A Troll in a Canoe

I am thinking of adding a cheap small electric trolling motor to a canoe or a small sailboat. I have never used one so I need a bit of advice.

I thought I could cut down the shaft since this is usually too long for a canoe (or kayak) or even my very small sailboat.

Rather than horse a 40 lb battery down to the waterside, I am considering a lightweight lithium ion batteries, perhaps one intended for powering an eletric tool. I assume the motor will not need full power to push such a small boat along and should therefore pull less amps.

I can't afford a Torqeedo, but I do have electrical smarts.

This is not for long-distance cruising, it is just for short distances when the wind fails as an alternative to paddling/rowing or if/when I need to make headway against a heavy wind and cannot for some reason use the sail. A half-hour duration is probably enough although more would be nice.

Any thoughts/opinions/related experience to offer?

 

Thoughts, quickly put: Doable and makes sense. I know you're aware of the potential hazards involved with lithium batteries, do be careful with these things. The cost of batteries will add up faster than you think. Not all portable tool batteries have adequate protection circuitry included for use within a parallel bank.

Take a guess at the thrust you'd need and calculate the current draw based on the manufacturer's specs for the motor you pick; you should then have a good idea of the needed battery capacity (thus cost) for half an hour of running. I think it'll come out pricier than you'd like but still probably feasible.

 

The mounting bracket on the Minnkota trolling motor is adjustable so that the prop is not too deep in the water, eliminating the necessity of cutting down the shaft.

 

Thanks! I would not parallel high current batteries; with tool batteries it's easy to change it if needed. I have seen a small Minnkota for about Cdn$128 which I think was a 20 lb motor; likely the smallest. My canoes need even less than that, probably 5 lb will move one decently, a headwind might need 10 lb which I suspect is all most paddlers can sustain for any amount of time.

I don't have data on tool battery capacity, rechargeable NiMH AA cells (pen-cells) are around 2AH these days so I am guessing the larger Li-ion ones are around 5 AH. The 30 lb Minnkota motor draws roughly 30A at full thrust; I might get 1/2 hour at 10A which for a 20A rated PM motor would be roughly half-speed, enough.

NiCad and MiMH would be less but cheaper so I could carry several. I have several at 12V and up in the workshop; not sure what to do for the connector yet but I can fabricate one a/r. Ideal battery voltage would be less than the usual 12V since I don't need full power but the lower voltage batteries tend to be for low power tools and therefore less capacity. Using 12V will waste power because the regulator is a series resistor, I understand.

Ideally I would have a busted power tool with battery, connector and surviving speed control that I could cannibalize, and a tool controller would be switching type - more efficient; no such luck though. I'll ask around the neighbours ...

 

I didn't think there were any trolling motors out there still with resistive voltage dividers for speed control.... I thought they had all gone to PWM or better? Maybe I'm mistaken.....

 

From what I read on the web you have to buy it separately on the some Minnkotas but it s standard on others. The infor may be out of date though.

 

All the bottom-of-the-line trolling motors still use resistor speed control. You get PWM at about $200 with Motor Guide and maybe $250 with MK.

Terry, you are right on to suggest 6 or 9 volts supply with the motor throttle on "high" (no resistor) to avoid wasting precious electrons.

Click on http://www.boatdesign.net/forums/boat-design/efficient-electric-boat-27996-15.html to see details of my experiments powering a 14' canoe with an MK Endura 36. I learned that an APC model airplane prop increases efficiency about 30% and fairing the round shaft tube to an NACA 0025 added 50% to my range at constant speed.

 

Impressive results!

 

Minn Kota have sold all the old resistive tooling to china and you can get a brilliant 84 lb thrust for $200 ( search under.... i force trolling motor ) ... as well as all the smaller thrusts down to about 40 lb....if you cut down the shaft you will have to acomodate the resistive wires ( about 3 ) inside the shaft by bending them back on themselves .....Personally I would just run the motor on 6v if its a 12v motor and has too much thrust ...I run my 24v on 12 or 24 via a heavy duty multi pole relay rather than use the resistive controller ....On a lake with no current I find I need the full 40 lb thrust (previous motor) to make reasonable headway with a 15 ft canoe with two up ...about 3 mph....so my advice is to buy big and cut the power rather than find you bought too weak a trolling motor .....

 

It's hard to imagine getting a trolling motor that's too small to handle my 12' lightweight canoe. It is usually effortless, unless I end up an hour from home with a strong wrong-way-wind, with arthritis and other old-age symptoms. With a troller I can either lie down to cut the air-drag or use the motor as a lightweight second paddler.

Before things froze up around here I tried a cordless electric drill with a weeding attachment shaft and a bent metal prop in the pool - it was probably enough thrust for 2 or 3k but not enough to compensate for a strong breeze.

The main issue is size and weight for me. I went to the trouble of building my own boat to get it below half the weight of a plastic boat so I can carry it under one arm. I don't want to lose that advantage as I sometimes have to portage a ways. But a 24V motor running at 12V may be better than a 12V job at 6V as it's hard to find a decent lightweight 6V battery.

 

Consider NiMH

The 'D' cells have a 10AH rating and most are rated for up to a 3*C draw. The cells are available for about $6 each on EBAY You need 10 for 12V or 8 would work with lower power. Throw in a charger for 8-10 cells and a holder for use on the boat and you will be way cheaper than Li batteries. 10 cells will weigh less than 4 lbs and give you close to 10 AH even above 1*C loads. If you charge them separately in a consumer type charger, no need to ever balance. Also look on EBAY for some of the older Shakespeare type trolling motors. They are very light and more than enough power. I have a unit with 27 lbs of thrust that will get my 700 lb rowboat home even in a strong wind.

 

I used to have a two-man raft that came packaged with this 12-volt trolling motor. The shaft unscrewed and you inserted the top half through a small hole (tunnel), through the raft, then screwed the shaft back together. It looked like a paint mixer. Yes, I was the laughing stock...until they saw it in action. ~Never seen anything like it since. Just wanted to share!
So what about using those 12 volt "power stations"? They are sold for camping and for running a compressor for a flat tire. Couldn't you just use a cig-plug on the trolling motor and plug it in? They are totally rechargable and the higher end ones have pretty fair amp hrs.

 

Google "Electric Paddle" - exactly what you need!

 

nothing wrong with those power stations but all you are buying is a gell battery in a case ...so check the AH capacity as some are quite small..might be cheaper to by the battery on its own or a bigger one ..I dont think anything less that 20 AH will be any use even with a small trolling motor