My cheap electric dinghy experiment

[Cadence]

Originally Posted by cptcptcpt

Don't forget a can of spinach to make the forearms bigger

I fights to the finish cause I eats my spinach.

[Colin A]

The only suggestion I would have would be to stick with Minn Kota or Motor guide as you can get parts from a lot of places for those motors and a few people even make aftermarket re pitched props for them. Trolling motors are great for low speed applications. Honestly if you redo some of the 24V ones with repitched props they can really move on a little aluminum boat .

[1950]

I use a MinKota 55lbs thrust trolling motor on an 8 ft lap strake wood dingy. It goes a little over 4 kn at full speed. I have gone over ten miles in river and open ocean on a old group 24 starting battery. I charge the battery from the house bank on the boat. I am very pleased with this setup.

[sec906]

There's another aspect to consider when weighing the various options. Don't forget that your motorized dinghy can be an emergency backup. It can be used to help pull or push your boat out of a bad spot, especially if your main engine is dead.

[SecondBase]

If you put the last three comments together it makes a case for 24 V. Colin - any speed observations you can share?

[Colin A]

Originally Posted by SecondBase

If you put the last three comments together it makes a case for 24 V. Colin - any speed observations you can share?

No it was a long time ago. A friend found an old OMC branded trolling motor it would push the 12' aluminum boat around where any trolling motor would (3 mph) We put a prop off a little gas outboard (maybe a cruise and carry? ) and it went pretty much hull speed and maybe a little over with the other prop (which I guess would be around 5 mph). This was one person on board. The amp draw went up thou drained the two car batts we had right quick. They pitch trolling motors to move a heavy boat against wind but not a light boat hence not ideal as primary propulsion. As I recall they are designed with a speed goal of 3.5-4mph. The issue is they don't seem to publish the pitch for their props so it's hard to tell.

[mitiempo]

Originally Posted by SecondBase

If you put the last three comments together it makes a case for 24 V. Colin - any speed observations you can share?

That means 2 batteries. More weight and complication.

[hellosailor]

A lithium battery might make sense. Consider, first you could save money by not buying the solar charger and controller at all. The lithium battery would be comparably 1/4 of the weight of the same amount of power in AGM, so it could be taken off or home to charge on a conventional charger. And they charge quickly.

Something in the 20-40A range would do nicely, since a lithium battery rated at 25A can be cycled nearly 100% and deliver that much power, while you'd need a 50A AGM in order to pull the same power at a 50% discharge rate, which really cuts the battery life down.

And there are some folks like Tracer who make the battery with a built-in charge controller, neoprene carry wrap (so it is fairly water resistant, good to go), charger and all. Pick it up like a junior bowling ball, or even put it in a bowling ball bag and carry it without anyone seeing a tempting battery to steal.

No solar panel, less wiring, no need for the bucket or box to integrate everything on the dink...The dollars just might be worth it. Just bear in mind, you only need a 50A lithium to replace 100A AGM. Arguably only a 33A lithium if you're really being kind to the AGM.

And the anti-theft aspect of "pick it up and take it home" really can't be beat.

[mitiempo]

Originally Posted by hellosailor

Pick it up like a junior bowling ball, or even put it in a bowling ball bag and carry it without anyone seeing a tempting battery to steal.

Watch out for the bowling ball thieves though.

[Lepke]

Originally Posted by SecondBase

Lepke,

Are you reporting 100% reliability over a year's time or more?

And what have been your total maintenance hours & dollars?

I'm kinda leading your questions into my thesis which is: Shouldn't serious Cruisers should be using electric propulsion on the dink not gas?

How come this isn't more common?

In my opinion, avoiding gasoline is a plus. Besides the explosive factor, it avoids the gas stability problems (even worse than diesel) that we have now thanks to the EPA.

I bought the motor used from Craigs list for $75. The po tried it on a too large boat as a trolling motor. Claimed it was only used once and the motor appeared so.
I've had the motor about a year w/o trouble. No failures, fuses, etc. I already had the charger and battery. I use the boat to do dock jobs, work on the side of the big boat, and operate about like a boat would going from an anchorage to shore. It's the smallest Minn-Kota motor and gives an estimated 3-4 knots in the Livingston. The battery is much easier to deal with than having fresh gas. I don't have to keep gas for just one engine. Battery is always topped off except I have left the motor on the lowest speed (by accident) for a day w/o seriously draining the battery. It gets left in the rain, etc.
It beats using a 2 cycle outboard. The 2hp Merc I used would never run more than 30 days w/o failure to start. Actually 30 days would be a record. Always a fuel problem, never solved, including new carb, lines, valve, etc. And I use fuel stabilizers. So far I haven't been able to give the 2 horse away.

[steve0h]

Originally Posted by hellosailor

A lithium battery might make sense. Consider, first you could save money by not buying the solar charger and controller at all. The lithium battery would be comparably 1/4 of the weight of the same amount of power in AGM, so it could be taken off or home to charge on a conventional charger. And they charge quickly.

Something in the 20-40A range would do nicely, since a lithium battery rated at 25A can be cycled nearly 100% and deliver that much power, while you'd need a 50A AGM in order to pull the same power at a 50% discharge rate, which really cuts the battery life down.

And there are some folks like Tracer who make the battery with a built-in charge controller, neoprene carry wrap (so it is fairly water resistant, good to go), charger and all. Pick it up like a junior bowling ball, or even put it in a bowling ball bag and carry it without anyone seeing a tempting battery to steal.

No solar panel, less wiring, no need for the bucket or box to integrate everything on the dink...The dollars just might be worth it. Just bear in mind, you only need a 50A lithium to replace 100A AGM. Arguably only a 33A lithium if you're really being kind to the AGM.

And the anti-theft aspect of "pick it up and take it home" really can't be beat.

I have to agree - you will be MUCH happier with LiPO batteries! So much more power that holds, where lead acid starts dropping off immediately. SOOOO much lighter, easier to handle. Initial expense higher, but long term they are actually less expensive, since they'll last 3-5 times longer than lead acid. MUST use a lithium chemistry solar charge controller, and while you are at it, get one that is MPPT, to get the most out of your solar panel. Yup, spendier. Worth every penny. That being said, the motor is the biggest initial expense, so you can wander down the cheaper route and it may be perfectly fine for the way you use it. I started out with a 55lb Minnkota, grp 90 deep cycle on my Hobie trimaran kayak, still toying with adding solar. Most of my experience is with an electric trike, does 45mph, goes 40 miles on 4 36v LiPO at full power - at that speed, even though geared to allow pedaling, the pedals might add 1.5mph if I really go Lance Armstrong on it - just not worth mentioning. Good for me though, dropped 90 pounds so far. It started out with lead acid, but I finally broke down and went with the lithium because the lead acids only lasted 1 year, and might have got 10 miles from a 12Ah pack. I did go solar with the lead acid batteries, rigged nine one hundred watt panels through 3 MPPT controllers (Morningstar - $750! but really good units - don't go with some of the cheapoes on Amazon, to get MPPT you will need to spend or be really disappointed) - I could cruise at 15-20 mph on solar power, but I had to put some panels on a trailer, and it got really crazy, especially in a cross wind. Same weight on the lithiums gets a LOT farther, and I really went solar to compensate for the shortcomings of lead acid, so my panels are sitting, waiting time for me to repair the ones that got hammered by a cross wind that flipped me over. The trike runs 72 volts, and the trolling motor is a 12v. I would go for as high a voltage as you can, they are much more efficient than low volts - too many amps to push.

[Peregrine1983]

I got out there today and installed the setup on my Takakat Lite dinghy. I have not installed the solar yet, but I was happy with the speed. I think this will work well for my purposes.

The gear:
Takakat Lite dinghy
55lb Newport Vessels trolling motor - $199
105 amp hour AGM battery from West Marine - $270

GPS had me at 4kts. The Newport Vessels website claims about 2 hours runtime at full throttle from a 100AH battery.

I posted a video here:

https://www.youtube.com/watch?v=8D0HvSKe4L0