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Inflatable boats have become hugely popular in the past year or two and they are very well suited for an electric motor, such as a trolling motor normally used for fishing.
When mounted on an inflatable kayak or canoe these small motors that are normally used intermittently for fishing now become the main source of propulsion, turning a paddling inflatable kayak into a pleasant cruiser.
There’s an impressive range of inflatable boats on the market and it’s important to choose the right model for your needs. When I bought my own kayak I used these criteria:
- Quality – how well is it made?
- Safety – can it capsize or puncture?
- How long will it last with reasonable care
- How easy to fit a motor mount?
- Inflatable Boat Motor Mount – Which Boat?
- What Size Trolling Motor For Inflatable Boat?
- DIY Kayak Trolling Motor Mount
- What size battery for a trolling motor?
- Can I charge my trolling motor batteries with a solar panel?
- Related Questions
- Resources for Trolling Motor For Inflatable Boat:
Inflatable Boat Motor Mount – Which Boat?
I can sometimes buy important purchases too quickly because I’m so enthusiastic about a project. While I did take some time, in retrospect I would have chosen differently.
The model use for this motor mount guide is an Itiwit inflatable 3-man kayak. It has all the features I’m looking for – it’s very stable, well-made and tough. What it doesn’t have is any means of mounting a trolling motor.
If I built another inflatable boat with electric motor I would choose the Sea Eagle 380x. This is one tough boat!
Trolling motors are rated in thrust measured in pounds-force (lbs/f) which has a direct relationship to the size and weight of the boat it’s mounted on. As a general rule allow 2lbs force for every 100lbs (45kgs) of weight to be pushed along.
My inflatable solar powered kayak weighs 17kgs unloaded, plus another 200kgs including two passengers, solar panels and control gear, making around 220kgs in total. By that reckoning the thrust I need to propel the kayak is:
- 220 kgs total weight / 45 x 2 = 10 lbs thrust
In fact, the smallest trolling motor does the job, even an 18lbs thrust model. However, in practice I like to add a little extra in case of winds, currents or weeds, so I chose a Minn Kota 30lbs thrust model.
This is a common misconception – all electric trolling motors push boats along at around 5 mph (8km/h) regardless of their thrust rating.
It doesn’t matter if you mount an 18lbs or a 55lbs thrust trolling motor on your inflatable, it will still travel at 5 miles per hour.
The only difference is that it may reach top speed quicker. If you’re considering mounting 2 motors to increase your speed, don’t – you will be wasting your money.
There are other electric options instead of trolling motors, but these are expensive and more for the sporty among us. For me, leisurely cruising is where it’s at!
Can you make a trolling motor faster?
Boat speed is determines by two things as far as the motor is concerned:
- Motor (propeller) revolutions per minute (RPM)
- Propeller pitch – the angle at which the blades cut the water
D.C. motor speed is determined by the voltage rating, which is a nominal value. A 12 volt trolling motor can operate above and below that value, so more volts will make it go faster – this is how variable speed controllers work.
BUT … over-voltage a d.c. motor too much can bring severe problems and maybe burn it out. Current is the enemy and this increases as the voltage increases, generating more and more heat inside the copper windings.
In general I wouldn’t over-volt a trolling motor more than 10%, so about 13V to 13.5V for my Minn Kota 30lbs 12 volt motor. (I do this in certain circumstances, for short periods when the battery voltage is pulled low by extra load due to drag from weeds or current.)
Standard propellers are based on solid design principles and while other props are sold as more efficient replacements, they have limited success. The blades may be shaped differently but generally any extra speed gained is due to a more aggressive blade pitch.
This invariably means more load current and extra heat, which is not good for the motor, It will possible reduce the life of the trolling motor or even burn it out. IMO it’s better not to risk it and be satisfied with the standard design.
Which is the best motor for inflatable boat use?
When considering a trolling motor for inflatable boat use, choose a well-established brand. A basic model like the Minn Kota C2 Endura will do nicely. It has stood the test of time – the company have sold over 8 million motors and have a solid reputation for service and helpful staff.
An obvious draw-back when considering mounting a motor on an inflatable is there are limited options for fixing any solid structure to it. Some boats do have special fixing lugs glued onto its surface so that a ready-made frame can be fitted. However, a great many inflatable kayaks and canoes don’t have these.
My solution is to fit a rigid floor made out of marine-plywood to provide a solid base to build on.
Common wisdom dictates that in the center at the rear of an inflatable boat is the best place to mount a motor. I tried this option but is became complicated. The structure was fiddly to put together and the motor was far away, meaning I had to devise an extended steering mechanism as well.
The photo below shows the rear-mounting arrangement:
Note how I turned the steering handle through 90 degrees so a long extension could be attached for steering. This was, and is, very successful. It gives sensitive and positive steering control.
I eventually opted to fit a transom cross-bar to uprights screwed to the plywood floor and fasten the motor to the right side. During trial runs with both rear and side motor mounts I detected no difference in kayak speed, although I didn’t measure it.
Inflatable Kayak Trolling Motor – How fast will a trolling motor go, side mounting?
Using a side-mount on a rigid kayak or canoe can make the boat tip a little uncomfortably, but this isn’t too evident as inflatables are broader in the beam – about 1 meter generally.
I have seen videos of rigid kayaks tipping alarmingly and at least one tipping over completely under the weight of a huge trolling motor and battery! It isn’t necessary. As we’ve seen, a small motor will push an inflatable along at a comfortable 5 mph.
How long it will do that is the subject of the next chapter.
The table below shows maximum current draw and associated thrust for a 30lbs thrust trolling motor at each of its 5 forward speeds:
In practice, I have found that these currents can be reduce by 30% when testing the amps pulled by my own Minn Kota 30. This is because the thrust needed for such light inflatable boats is low and so the current draw is lower.
Nevertheless, it makes good design sense to use these maximum numbers for calculations.
Trolling motor run time is directly related to battery size. Batteries used for this application need to be deep-cycle, which means they can be discharged up to 80% without damage before needing recharge.
Traditional lead-acid batteries are very heavy. I purchased a 90Ah Varta dual-purpose lead-acid marine battery as my first attempt to motorize my inflatable kayak – it weighs 30kgs and I used it only once!
Can You Use A Car Battery For A Trolling motor?
Normally, this isn’t recommended. Car batteries are designed to deliver 100s of amps for short periods. As soon as the car engine starts, the charging circuit immediately starts to replenish it. If discharged regularly more than a few percent, the life of the battery is seriously reduced to 20 or 30 charge/discharge cycles.
There is one circumstance in which a car battery can be used to power a trolling motor and that is if it is also connected to a solar charging setup. I used a 44Ah car battery for trips across the bay all summer with no damage due to the fact that I connected it to 300 watts of solar panels through a solar charge controller.
This is a good arrangement if trips are short, say less than 1 hour at a time.
Is there such a thing as a lightweight trolling motor battery?
The best lightweight battery for running a trolling motor is type Lithium Phosphate (LiFeP04). For comparison, a 44Ah lead-acid car battery weighs in at 11kg while a similar lithium phosphate model weighs just 4kg!
Of course, this weight reduction is a great boon in small inflatable craft but this isn’t the only advantage. LiFeP04 batteries are naturally deep-cycle. They can be discharged 100% without damage and for most of that time the terminal voltage remains relatively stable. This safe technology is definitely the way of the future.
Lithium-ion batteries are even lighter but not considered as safe.
What is the best battery for a Minn Kota trolling motor?
I recommend any size Lithium Phosphate. Your run-time is a direct function of size in Ah, so it’s a balance between cost and desired run-time. Very simply, divide the amp-hours by motor current from the table shown previously and you get run-time in hours.
For my LiFeP04 30 Ah, which generally run at speed 4, I can expect this run time:
- 30Ah / 20A = 1.5 hours
As you might guess, it’s a little more complicated than that. My motor pulls less than the maximum shown, but also the relationship between battery current, temperature and capacity means that you never get as much out of a battery as you’d think.
Can I charge my trolling motor batteries with a solar panel?
Solar charging makes a big difference to trolling motor run-time and turns an inflatable into a veritable cruiser. It’s rare to travel more than a few hours before stopping, either to picnic or fish.
Basically, fitting a substantial amount of solar panels to your boat means you never have to worry about a discharged battery again. Just make sure you have a reliable PWM or MPPT regulator and you’re good to go.
12v trolling motor battery life with solar
What side of a boat do you mount a trolling motor?
A trolling motor can be mounted on any side of the boat. Strictly speaking the bets position is at the rear on the center-line, but this is often not practicable on many small craft.
How fast will a 45 lb thrust trolling motor go?
A 45 lb thrust electric trolling motor will push a boat forward at approximately 5mph. All trolling motors are the same. Trolling motor thrust has no relationship to speed.
How much weight can a 30lb thrust trolling motor push?
A 30lb trolling motor will push a weight of 1500 lbs.The general rule is to allow 2lbs of thrust for every 100lbs of load to be pushed.