Trolling Motor(s) for Primary Propulsion of 15' AL 'skiff'

Twin 34 Enduras with P+G Controller now operational..

Hi everyone! Took me a while to get back to this, but I finally got my jonboat operational with the P+G P8 wheelchair controller and twin Enduras. Some info at:

http://www.cfnet.net/tm/v2.htm

And messabout - sorry I didn't get back to see your offer! The P8 I used came off an Invacare. If you have the thing still, put at least the cables and connectors on eBay. While the p8 (if you have it) needs to be modified so it will run without the brake solenoids, the cables/connectors are hard to find.

Comments, questions, suggestions all appreciated!

Chris

 

cool. So how well does it work?

 

Hi srimes,

Well, I think the wheelchair controller and skid-steer is working great with the two Endura 34's.

But the jonboat is an efficiency disaster. Sort of 'pushing a brick lengthwise thru the water'.

I really need a transomless/swallowtail/canoe-style efficient, light, long, displacement design alternative.

Ultimately I still want to weld up an ELCO-style cruiser out of AL. But I'm not likely to get to it this season.

Perhaps I can throw together some kind of light Catamaran - with canoes, plastic cheap kayaks, AL culvert tubes, whatever - for the time being. Or just keep the jonboat cruising at 2.4 - which is OK - after the sun goes down.

As it is, I get maybe 2.6 mph at 20A into each motor. It will peak at 3.4 mph or so before the 30A breaker in the 24V supply line trips. This with the standard 2-blade 'flexible' Endura props - probably efficiency disasters as well.

As always, suggestions, comments, ideas always appreciated!
Chris

 

You have proven that joystick control can work, if that was your goal.

Is there any advantages to simpler steering is the question.

The power draw for the speed you are getting is way too high if you're looking for efficiency. Could be other things causing this besides your jonboat. Even a flying brick should not take that much power for the slow speeds you have indicated.

If you don't have deep cycle batteries, they won't last long. Even the dual purpose marine type.

Weedless props are very inefficient, you might try google of shorty evans which sells older non weedless- if they are still in business.

Your wiring losses might be too high, need jumper cable type stuff for the 20+ amps you are drawing.

Just some thoughts off the top of my head, hope it helps.


Porta

 

Thanks Porta,

The P+G P8 wheelchair 4Q/joystick 50A 24V 'battlebot' package is pretty cheap on eBay - at least it used to be - so I thought trying a joystick might beat squirming around with the tiller on the Endura.

For 'evening cruising' on calm water it works conveniently. But if its rough, my bouncing around transmits to the joystick - not so good

As you point out - efficiency is terrible. But the batteries I have seem up to it. They are deep cycle full marine - not 'dual purpose' marine. While they are WALMART, they are manufactured by Johnson Products. I rarely discharge them more than 30% - and even after 2 years now (2007 date code) they seem fine. I charge them with two 3-stage B + D 12V/12A chargers

Yes, 2 of 'em at 60 lbs each is heavy. But I never really could see getting LiPO, AGM or whatever that might weigh less - as I am 210 lbs, the AL jonboat perhaps 100 - 150 lbs, the motors another 30 lbs - so as a percentage displacement difference, expensive but lightweight batteries didn't seem worth it to consider.

With a single MK 34 I used an aftermarket 3-blade Kipawa prop. To keep the twin arrangement balanced, I switched back to stock to match the one on the new second motor.

I'm going to put the Kipawa back on one - run it 'unbalanced' - and then try to get the power going into each motor in a 'straight ahead' joystick condition. That should tell me if getting a second Kipawa is worth it.

I've only put a few hours on this arrangement - the P8 replaced a single channel electric bike Curtis 1505. (w/5k pot controller) But the P8 does seem to run hot to me - even at only 20A/channel. We shall see.

Next I'm toying with running the 2 motors in series - back on the 1505, or perhaps a 36V controller (maybe a Kelly). Should reduce wiring currents and perhaps switching losses (run at a higher % of V in.) - but of course I'll need identical props. Then its back to a rudder/tiller arrangement - something out of plywood with hinges for a pivot etc.

Further thoughts always appreciated!
Chris

 

why not try playing around with the trim to see if it can easily be more efficient? I like how you put the batteries in the front to balance it out. I'd try:
a) sitting in the middle w/ the batteries still in front for nose-heavy trim, and
b) try running the boat backwards like that.

for a more efficient boat cheap it's hard to beat building on with plywood. Stitch-and-glue or even screw-and-glue with chine logs is quick and cheap. Fun too.

 

Thanks srimes,

Sitting in the middle definitely helps. With the transom now up more out of the water, drag is definitely down - even though the bow is almost submerged. (even small chop crashes over - so its not practical).

I might go back to looking at plywood - maybe again for a catamaran prototype etc. I did look at stitch' in-glue - a number of the Glen-L designs, but here in Lake George, NY the shore is often very rocky or bottom covered with good size boulders. Since I need to beach my little electric often, I pretty much have settled on welded aluminum - not the usual 1/8 - .125 - but 1/10 - .100 - which is enough I believe, and is of course lighter. But this won't happen this season.

I'm going to try the propeller tests next - when the thunderstorms abate..

 

When I've tinkered with motors in series years ago, I got erratic performance. This was in another application, not with troll motors though. The power delivered by each motor varies from second to second depending on what is happening loadwise with the other motor is what seemed to occur. Almost act like 2 variable resistors in series. If one momentarily draws more power, then the other is left with less. When I ran at no load and stalled the spinning shaft of one motor, then the other motor would speed up in response.

Hope this helps.

Porta

 

Thanks Porta,

Fortunately, Lake George has little millfoil or other weeds that might stall one of the two motors. But if I see that series is workable, what you mention suggests that I probably should put a breaker in series as well. I've got a couple extra 50A, and one of them should at least protect the unstalled motor - just in case.

Chris

 

The rain finally stopped and this morning was clear and calm. Got to compare the aftermarket Kipawa 314 propeller with the stock MK 'weedless'.

At least for this setup, I won't be spending money for a second Kipawa.

With the Kipawa on it, at 40A into it, the MK 34 showed 10.0 Vin - and jonboat speed was 2.7 - 2.8 mph. Putting back the stock prop, at 40A into it, Vin was 10.75 - speed 3.0 mph.

So the Kipawa is going the wrong direction - more current, less voltage, less watts, more losses. (But it does make sense, since the Kipawa was designed for the stock 12V MK - where its never going to actually see 12V because of the wire/switch losses - and will deliver more than the stock prop at a given MVin.)

At 30A/motor, 9Vin, with stock props its about the same 2.8 - 2.7mph as it was with the Kipawa. But the P8 wheelchair controller - with 24Vin - is now delivering very short power pulses (to 'average' 9V) with the same 20kHz switching losses. Seems likely one reason why it runs so hot and battery drain seems higher than it should be..

I am going to rig up some cables for series running the motors. Makes me wonder if the 'most efficient setup' for the p8 might actually be 4 motors - 2 series pairs. Ugh.

Comments, thoughts always appreciated.
Chris