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Thread: Trolling motor and battery question....

  1. #1
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    Trolling motor and battery question....

    4 years ago I bought a small sailboat; and got a trolling motor and battery for it.
    I quickly decided that it was impractical and never used them. Just too much "stuff" for the little boat.
    I just bought a bigger sailboat and expect they will work there; if I can find some way to charge the battery. I hope not to use them, but if the wind dies completely and I am a few miles from home, it would be nice to have something.

    So, my questions....
    1) I charged the battery and it quickly went to 12.2v, which I think means it is dead. Checked the level and it was full.
    My charger has a recondition setting which supposedly forces the sulfate off the plates and back into the electrolyte. I did that for a day and then charged. Repeated 3 times. At the end of the all that, it was 13.0v. After 3 days it is still 12.9v. That sounds good.
    Did I actually FIX the battery, or will it fail after light use?
    2) The battery 101ah and the motor draws 30a. Does that mean I can go 3 hours? That ought to be enough to get me home, though a bit slowly.
    3) I will be mooring the sailboat, so recharging the battery (this one, or new one...) off line power will be difficult. Would a solar apparatus work? If so, what would I need>

    Thanks much.

  2. #2
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    put it in a bucket and turn it on. see how long it goes. Solar is the way to go. but how often will you use it. more often need more solar amps to catch up.

  3. #3
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    Testing it? Yeah, that might work.
    I just want the solar to keep the battery topped off. An amp ought to be plenty.

  4. #4
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    As a long-time sailor, I am going to say consider a gasoline or propane (Tohatsu LPG 6) outboard. Ditch the trolling motor. It will give you very little control of the boat, and very little forward speed. I'm not sure where you sail, so there are a lot of variables. If you're on a protected small lake all the time, it may work for you, but you may have a day when you're going upwind and trying to beat weather and that trolling motor is going to struggle to make headway. There are such things as "electric outboards", which differ from a trolling motor. A trolling motor is (as the name suggests) for trolling in a bass boat or flats boat where you are wanting to make around 3 knots or less just dinking around in the shallows looking for fish. An electric outboard is actually made to have the torque and horsepower to move the boat at hull speed. They cost about as much as a gas or propane outboard- around $2500. Torquedo is an electric outboard manufacturer you can check out.

    To answer your question- yes, in theory the 101 amp battery should run your 30 amp trolling motor for about 3 hours. For solar, you're going to need panels and a solar charge controller. The charge controller should be able to identify automatically when the battery is topped up and not overcharge the battery. A 100-watt solar panel is going to produce about 30 amps of power per day, depending on where you live and how much sun you get. Charging your battery all day with solar will give you 1 hour of run time on the 30 amp trolling motor. I would want at least 300 watts of solar panels if I were you. Honestly, it's a lot of trouble and cost, which is another reason I would go with a propane our gasoline outboard.

  5. #5
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    If you carry a paddle I would suggest a kayak paddle. It's much more efficient.

  6. #6
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    Quote Originally Posted by Tom Bender View Post
    If you carry a paddle I would suggest a kayak paddle. It's much more efficient.
    The boat is a Precision P15K; http://precisionboatworks.com/boats/p15/index.php
    A kayak paddle would be tough to use with a 7' beam.
    It is in great condition and lists for $13,000; got it for $2,000. So spending $2,500 on a motor would be tough to justify.

  7. #7
    Just try it out and see how it goes.... BUT.... be prepared for it to not be enough.

    A small 12v electric trolling motor (30-50# thrust) will do fine on the back of a 15í sailboat like that for use around port or around a small lake when there is very little wind or current. My 30# thrust unit will not push my 14í aluminum jon boat upstream in the local rivers or against the tide. A 55# thrust model would do OK pushing a flat bottom fishing boat upstream - but likely donít do well when pushing a keel through the water... And I would not trust it was enough power against an unfavorable tide.

    If you want to buck current/tide - you will probably need one of the newer 36 or 48v electric trolling motors around the 100# thrust level. The downside of those is $1k + 125# of batteries.

    Another possibility is to use one of the cheap little Chinese 50cc 4 stroke or 2 stroke outboards. They are listed as 4 hp but are actually 2 hp output. They weigh about 20#. Price is $250-350 new. A new Suzuki/Mercury/Yamaha 2.5hp is a good candidate as well but runs around $1k. Those weigh around 40#. 1 gallon of gas will get you a long way but you will be going 2-8mph... but they will have enough oomph to buck current, tide, and wind. These are also a very good choice in port or around bridges.

  8. #8
    Quote Originally Posted by Wade Lippman View Post
    The boat is a Precision P15K; http://precisionboatworks.com/boats/p15/index.php
    A kayak paddle would be tough to use with a 7' beam.
    It is in great condition and lists for $13,000; got it for $2,000. So spending $2,500 on a motor would be tough to justify.
    I just googled '7hp trolling motor' and found several brand new gas outboards just on the first page, that'll push that boat around quite nicely, for under $700...

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  9. #9
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    Quote Originally Posted by Wade Lippman View Post
    The boat is a Precision P15K; http://precisionboatworks.com/boats/p15/index.php
    A kayak paddle would be tough to use with a 7' beam.
    It is in great condition and lists for $13,000; got it for $2,000. So spending $2,500 on a motor would be tough to justify.
    That's a bit smaller than I envisioned. A trolling motor isn't ideal, but if it works it works. Great deal ya got there. The issue will be where to put the solar panels if you go that route. You can always have a panel that you leave out when not using the boat and put away when you use it.

  10. #10
    I would want to know the Amp output of the solar panels and how long it would take to charge your battery if run down. I thought that those solar chargers were used more to trickle charge to keep a battery topped off or maybe to support an occasional bilge pump run, and not for charging a low battery. (I could be wrong on this as technology has improved) Also, if it charges slowly, you battery life diminishes the most while it is not charged to capacity. My 2 cents.

    Good luck!

  11. #11
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    I actually tested the battery!
    I put the motor on 60% power (18a) and ran it for 5.75 hours. It would have gone longer, but I figured that was enough.
    It was down to 11.3v, from the starting point of 12.9v.
    I then charged it back to 13.3v.

    While the trolling motor might not be adequate, I have it and a battery, so I will try it and see how things go. If it goes 1mph on 100%, I will upgrade to gasoline.

    A couple questions....

    1) I know a reasonably priced solar panel won't charge it; I will have to get it back to shore for that, but will a 0.4a panel keep it full without fear of overcharging?
    2) What do I do with the battery over the winter? Let it die and then recondition it in the Spring? Charge it every couple weeks? Something else?

    Appreciate everyone's help.

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