Typical Wh/Mi for an electric kayak?

swbluto

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I'm trying to design an electric kayak for a 40 mile trip and I'm trying to get some reasonable figures. I was impressed with the kayak I rowed because I think I'm probably only capable of 30 watts on average and it was going 4 mph, so I was curious how far I could propel an electric kayak with my 1000wh battery. I was trying to look for a "power vs speed" graph for kayaks, but I couldn't find much - the most I could find was the theoretical top speed of a kayak given the boat length and width and I'm not really sure if that's meaningful (It seems if you throw enough power at it, it should go faster than the 'limit'?).

So, just curious if anyone has any figures. If you know the voltage, ah, speed, distance, whatever info you have, it'd be much appreciated!

I'm looking at the touring kayaks because it seems like they're designed to be fast, efficient and easy to go long-distance, ideal for trying to squeeze as much range as possible out of an electric kayak. The "everyday kayak" on amazon definitely doesn't seem to match the swiftness of the true blue touring kayaks.
 
http://www.keelhauler.org/khcc/seakayak.htm

Looks like a "typical kayak"(?) requires .05 hp or 37 watts to maintain 4 knots or 4.6mph. Assuming a prop efficiency of 50% and motor efficiency of 90%, it appears that the achievable watthour per mile at 4.6mph is (37/4.6)/(.9*.5) wh/mi or 17.8 wh/mi. Does that match anyone's experiences?
 
http://endless-sphere.com/forums/viewtopic.php?f=7&t=13639

Trolling motor efficiency data points.

Torqeedo ($2000 brushless motor): 50%
Average $100 trolling motor: 20%

Hmmm.... that makes my 17wh/mi. figure jump to at least 40wh/mi assuming the cheaper trolling motor. :roll:

That means my range would be less than 30 miles. Need to improve that without breaking the bank.
 
http://thetorqeedoshop.com.au/propeller-trials-on-seaeagle-kayak/

Looks like test data using a torqeedo 801 3 blade prop on an original torqeedo 1003 trolling motor to drive a SeaEagle inflatable kayak.

SeaEagle-kayak-prop-tests.jpg


SE330K_DSB.jpg


(Looks like a pig, seems to be the equivalent to a 37" wide by 12' long kayak.)

260 watts at 4 knots (4.6mph) suggests a wh/mi of 260/4.6 = 56 wh/mi.

What would the wh/mi be like to drive a hard 24inch wide x 17 foot long kyak using a $100 motor and a torqeedo 801 3-blade prop? Hmmm...
 
Looked at dedicated pedal kayaks like this guy's 20inch wide Current Designs Expedition kayak with a spinfin pedal unit (http://www.elmtreedental.com/AR_Pedalkayak.html) and the 30inch wide hydrocycle (http://www.hydrocycles.com/learn.php#fishing), and calculated a wh/mi efficiency somewhere in the 12.5wh/mi minimum at 7mph with the 20inch kayak and 20wh/mi. with the hydrocycle at 5mph. Seems like both could be adapted using an electric drive on the cranks with some fabrication. Maybe with a freewheel crank, it could be just like an ordinary crank-driven electric bike? That seems like it'd be the ultimate in a fast, long-range electric kayak. Not entirely sure how the pedal drive units would sustain impacts with rocks and the ground in shallow water, which I'm sure would eventually happen. Also not entirely sure how reliable the drive systems on these kayaks are - they obviously don't have the benefit of large-scale consumer testing over many decades given their limited market size.
 
How's this for a guess - I have a 16ft skiff powered by a brushless outboard that does about 6mph (I guess) on 600w. That's 100Wh per mile. A skinny touring kayak might use half that ie. 50 Wh per mile. Also, lead batteries in a kayak that can carry the weight might give it more stability which will be partly lost if you don't have a paddle to help with balance.
Coming at it from the other direction, there are people who have virtually doubled the efficiency of trolling motors by doing three changes - 1, change the prop to a model 'plane prop for i.c. engines. 2, change the speed control switch to a PWM controller for brushed motors. 3, put a streamlined fairing around the circular leg.
I'm not sure where the account of this is but a good place to start looking would be www.boatdesign.net
 
alan-c said:
Coming at it from the other direction, there are people who have virtually doubled the efficiency of trolling motors by doing three changes - 1, change the prop to a model 'plane prop for i.c. engines. 2, change the speed control switch to a PWM controller for brushed motors. 3, put a streamlined fairing around the circular leg.
I'm not sure where the account of this is but a good place to start looking would be http://www.boatdesign.net

Oh, interesting insight about the prop. It seems that the SpinFin pedal unit which was designed to be as efficient as possible uses an airplane kind of propellor.

drive%20unit.JPG


Definitely different than the run-of-the-mill weed-and-kelp-slashing propeller.

kipawa_on_motor.jpg


Putting a streamlined fairing around the leg seems to make good hydrodynamic sense.

So maybe 25-30wh/mi. is achievable on an ordinary 23"-24" wide, 12ft-17ft long kayak with an appropriately modified trolling motor at 5 mph?

Seems like pedaling capability would be great for long-distance capability, but seems to be a pretty expensive option no matter how one cuts it on a kayak. (The flippers kayak is $1700, the WaveMotion pedal kayak is $3000 and the spinfin pedal unit is $700 + labor to install it.)
 
Now I'm looking at the inflatable kayaks, specifically the Advanced Elements FireFly Inflatable Kayak.

Weighs 19 pounds, 8ftx35" and 23" X 18" X 5" folded. Would be perfect for touring by bike as the kayak could be packed up and put on the bike-rack, but it's decidedly not a "touring kayak" in the sense of long-distance and fast, lol.

Oh well, maybe if I put some 300 watts of solar cells on-top, it'll be good enough? Would probably make a trolling motor of sorts from an RC motor for portability.
 
Dont get the FireFly, i just had one and returned it.
Got it from REI, but wasnt happy with the lack of skirt, and handling.

I then bought a Sevylor Quik Pak K5. It's much better.

The FireFly has no skirt, so you get all wet.
It's also shorter about 7feet as compared to 10feet for the K5,
and so is slower, and tends to drift more.

I posted on my K5 electric today in this thread

http://endless-sphere.com/forums/viewtopic.php?f=39&t=53214


Ill get some pics of it tonight.
 
Also the K5 packs into a backpack which is really cool.
It weights 24lbs
I am planning to take it hiking, but without the motor and battery, as those are too heavy.


Here is a pic form Walmart.

http://www.walmart.com/ip/15763647?wmlspartner=wlpa&adid=22222222227008368177&wl0=&wl1=g&wl2=c&wl3=13955755510&wl4=&wl5=pla&wl6=34918625110&veh=sem



I got mine on Amazon prime though.
 
silentguy said:
Also the K5 packs into a backpack which is really cool.
It weights 24lbs
I am planning to take it hiking, but without the motor and battery, as those are too heavy.


Here is a pic form Walmart.

http://www.walmart.com/ip/15763647?wmlspartner=wlpa&adid=22222222227008368177&wl0=&wl1=g&wl2=c&wl3=13955755510&wl4=&wl5=pla&wl6=34918625110&veh=sem



I got mine on Amazon prime though.

I have a 1.5kwh of lithium batteries, I was planning on taking those on my bike and bringing the inflatable kayak along and use the ebike battery as the kayak's battery. However, it seems that the trolling motors are pretty "big" (Unwieldy to carry on a bike), so I'm thinking I would construct my own from an RC motor. Don't know of any RC motors that get the low KV desired for trolling, however, would probably require rewinding the motor. And, I'm not even sure what the optimal turbine speed is.

Well, nevermind, I'm thinking that using a regular low kv RC motor would probably work OK with partial throttle to get the desired turbine speed. At partial throttle and 24v, I believe that an infineon sensorless controller would probably work OK, though I'd have to test that. (Would be more durable for aquatic apps than an ESC at partial throttle)

Edit: Torque... hmm.... yeah, on second though, RC motors might not have enough torque for water apps. Or would they? Don't know.
 
Take a look at Hobiecat kayak with their mirage drive. I've been dreaming of one with a geared hub on it.....
Kent
 
For your 40mile trip you are going to need a lot of battery, or have to supplement with paddling.

My kayak is slow about 2mph top speed
It took me almost 2 hours to go 3 miles.

So that would be 26 hours to go 39 miles.

Even a 100Ah battery wouldnt make that.

Not sure how long my 85Ah battery will last,
but some fisherman told me they can troll at low speed all day,
for 5 or 6 hours.
 
Here's kind of a zaney idea that might help. Normally I eshew adding solar panels to bikes and stuff because the large amount of energy use just doesn't make sense. However, even at 4mph and say 30 wh/mile, you could have considerable range extension by using a bimini cover with solar panels. It's not impossible to imagine a 100w solar panel bimini. You could have nearly unlimited range in direct sunlight!
 
Oh also, should be able to bump the efficiency of a cheap trolling motor to higher than 50% by removing the controller, and simply running with the appropriate battery voltage for roughly the output you desire. The controllers they put in those things tend to be RESISTIVE yuck. Easy to fix with a brushed motor though.

kayak-bimini-05.JPG


A 100W panel doesn't seem crazy.
 
grindz145 said:
Oh also, should be able to bump the efficiency of a cheap trolling motor to higher than 50% by removing the controller, and simply running with the appropriate battery voltage for roughly the output you desire. The controllers they put in those things tend to be RESISTIVE yuck. Easy to fix with a brushed motor though.

kayak-bimini-05.JPG


A 100W panel doesn't seem crazy.

You'd think that at least some of the trolling motors would be designed to be as efficient as possible to have the longest running time. I mean, I wouldn't trust the $80 trolling motors necessarily, but it seems like there should be some middle-of-the-range trolling motor that's designed to be pretty efficient and doesn't cost too much, as an efficient design just needs an appropriately chosen propeller and a cheap PWM controller - a brushed motor would dock an extra 10-15% efficiency, though that's relatively minor. (The torqueedo seems way too expensive for what it actually is.)
 
I read an article where Pro Bass fishermen are buying 1000$ LiOn Marine Battery packs so they can go faster,
and fish longer, than with Lead Acid AGM batteries.

For that kind of money its out of the range of normal people.
 
Well, the trolling motors are typically run at very low speed by most fishermen, my guess about 1mph.
Thats all you need to troll for fish.
And with a big lead acid battery at that slow speed you can go all day.

Once they really want to get speed they switch to their gas outboard.
 
Probably the fastest kayak around: The Hydrofoil Kayak!

[youtube]uO54ZvDwt18[/youtube]

Now if I could somehow get hydrofoils to work with an inflatable, that'd be awesome. Thinking I'd probably need to create a solid, rigid surface underneath the kayak which would be negate the benefit of the inflatable's portability. (Unless, somehow, that rigid surface could be made foldable. Doesn't seem impossible... Might need a certain kind of hinge... not sure what exactly...)

Wait... It looks like it has to go faster than 6 mph to get it to hydrofoil according to http://www.keystonekayaks.com/new_kayak_019.htm. Would that really be more energy efficient than propelling a regular inflatable kayak at 2-3mph?

Oh, wow, someone has already done an electric hydrofoil kayak. Requires 1 hp (750 watts) but it's booking!

[youtube]jh_RhkejWLw[/youtube]

(If it's 10 mph, that's 75wh/mi.)
 
I think inflatable is going to be too soft and bouncy to make a hydrofoil work.
Also it's prob hard to get it up to over 6mph.

Even with paddling and a motor, it's hard for me to get 3mph.
The inflatables are not that fast.
 
How come kawak travelling is so inefficient? On water it should have less friction so you should be able to have more distance per wh rather than the opposite
 
cwah said:
How come kawak travelling is so inefficient? On water it should have less friction so you should be able to have more distance per wh rather than the opposite

You actually get a TON of drag from the water. Think about how easily a bicycle freewheels, when compared to how easily a kayak maintains speed through the water.
 
Sweet! He's not going very fast though :D Top speed for an average kayaker might be 4-5 mph, with considerable effort. What's the top speed for an average bicyclist? The drag is indeed more, however the average power is lower on the kayak, because you can't go very fast.

Hopefully someone who has an equation can help out. I'm imagining that the kayak drag will go up as a cube or something, and the bicycle is closer to a square. A 100W panel would do very well, as I mentioned before, with some type of solar bimini.
 
grindz145 said:
Hopefully someone who has an equation can help out. I'm imagining that the kayak drag will go up as a cube or something, and the bicycle is closer to a square. A 100W panel would do very well, as I mentioned before, with some type of solar bimini.

Power is cube to speed for both kayaks and bicycles. The dominating factor, drag, and the underlying physics are common to both as air and water are both fluids. Just that water is a much denser fluid then air which is why kayaking is so much more inefficient than bicycling.

At lower speeds, as typical on a bike, the power curve on a bike might look square, but it's not. Square and cubic curves have the same kind of shape to the human eye where x>=0, though calculation would distinguish between the two.
 
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