. In the end the difference is minimal.

The information you have provided from Minn Kota does suggest that the difference in efficiency of the motors is higher than I thought but runtime is really not that much better.

[Esox_Magnum]

I base my opinion off personal experience, takes a 55# a higher thrust setting to get the same speed a 80# needs. So if your on a 7-8 setting on a 55 the 80 will do the same thing at 4-5.

We did this last night took 2 boats, mine a 17' Skeeter S 135 and my buddys 1650 Crestliner fishhawk tiller. I run a Maxum Pro 80 he runs a 55 Powerdrive, to maintain the same speeds roughly 2mph he was turned up to almost 8 on a scale of 0-10, I was sitting at between 30-40 on a scale of 0-100. He does have better batteries than me but I'm stuck with the POS Everstarts till they die and from past experience that won't be long. Guessing I'll see better preformance when I put a set of 31 series Interstates in.

I do know his motor wont last more than a day, mine I havent checked yet whats left at the end of a day but willing to bet over 50%

Again all my thoughts are based off what I have experienced, I don't know all the technacal jargin.

[jac714]

Every thing electrical whether it is an inductive load (electric motor) or resistive load (heating element) is governed by Ohm's law which states that P=IE where P=Power in watts, I=current in amps, E=voltage. Given that, if you increase the voltage to a motor you reduce the amps need to produce the same amount of power.

Therefore if we use a 55# motor as an example, and use the assumption that it will require 100 watts (just to make my math simple) at 12 vdc it will require 8.3333 amps to produce that wattage, at 24 volts it will require 4.16666 amps.

Then if we accept the fact that amps from two barreries wired in series is additive that means that a 24 volt system requires less amperage for the same power and that we have twice as many amps available that the battery life must be exponentially longer.

If you really insist I can do the math and plot a graph for a 12 and 24 volt system producing the same power, or you can take the word of a 13 year veteran nuclear engineer of the subamrine force atlantic fleet.

My intention is to upgrade my 12 volt trolling motor to a 24v or even better a 36v (if I can find the space for the additional batteries) this winter.

[BobT]

Quote:

Given that, if you increase the voltage to a motor you reduce the amps need to produce the same amount of power.

You’re forgetting something. The only thing constant in your illustration is the load. All other variables, Voltage, Current, and Power are not constant. You can’t apply Ohm’s law as you describe. Increasing voltage to a motor WILL increase the power and that power increase will be exponential. An inductive load like a motor or a resistive load like a heater are rated for a specific power (horsepower, watts, whatever) at a specified voltage based on its design.

A 12v motor is designed to operate on 12v and nothing more. If you apply 24 volts to that 12v motor I guarantee it will not use half the amperage. It will use approximately twice the amperage until the windings short-curcuit due to thermal breakdown. The output power will jump to about 4x its rated power for that short time too.

A 24v motor rated at the same horsepower as a 12v motor has completely different windings that increase the impedence of the motor and that is what reduces the current demand. Apply all of Ohm's laws. By increasing the impedence of the motor to reduce current to the correct level that maintains the horsepower rating we then get the results you are talking about.

Here, I'll give you quick example. I'll use a resistive load so we don't have to get into the characteristics of impedance. The result is very similar either way.

1000w load @ 12vdc

Applying Ohm’s law, P=EI, we can determine that the current draw from this load will be

1000w / 12v = 83.33amps

Applying Ohm’s law, E=IR, we can also determine that the load resistance will be

12v / 83.33A = .144ohms

Load resistance is constant so if we increase the voltage (x) on this load to 24v we can determine that the current will increase proportionally and the wattage will increase exponentially (x^2). Since we are doubling the voltage our wattage increase will be 2^2 = 4 times.

E=IR

24v / .144ohms = 166.66amps

P=EI

24 * 166.66 = 4000watts

You can see that our power output has increased to 4x the rating of the load at 12v. The load is rated for 1000w at 12v because that is what the wiring can handle. The wiring will not handle a 4000w power output and the result will be a quick demise of the wires as they burn up.

The same thing happens in a motor if you just increase supply voltage although with some very small differences due to the effects of motor impedance resulting from inductance.

[jac714]

It should be obvious to the most casual observer that you cvannot put 24 volts to a 12 volt motor. That will indeed produce immediate problems.

You are missing the point that for the same output you will need less current at a higher voltage. The load in this case is the output of the motor which is constant the varibles are the voltage and current. If one is increased the other must necessarily decrease.

[osok]

Ummmm......Before this thread runs away I just want to thank EVERYONE for their input. I am going to bite the bullet and go with a 24v system. Right now I have 3 on board. 2 run my accessories and 12v transom mounted motor, the other is reserved strictly for cranking. I have some reserves about running my electronics/accessories and start my engine all off the same battery, so that's why I have the 3rd.

I've lived around boats my whole life and worked on them for half of that, all in saltwater. Electric trolling motors are offering a new learning curve for me. Thanks again everyone.... So can anyone explain to me the nuances of catching a friggin walleye

Osok

[BobT]

Quote:

You are missing the point that for the same output you will need less current at a higher voltage. The load in this case is the output of the motor which is constant the varibles are the voltage and current. If one is increased the other must necessarily decrease.

You are still missing the point that you are demanding the same power output and you're not taking the power supply into consideration.

Two produce the 24v you need requires two batteries. Batteries connected in series to provide 24v do not increase current supply. The total current supply from both batteries is the same as the current supply for one battery.

Connecting those same two batteries in parallel will double the available current supply but the voltage remains unchanged. Therefore, the run time remains virtually unchanged without considering the small difference in efficiency.

Let's go back to my example but now let's change it so the output power is the constant rather than the resistance.

1000w load @ 12vdc

1000 / 12 = 83.33 amps.

1000w load @ 24vdc

1000 / 24 = 41.67 amps

(2) 105ah batteries connected in parallel will provide 12v and 210ah of energy.

210 / 83.33 = 2.52 hours of run time.

(2) 105ah batteries connected in series to product 24v will provide 105ah of energy.

105 / 41.67 = 2.52 hours of run time.

Obviously this is a raw power (watt) calculation and does not take efficiency into consideration or impedance but you can see the run time is the same.

[jac714]

Why then are the vasty majority of industrial motors 450v rather than 110?

Additionally if this is true why are batteries on Submarines not 12 v? Because a higher voltage will require less current and the fact that higher voltage dc motors are more efficient. The submarie force is always looking for ways to reduce the size and weight of the equipment and the batteries that supply power to them and they have standardized on approximately 250vdc for the most efficient use of space and power output.

I am done with this it has become a waste of time.

[BobT]

Quote:

Why then are the vasty majority of industrial motors 450v rather than 110?

Do you mean 460v 3-phase? Because as you see with the math above, higher voltage motors do not require the amperage of lower voltage motors. Imagine the total current draw of some of these plants if they all used 110v motors. It would be outrageous. Three phase power also enters the equation and there are distinct advantages there as well. When you can lower the amperage you can use smaller supply wires too. Amperage doesn't go down just because the voltage goes up. It goes down because the resistance (impedance) in the motor went up and this is what controls current. The end result is that the motor power remains the same and power measured in time is amp-hours, kwatt-hours, BTU/hour, etc.

What you have to be careful of is to consider every part of the equation. Motors designed to operate at higher voltages do in fact use less current to produce the same output power but in our application we were comparing two motors rated for the same output power and supplied by the same limited power supply. What differs here, and this is important, is that the power supply has a limited amp-hour rating. This means that when talking about how long the batteries will last we have to consider the power/time characteristics and not just current alone.

Remember, in my first post I recommended 24v because of the various reasons I pointed out. I'm not saying 12v and 24v are equivalent.

Sorry we took this thread off course.

[rmb]

only problem with the above run time relationship is that you didn't apply Peukert's Law to calculate the run times. if i remember correctly the normal amp hour rating is over a 10 hour period. so a 100 amp hour battery / 10 hours is rated at 10 amps for 10 hours makes sense.

we could use this relationship to do all run time calculations if we always were drawing 10 amps. but we aren't drawing 10 amps. If we use Bob's numbers from above of 83.33 amps and 41.67 amps and determine run times.

Peukert's law is as follows:

Cp=(I^k)x T

where:

CP is the capacity in amp hours

I is the discharge current, expressed in A.

K is the Peukert constant (1.1 to 1.3), dimensionless.

T is the time of discharge, expressed in h.

using a k of 1.2 (just selected the mid of the range) it varies with battery age and other variables.

12v system

200 amp hours (additive since running at 12 v) = (83.33^1.2)x T solve for T = .9909 hours

24 V system

100 amp hours = (41.67^1.2)xT solve for T = 1.138 hours

roughly 15 percent longer run time for the 24 v. as the amp draw increase the run time difference between 12 and 24 would differ exponentially greater also as the amperage goes down the run time difference would vary exponentially less.

this makes sense that as the required thrust/amp draw increases the manufactures go to 24 and 36 v systems to take advantage of this and also why 12 v really is just as effecient as those higher voltage systems at lower amperage draws.

wow, way off course but very interesting, in my opinion.

[BobT]

I never denied that the 24v system would result in longer run times and I even stated that I was surprised at how significant the difference was based on the information posted from Min Kota's HSOforum.

What I was trying to stop was the idea that increasing voltage to a motor will decrease current. This is an incorrect assumption and a dangerous one to throw around. It isn't because the voltage was increased that the motor uses less current, it's because the motor was redesigned with its impedance increased to maintain a specific power rating at the higher voltage, usually expressed in kwatts or horsepower. Increasing the voltage to a load will result in higher power output unless you can increase the load's impedance accordingly.

Another mistatement I was trying to express was that when we are talking about a finite power supply such as the capacity of two 12v batteries, amperage alone is not the determining factor in determining run time. Just becasue the 24v motor uses less current does not mean it will last longer than a 12v motor. The capacity of the batteries wired in parallel (12v) is double what it is wire in series (24v) and so if the 24v motor is using half the current, the result will be that both motors will operate for the same amount of time.

[rmb]

your last comment is the one that i can't get on board with. Peukert's law is specifically in regard to run time of a finite power source based on amperage draw rate in comparison to the rated amp hours available at a finite power source.

it is this exponential relationship between amperage and run time based on the rate of current draw that makes your last statement questionable.

we can all agree that wiring 2 batteries in 12v is additive to amp hours resulting in say 200 amp hours for 2 100 amp hour batteries. this part of your statement is absolutely true and undeniable. notice i did double the amp hour rating in the above calc for the 12v system.

the part that is not true is that you can take amp hours of a finite power source at any amp draw and divide out the rated amp hours for your run time analysis. this just is not true.

the relationship of run time vs amp draw from a lead acid battery is exponential not linear. if it was linear then you would absolutely be correct. in that scenario you would have a Peukert constant of 1. Then everything that you state about run time being approximately equal between the 2 systems would be absolutely correct. the problem is the peukert constant is always greater than 1 so a non linear relationship occurs.

of course this is all based running systems with near identical mechanical losses and the system is properly designed for the voltage being applied. throw all of this out the window if you were to take a 12v system and run it at 24 v. that would be just silly and most likely run time wouldn't be based on amp hours but on how quickly you melted the wiring.

i agree with your second comment that is undeniable. i just can't get on board with the last one for the reason layed out above. but i am cool with just agreeing to disagree on that one. take care and good fishing.

[Get'n Jiggy]

You gotta love these guys, you ask which trolling motor is best and you get a course in electrical engineering!