How can I get more speed 12v 45lb thrust

ALkayaking

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I have a 12 volt 45lb thrust Minn Kota power drive custom mounted it on the back of my 13'.5" kayak. It works great but how can I get more speed? I've just started researching this and I'm a long way from any of the technical knowledge needed hoping somebody here could help
 
ALkayaking said:
I have a 12 volt 45lb thrust Minn Kota power drive custom mounted it on the back of my 13'.5" kayak. It works great but how can I get more speed? I've just started researching this and I'm a long way from any of the technical knowledge needed hoping somebody here could help
Depends.

If your speed is limited by prop RPM, more voltage will help. This means a new battery. You will likely need a new controller as well. What kind will depend on what sort of motor it is; the two options are brushed and brushless. If it doesn't say brushless it's probably brushed.

If your speed is limited by available current (i.e. torque) a larger battery will help by decreasing voltage sag.

Note that it is likely you will quickly burn out the motor if you run it significantly above its rating; brushed motors don't last long when you overload them for long periods of time.
 
Thanks for the reply. It's a new Minn Kota power drive 12v 45lb thrust running on 100amh battery . Bought in Oct don't want to mess with any volt/amps risk a burn up. I just started researching this morning seen nothing so far with a good outcome for life of the motor. I Put a 3 blade prop on in helped some getting 6 to 7 mph I know there's potential for more out of a motor made for 2,500 lb boat on a 300 lb kayak. Prop made for high speed low torque maybe. Just learned torqeedo is planetary drive has my ears smoking wondering if possible to be done 🤔🤔🤔
 
Hull speed for a 13.5 foot boat is 5.7 MPH. That's the max efficient speed. To go faster you need lots more watts to get it to plane.
http://recumbents.com/wisil/hpb/hpbcalculator.asp

Trolling motor props are designed to shed weeds, not go fast. If you think you are limited by the prop and want to go faster you can swap out the prop for a fiberglass model airplane prop. Maybe try a 10x10 prop. They are cheap.

Warren
 
Man I didn't realize how hard it be to get a little more speed out of a 300lb kayak with a motor built for 2,000lb. This is all still pretty new motors on kayaks I sure some where someone is working on it maybe just hoping for 10 mph seems simple enough
 
If it's meant for a much heavier boat than the propeller likely has a low pitch (theoretical distance traveled forward for every revolution). So you are probably at max rpms for the 12V, but the motor likely has untapped torque. If you put a propeller on with a larger pitch, then I imagine you could use the motor to it's full potential and go faster. You'll want to be careful not to put a prop with too much pitch or you will overload your controller and/or motor.

-Ben
 
Its the prop.
My 30lb thrust motor taps out at about 5MPH on 3S Lipo pack as well. I can pull a boat, but it wont go any faster than 5MPH.
Its an untapped market supplying Kayak prop options for trolling motors.
 
Fiberglass model. You can drill out the hub to match your motor shaft. $3.95
https://www.apcprop.com/product/10x10/
You will also need to add a keyway or something to keep the prop from spinning on the shaft.

There's an 8x8 and a 12x12 available too, but I'd suggest starting with the 10x10. Maybe order all 3 to see which one works best. Too small and you wont have enough thrust. Too big will lug down the motor and maybe overheat it. One you find the right size you can get a carbon fiber version for about $25.

Warren
 
Note that we tried a whole bunch of props to find what worked best for human powered boats. I'm thinking that trolling motor consumes 100 - 200 watts, so it should use props that are about the same size. Two bladed ones worked better than 3 or 4 bladed.

More than you ever wanted to know about going fast on small amounts of power:
http://recumbents.com/wisil/hpb/boat.htm

Warren
 
MotorboaterBen said:
If it's meant for a much heavier boat than the propeller likely has a low pitch (theoretical distance traveled forward for every revolution). So you are probably at max rpms for the 12V, but the motor likely has untapped torque. If you put a propeller on with a larger pitch, then I imagine you could use the motor to it's full potential and go faster. You'll want to be careful not to put a prop with too much pitch or you will overload your controller and/or motor.

That's exactly what I was thinking.
 
Water is a fluid so you have a drag is the cube of your speed problem.

To beat this you either need a more efficient hull, less wetted area, or a shitload more power. Making your electric kayak fast will be expensive, but also very possible. Maybe the prop isn't that efficient, but solving that issue will only help so much.
 
flat tire said:
Water is a fluid so you have a drag is the cube of your speed problem.

To beat this you either need a more efficient hull, less wetted area, or a shitload more power. Making your electric kayak fast will be expensive, but also very possible. Maybe the prop isn't that efficient, but solving that issue will only help so much.

A kayak has an inherently much slipperier hull than a jon boat or a motorboat, such as a trolling motor is intended to push. And it's much lighter. The problem isn't efficiency or his power requirements; it's that the prop is in too low a gear, so to speak.
 
You were basically given the correct answer in post 5 by recumbents.com. Your boat has a hull speed.

I have never visited the watercraft sight before because pure electric is a waste of time in boats except as a very short distance play toy and even then, its a very expensive prospect.

At 13.5' long and 300 lb your kayak is likely a one person and would likely have a waterline beam of around 26"-28" at 300 lbs. Your right about at max weight on that boat so Recumbants.com is not too far off the mark. I will give you 6.2mph as
your kayak has around a 5.6:1 length to beam ratio. That is not enough ratio to exceed theoretical hull speed by more than a small amount over what recumbants.com posted You need at least 10:1(Plank on edge/ think catamaran hull) to exceed hull speeds in a displacement hull. Even then it is at the expense of stability and horsepower.

Your boat basically has no planning surfaces and WILL NOT go faster no mater what prop you put on it. All you will get is a bigger wake. All the power is being used to make a wake.

At 5.7-6.2 mph as suggested you will quickly sag the 100 amh battery. Probably not more than a couple hundred yards. If you are willing to slow down to 4.2 mph, your range will be infinitely further. On the order of a few miles, enough to get to your fishing spot.

You could put a 10 hp outboard on your kayak and the result would be sinking as the wake overwhelms the boat at about 7-8 mph. The stern would be way down in a hole and the minute you backed off the throttle to prevent rolling over the boat would loop out. Go vertical and sink straight down by the stern. Been there, done that as a kid. Old salts on the beach knew what was going to happen and just sat down with their popcorn to watch. I was not amused that they were rolling on the ground laughing. Now I know and design boats.

I now have a full displacement boat of 26' that weighs 10,000 lb. I drive it with a very slow turning 18hp diesel and controllable pitch propeller. I get my hull speed of 6.7 mph at 8 hp output from the engine. At full throttle I get 7.2 mph at 18 hp. Drop the boat back to 6 mph and I use 4.5 hp to drive the boat and my range exceeds 1,500 miles. At that speed range is more limited by making electricity with the alternator as the alternator can pull more than 4.5 hp
 
Minn Kota makes a 36v 112lb thrust unit. It's basically the same weight too.
images (17).jpeg

I used them on J-24's, and had 2 on my 31' trimaran. Night and day difference compared to 12v
 
If you need to stick with your existing unit, most of the minnkotas are bushed motor, with a potted controller in the head, and two power wires going down the shaft. You could hack that and add a more powerful controller, but waterproofing will be important, esp if you want it to run after a capsize recovery. If you go that route, you could also mount the controller in the boat, with just the power wires running to the motor with the shaft caulked tight.

Have you checked your existing motor for water intrusion? I've serviced several of these that ran, but with bad power, where the lower unit was full of water. It can get in around the prop shaft seal, even when the top is fully waterproofed.
 
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