Upgrading trolling motor prop

[BS Flinn]

Hi;

I'm running an 86lb thrust trolling motor on a 200lb boat, the idea was to use it like a 1.25hp electric outboard, of course being an amateur I didn't stop to think that a motor designed to move a 5000lb boat at 4mph wouldn't push a 200lb boat much faster, I'm fairly pleased with performance as is, but who doesn't want to go faster?

So what I'm considering is buying a aluminum prop about the right size and pitch, filling the hub in with epoxy, and using a drill press to drill a hole the right size for the shaft of my trolling motor, carving a groove on the back side for the trolling motors pin.
Is this idea in any way feasible?

 

[gonzo]

If you can find a propeller that matches the hub diameter it should be fine. However, propellers for small outboard often have a small diameter hole and are locked with a pin like in a trolling motor. https://www.amazon.com/NovelBee-Pro...t=&hvlocphy=9023904&hvtargid=pla-836048483235

 

[BS Flinn]

Thanks Gonzo, I'll try searching for those.

 

[SolGato]

You need to know what the existing prop pitch, diameter, and blade count is before making decisions about trying a different prop.

Using a larger more aggressive prop designed for an ICE outboard motor which uses gear reduction without a way to monitor current draw is a great way to ruin your trolling motor.

Most trolling motors don’t have good thermal overload protection and use components that just barely meet the minimum requirements to be able to handle max loading.

If you don’t have a clamp meter to be able to monitor amp draw under loading conditions, definitely make sure you install a fuse inline that is sized accordingly for the max amp draw of the motor, or better yet just under.

While you are correct that you may be able to make use of a higher pitch prop since you are pushing a light displacement vessel, you must proceed with caution, especially if the motor has a ESC that uses PWM to control the motor.

Trolling motors with fixed speeds are a bit more forgiving when overloaded.

Kipawa is an example of one company that makes direct bolt on props for common trolling motors that will give you a bit more performance and efficiency.

Otherwise, I would suggest a Torqeedo or EPropulsion 2 blade for all out performance, but you must monitor amp draw under load to verify you aren’t overworking the motor’s ESC.

There’s also plenty of info out there about using RC model airplane props which is another popular option.

 

[BS Flinn]

thanks SolGato,

My motor has 5 speeds forward and 3 in reverse, draws 24 volts and 48 amps, I have an inline 50 amp breaker, probably be easy to wire in a fuse for testing.

unfortunately almost all the props that might fit are righthanders, I've run across a few videos on youtube about how to fix a trolling motor that's running backwards so I suppose it might be possible to reverse it.

Kipawa said they've never even heard of the trolling motor brand (Goplus) and their props probably won't fit because they're for minkota and newport, haven't heard back about whether they can tell if they'll fit by dimensions.

Goplus says they don't sell replacement parts, but they'll send parts free if it's on warranty, they have no info on the specs of the prop, it actually seems like trolling motor companies put a fair amount of effort into not publishing the specifications of their props to avoid losing sales.

I'll take a look at RC plane props and see what I can find there, thanks for the tip.

I'm also looking into having one printed.

 

[SolGato]

A lot of trolling motors available today are just rebranded versions of brand name motors, sometimes sold out the back door of the same manufacturing facility, sometimes made in quantity for a “new brand” and sold through retailers like Amazon and EBay.

If you match the specs and the physical properties of the motor head and motor housing, you can usually identify what it is a “knock off” of.

Chances are your motor uses a standard shaft size and shear pin that matches a “brand name” which means there are likely already prop options available, you just need to compare specs and take some measurements and check with someone like Kipawa to try to identify it.

For reference, a common trolling motor prop pitch is about 4”.

 

[portacruise]

The turbulence caused by the downshaft to the Motorhead causes more drag than someone might think, especially if you'll be ramping up to a higher speed.

Here's a link #252 that should help, if you will be exploring model RC props, which I think will give more speed and efficiency compared to just about any lossy IC, or weedless prop, just my humble experience. Keep in mind that #252 Troll Motor used was 12 volts and maybe about 1200 RPM, your 48 volt probably runs at twice the rpm. So one of the lower pitch APC Marine pusher props might be the way to go depending on which direction your troll shaft rotates. Cost of the APC props is very low, I usually buy a handful in the range to experiment with which allows me to tweak choices to get the best result from on the water measurements. Avoid electric props which will be too fragile.

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

 

[BS Flinn]

Thanks SolGato and Portacruise


I think the pitch on the prop is 5", I set it on a flat table, measured 3" from center along one blade, balanced a straightedge across the blade, and measured the distance from the straightedge to the table 9 5/16" apart and came up with 2 1/2", double that for the full circle.

That thread is very helpful, thanks again I take it that I want righthanded puller props to use as lefthanded pushers, or do I need to find a left handed pusher?

I'm quite surprised that there aren't more people doing this considering the massive push to go electric and the crazy high prices for electric outboards.

 

[gonzo]

I don't quite follow your method. The pitch is for the blade, not for a circle. You need to find the center of the blade along the radius. At that point, measure the angle of the blade face. Manual Procedure for Propeller Pitch Measurement https://www.propellerpages.com/?c=articles&f=2006-03-27_manual_pitch_measurement

 

[portacruise]

Thanks SolGato and Portacruise


I think the pitch on the prop is 5", I set it on a flat table, measured 3" from center along one blade, balanced a straightedge across the blade, and measured the distance from the straightedge to the table 9 5/16" apart and came up with 2 1/2", double that for the full circle.

That thread is very helpful, thanks again I take it that I want righthanded puller props to use as lefthanded pushers, or do I need to find a left handed pusher?

I'm quite surprised that there aren't more people doing this considering the massive push to go electric and the crazy high prices for electric outboards.

Some pedal boat companies and one troll Motor company has used APC props.

EP Carry - Shop Now https://www.electricpaddle.com/shop.html

As you look at the size stamped face of the APC TRACTOR (@ the thicker leading Edge of the foil), the rotation is CounterClockWise, the way I understand it. The prop will also propel normally if mounted upside down CCW with the thinner edge leading, but at lower efficiencies. All of the 3 blade and above propellers that I have tested over many years are less efficient, in my particular micro boat application, compared to the 2 blade, whether they be APC brand or any other conventional outboard motor type. The APC Electric props test out a little more efficient even despite their flexing, probably because of their lower friction thinness, when operated below their breaking point. I believe that any shape that increases total surface area of the propeller blades increases surface area water friction and causes loss of efficiency ( theoretically a one blade propeller is the most efficient, as I recall). But of course there are practical trade-offs weighed against efficiency, when selecting the best propeller, depending on what someone is trying to do for their particular boat. JMHE.

 

[SamuelChukweze]

Your idea sounds creative, but modifying a prop might not yield desired results due to the motor's design. You could explore prop options designed for trolling motors. Keep in mind, altering the motor may void warranty and affect balance. Consult experts for safe solutions.