The Electric Boat Thread

[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 3181 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 3178 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

[Lock]

Tks John

Good page here about nozzles:
http://www.solarnavigator.net/kort_nozzle.htm

*Usually* jet drives only come into play at much higher speeds?
Lock

[Jeremy Harris]

Thanks for that, John. I had wondered when surfing the boat fora as to whether some posts about an electric surfboard were by you - although I guess there must be a few "John"s in CR!

Conventional jet drives/pump jets are pretty inefficient at low speeds, as they generate thrust by moving a small mass of water relatively quickly. For good efficiency we need to move an adequate mass of water backwards at a velocity that is just enough to provide enough thrust to balance the drag of the boat. I think it should be possible to design a high volume, low velocity, jet drive for good efficiency, but the frictional flow losses in the duct would need to be taken into account when comparing efficiency with a prop.

It might be possible to use something like a centrifugal pump, rather than an axial flow impeller, to build a low velocity jet. I've no idea as to how viable such an approach might be, but there is a ready source of parts available in the form of old turbocharger parts that might be worth exploiting. I'm guessing that a centrifugal pump might be more weed tolerant than a prop or nozzle system though.

Jeremy

[www.recumbents.com]

We found that the model airplane props like the 12x12 or 14x14 APC glass filled props work best for low power applications like human power boats. I suspect that they would work great with a model airplane motor as well, but you'd need to gear it down to around 300RPM for boats use. Kort nozzles, squid drives, flappy wings, sidewheelers, etc have all been tried, but the prop is most efficient. Also it helps that the APC props are cheap, at under $20 each. Worried about weeds? Make it a "center drive" system to make it easy to lift out of the water to clean the prop.

-Warren.

[joco]

look at those motor guys.

http://www.wmjmarine.com/engine-system- ... uster.html


joco

[Jeremy Harris]

I've made some progress with my RC brushless motor boat drive system. I found a right angle gearbox, intended for use with an electric drill, that has good bearings, and alloy case and best of all helical bevel gears. It has a slight reduction ratio, too, just 1.25:1, but that helps a bit.

Here's a picture of the unit, before I've made up a skeg and a fairing around the lower leg (to reduce drag):



I machined up alloy housings to hold the motor shaft and also an additional bearing and lip seal for the prop shaft. The propshaft is machined from a bit of stainless bar. Next stage is to test it in water, it runs fine in air and seems to have virtually no drag on the motor, which is good.

Jeremy

[dontsendbubbamail]

How about a description and closeup picture of the lip seal? I would like to understand how you are doing that.

Bubba

[Jeremy Harris]

The seal is just an ordinary nitrile rubber oil seal, as used in cars, trailer axle bearings etc, usually to keep oil in. They work just as well at keeping stuff like water out. I got mine from this ebay seller: http://cgi.ebay.co.uk/12X24X7mm-ROTARY- ... dZViewItem

Unfortunately I can't easily take a close up of the seal now, as I've loctited the screw that holds the prop on, and I'd need to take it off to get a decent picture.

I've been working on a boat design though, making models for a tortured ply canoe. I got the idea from this website: http://www.sloejd-kbh.dk/tema/skibe/Kano_GB/Canoe.html

Here are some pictures of the models I've made so far, the centre one is closest to what I think I'll build:



Jeremy

[dontsendbubbamail]

Now I understand. I thought that you were talking about something you had machined.

Bubba

[12p3phPMDC]

The drive is coming out nicely Jeremy.

Are you going to mount a bearing and a seal
on the bottom of the boat in order to steer unit?
Or are you going to mount like an outboard?

How do you plan on steering the unit, a simple lever arm with reverse steering?

[Jeremy Harris]

Thanks for the compliment. The plan at the moment (it may change!) is to fit the drive leg into a hinged section of the hull at the stern. I want this to look like an unpowered canoe as far as possible, and would prefer not to mount the motor like an outboard for that reason.

I'm aiming to have a narrow transom at the stern, with the sealed box rear triangular stern section, containing the motor, removable. The motor shaft will be inside a sealed tube with steering bearings, probably made from Nylon. The lower part that sticks out the bottom of the triangular stern section will be faired and fitted with a skeg to protect the prop. The motor itself will be well above the waterline hidden inside the dummy stern section.

This arrangement will allow the whole stern section to be pivoted upwards from the top edge of the false transom, allowing the prop to be swung clear of the water for shallows, clearing weed etc. The electrical connections to the motor will be by waterproof connector and I'm planning on arranging for the steering to be connected automatically by a push/pull rocker arm, with the push/pull connections poking through the false transom, well above the waterline. This system will be very like those used to connect flying controls on some removable or folding wing aircraft (a look at some photo's of old carrier aircraft with their wings folded may help show how this works). I could opt for a steering cable, but it'd be one more thing to connect/disconnect when the motor "box" is removed, plus it might limit the hinging movement a bit.

I'm finishing off a 1/8th scale ply model of the canoe at the moment, to see how things may go. Next stage is to build the canoe full scale and see if things work as planned.

Jeremy

[Zoot Katz]

I sure liked the slipper design.

How large a rudder would need to be attached to a canoe?
Seems simpler than steering the prop shaft and no penalty if it only has to be as deep as the skeg or maybe kick up for beaching.

[dontsendbubbamail]

I have been running a 17 lb trolling motor on an 18 foot canoe. Anything extra in the water in addition to the motor causes extra drag. It may be debatable as to how much drag. If there is any wind, it can push the canoe around and make staying on course or turning very hard to impossible unless I put a paddle into the water and use it as a dagger board. A small keel down the length of the boat would be a solution if you don't care about quick turns. I plan to make a bracket to hold the paddle so that I can take it out when not needed.

My vote would be for a removal dagger board and no rudder.

Bubba

[Jeremy Harris]

Zoot, I like the slipper design too, but it's a bit harder to make than a canoe, I think, plus would need a trailer. I'm using the canoe as a starting point, to see how well the motor etc works. If it's a success, then I think I may go for something a big bigger, like the slipper launch, with a fully solar power system. I doubt I'll be able to do more than augment the battery power with solar cells on the canoe, without having ungainly solar panels stuck everywhere. I should be able to mount enough cells on the canoe to get maybe 20 watts of boost though, which will make a significant difference to range, plus allow for solar charging whenever the canoe is sitting idle.

Bubba, Thanks for the tip about the directional stability. I think I'll add a small keel down the length of the canoe, both to fix this and act as a bit of hull protection. I'll carry a paddle as well, so I can use that for any really sharp turns, although I hope that just turning the motor will be enough most of the time.

Jeremy

[dontsendbubbamail]

You may want to consider some kind of remote steering. With my 18 foot canoe, if I sit at the back and tried to steer, the front would stick up in the air and act as a big weather vain. I solved this problem by making a transom that allowed me to put the motor directly behind the canoe. The head of the trolling motor was removed and the wires extended so that I could sit in the middle of the canoe to control the speed. A board was mounted in the place of the head and two ropes tied to the ends so that I could steer from the middle of the canoe.

A flat stern canoe would be my first choice even if it is not as efficient as a double end canoe. A well behind the rear seat is my second choice. My third would a transom like I have.

It is really cool as to how close you can get up to wild life with this setup. I have been cruising up a river and come within 25 feet of a heard of deer drinking from the river and not spooked them.

Bubba

[John in CR]

Jeremy,

One thing to keep in mind with steerable thrust is that you want to build a stable canoe, since the thrust when turning will also try to make it flip. Of course batteries in the bottom will help counter that effect, but be careful with that high output RC motor.

John