Electric trolling motors are commonly found on smaller and medium boats for propulsion during trolling. When compared with internal combustion engines, they have both pros and cons that one must be aware of.
On this page:
- Electric Trolling Motors Benefits and Drawbacks
- Power vs. Thrust
- Motor Thrust vs. Boat Weight and Length
- Bow Mounts vs. Stern Mounts
- Shaft Length and Shaft Adjustment
- Bow Mount Trolling Motor Bracket
- Foot vs. Hand Control
Electric Trolling Motors Benefits and Drawbacks
Benefits of using electric motors for trolling are numerous:
- propulsion is much quieter. Many predatory species don't like to hear sound of explosions that happen in cylinders of petrol or diesel engines - and they can hear it, no matter how good engine soundproofing is. On the other hand, electric motors also benefit from using things like quality ball bearings, permanent magnet rotors, brushless wiring etc.
- electric motors are always ready to run since there is no need to turn them on. Their idle power consumption is zero, except for the electronics - modern electronics that is based on MOSFET H-Bridges and PWM controllers using mostly CMOS technology chips drains batteries with currents that are often measured in just miliamps. If you have remotely controlled electric trolling motor, be aware that your receiver and transmitter do require some idle power, but they often have separate power sources and many safety measures like automatic power shut down of trolling motor in order to preserve battery. In any case, electronics used to monitor and control electric trolling motor use just a fraction of power required for electric motor itself.
- since they are used for trolling, where required power output is relatively limited, combined with modern technology, electric trolling motors are relatively small and lightweight and can be easily mounted and dismounted.
- generally, they are very easy to operate and maintain.
But, they also have some drawbacks:
- they are lightweight, but batteries that they require can be heavy, especially if they are intended for longer operation without charging.
- for larger boats and larger trolling speeds, required batteries are either very heavy or very expensive.
- when propeller powered by diesel or petrol engine gets caught in ropes, nets, seaweed and similar, those engines simply stop to operate with no damage to the engines. Unless, propeller safety pin gets sliced off. But, when propeller powered by electric motor gets stuck, electric motor will drain surge current that can destroy motor, electronics, cables ... Fortunately, modern motor controllers have many safety features that can prevent such accidents.
However, there is something called 'circuit breaker' :o) and no matter how good and reliable electric/electronic equipment is, special care must be taken when designing electric schemes and implementing circuit breakers. If maximum operational current of your electric motor is, for example, 45A and maximum 5s current (or maximum allowed current in short period of time - 5 seconds in this example) is, for example, 60A, then protect that motor with 50A automatic circuit breaker. If something happen, it will switch off motor and protect it from damage caused by excess current.
Standard direct current voltage on boats is nominally 12V. It is usually provided by single or multiple (connected in parallel), six cells, lead acid batteries.
In order to produce certain amount of thrust, electric trolling motors require power.
For example, using 12V battery, Newport Vessels 55 Pound Thrust 8 Speed Electric Trolling Motor creates 55 pounds (25kg) maximum thrust, drawing 52A - that is around 620W of input electric power. 50 or so amperes require at least 13mm2 (AWG 06) wires. Stronger currents would require thicker cables or would produce larger heat losses in cables and that should be avoided.
In order to produce more power, but without increasing thickness of cables or heat losses, voltage is increased to 24, 36, 48 or even 72V. Be careful, voltages up to 36V are more or less safe, but 48V and higher can be dangerous, especially if your hands are wet (sea water, rain, sweat ...).
Example: 50A (again!) current require 13mm2 cables. When 12V batteries are used, that is around 600W; 24V would produce around 1200W; 36V would produce 1800W; 48V would produce 2400W and 72V would produce 3600W - using same cables!
Note: If you have 12V motor, DO NOT connect it to 24 or more volts batteries. Or 24V motor to the 36V (or any other) battery, etc. Why? If you don't have good circuit breaker(s), you will destroy your motor, its controllers, maybe cabling, battery, could cause fire etc. And this is serious warning.
Example: 600W, 12V trolling motor requires 50A (yes, again!). What would happen if we connected it to 48V battery directly? Could we get our boat to planing speed?
Well, at first, electric motors tend to pull high currents due to low resistance of coils. But, to simplify the things, lets just say that that electric motor would draw (at least!) 200A instead of 50A and would consume 9600W of power - instead of 600W. That is 16x difference. If you can bench press 100kg, what would happen with you if somebody load your bar with 1600kg? Exactly that would happen with trolling engine, cables, batteries ... And that is the reason why it is so important not to play with motors, batteries, cables and anything that can cause some damage or even harm people or animals.
Goal of this site is to provide people with information about fishing and help them spend some quality time outdoors - so, instead to try to figure things out, not only about cables and batteries, if you are not sure, ask some local professional for help and assistance - in the long run, that will save you both money and time.
Cables connect batteries, electronics, motors and other devices. They are used for transferring power to those devices.
It is important to read the manuals and follow instructions and recommendations given by manufacturers of used devices. If you are supposed to use for example 10mm2 (AWG 07) cables, use those cables or thicker.
If you are supposed to used 50A circuit breakers then use 50A or weaker circuit breakers - if you use weaker circuit breakers, you could end up with many 'false-positives' and that can be annoying. Never, but really never use circuit breakers rated for stronger currents.
Some manuals state cables in mm2 or AWG, some both. Just to be sure, here is a an AWG to mm2 conversion table:
|AWG 01 = 42,4 mm2
AWG 02 = 33,6 mm2
AWG 03 = 26,7 mm2
AWG 04 = 21,2 mm2
AWG 05 = 16,8 mm2
AWG 06 = 13,3 mm2
|AWG 07 = 10,6 mm2
AWG 08 = 8,35 mm2
AWG 09 = 6,62 mm2
AWG 10 = 5,27 mm2
AWG 11 = 4,15 mm2
AWG 12 = 3,31 mm2
|AWG 13 = 2,63 mm2
AWG 14 = 2,08 mm2
AWG 15 = 1,65 mm2
AWG 16 = 1,31 mm2
AWG 17 = 1,04 mm2
AWG 18 = 0,82 mm2
There are of course thicker and thinner cables than those presented in this table, but this table covers at least 99% of cables used on fishing boats - for more info, check AWG to mm2 Conversion Chart and Calculator article.
Power vs. Thrust
Thrust of electric trolling motor depends on applied power, but also on many other factors.
To explain things little bit, math and physics come to play - sorry :) If you don't want to bother with physics and math, jump down to the bold 'In real life' :)
Propeller thrust is usually given in pounds and/or kilograms, but that is something that will cause any physicist to grab his/her hair :)
Force is always given in Newtons (N) and body in vacuum that has mass of 1kg on surface of Earth will 'press' Earth with force of ~9.81N (1kg x 9.81 m/s2 = 9.81N).
Anyway, back to propellers - if propeller is accelerating 100 kg of water each second to the speed of 1m/s, then that propeller is producing 100N of force. And that 'would be equivalent' of ~10kg - my Physics teachers would probably kill me right now, but I had to write it that way :). Kinetic energy transferred to the water in each second is power required by that propeller (lets assume that there are no losses of any kind) - that is 100kg/s x (1m/s)2 / 2 = 50W.
For short, our hypothetical motor would produce '10kg of thrust' and would consume 50W. But, that maximum theoretical speed of that boat would be 1m/s - that is around 2 knots. Not much.
So, if we need 100N of force, but we want our boat to be able to go 2.5 m/s - 5 knots (at least in theory), water should be accelerated to at least 2.5m/s. To produce 100N of force, using water that is accelerated to 2.5m/s, propeller would need to 'grab' only 40kg of water per second.
Required power in this example would be 40kg/s x (2.5m/s)2 / 2 = 125W. So, we had to increase motor power output by 2.5 in order to produce same amount of thrust but at 2.5x higher speed - in theory.
In real life, trolling speeds using electric motors are usually rather low, when compared with planing speeds of fishing boats.
Exact current consumption must be read from manuals and verified using various ammeters.
Following table show some real life data - please, we have really tried to verify every single bit of information not only in this table, but on entire DeepCycleMarineBattery.com. Data presented in this table can be changed without previous notice. But, they show dependency between voltages, currents, power, thrust etc. in various electric trolling motors.
Note: Links in the table are Amazon affiliate links - they open in the new window, so feel free to check them for more reviews and recommendations. Of course, there are many more manufacturers, but they all generally stick to these 'sweet points':
- 12 V are used for a thrust up to a 60-65 pounds,
- 24 V are used for a thrust up to a 100 pounds,
- 36 V are used for motors that provide more than 100 pounds of thrust.
Minn Kota Riptide EM 160 Engine Mounted Trolling Motor is actually two trolling motors - hence, little lower voltage than expected, with maximum current still being less than 60A per wire.
We don't agree with the values for 'Recommended Circuit Breakers' marked with '*' - these are statements from their manufacturers. Are they mistaken or not, we don't know. Anyway, values marked with '*' should be taken with caution, since they are generally too low and can cause many 'false positives' and can be rather annoying, to say the least.
Have in mind one important note - in this table, we have omitted maximum boat speed, even theoretical speed (one that does NOT take into account 'propeller slippage'). For example, if you compare Minn Kota 80 and NRS-86L, Minn Kota model provide less thrust, but consumes more power - does this mean that this model is inferior to NRS-86L? No, it means that it is better suited for lighter and faster boats and NRS-86L is better suited for heavier and slower boats.
As one can see, manufacturers avoid using currents stronger than 60A for electric trolling motors. Stronger currents would require thicker cables and larger batteries. It is simpler to increase voltage and keep currents below 60A.
Note: if you have 2kW electric trolling motor running at full power and your cables are dimensioned to allow 5% of voltage drop, then your cables will dissipate around 100W of heat - 100W of losses! That is why one should never use thinner cables than recommended - in fact, if you have room and money, use thicker cables!
Also, never, but really never insulate your cables - feel free to run your trolling motor at full power for 10-20 minutes and try to grab your cables with bare hands - although good cables can easily handle 105°C (enough to cause burns on your hands) - if your cables feel warm, it is OK, but if cables are hot, I would recommend thicker cables.
Motor Thrust vs. Boat Weight and Length
General recommendation for electric trolling motor thrust is about 2kg for every 100kg (approximately 2 pounds of thrust per 100 pounds) of loaded boat. Note we said 'loaded boat' - that means weight of the boat fully loaded with fuel, batteries, gear, and maximum number of passengers. For example, 2000kg (~4400 pounds) boat requires around 40kg (~90 pounds) of thrust for trolling in calm to moderate conditions.
If you prefer to fish during calm weather, using live bait (slower trolling speeds), then you can take even weaker trolling motor. But, if you like fishing during not-so-calm weather, some power reserve is required (10-20 pounds of thrust more).
For example, Minn Kota 55, has 55 pounds of maximum thrust, operates at 12V and has 60A recommended circuit breaker. As a rule of thumb, this motor is enough for 2750 pound boat. But, if you add one more battery and use Minn Kota 80 (80 pounds of thrust, operates at 24V, same 60A recommended circuit breaker and same cables), you will extend your fishing time on single recharge and easily increase your trolling speed when required. Not to mention, that this motor can push 4000 pounds boat around with ease. In this example, I used Minn Kota motor just for an example, of course.
|Boat Weight (pounds)||2000||2500||3000||3500||4000||5000|
|Boat Length (feet)||<16||~17||~18||~19||~20||21+|
|Minimum Recommend Thrust (pounds)||40||50||60||70||80||>100|
|Recommended Thrust With Power Reserve (pounds)||55||55/80||80||86||101||>112|
If you prefer metric system, have in mind that 1 pounds is 0.453kg and 1 foot is 0.305m.
So, when deciding on how much power you actually need, take into account loaded boat weight, weather conditions, fishing style and similar. Best of all, read trolling motor manuals before purchasing them.
Bow Mounts vs. Stern Mounts
Both options have their strengths and weaknesses.
When trolling motor is mounted on the bow (that is front of the boat/ship), main advantage is that engine is not on the stern, where most of the action takes part during trolling. Steering with bow mounted motor is usually done using extension steering rod or remotely using electric servo actuators.
When trolling motor is mounted on the stern (aft part of the boat/ship), it can be transom mounted or mounted on the existing outboard engine as simple add-on. Transom mounted trolling motors have benefits of being totally independent from main boat propulsion.
Outboard engine mounted electric trolling motor systems are steered using main steering. They are usually positioned so that their propellers are submerged when main engine is not operational and they are out of water when boat is planing.
On any larger boat, bow mounted trolling motor should have a really long shaft in order to run propeller at required depth. Also, such mounts can cause propellers to emerge out of water, which, in some models, can increase RPMs and can lead to motor damage.
Bow Mount Trolling Motor Bracket
Not all boats are suitable for mounting a trolling motor. If you prefer to mount your trolling motor on the bow, but you simply don't have position onto which to mount the motor, you should get bow mount trolling motor bracket or mount.
Such bracket is usually made by trolling motor manufacturers to fit various boats like kayaks, inflatables and other boats that can be powered by that electric trolling motor model.
In some cases, trolling motor bracket must be improvised (actually it should be custom made, not 'improvised'), just keep few thing on your mind:
- such bracket should be done by experienced professionals that already made such brackets and motor mounts,
- bracket should be made from stainless steel (strong, durable, heavy, expensive), aluminum (not so strong and durable, but strong and durable enough, lighter, and price depends on many things), plastic or even wood. Wood is fantastic and often underestimated material, and can be used for smaller and weaker electric trolling motors. If you are unsure - go for aluminum and don't think too much about it,
- bracket should allow quick mounting and dismounting of trolling motor, so that it can be easily positioned on and removed from the boat,
- depending on electric trolling motor, bracket should allow changes of shaft positions regarding optimal shaft angle and optimal propeller depth.
Bow mount vs stern mount is an everlasting story - when you have your trolling motor mounted on the bow, your stern is free from additional equipment. Also, steering with such boat is simplified and boat becomes very 'agile' - after all that is the reason why cars have steering using front wheels :)
Shaft Length and Shaft Adjustment
Regardless if motor is mounted on bow or stern, propeller must run at optimal depth and at optimal angle.
Optimal depth is usually between 6 and 12 inches (15 and 30cm) below surface, but this is model dependent (size and number of propellers, RPM, trolling speed etc) - read the manual of your trolling motor. Anyway, if you are off by inch or two, that is OK, but be sure not to have half of your propeller outside of water.
Propeller should be working horizontally - if it is pushing water upwards or downwards, motor is wasting energy. For the same trolling speed, it is draining battery with higher current - operating time can be significantly reduced.
Foot vs. Hand Control
Controlling trolling motor during fishing is very important in order to have successful fishing. Some trolling motors have foot controls, some have hand controls and some have both options.
Main advantage of foot controls is that you have both hands free for fishing and fighting the hooked fish. On the other hand, it is sometimes hard to coordinate foot and hands especially in wavy and windy conditions.
Most of the people are simply used to hand controls and choose that option.
Regardless if foot or hand controls are used, commands can be sent over wires or even wireless. Remote controlled trolling motors sometimes even have extended range option, so if you see empty boat trolling 100 or so meters/yards off the coast, maybe it is controlled remotely :)
Anyway, there is no simple formula for finding out the 'perfect' boat/trolling motor/batteries combination for any possible situation.
But, this page gives you information about possible issues one can have and compromises one must make in order to go out there freely and enjoy the fishing.