Electric motor options for inflatable dinghy

[Peregrine1983]

Not sure if you’re asking me, but I was able to get about 3.5 knots in flat calm with just myself and the battery aboard my Takakat lite 12’ dinghy.

[sparrowhawk1]

Yes I took too long to be able to edit that question in to my original response let me tell you that's(3.5) awesome. Oops wrong person. Still cool and I totally understand switching to gas for greater range.

[Peregrine1983]

Yeah it worked well for going to the mooring and back aside from the charging issue. I just brought the battery home a few times to charge it. Keep in mind though this is a 55lb trolling motor on a light catamaran style dinghy. I nearly always opted for speed setting 2 or 3 and rarely ever 4 bc I wanted to conserve juice, so I was usually going slower.

[liquidice]

Originally Posted by Peregrine1983

Not sure if you’re asking me, but I was able to get about 3.5 knots in flat calm with just myself and the battery aboard my Takakat lite 12’ dinghy.

Thanks for the earlier, very complete final reply. (Those are close to my same speeds, also flat).Gasoline is so so powerful. 33.7 kwH in a gallon. (Per EPA) A small 4 stroke is very efficient, powerful, and I agree ethanol free is the way to go (I can’t get started on the ethanol lobby again...). When the safety of your loved ones is on the line, you do what it takes, what works. Electric has come a long way, but just like in the endless “is X a blue water boat?” threads, you use the right tool for the job. As you say, electric is great for the mooring ball run. More people are choosing electric for this job, or rowing, and it’s great. But just like yard tools, if your mowing a city yard, electric is great. If you’re mowing the highway embankment, gas is the way to go.

[liquidice]

Originally Posted by sparrowhawk1

I think everyone would like to know what speeds you get with your inflatable dinghy and 30 pound thrust

Yes, as below I am not sure, but it feels fast and we use it to go in harbors or anchorages or hop around little islands in shoaly places. I’d say like 3 kts? 2.5? That’s with 450 lbs of people, a big old marine battery, and some food and drinks. For sure I cruise right past kayakers, dinghy rowers, kids sailing optimists, and all the other harbor excitement. I’ll look to measure top speed. Also I keep a cycle of batteries so I’m always cruising a full one.

[Peregrine1983]

Originally Posted by liquidice

Thanks for the earlier, very complete final reply. (Those are close to my same speeds, also flat).Gasoline is so so powerful. 33.7 kwH in a gallon. (Per EPA) A small 4 stroke is very efficient, powerful, and I agree ethanol free is the way to go (I can’t get started on the ethanol lobby again...). When the safety of your loved ones is on the line, you do what it takes, what works. Electric has come a long way, but just like in the endless “is X a blue water boat?” threads, you use the right tool for the job. As you say, electric is great for the mooring ball run. More people are choosing electric for this job, or rowing, and it’s great. But just like yard tools, if your mowing a city yard, electric is great. If you’re mowing the highway embankment, gas is the way to go.

True words my friend!

[rsn48]

I'm planning on installing either the largest Efoy or middle powered one; I'm wondering how well that electrical system will charge the lithium battery of an Epropulsion.

[sparrowhawk1]

Originally Posted by liquidice

Sounds like the battery is being discharged normally and then you get the low thrust. In my experience with budget solar solutions, the panels charge slower and slower as you get towards full, and many panels lack the voltage to charge to full. There are many and more theoretical physicists and electrical engineers on the forum, and I wouldn’t presume to challenge their authority. It sounds like you’re good with the new battery which comes +\- 80% charged. As you use the charge to spin the prop, it goes down, and then you recharge with the solar. Most panels I see in use charge 12v deep cycle marine batteries up to 50% and it takes at least a day or more depending on the latitude/panel(s)/cloud cover/angle/discharge prevention in the solar setup. Most solar setups I see are used to maintain the charge in the house battery bank for lighting, radio, and other low-draw applications.
I use a MinnKota 30 lbs motor on a 8’ rollup floor zodiac. I use a 12v deep cycle battery to power it. The working life on a “full “ charge depends on load but generally it runs fine for at least an hour. I charge the battery on shore power using a battery tender brand battery charger/maintainer and it takes 8 hours to get back from below 50% to 50%, and a full day to go from 50 to 80, and another day from 80 to 100.
I suggest 2 batteries, one charging on the big boat while the other is in use. Have you checked your charge levels? Maybe you’re not getting charged back up just from solar by the time you’re looking to use the battery again.

After using my system for a few years I figured I'd give an update. I can do a 15-minute run to shore 15 minute back every sunny day. You definitely have some misconception about how solar works especially a 4 amp Max on a 100 amp hour battery. It will put out maximum until my battery voltage reaches 14.6 which at 4 amps means it's basically topped. Then it will cut back on the amperage holding it at 14.6 (cheap controller ) most solar panels put out 20 volts so they have no problem topping up the batteries, actually that's what they're best at. I don't go to shore everyday so on those days the basically full battery charges all day so I know it's being held at 100% at least once a week also the fact that it hits 14.6 well before noon lets me know it's topped. having the solar panel hooked up all the time makes the battery voltage a few tenths of a volt higher when running. the difference between 12 volts and 12.4 volts is huge. I try not to ever drive it more than a half hour each way, and if I use it for more than 15 minutes each way I'll let it charge completely the next day. like my dad used to say the proof of the pudding is in the tasting. But the math also works out. conservatively the solar panel will put out the equivalent of 4 amps for 5 hours and 1/2 hour at 30 amps is 15 amps so everyday I'm replacing what is used with at least 1/4 more. also having the 4 amps going in when I'm running it cuts down on the peukert effect slightly. Having a voltmeter is critical it can be used like a fuel gauge, when the motor is running I never run below 12 volts. Watching the voltage drop as I'm using it can give me a good idea of the state of charge of the battery. I have an extension cord connected from my house batteries to a boost converter so if I had to go to shore on cloudy days I could use the house to charge.

[sparrowhawk1]

For going longer distances when the wind is good I use a kayak Spinnaker. The umbrella works as well and is easier to deploy but has to be held on to.