electric trolling motor props

[Twofish]

Hi. I am new to this forum so please bare with me. I'm looking for information. I have a 1980's 55lb thrust minkota trolling motor. My prop is broken. Its a plastic prop. I researching minkota for a new prop I found out they are no long manufactured. So finding one has proven to be impossible. As this style of prop is held on with a cotter pin and no bolts. I was thinking of cutting threads into the prop shaft and getting a newer prop and mount it. Do you think this is a feasible option or do you have another idea that might work. I have tried locating a prop from several different places other than minkota but to no avail. Any help in this matter would be greatly appreciated.

 

[Will Gilmore]

Welcome to the forum, Twofish. There are several companies that have started making high performance props for trolling motors. The stock props are intended to move fishing boat quietly through the water in a lake. They perform a very specific job. Depending on what you hope to do with your motor, you can look at a number of options. Here's one example:
New Trolling Motor Prop?? https://www.mbgforum.com/topic/18044-new-trolling-motor-prop/

10x4P - APC Propellers https://www.apcprop.com/product/10x4p-lh/

I've looked into this only a little bit for using a trolling motor as auxiliary power on a 20' sailboat.

There are a number of sailors, I know of, who have 3D printed their own props. I don't know how that has worked out for them.

-Will

 

[seasquirt]

I was thinking of cutting threads into the prop shaft and getting a newer prop and mount it.

Hi Twofish, cutting threads can be successful if done very accurately by eg. a tool maker, but it would be quite expensive, you'll have to dismantle your leg, then re-assemble it as good as factory, and if they don't do an accurate job thread turning, you will likely get vibrations. Then you still may have trouble getting a suitable almost identical propeller to fit the modification. I assume by cotter pin you mean split pin, and it's not impossible to drill a pin hole into a threaded plastic prop, whose thread's inside diameter fits snugly over the output shaft of your OB. Does your output shaft's outside diameter match closely to a threaded prop inside diameter ? If the most suitable prop's threads' root diameter is a bit smaller, it can possibly be turned out to a bigger diameter on a lathe, to slip snugly on the shaft, then drill the pin hole after fitting and measuring. Or find someone who can copy your original prop on a 3D printer, then when you have the programme, you can make more the same, or tweak the shape for your specific needs. The best shaped prop, but with a hole too big, could have its thread plugged and glued, then bored to suit your shaft, which would be cheaper than having your shaft threaded.

 

[portacruise]

A 35 + year old Troll Motor may not have much life left if it has been used pretty often. So you might take it to a repair man for evaluation before sinking any more money into it -and have it go bad in a year or so. Ask a repairman if he can convert the closest match from today's existing props by drilling a hole across the Hub and going through the split pin hole. Replacing with a new motor Armature which is already threaded (assuming they have one that fits), would likely be lower cost compared to cutting threads on a possibly hardened shaft.

Or APC might be the way to go, assuming you're reasonably handy with an electric drill, or can have a troll Motor Repair do it. You might start with the 10x4p referenced above, which already has the correct size mounting hole drilled out, but again, a hole would have to be drilled across the hub for the split pin mounting arrangement. Those propellers come in a wide variety of pitches and diameters and are very cheap to experiment with, compared to the price of a new replacement propeller. Depending on the direction that your shaft rotates, you will probably need a pusher propeller which are designated with a "P" at the end of the measurement. Although the APC propellers are meant for model airplanes, they have proven to be way more efficient than any of the factory "weedless" designs, but of course they are not weedless, if that is important. The APC props would be mounted with the thicker Leading Edge facing the motor, and 10x6p as well as the referenced 10x4p have been done successfully.

Post # 252

Efficient electric boat https://www.boatdesign.net/threads/efficient-electric-boat.27996/page-17?fbclid=IwAR3GiokK4ire6MZ2ZPeLdDKQ5VOfxotlGDC96tubY50D62hhgmLYAquQWnE#post305142

 

[alan craig]

Portacruise's link tells you all you need to know about efficiency. I would just add that model aeroplane props collect weed like a giant weed collecting thing so if you have weed in your area it might be worth considering using a prop from Epropulsion or Torqeedo if they have one which fits. Also I searched "prop for minn kota" and there seems to be plenty of pin driven after market props.