Ultra-budget electric kayak made from scraps, need all kinds of advice.

[Factoryninja]

If you can get the shaft angle at or below 7 degrees you'll see a marked improvement in propulsive efficiency and also why (well at least one reason) the long tail's have huge, long shafts.

The hard pull you're experiencing is prop walk and typical of anything spinning without a counter rotational balancing element. Cant the shaft off to the side a little off the centerline, say a couple of degrees to start and this will help mitigate this a bit. A small vertical trim tab will help too.

A fairly small plate above the prop, mounted at least 10% of it's diameter away from the tip, will help with ventilation.

If you were actually doing 10 MPH, this is a S/L ratio of 2.55 (assuming a 12' LWL), which is about what you can expect of this hull form and will require a lot of output from your rig to maintain. Pushing past this point will be difficult given the available power and hull form. At these S/L ratios, the hull form wave making resistance rises exponentially, so the power needs do as well. Your wattage requirements will drop considerably if you back down below 2.0 S/L and possibly more than 50% lower, if you back down further than say about 1.3 S/L.

Making your own prop isn't the best choice, even if it seems to be easy enough. Ideally, you'd want to "gauge" the prop's pitch and diameter, so she's pulling the recommended amperage at full speed, no more or less. When testing, run her up to max speed and see what's see's drawing. If she's under amp'd a touch, add some pitch and/or diameter and the reverse is true was well.

I'd like to see a video or at least some photos of this underway at various speeds. At full speed, I'll bet she's squatting quite a bit and given the weight she's carrying, a huge quarter and stern wave train is well developed. You can play with things like cup and rake to squeeze a bit more from her, while still keeping the motor in it's load range, but these will be marginable improvements at best.

This hull and drive is likely working on the old "inclined bottom" principles, so you're seeing much higher speeds than conventional wisdom would normally suggest. If you'd like to go faster, just cut off the last 2 feet of hull and glue a piece of plywood over the cut out portion of the hull, vertically, making a little transom. Though you'll lose some length and volume, you'll also have better cleavage for better flow exit at the stern, which will help a lot. If the hull is left the same, you'll run smack into (now currently are close to it) a "drag wall" that's unsurmountable, with current power available. Further, an instability will soon arise, if you do manage to push this puppy past say 3.0 S/L. I've personally enjoyed being towed by a powerboat, while in a canoe, to explore what happens when you push a displacement hull form well past it's limits. It's a fun ride, while it lasts, but it will roll over, you can bet on it, though on a warm summer's day in an empty canoe, no big deal. With your gear taking a swim, maybe not as much fun.

Thanks for the useful tips, Par.
I ended up making another prop and shaft with -vastly- improved performance, I'll pop back in here when time permits and detail the results. I did encounter the beginnings of instability and thus the speed limit of the boat, a point past which even though it would have gone faster, I didn't dare, as I did not want to get wet, and it was again close to the inverter's limits.

 

[kilocahrlie]

Ditch the motor and prop and add a J.A.T.O. bottle. And get a good helmet.

Just kidding.

I'd quit re-inventing the wheel and get a nice electric trolling motor and be happy and catch a bunch of fish. You and I are not going to beat Minn-Kota's or Evinrude's or anyone in the business' years of engineering, practical experience, and refinement. So many things have been idealized already, why start with flintknapping a propeller? You'll get a lot more miles out of that battery.

 

[Factoryninja]

Ditch the motor and prop and add a J.A.T.O. bottle. And get a good helmet.

Just kidding.

I'd quit re-inventing the wheel and get a nice electric trolling motor and be happy and catch a bunch of fish. You and I are not going to beat Minn-Kota's or Evinrude's or anyone in the business' years of engineering, practical experience, and refinement. So many things have been idealized already, why start with flintknapping a propeller? You'll get a lot more miles out of that battery.

Why flintknapping a prop? Two words, money and fun. Got little of the first, having much of the latter. Long story short last weekend I made a 7 foot 3/4 inch shaft, cut the first crude 15 inch 2 blade prop into 4 pieces, making a 4 blade 8 inch prop with a 45 degree blade pitch and had a go. It was -fascinating-. The initial launch was slower just because of motor spoolup time. The hookup with the water was -vastly- improved. It took 3x as much rpm to hit a given speed, but far less current load on the system to do it. Speeds that had the inverter begging for mercy with the first prop with the gauge in the red barely hit 33% this time. Little to no ventilation or cavitation, no abrupt water-churning thresholds appeared. The faster I ran it the faster it went.
Pushing it till the inverter was close to maxed out resulted in much faster speed than first try, but ran into that exponential power demand increase right about the same time the thing was going so fast as to be starting to get a bit scary. It was throwing a wake fierce enough to slap the boat around when I stopped, and pushing an almost whitewater wave in front of it. The shaft was still so out of balance that the system vibrated heavily which began to smooth out about 600 to 800 rpm. I was wondering what was going to be the limit first... how much the inverter could sustain, or how fast I dared to drive the thing. The nose was starting to come up, and I was beginning to get used to driving it judging the sustainable cruise by scrolling on power until the inverter was one notch on the bargraph away from maxed out, running at or around a continuous 2 kw, and I bottomed it out, hit something with the prop and snapped the shaft off.
This is just getting good. I don't want to go any faster now. For an 8 foot micro boat whatever that speed was it was almost scary and required considerable concentration to pilot it. I'm not going to get that out of some overpriced off the shelf trolling setup. I'm going to retrieve the shaft, and rethink the drive now that I've learned a bit. Might ditch the longtail thing and whip up a compact pulley, belt or chain drive, put the motor inside the hull down low, and the prop just off the tail, add steering and I've actually got a pretty decent toy, here.

 

[Dave T]

My main concern with your setup would be safety. Your powering this with a 120 volt AC inverter that can supply up to 16 amps more than enough to electrocute you especially with water involved. You have a large 12 volt battery full of sulfuric acid between your legs. I've seen car batteries that have exploded. According to ohms law amps times volts equals watts so if you are pulling 16 amps at 120 volts that's 1920 watts and since you can't get more power out than you put in 1920 divided by 12 means you would be pulling 160 amps from the battery and this would be if the inverter were 100 percent efficient which they're not so probably at least another 10 percent from the battery. pulling this kind of amps from a battery continuously is not good it will overheat which produces a lot of explosive hydrogen gas and you need real heavy cables. I do not mean to discourage you on this project as I like to see people think outside the box and build things especially boats from available materials for little money but give a lot of thought about safety. My suggestion would be to make it into a take apart catamaran with two hulls mounting the motor and battery between them with either another plastic kayak or a couple of simple plywood hulls this would be much more stable and would allow another person. You could use the same set up as you have now or a better way would be to find a junk outboard and mount the electric motor on it you would need probably about a 10 horse for the RPM and power you are running this would give you vectored thrust for steering as well as FNR the prop would be much more efficient and you could reduce the diameter if needed.

 

[Irie]

I did a 10 HP electric outboard conversion. It worked well enough but didnt utilize all the motors potential because of the gear reduction. It did get the boat up to 8mph, but I was disappointed with it leaving so much unused potential.

So, I built a steerable, trimable, sub/surface drive from scrap aluminum I had. Still a work in progress, but you may find it helpful to your project.


Lots of Minn-kotas on my little lake but I have yet to see one do this.....


Its a 48v system, me1004 pmdc motor 12hp continuous, 25 HP peak, alltrax spm 48-400 controller, and (2) 48v Chevy volt modules in parallel , 10.5x12 pin drive prop. It does 25 mph burning 13.7 kW. I've got a thread about it here. I do agree with everyone that you should invest in a prop. An 8" aluminum Long tail prop can be found for under $20, might work well in your application.

 

[Factoryninja]

I did a 10 HP electric outboard conversion.

Holy SxxT! And I thought -MY- little toy was cool!
Is that a tach sensor on that coupling? Good for tuning the system, all I got is seat of the pants feel for RPM and an LED bargraph display on the inverter to judge the general range of current draw.

I, am, impressed. Guess I'm not the only one fond of nailing kilowatts onto small boats, but mine is as rudimentary as it gets, that whole setup is very well developed. Nevermind shaft support, I went full-on primitive by just nailing the shaft onto the motor itself and betting the heavy oversize industrial bearings can take it. Lack of a thrust bearing would eventually show, but not for a long long time.

I liked using the high voltage setup because it minimizes current handling at all stages except battery to inverter. As I read your build I was wondering about what kinds of currents you'd have to be pushing around at only 48V to develop that much more power than I'm stuffing in a kayak, but you're also rocking automotive hardware operating at a whole different scale.

How bulky is the rest of the hardware, controller for instance but particularly the battery? I lucked out... my inverter and controller weigh about 2 lb and a half a pound respectively, don't bulk up much either.

Seeing THAT, though, I'm starting to think about spending some actual money on mine. I've hit the limits of what I can do with my limited tech hacker junk supply and if I want to take this any further I gotta buy some stuff. I had no idea props were that cheap.

By the time I blew my prop off I realized I was getting sick of the longtail thing already, though. It corners like a locomotive with about a half mile turning radius *exaggerating here but you get the point* even digging as hard as possible with a paddle, and all that did was set off grumbling turbulence under the kayak and jack up the current draw heavily while turning very, very poorly. Turning was such a hassle that it was faster and easier to stop the motor and paddle the boat 90 degrees in place and then start it up again than actually try to corner with it. All turns while moving were long, wide arcs.

To address other concerns voiced here...
If I go much further with this beyond the crude testing stage, a lot of things would be made permanent. Right now the controller isn't even mounted, nevermind waterproofed, neither are the inverter and battery. The controller is just wedged into the plastic and foam gap behind the seat, the inverter and battery on the floor. Version II ended with the shaft and prop at the bottom, and a pretty good idea of what a single battery, a few kilowatts and a badass motor can do with a kayak this tiny. If I do a version III, it'll have,

The high voltage electricals in a box.
The battery behind an aluminum firewall at the front of the boat. It'll ruin what little legroom the battery leaves me as it is, but hey. I, too have seen a battery blow more than once and it ain't pretty.

I'm pretty sure this isn't enough to do it... I know I was loading that bad boy pretty hard, but it never got warm, nevermind hot. It's a pretty damned big battery, lot of thermal mass. Pushing 2kw, if we assume about 10% losses in the battery that's about 200 watts worth of heat dumped into and dispersed through 80 lb of mostly lead. Even if I'm off by 100% and it's more like 20% losses in the battery, that's still 400W trying to heat an 80 lb block of metal and acid. I think the battery would be dead before it could self-heat enough to risk ignition internally unless an anomaly happened along the lines of a prolonged dead short.

Also, I get the impression that large deep-discharge marine/RV batteries like this were specifically designed for RV and boat inverter applications... the inverter itself was certainly designed for THEM, says so right in the manual... So I'm pretty sure the battery/inverter part of this is happily running in the spec it was designed for.

Still, hydrogen will do its thing given a chance, and yeah... my max load right now is likely to be in the 160-170 amp range. Since I can't have any real idea how the battery will take that long term, better safe than sorry, so it'll get a firewall.

And the drive system's gonna become something like an inboard/outboard deal. This whole thing is just begging for an over-the-shoulder chain drive with the motor on the bottom of the boat throwing a chain up to a short shaft where the motor is now, leading back down to a decent prop hung off the tail. Adds about 10-15 lb to the system but I really would love to have that motor at the bottom of the boat.
-F

 

[Irie]

Thank you. Its a fun little boat, kinda like an aquatic golf cart. There is a tach sensor on the coupling, its very inexpensive, but quite useful. The controller can handle up to 460 amps. With the prop I have on now 10.5x12, it'll draw around 350 amps at 42-45 v and do 22-25 mph. The 9.25x10 prop draws around 250 amps at 44-46 v and does 20-22mph. The controller hooks to a laptop and gives me real time monitoring of throttle , battery volts and amps and motor volts and amps, controller temps, etc. It also logs a bunch of info to an excel file. I just haven't had much time to do anything with that.

I have the controller, contactor and fuses mounted in the center console. Initially the battery lived there too, when the boat was sporting the converted outboard. After I installed the surface drive I moved the batteries in with the motor ( this can be seen in one of the videos, I'll also get some pictures). I also upgraded the wire terminations to better handle the higher amps of running a direct drive. Each battery weighs 43# and the controller and other hardware is only a few pounds. Its all very compact.

I am no expert on boats but I would advise against going with the chain drive and instead stick with the longtail design and directly drive the shaft. Why add all that goes into chain drive when you don't need it? My suggestion would be to thru bolt an aluminum plate inside and outside sandwhiching your hull where the motor is mounted now. Add a fishing seat swivel base to give you steering , then attach motor to that. Nova jaws or similar to couple shaft to motor. Some form of thrust bearing, torque tube , another bearing near Long tail prop. But again I'm no boat expert, these are just my thoughts.

I'd be willing to bet you'll do a version 3, once you start its hard to stop, always trying for more... I had said I was going to be happy and just enjoy the 8 mph outboard conversion.. About a week later I was building the surface drive......

 

[Factoryninja]

More fun...
So I went and retrieved my prop a week after losing it. Was much more difficult than anticipated. Dark murky bottom, decaying leaves, shadows. Made much more difficult by the fact that the shaft was black anodized aluminum. The only visible part was the prop itself made of rough-hewn raw aluminum. Turns out the rough-hewn part helped.
Ended up using the inverter to power a huge 300 watt sodium light with a square plastic housing I salvaged from another industrial place a long time ago. Added a chunk of copper to one side as a balance weight and the thing floated ok. Carried it out there and towed it around through nightfall. Right before I was about to give up, (isn't that always how it is?) the light revealed the prop about 7 feet down. There were two steel couplings 4 bolts and a couple of hose clamps, the rest was all aluminum so retrieving it was tricky as hell, but eventually snagged a coupling by fishing with a huge neodymium magnet and some paracord. Leaving it rough edged was an unexpected savior move. I didn't bother to round off the edges, the prop blades are rectangular, and it was the artificial nature of a 90 degree angle in a reflection among an infinity of organic shapes underwater that let me spot the thing at all. Towed my light home with the shaft on board feeling very pleased with myself.

And you're right, there will be a V3, by now I want to make this thing not just work but work well.

Reason I want the chain drive and a short tail is, much easier to build it not to vibrate and I think it'll steer much easier. The shaft is 7 feet long so the center of thrust is coming from almost as far behind the boat as the boat is long. Using a paddle as a rudder is fairly ineffective and mostly just makes turbulence. Plus making a shaft that long that stays concentric with the motor shaft and doesn't sag or bend has proven difficult. The prop and shaft I just retrieved were much, much better than the first, but still vibrated so heavily that at certain RPMs it was making a steady banging noise from flexing aluminum structural parts in the motor mount colliding with the hull. I'm now not sure if I even CAN make a decent longtail shaft with the tools available. I will be trying again though. Probably -will- buy a prop, but for now it's nice to have a homemade one, as crude as it is, just because damn, did it work a lot better than I expected.
-F

 

[Factoryninja]

Also, Irie: I've gone longtail so far, and now thinking about going to a chaindrive to toss the rotation up and over the rear of the hull while relocating the motor to the bottom of the boat because I'm trying to dodge the age-old problem of having a prop shaft creating a hole in the bottom of the boat. You may be able to get away with it with a small wet well in an otherwise relatively large boat, but if I just mount the motor on the floor behind the seat inside the hull and punch a hole out the bottom for the shaft, I'll take on water. The kayak needs almost a foot of draft with all that weight in it, and the "displacement hull" nature of it becomes very obvious at speed because it is punching through the water far more than it is riding on it. I haven't got anything like a flat surface I can turn into a seal, either. Pretty much every millimeter of the hull is a complex curve of some sort. One way or another I think I'm stuck mounting the motor above the waterline to avoid getting complicated, unless I can whip up a belt or chain drive to carry rotation up and over the rear end.

 

[Irie]

Also, Irie: I've gone longtail so far, and now thinking about going to a chaindrive to toss the rotation up and over the rear of the hull while relocating the motor to the bottom of the boat because I'm trying to dodge the age-old problem of having a prop shaft creating a hole in the bottom of the boat.

I didn't mean go thru the hull with the shaft, I'd keep the motor where it is. All my suggestions were meant to keep everything where it is now ,just reinforce and add steering. Moving the motor inside and throwing a chain up to the propshaft would still leave the prop shaft in essentially the same place, unless I'm not looking at this right. Do you have more pictures? I think my biggest question would be what benefits would the added complexity bring?

 

[Factoryninja]

Haven't any more pictures, but easy enough to describe if you saw the first one.
Haven't decided if the complexity and energy losses are worth it yet. I like the longtail thing for simplicity, direct shaft drive, zero mechanical losses.
But the reason I'd like to move the motor is stability. Right now the motor's one of two heaviest objects in the boat, battery being the other, and it's mounted as high on the boat as physically possible to be able to do the longtail thing.

Plus the longtail thing hurts maneuverability and keeping track of where the prop actually is is a pain. Repeatedly snagged it in weeds a ways behind me.

Idea is, chain drive, fairly simple to whip up out of bicycle parts, put the motor on the floor in back. Inside the hull on the floor. Place where the motor is now, on top of the back deck, just put an idler shaft. Horizontally mounted. Put a skeletal structure off the back like a typical outboard motor shape minus the engine, shaft spins a chaindrive down to a prop mounted there outboard motor style just off the end of the boat.

4 sprockets, one shaft, not counting the prop, two chains. Not too sure about chain drive water tolerance, but chain drives are also notoriously tough.

Could also go with a couple geared 90's and throw a shaft drive straight down off the end of the tail to the outboard-style prop. Either way, it puts that massive weight on the bottom of the boat instead of the top, doesn't add a lot of weight, it's easy to make that steerable either with a chain drive and a rudder or, if I did a drop-off-the-tail vertical shaft drive, make the prop itself steerable. Boat'd be far more maneuverable in close quarters without the 7-foot pole hanging off the back.

Relatively simple mechanically to put together, bit more robust and bottom-out tolerant than the longtail, plus it adds a thrust bearing, stops using the motor itself as a load bearing structure, (yeah, the motor can take it, probably forever, but it's just not a mechanically satisfying way to do it) and it'll vibrate a whole lot less when it isn't spinning a 7 foot long shaft.

Probably have to wait till winter to put that together though, haven't got enough time left to whip up a decent chain drive before the pond freezes. Probably spend the rest of the time between now and freezeover playing around with what I've got and adding safety features. I already added a battery box- not as good as a firewall, but now the boat won't necessarily be 2 inches deep in acid if the battery fails.
-F

 

[portacruise]

Haven't any more pictures, but easy enough to describe if you saw the first one.
Haven't decided if the complexity and energy losses are worth it yet. I like the longtail thing for simplicity, direct shaft drive, zero mechanical losses.



PC: Lubrication, rusting, additional weight plus safety hazards with fast moving chain and sprockets would be consideration, if I were doing this (miniscule energy losses).



But the reason I'd like to move the motor is stability. Right now the motor's one of two heaviest objects in the boat, battery being the other, and it's mounted as high on the boat as physically possible to be able to do the longtail thing.



PC: There are much lighter/compact 120v motors rated about the same and they tend to be low cost because of mass production and surplus availability (treadmill motors, etc.).



Plus the longtail thing hurts maneuverability and keeping track of where the prop actually is is a pain. Repeatedly snagged it in weeds a ways behind me.




PC: If you use spring steel for the long tail the length can be much shorter ( down to 40" in some cases) and prop still run horizontal with less vibration due to shaft flexing. A raked back 5" small Aluminum prop from Asia is better for weeds and snaking thru bottom collisions.



I already added a battery box- not as good as a firewall, but now the boat won't necessarily be 2 inches deep in acid if the battery fails.


PC: AGM sealed lead battery will handle heavy currents much better than common deep discharge type, plus last much longer and can be "dump" charged quickly- info on e- boat drag racing available and will be helpful. If you should go longer distances or to sustained speed/acceleration loops with your pond you would need more battery capacity. Hydrogen is generated on charging only, but accumulates at the top of battery box, vent caps, etc. I've had pops even with an open battery top cover while under propulsion.

-F

Here's a link to flex shafts: http://www.boatdesign.net/forums/boat-design/efficient-solar-powered-electric-kayak-52833-6.html

Hope this helps.

PC

 

[Factoryninja]

I checked out the link to the other electric kayak stuff, but not much useful there, actually. It's all toy-scale stuff, the cordless drill hobby thing. The Turnigy motor looked slightly promising, 2 kw in a motor only weighing a couple of pounds, but 1: I'd have to effectively scrap everything I've made so far to build around it, and 2: again, it's starting over and throwing what would rapidly become a lot of money at it.

The junk I'm working from, I got for free.

As this has evolved, part of the goal here has become to make the application halfway solid just so I can see how far I can push that massive industrial motor. I got a hunch it will take an awful lot more than that tiny Turnigy motor which I'd suspect was somewhat overrated for hobby use. It may take 2 kw but I bet its lifespan at that level is measured in hours, maybe minutes.

The only limit on my collection of Baldor industrial motors appears to be how much they can take before they heat up intolerably or to the point of compromising lifespan... and judging by the industrial-grade level of overbuild and the results so far out of a motor supposedly rated at only about 400 watts being driven at around 2,000, I suspect this 1/2 horse would take 5-8 HP indefinitely.

I've got an even bigger one rated at 3/4 HP I think would probably happily accept being driven at well over 10 kw if I had anything like the hardware to apply that kind of current to it. I didn't bother trying to use the big boy because my 16 amp controller can't deliver much more than 2kw anyway and neither can my inverter. Plus which, before I put prop to water I had no idea what even a 1/2 hp motor would do nevermind going big.

I'd like to go with AGM, used to run an Optima bluetop for starting and a yellowtop for driving the system in my old teenage car, but again, $$$. I already had a pair of marine batteries lying around.

I might have tried to try and scavenge something like a treadmill motor, but again I'd be dealing with a motor that, when they say it's "1 hp" it's usually heavily padded for impressing the consumer and represents some theoretical possible maximum the motor can't actually do without burning out in 10 minutes.
When I was a teen in the philippines building audio amps in the early 90's, I was building stuff in the 500-watt range, big heavy stuff driving 12" subs. I used to laugh at the rich kids who'd buy a 700$ Sony bookshelf system advertising itself on the box "1,370 watts PMPO" which was a philippine market false-advertising made-up specification "peak music power output" intended to impress with big numbers. In no real universe could those systems get within 10% of the power they claimed- look through the back grill on the cheaper ones at the magnets on the speakers and the speaker itself says, "15 watt 8 ohms." Advertising people just pull whatever made-up numbers they think they can get away with out of their a$$ and then hedge against accusations of false advertising by claiming it's a rating based on a maximum possible power spike or some nonsense. Industrial grade stuff tends to be wildly -under- rated for reliability under 100% duty cycle and an expectation of almost literally indefinite lifespan. The motor I'm using has tens of thousands of hours on it from its former life driving a truly huge chain conveyor in a semiconductor processing machine throughout that machine's entire 18-year service life, but displays absolutely zero wear I can detect, including the bearings. There's a bit of carbon brush dust inside, that's all. Since it was in a protected environment it still appears brand-new fresh off the shelf, like it was manufactured yesterday.

I'm pretty sure if I did to a "1 hp" treadmill motor what I just did to a Baldor half-horse, the treadmill motor would have suffered a meltdown by the time it got to the far end of the pond.
-F

 

[Bod]

fun looking project! i plan to attempt something similar myself at some point as the trolling motors iv tried are useless and decent electric outboards are very pricey!

the idea to mount the motor low seems great how ever the chains and sprockets idea seems very unnecessary. much better to put a bearing through the hull for direct drive. i accept the concern about leaks but just do it properly?! mount the bearing at correct angle in a plate of some description then cut a hole in the hull and bolt it in with sealant. perfect seal... from my viewpoint the chain sprocket idea will end up with more water in the bilge as water will splash into the hole where the chain exits. you are building what is gonna be a very fast kayak so spray is inevitable.

have you considered a rudder? you can buy very lightweight rudders for kayaks now which could be made diy if thats your preference. direct drive would allow more space for a rudder.

i like that your are using ac power. seems to be the method that will give best all round performance and economic/energy efficiency. im planning to do this with something a bit bigger like a grp dinghy and putting flexi solar panels on it.