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Discussion Starter #1
I have a new mooring which is pretty far away from the dock at the club. I get to use the club dinghy to get out the boat but I'm little old to be rowing 200 yards against the tide and the wind, and am wondering if a 40 or 55 lb. thrust trolling motor temporarily attached to the dinghy and then stored in the sail boat would work to get me to and from the mooring.

Being a murphy's lay kind of guy I could use it an an emergency motor and attach it to the ladder on the other side of the transom from the 5HP Honda.

Any thoughts?
 

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How big of a battery does the dinghy have?

I used a 45lb trolling motor on my Olson 30' for a while to get in and out of the harbor. It would get the boat to about 3kn after a while. On a small light row boat I would imagine it would work fine.
 

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Discussion Starter #3
How big of a battery does the dinghy have?

I used a 45 lb trolling motor on my Olson 30' for a while to get in and out of the harbor. It would get the boat to about 3kn after a while. On a small light row boat I would imagine it would work fine.
The dinghy is a club dinghy. It only has oars. But then the battery only needs to go for 200 yards to the mooring, and then about 6 hours later 200 yards back to the dock. And then I take it home and charge it up before the next use.


The Dinghy is only about 6 feet long.
 

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Very roughy numbers (and be warned electric conversions aren't my strong suit).

A 45lb thrust motor drawn up to 42amp.
400 yards ~= .2nm

Assuming 3kn speeds (at full throttle), then it would take you about 5 (.066 hours) minutes there and back...

So you need 42amps * .066 hours = 2.77 amp hours to run to the boat and back. Double this for reasonable life and you need something like a 5ah 12v battery. A 12lb motorcycle starting battery has 18ah, so that should be good and give you a little reserve.
 

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Discussion Starter #5
Very roughy numbers (and be warned electric conversions aren't my strong suit).

A 45lb thrust motor drawn up to 42amp.
400 yards ~= .2nm

Assuming 3kn speeds (at full throttle), then it would take you about 5 (.066 hours) minutes there and back...

So you need 42amps * .066 hours = 2.77 amp hours to run to the boat and back. Double this for reasonable life and you need something like a 5ah 12v battery. A 12lb motorcycle starting battery has 18ah, so that should be good and give you a little reserve.
Sounds great! it would certainly take me more than 5 minutes to row 200 yards. Of course I could help it along with some rowing too.
 

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I use a little 30 lb thrust Minnkota with two jet ski batteries to push various small boats and inflatables. I run it on one battery until that battery dies. When I switch batteries, I know it's time to start heading back. I've covered many miles this way.

Your idea should work fine, I think you'll be surprised at how well it works.
 

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There's a guy on my dock who uses a trolling motor to take his Catalina 25 in and out of the harbor all the time. Other than being a bit slow if he has to buck the wind on the way out it seems to work fine. It's about 15 or 20 minutes each way, but he can probably reduce that by about half by sailing in the outer harbor (if the wind cooperates).
 
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Forgive me if this is obvious, but if you're going to be putting a motor and battery on and off the dink so frequently...make sure there are bridles on both so that when you drop them, they don't go to the bottom. Small, wet, heavy, all good reasons for Neptune to make a grab for them.

Or, if other folks start to covet them, you might get the club to just buy a motor and a couple of larger batteries for it.
 

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This is a very timely thread. I have a little inflatable raft with 30 lb trolling motor that I use for a tender. I've had it 2 years, but only used it once, so I really don't want to put much money into it. The one time I used it my group 24 was way more capacity, weight, and bother than I needed. So I've been debating getting a smaller, lighter SLA battery next time I want to use it. But I didn't know how much capacity I need, so the notes here are perfect for me.

I had been considering 35 Ah, but based in what I'm reading here, I think I might go with 18 or 22 Ah, and if that's not enough buy a second identical one to swap out.

 
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Since it is the Club's dinghy, do you need to return it back to a dock so it would be available to others? If so, why don't you try and get the club to buy the motor and battery so you don't have to take the motor on and off. A charging set up at the dinghy dock should suffice for all to use. Using a good deep cycle battery, the trolling motor should last a long time. Just a thought.
 

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I have a 33amp hour battery for a wheelchair (23lbs) and a 30lbs thrust trolling motor that pushes my 10ft dinghy along just fine for 2hrs.
This is a very timely thread. I have a little inflatable raft with 30 lb trolling motor that I use for a tender. I've had it 2 years, but only used it once, so I really don't want to put much money into it. The one time I used it my group 24 was way more capacity, weight, and bother than I needed. So I've been debating getting a smaller, lighter SLA battery next time I want to use it. But I didn't know how much capacity I need, so the notes here are perfect for me.

I had been considering 35 Ah, but based in what I'm reading here, I think I might go with 18 or 22 Ah, and if that's not enough buy a second identical one to swap out.

Two years later, and I haven't used the dinghy enough to warrant buying a smaller (35Ah) battery. But I'm going to be using my inflatable raft a little more in the near future. So I'm thinking of buying a 35Ah wheelchair battery. The one I found is an AGM type, available from an area dealer who I would like to support:

Tri-State Battery Warehouse : UB12350 Sealed Lead Acid (AGM) [U1T] - $67.50

http://upgi.com/Themes/leanandgreen/images/UPG/ProductDownloads/D5722.pdf

My main question is over how best to charge this AGM battery when it's not in use in the dinghy. I've never had a self-standing AGM battery before, so I'm want to be sure I do it right, whether charging on AC power or while motoring.

My new (to me) Catalina 34 has two brand new 4D East Penn Intimidator AGM house batteries, with a 50/1000w Magnum charger/inverter. The controller is set up for AGM charging parameters. So is there some way I could attach this little battery to the house bank and piggy-bank off the alternator and the AC charging system? If so, what is the best way to mechanically do the attachment? Also, I am concerned that connecting the discharged smaller battery to the fully charged house bank could lead to a very high current flow that could damage the batteries and/or wiring? How do I regulate the very high current that may happen as soon as I make the attachment? Or do I just put a fuse/breaker on that line that trips if current is too high? (There will already be a breaker on the battery post for use with the trolling motor, so that would probably prevent catastrophic problems, although it doesn't regulate the flow if the current is too high.)
 

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I use plug in battery style motor. 40V, charge it like a tool battery and insert it into the motor and off you go. Gives me 30 minutes on a charge. 15 lbs weight 35 lbs thrust. I've never met anyone else in the world who owns one, but they sure are cheap and easy, so not sure why.
 

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I am not sure what you are talking about. Is this a battery, or a motor?

I already have a trolling motor. I'm just looking for a 12v battery for it. Don't want to lug a group 24 around, and willing to accept lower capacity for lighter weight.
 

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if you haven't already purchased the batt, save yourself some money. go to Walmart and buy a marine batt. appropriately sized for your motor. it is still AGM but will be about $100. while there they have a very nice batt charger that will charge AGM and old std style batteries. it weighs about 1 lb for the charger.

now how do I know that will work well. I have a 55LB thrust trolling motor along with the Walmart batt and charger. I use the charger for the marine batt as well as tractors, motorcycles and cars.
 

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if you haven't already purchased the batt, save yourself some money. go to Walmart and buy a marine batt. appropriately sized for your motor. it is still AGM but will be about $100. while there they have a very nice batt charger that will charge AGM and old std style batteries. it weighs about 1 lb for the charger.

now how do I know that will work well. I have a 55LB thrust trolling motor along with the Walmart batt and charger. I use the charger for the marine batt as well as tractors, motorcycles and cars.
Please post a link to Walmart's battery. I haven't seen a small marine AGM battery at any of my local Walmart stores.

Also, the link I posted shows the battery for $67 with no shipping (since I'll pick up in their store), so not sure how a $100 Walmart battery saves me money. Other sites are showing 35Ah wheelchair batteries for as low as $55 after shipping:

UB12350 12v 35ah Battery Apex Battery

Keep in mind that I already have two group 24 marine batteries, and have used them in the raft before. They have more capacity than I need, and more weight than I'm willing to haul on and off the raft. Plus, on a soft bottom raft there is a risk of them tipping over, so an upgrade AGM or SLA is required. I've been looking at wheelchair batteries, since they're built for high discharge usage. I'm not aware what "marine" features are needed, aside from the inflated price that comes with the label.

Also please post a link to the one pound WalMart AGM charger. Once again, I can't find it on their website, and the local stores don't have one that I can look at in the store. And their employees are clueless.
 

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Please post a link to Walmart's battery. I haven't seen a small marine AGM battery at any of my local Walmart stores.

Also, the link I posted shows the battery for $67 with no shipping (since I'll pick up in their store), so not sure how a $100 Walmart battery saves me money. Other sites are showing 35Ah wheelchair batteries for as low as $55 after shipping:

UB12350 12v 35ah Battery Apex Battery

Keep in mind that I already have two group 24 marine batteries, and have used them in the raft before. They have more capacity than I need, and more weight than I'm willing to haul on and off the raft. Plus, on a soft bottom raft there is a risk of them tipping over, so an upgrade AGM or SLA is required. I've been looking at wheelchair batteries, since they're built for high discharge usage. I'm not aware what "marine" features are needed, aside from the inflated price that comes with the label.

Also please post a link to the one pound WalMart AGM charger. Once again, I can't find it on their website, and the local stores don't have one that I can look at in the store. And their employees are clueless.
ok don't bite my head off for not reading entirely. I missed the word SMALL in your want of a battery. yeah I have a fullsize batt weighs a lot.
for the charger -- https://www.walmart.com/ip/Schumacher-XCS15-15-10-2-Amp-Marine-Battery-Charger/15140196


that is the one I use
 

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ok don't bite my head off for not reading entirely. I missed the word SMALL in your want of a battery. yeah I have a fullsize batt weighs a lot.
for the charger -- https://www.walmart.com/ip/Schumacher-XCS15-15-10-2-Amp-Marine-Battery-Charger/15140196


that is the one I use
Sorry, I've been a little prickly lately. Too much work and not enough sailing. I do appreciate your efforts to help me. And I'm the first one to admit that I also read sloppily at times...or maybe all the time. ;)

The charger looks interesting, so I'll look into it. Thanks!

I'm also interested in figuring out a way to charge the battery off my alternator. So if anyone has advice on how I can connect a depleted trolling motor battery without creating a massive electrical load as soon as I make the connection, please let me know.
 

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I'm also interested in figuring out a way to charge the battery off my alternator. So if anyone has advice on how I can connect a depleted trolling motor battery without creating a massive electrical load as soon as I make the connection, please let me know.
I'm wondering if you've made any progress figuring out your battery and charging situation for your trolling motor? I'm seriously considering this setup for next season as my gasoline outboard is deader than dead and I can't bring myself to buy another gas outboard knowing it will quickly succumb to the same fate with very infrequent use. I would think an echo charger or similar would be the ticket for charging off the alternator.
 
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