I use a 46 lb trolling motor on my canoe and just wondering how big of a difference a 55 would make. Looking for a bit more power to help scoot around faster and not sure how noticeable it would be. I don't know much about motors, this is a minn Kota by the way. Thanks for any info
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46lb????? I have a 45. I am curious on this one as well.
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Boat speed is proportional to the cube root of the power.
Translation: You would hardly notice the difference.
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Yeah, must be an older one or something, haven't seen another 46 whenever I look, just 45's
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Well I'm a numbers kind of guy and the 55 would be a 20% increase in power if everything were equal. However it always seems like little things enter in and you never get exactly what the numbers say. For instance one motor may be more efficient than the other which will show up in battery life rather than speed and push. I'm running a 27 lb motor on my toon and most of the time it's fine, but in a strong wind I wouldn't mind a little extra push. But more power comes with a shorter battery life unless you find a more efficient model. If you can afford to loose run time a little more power is always nice. Good luck. Later J
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Are you gonna sell the 46? If so how much?
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Ron, I agree with your conclusion of not a big difference, but I'm
with your physics. Are you using kinetic energy or how are you coming up with that simplification? Besides that doesn't work when you use pounds of thrust (force) like an electric motor is rated, versus power. Especially when you get into all of the units that have to be converted correctly. If I wasn't so lazy I'd try working the physics to relate the two numbers, but I think your bottom line is all he really wanted, which I believe is accurate. 20% isn't a big difference, if your previous top speed was 3 mph your new top speed would be 3.6 mph. Assuming all other factors are constant. Sorry had a flashback TMI I'll go back to sleep. Later J
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At 46 pounds of thrust, drag is exactly 46 pounds, too. Drag is proportional to the square of velocity, so it isn't linear and increases sharply in a curve that curves up.
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At top end speed for your craft, I agree max motor thrust equals drag force. And you are right drag is not linear so my previous prediction of a 20% increase in speed isn't accurate it would be less than what I predicted. So it's really not worth changing the motors in question. Later J
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[quote SkunkedAgain] ... I'm running a 27 lb motor on my toon and most of the time it's fine, but in a strong wind I wouldn't mind a little extra push. But more power comes with a shorter battery life unless you find a more efficient model. If you can afford to loose run time a little more power is always nice. Good luck. Later J[/quote]
Exactly right! Headwinds are another consideration and important particularly if you regularly experience them or having that extra thrust means you can enjoy fishing longer without having to head in before the wind picks up as is often a pattern.
Wind changes everything including efficiency. For example, though true that moving around slower with the smaller thrust motor is generally more efficient, if you are making no progress or very slow progress heading back into the wind, then all efficiency savings is lost compared to the more powerful motor which can get the job done with less running time and in this scenario, using the higher thrust is more efficient.
I got the feel for that rowing into a headwind.
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I run a 16 foot 8 inch old town osprey canoe. I have used a 30 to 80 lb thrust motors. Anything over 60 pounds of thrust is a dual battery set up. I don't recomend that due to weight constraints placed on a canoe.
The speed differnce between a 45 to 55 in my canoe is half a mile per hour difference (0.4 Mph to be exact). From 3.1 miles per hour on the 45 to 3.6 on the 55 thrust. It might not seem like a big difference, and it is not while fishing. In fact the slower trolling speeds are difficult to maintain on a windless reservoir with the larger motor. However I use my canoe for duck hunting. I run with my motor stuck I the mud all the time and that is where 10 pounds of thrust makes a huge difference. With wind against you and your prop mostly buried in the mud it is the difference between going and not going.
The battery life is the biggest factor. It turns out you get a few extra minutes on the smaller motor vs the larger, but it turns out to be virtually the same distance when you calculate speed. I hunt Willard spur and all this was worked out on a GPS. The 35 pound thrust motor is actually better for trolling at the lower speeds and lasts longer due to less switching between speeds from higher to lower with a larger motor.
All that said, I own 3 different motors. A 35 pound, a 45 pound and a 55 pound. All Minn Kota. I prefer the 45 and the 55 and only use the 35 out at fish lake and Utah lake when trolling is most important at low speeds. But when it comes to running in the mud the 55 or 60 is superior. Interesting after thought the dual battery 80 burned batteries and did not go any faster. It did go much better in the mud, but because the speed of the canoe is limited to hull hydrodynamics, and the weight of running 4 batteries to get where I was going, and.... Well you get the idea.
Happy canoeing!
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Well I don't really troll fish but when I cast And work an area i'm Usually trolling in reverse which I've found has a good speed and I usually pack two batteries in the canoe, it's a grumman18 foot so she can pack some weight. I also duck hunt and just want some more punch when it gets windy to get from a to b.
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On a windy day a field duck hunting the 55 to 60 motors are superior in every way shape and form. I use a side
dle mount for mine. I load my canoe up so heavily sometimes with decoys, that the decoys kind of act like a sail. I use every inch of the 55 to get where I am going and to get back again. I use 3 batteries on Willard spur and with regularity get down to the bottom of the third battery. The 45 could not handle the full load out of 2 people, dog, decoys and gear. The 55 can, and then some.
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Just a couple of thoughts about this topic.
Thrust changes with speed. This has to do with the angle of attack of the prop in the water.
Top speed is a function of max RPM and prop pitch -- not just thrust.
The notion that a 45LB thrust motor is going to provide 45LB of thrust at 0MPH or 5MPH is not correct. Nor is it correct that speed will top out when the drag equals the motor rated strength.
Speed will reduce the thrust particularly on those very low-pitch, wide blade MinnKota props.
A lot of what I just said is somewhat moot because MinnKota does not make smaller, higher pitch props -- which would be nice for applications like speeding around in low-drag canoes.
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You would be wise to upgrade to a 24 volt if your already packing 2 batteries. More efficient use of power. Plus the higher thrust units are built to use it more efficiently.
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I am glad you brought that up. I have a now discontinued 40 Maxxum from Minn Kota. It has percentage instead of 1, 2, 3, 4, 5. Nice motor and it is very conservative on batteries.
Then I bought the Endura 45. More lb thrust but the prop is a lot smaller. It is not as energy efficient at all. Not sure why the prop is smaller.
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This is what I have found: get the biggest motor you can for the $$$ + the battery makes things work better (size)..
Most trolling battery's are a 27 series but I have found that a 29 will keep a charge 1/2 again longer then a 27, + the bigger motor will run longer on a charge..
When needed you can turn up the bigger motor , but the smaller one will be running on higher amps all the time to get the same power..
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I agree with the efficiency of the 24 volt system for running electric motors. Just not on a canoe. You actually get less miles out of the dual battery. On a larger boat it works, not on a canoe. I have used a 6 horsepower long shaft on my canoe, and the speed and power is just not useable on a canoe's hull. I used a 24 volt 80 lb thrust and the range was just not there. Wasted thrust was probably to blame with the prop in the mud and he other half in the air. On open water 24 volts is superior. But dual battery arrangements go up significantly in price and maintainance.
Small and cheap is the name of the game in a canoe. Dual battery arrangements are not small, cheap, or convenient for that matter. Now on a 12 foot or larger aluminum boat. 24 volts pull ahead quickly.
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I disagree with several of your statements, thrust varies with speed because drag forces have increased not prop angle. Prop angle changes very little at electric motor speeds so don't confuse the issue there.
Props are designed to be efficient for the torque and RPM the motor will provide. You need to find the efficient combination that will put the most expended energy to work. I'm not an electric motor designer but I am a mechanical engineer and snowmobiler and the art of tuning your system to be the most efficient is what will make you the best at your job. You have limited amps in the battery and you need them to be focused to deliver what you need. (Speed or distance) you try to avoid the slippage of the prop that doesn't do you any good.
Top speed is a function of RPM and prop pitch and efficiency. You can use too high of pitch of prop and overheat your motor or too shallow and never get any push out of it.
It is true a 45 lb thrust motor won't give you a full 45 lbs of push but that is because of inefficiencies. But it is correct that top speed is where drag force equals available thrust not rated thrust, again because of system inefficiencies. Maybe we were somewhat saying the same thing, but the way you phrased it tried to discredit things that are true.
Bottom line is every motor will be a little different due to its efficiency and Jmazes input is probably as good as you can get outside of a side by side test. For me a lower thrust motor works perfect because I use it to troll and it gets me right at the best speeds, but if you use the motor to get somewhere faster then the bigger motor is probably the best option. Later J
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I disagree with several of your statements, thrust varies with speed because drag forces have increased not prop angle. Prop angle changes very little at electric motor speeds so don't confuse the issue there.
uhm, it would help if you didn't confuse the issue.
I never talked about prop angle changing at electric motor speeds.
If you don't understand that forward speed decreases thrust particularly on low-pitch props, you don't get the whole propeller thing. I didn't ever say that top speed won't occur where thrust equals drag. I said that at speed your motor will not put out its rated thrust -- because the prop Angle of Attack (not the pitch) changes. So top speed will occur when drag is below the rated motor thrust.
Everything you said about efficiency is 100% correct. Matching the right motor and prop for the application is critical.
MinnKota motors and props are set up to be trollers... which is why they use those big, low-pitch props. They are great at holding a constant low speed in a variety of conditions.
But the question was about going faster in a canoe -- which are generally low-drag vessels.
For that application a smaller diameter, higher pitch prop would be very helpful.
Unfortunately such props are not readily available.
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