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wyb2 · 15-10-2017, 08:16

Quote:

Originally Posted by mitiempo

Most seem to have missed my earlier post. A 100 AH battery only gives you 100 AH @ a 5 amp draw. At 50 amps ( what a 55 lb electric outboard uses at full throttle) the battery will give you less than 70 AH. If not going below 50% SOC for battery life that gives you 35 or less AH which is about 40 minutes at full throttle or less.

Yeah I saw it, I was going off the 60-70 ah number under the assumption that I would choose getting back to the boat over proper battery maintenance. The 40 min number definitely seems more reasonable, maybe even still a little high. I've only run ours on full throttle for 10 min or so at a time, and the motor's "charge indicator" drops at a pretty alarming rate.

At throttle position 3 or 4 (of 5) I can happily motor around for an hour or so without worrying, but against a stiff breeze or current, sometimes that makes for painfully slow going.

Captain Puget · 15-10-2017, 12:53

The battery is a little expensive, but a carbon foam battery (firefly) might prove more durable/ longer lasting and avoid the 50% drainage limit problem.

Divevac · 16-10-2017, 08:21

We have no desire to have gasoline on board whatsoever while cruising. With plenty of solar and wind generating capacity, your interesting project fits squarely within our thinking. What make and model of trolling motor have you been using?

Peregrine1983 · 16-10-2017, 08:32

Quote:

Originally Posted by waterman480

The only issue is that salt water rated trolling motors are about double the cost. Not sure of the lifespan of the fresh water motors in salt water.

This is marketed as a salt water/fresh water motor. It's the Newport Vessels 55lb NV series and it was $199.

https://newportvessels.com/electric-...ust-nv-series/

Scout 30 · 16-10-2017, 08:58

I think that for this to be a truly viable option the battery needs to be charged on the mother ship from a large solar array or generator. The best configuration would include 2 batteries with one being charged while the other is in use. I also think an efficient rowing/sailing dinghy would be the best hull type for this use.

Peregrine1983 · 16-10-2017, 09:24

Quote:

Originally Posted by Scout 30

I think that for this to be a truly viable option the battery needs to be charged on the mother ship from a large solar array or generator. The best configuration would include 2 batteries with one being charged while the other is in use. I also think an efficient rowing/sailing dinghy would be the best hull type for this use.

Bottom line is it all depends on your use of the dink. Several trips every day at full throttle will run down the batt pretty quick just on solar.

I want to devise a quick-connect charging system to hook the dink up to the mothership's system for cruising.

Scout 30 · 16-10-2017, 10:31

Quote:

Originally Posted by Peregrine1983

Bottom line is it all depends on your use of the dink. Several trips every day at full throttle will run down the batt pretty quick just on solar.

I want to devise a quick-connect charging system to hook the dink up to the mothership's system for cruising.

With a system like this I'd never run it at full throttle unless it was necessary to battle a head wind. The main thing is you've got to be able to completely recharge the battery every day. If you can't do that this is just a lesson in futility. Of course the less you use it the less you have to recharge it but if all this system does is limit how much you can use your dinghy then it's not really viable. Being able to recharge the battery quickly & completely is the key to this working. Solar is an awesome idea. You just need a lot more of it.

JamuJoe · 02-11-2017, 14:03

I may have missed this, but what size & weight is your dinghy? I'm considering the same project with my dinghy with either the 62 lb or 86 lb thrust Newport Vessels trolling motor. Their reps have been good at responding to my queries, but not very encouraging.

JamuJoe · 02-11-2017, 14:20

Quote:

Originally Posted by wyb2

We have an eerily similar setup (200 W solar, victron blue, charging 4x 6v golf cart batteries, 60 lb trolling motor on the dinghy with 100 ah FL battery). No charging on our dinghy, we bring the battery on board to charge. Have it wired through blue sea ACR (battery isolator). Breaker is on the main system side - breaker on lets the ACR connect the dinghy battery based on system voltage - breaker off disconnects ACR and dinghy battery from the main system.

The 200 w of solar is not really cutting it (darn fridge), so we only charge the dinghy battery when the engine is running. Will be adding to the solar array soon.

I get a little range anxiety on a longer dinghy rides when fighting a decent wind or current, curious if you actually get 1+ hr at full throttle. I haven't tested my luck that far yet.

wyb2 - I've also been considering this for our 11' RIB with either a 62 or 86 lb thrust motor. 200 AH of AGM's. How does yours do as far as speed & range in slack calm water? I've got plenty of charging on the yacht (solar, wind, genset) and can easily see a quick connect to the dinghy while on the davits. Solar on the dinghy would assist while we're off on the beach. My First Mate hates speed in the dinghy, and I don't like gasoline on board.

Peregrine1983 · 02-11-2017, 14:37

I have a Takakat Lite dinghy (about 70lbs and about 12' long). The battery is another 75 pounds + me (180) + gear. The motor is probably pushing around about 300lbs when it's just me.

I have the Newport 55lb thrust motor. It's no speed demon, but it does the job silently, every time, and without any fuss.

A few weeks in, I can confidently say this setup works perfectly for me and I don't miss my gas motor. This solar setup has also been perfect for my purposes - but I must stress that my use of the dink is only to run out and back to my mooring a couple times a week. For more constant use you'd probably want a larger solar panel (or a way to plug into the mothership) to keep your batt up. The 50w panel has been fine for my limited use - the 100AH AGM battery is always at about 12.5v.

I ran out to the boat and back on Monday evening when we were still getting hit with the tail end of a little Nor'easter. The dinghy was fine going directly into the wind - the bigger problem was being blown sideways off course as the wind was perpendicular to my destination on both legs. I had to motor with the bow at quite an angle. More power would have calmed my nerves a bit, but I made it.

wyb2 · 02-11-2017, 17:26

Quote:

Originally Posted by JamuJoe

wyb2 - I've also been considering this for our 11' RIB with either a 62 or 86 lb thrust motor. 200 AH of AGM's. How does yours do as far as speed & range in slack calm water? I've got plenty of charging on the yacht (solar, wind, genset) and can easily see a quick connect to the dinghy while on the davits. Solar on the dinghy would assist while we're off on the beach. My First Mate hates speed in the dinghy, and I don't like gasoline on board.

In calm water it's great. Had about a 1.1 mile trip one way to a dinghy dock a couple weeks ago, made the round trip twice on one charge (105 ah battery). Ran the motor on 3 of 5 to save battery, so it took about 20-25 minutes each way. It'll go 4.5 knots on speed 5, but definitely wouldn't have made the trip twice at that speed.

It's against a significant current or headwind that you'll start to feel the range anxiety.