The Electric Boat Thread

[Jeremy Harris]

Nice photo of the Sneakeasy. I'll admit to this design being the one that made me look closer at the simple designs from Phil Bolger - he seems very adept at producing easy to build boat designs that are also well-known to have a relatively low hull resistance.

I think I may opt for converting a canoe initially, just to do some power unit development. I've been giving the stability issue some thought, including some ideas of ways to counteract that "adverse roll" effect that Warren has helpfully pointed out.

I've now started to build an experimental stern tube assembly, using a length of 1" x 16g alloy tube with a machined flange brazed to the end to fit the direct-drive motor. I've ordered a length of 12mm diameter stainless steel tube to act as a prop shaft. This will be directly coupled to the motor shaft and run in a bearing at the prop end, with a simple lip seal to keep the water out. Hopefully this will be relatively low drag; I'm hoping that the slight reduction in motor efficiency from running at low-ish rpm will be offset by the large reduction in drag from not using a reduction drive. If this doesn't work, then I will need to looking at bigger diameter, lower Kv, motors, perhaps a modified bike hub motor or perhaps an "alter-motor" using a motorcycle alternator core.

Here's a photo of the motor mounted on the stern tube.



This assembly weighs just under 1kg (around 2.2 lbs) so is pretty light and on track for my target of no more than 10kg for the complete power system, including battery pack.

As an aside, that machined flange was simply push fitted on to the end of the tube and then brazed with Technoweld (see here: http://www.techno-weld.co.uk), a low-temperature alloy "welding" process that is pretty easy to do at home with a standard blowtorch.

Jeremy

[Lock]

I used to work for Rio Lago Cruise

Man, there's a blast from the past... How're they doing anyway? IIRC the original ownership of Rio Lago capsized (financially) shortly after launch and ETEC took over because Rio Lago still owed ETEC for the electrics.

What was interesting for me at the time was the ETEC fast charge capability...
Lock

[joco]

talking about eltric boat.

i got a small min kota 17 pound here.

would like to get some info on how long it could last on my kayak.6 but i would have to guive you all the battarie data for this.?


joco

[D-Man]

I run 2 motorguide motors on a 16 foot aluminum boat fully rigged. Front and Rear. With both on at the same time, I can go 4 mph on 12volts. With (2) 115ah 12v batteries, I can easily go for 12 hours on the lake at medium/high speeds.

[Jeremy Harris]

That's useful info, particularly as I've read reviews about the Motorguide units being a bit more efficient than the Minkota ones.

Assuming that you're discharging the batteries by no more than 80%, then it looks like your average power consumption is around 180 watts for the two motors, maybe a bit less. I suspect an alloy fishing boat is going to present at least double the water resistance of a canoe, may be more, so my guess as to the power needed might be close.

I'm hoping to be able to keep the average power drawn from the battery pack down to around 70 watts, hopefully less, although this will depend very much on optimising the design.

joco,
My guess is that a good estimate for the Minkota might be to have enough battery capacity to supply around 100 watts average power for the endurance you want, factoring in that a lead acid battery will only deliver 80% or so of its rated capacity. If you're using a 12V battery, then I'd guess that you may need around 10 Ah of capacity for every hour of endurance you want. If you're using a 24V battery pack, then you might need half this capacity per hour. You may find that these figures are a bit out, depending on the actual resistance of your kayak hull, but I suspect they are close enough for an initial set-up.

Jeremy

[paultrafalgar]

One of the delights of a canoe is being able to go up really shallow rivers. If you fix a motor through the bottom of the boat you immediately increase the draft of the boat. Also you introduce the potential leakiness of the hull/motor shaft joint. Also, you are opening yourself to difficulties deweeding the prop.
If you fix a 2" diameter bamboo pole, 6 foot long to the front of your cockpit and hang a float and motor on each end, you have done away with the problems mentioned above. What do you think?

[Lock]

...through the bottom ...increase the draft of the boat ...potential leakiness ...difficulties deweeding the prop.

Agree 1000%
Have also seen plans to affix Minnkota-type motors to the bottom of the rudder. Alternatively, might be able to run a chain drive through a pipe and mfgr.yer own electric outboard w/motor out of the water so only splashproof not fully waterproof? Even just go long-tail? Yah, anything to avoid throughhulls!
tks
Lock

[Jeremy Harris]

I agree that it's be nice to keep the shoal draft capability, but even with an outboard you still can't motor up shallow water. Whatever way you look at it, prop drive needs enough depth of water to work, whether it be an inboard or outboard installation. In fact. you can "steal" a bit, to reduce the draft, with an inboard by building a shallow tunnel in the centre of the hull, which makes such a rig able to motor in shallower water than an outboard.

I'm really looking to build something for use in fairly slow moving, fairly deep, inland waterways and lakes. I want the best efficiency I can get from the whole system, and am not prepared to accept the 30%+ losses from any form of belt/gear/chain transmission (at these low power levels friction in the transmission really saps efficiency). Although a bike chain can be efficient at moderate power levels, I've found that it still saps around 10 - 15 watts or more. Better that the belt drive which needed about 15 watts to turn, but still a big loss.

I'm working on making the prop swing up for beaching and weed clearance and will post a picture IF I can get it to work. One option I've looked at is to run a "centreboard" case down the stern of the canoe, with the slot coming right out aft. This would allow the prop to just swing up behind the stern. The difficulty this arrangement has is with placing the rudder, but I'm trying to make it an "all-in-one" solution, with the rudder swinging up with the stern tube.

The advantage of the stern tube is that sealing is easy, just a lip seal on the lower end and fill the thing with light oil. The pressure of the oil matches the water pressure, so in practice the seal isn't really being asked to do much. The inboard end of the stern tube is above the water level, so needs nothing more than an ordinary sealed bearing.

Jeremy

[Lock]

`Kay... Don't know what I am talking about so I can think "freely"

Thinking paddlewheel...

...hang on... think of a four-foot wide cylinder that is the foot of a isosceles triangle where the apex joins to the stern with a joint like a bicycle head tube (so only motion is side-to-side), and the cylinder floats to provide lateral stability (instead of ama/proa) for the whole boat but also has built in magnets and coils so can be spun with electrons? So no chain or sprockets etc, direct drive brushless hub motor, wound for very low rpms? If cylinder is buoyant enough could add netting in the triangle for additional cargo space.

No weed problems (maybe) with paddlewheels? Triangle steerable via cables to provide steering?

Just my $0.02 Cdn
Lock

[paultrafalgar]

You'll need a patent for that idea, Lock, it's a goodun!
So to elaborate the arrangement is like an old-fashioned lawn-roller. Each end of the shafts there is a disc with many coil/magnets stuck around the periphery and the central roller has corresponding coils/magnet opposite those on the end caps. Along the length of the "drum" are lengthwise struts glue to the drum which act as paddle-wheels. And just like a push trailer for an ebike, the whole arrangement can be decoupled and left behind if you want a workout.
Nice!
You could probably use a stepper-type motor for such a slow rotating drum.

[Jeremy Harris]

Neat idea, a bit like a hub motor for boats.

I wonder how efficient a paddle wheel can be? It works pretty well for rowers/paddlers, who seem to be able to convert a lot of their power input into useful work. I like the idea of freedom from weed clogging, too, plus it gives a good shoal draft ability.

Definitely worth a bit more research, particularly as the motor rotor could be integrated into the paddlewheel.

Jeremy

[Lock]

Read this thread:
http://www.boatdesign.net/forums/surface-drives/paddlewheel-25292.html

...and be sure to watch the video!
http://www.youtube.com/watch?v=-QjRM-cQpHw

[Jeremy Harris]

Interestingly, it seems as if paddle wheels can be as efficient, or even slightly more efficient, than propellers, at least at low speeds (about 70% seems to be the figure quoted in several places; few boat props do better than about 60%).

A direct drive bike hub motor with a high turn count, something like a Crystalyte 4011, would be able to directly drive a paddle wheel of around 0.5m diameter with reasonable efficiency, for typical canoe speeds of around 4 to 5 kts. It'd be an interesting project to build an add-on beam for a canoe, with a separately driven wheel on each side. Such a design would be able to operate in any depth of water that the canoe would float in, plus would be very manoeuvrable, particularly if reversing controllers were used.

Jeremy

[Lock]

Rick Willoughby is a very capable guy... Some videos here:
http://www.youtube.com/RickWilloughby

In the thread he says:
"The efficiency is primarily related to the slip of the paddles. The peripheral speed would ideally be 10% faster than the boat speed meaning the paddlewheel would be a bit less than 90% efficient. This usually results in a massive wheel relative to the boat. A wheel of practical proportions can usually give better than 75%."

Another problem mentioned was windage...

So I am not sure *how* massive except that one large "roller" aft might be more esthetic than two larger rollers athwartship with OD managed down by increasing beam of the one longer aft cylinder...

FloatingTrike.jpg (55.09 KiB) Viewed 1389 times

[Jeremy Harris]

An electric version of that water trike might be fun, perhaps with a few kW of brushless power inside those big wheels..............

Anyway, I've been giving some more thought to the thorny problem of getting a stern tube fitted to a canoe and have had an idea. The problem with a canoe hull is that it doesn't have much rocker, so the prop shaft needs to run at a fairly steep angle, reducing efficiency a bit. I've got one of those flexible drive shafts in the workshop, and it's pretty low drag as long as it's not asked to bend too sharply. The gentle bend to go through the hull and hook up to a short propeller shaft on a skeg is easy, and means very little bearing drag. it also makes sealing the hole in the hull fairly simple, too.

The flexible shaft would make retracting the prop up into a weed box inside the stern of the canoe easy, the shaft can be protected in the retracted position with a very shallow keel, just to stop the shaft getting crushed when/if the canoe gets beached. All it needs is a bit of flexible hose slipped over the flexible shaft to seal it, with a new shaft and lip seal at the prop end fitted into a short length of rigid tube. I could fill it with oil as I'd planned to do with the solid stern tube, to both lubricate the bearings and keep the water out.

Rather than butcher the old shaft I have in the workshop, which only has plain bearings anyway, I've ordered a new one with ball races at either end. I've seen these used on one or two of the human powered boat sites, so it looks like it should work OK.

Jeremy

[northernmike]

Jeremy, your flex drive shaft is perfect! I used to race an R/C boat with a flexible shaft, an ECO class mono - the MOST important thing in the equation is the prop..

We were in the habit of cutting down Octura props - by 1/2 - keeping the trailing edge, effectively re-profiling surface piercing props to look more like airplane propellers.

Here are some close to equivalent from Graupner, but ours were even thinner:



This let them wind WAY up - like 27,000rpm - and MAN they pushed. I bet if you took a trolling motor prop and modified it you'd have good results - but tweaking is key. Basically tune the prop so the motor spins at the most efficient speed - just keep cutting it down until the motor speed load is correct, and then tweak the pitch.

Have you seen these?



Torqueedo, electric outboard from Germany using outrunners and LiPo

[Jeremy Harris]

Interesting that you mention those props, as I have an old bronze Octura X482 prop sat here on my desk that was machined down slightly and used as a thruster in a small underwater ROV. It was fitted into a Kort nozzle and produced about 10lbs of thrust, I believe, even though it's less than 3" in diameter. It was directly driven by a brush motor at a fairly high rpm, so wasn't too efficient. It looks just like the ones in your picture, though.

I may experiment with using a nozzle, probably a Rice type, to increase prop efficiency at the low cruise speeds I need. All I've read suggests that nozzles can be useful at slow speeds.

I've read the specs on that Torqeedo trolling motor and added them to a list of data I've been collecting on motor power, thrust, boat speed etc that I've been collating to try and get an idea on the sort of real-world efficiency that such a unit can give. As far as I can tell, these trolling motors are optimised to give a high static thrust in order to drive high-resistance fishing boats. For a very low drag boat, like a canoe, the trolling motors are none too efficient. They seem to be designed a bit like "tug boat" propulsion systems, but can probably be improved with a better prop. They do have very high drag underwater parts though, so I'm hoping I can make a significant improvement with a flex drive.

The prop I have to play with (from my junk box) is a two blade, 8" diameter, about 8" pitch alloy one from a small boat inboard motor of some description. It has a hub diameter of about 1 1/4", so has the potential to be fairly low drag. The question to be answered is whether or not it's an efficient shape. Some of the stuff that the human powered boat people have been doing seems to show that higher aspect ratio (longer, thinner) props are more efficient, although the early modelling I've done on what I think are my prop specs seems to show that it might be around 65 to 70% efficient at the speed and rpm I think I'll be running it at.

These drill flex drives have the advantage of being nice and cheap, although it remains to be seen as to how well they stand up to being used like this.

Jeremy

[Lock]

All I've read suggests that nozzles can be useful at slow speeds.

My understanding is not so much slower speeds but with a narrow speed range that prop and nozzle are designed for. They are ubiquitous in the tug industry where the boats are towing loads for long distances at a target speed. Fuel savings (ie efficiencies) add up.
Outside the narrow speed range they are designed for efficiency drops off fast. Can be offset by designing the nozzle as steerable to obviate any separate rudder. Oh yah, and designed right they are excellent weed eaters
tks
Lock

[paultrafalgar]

Can you explain "nozzle" and "trolling" for the nautical virgins amongst us, please?

[Lock]

"Trolling" is just a term from fishing that implies a slow steady speed w/lines or net in the water...

Nozzle ("Kort nozzle" or "Rice nozzle" after designer/promoters) on a tug:

Kort.jpg (55.12 KiB) Viewed 3122 times

...and in the air termed "ducted fans" as seen on hovercraft, plus the electric jet model builders have been using them quite a bit like this:

EDF.jpg (13.9 KiB) Viewed 3119 times

...Folks that have been making emotor outboards etc have reported eff.gains by adding these nozzles also.

whispermotor.jpg

(13.93 KiB) Downloaded 1347 times

Lock

[paultrafalgar]

Ta, Lock!

[Jeremy Harris]

I agree about nozzle efficiency and the design speed range, but it might work for an inland waters cruising craft, where the speed will be a near constant 4mph or so.

Whilst digging out more stuff on efficient low power propulsion systems for boats, I came across this: http://www.autocanoe.com/. Looks like a fun candidate for both road and water use, plus it includes paddles........

Jeremy

[Lock]

I came across this: http://www.autocanoe.com/. Looks like a fun candidate for both road and water use, plus it includes paddles...

Hmmmm... I'd be cautious about anything touted using an oxymoron like "Happy Wife"...<hehe>

In that pic:

Autocanoe.jpg

(104.16 KiB) Downloaded 26 times

How exactly would you (well, female brought along for purpose) actually paddle the thing? Wouldn't the wheel cowlings be in the way? Could oars w/locks be employed instead? Dunno. Also, in the same "happy" pic, there seems to be quite a bit of turbulence/water being lifted/left behind by the paddles/wheels?

My suspicion is that the Autocanoe serves better on the hard than afloat!

And, according to the Internet Archive Wayback Machine:
http://web.archive.org/web/20031217064815/http://www.autocanoe.com/

The part about "Coming soon Electric powered Autocanoe!" has been posted on their site since December 2003 approx.? Hmmmmmmm.....

No pics on the site yet (after 5-6yrs) of smiling happy clients who have built the plans?

Never mind a movie of how it performs on land, I want to see/know how it performs on water!
...and if they are still married.
Tks
Lock

[Lock]

I should qualify my remarks about monomarans esp.canoes... I had a couple of classmates in high school that went away for a canoing weekend once and never came back

I stumbled across multihulls a long time ago and never looked back.
tks
Lock

[John in CR]

It's not a narrow range where nozzles are more efficient, just below a certain speed of near 20 knots where the added drag through the water of the nozzle overcomes the decreased slippage of using the nozzle. The prop required is completely different as with ducted fans and that Kort nozzle on the tug. Weeds and sticks would be the biggest concern to me though with a small shallow water rig.

I think a jet drive would be the ideal for a canoe type boat using an electric RC motor, but the design info just isn't out there for proper sizing to match your motor and speed. Jetski type stuff is too big, and the RC stuff is too small with questionable durability. I did run across a stainless rig that a guy machined for a big RC boat a few years ago that had to be pushing well over 50lbs of thrust, but I couldn't find any contact info for him.

My son and I are going to build an electric surfboard using a pair of inrunners and RC boat jet drives, but that's been put off till at least July.

John