Multiple trolling motors for electric only lakes?

Discussion in 'Propulsion' started by YotaTruck, Jul 22, 2013.

  1. YotaTruck
    Joined: Jun 2013
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    Location: NJ

    YotaTruck Junior Member

    Here in NJ we have a lot of electric only lakes (especially in our state parks) that would be nice places to take the family out for a day on the water/picnic, etc... The problem is that if you're taking the family out you need a larger boat-a decent trolling motor isn't bad if it's two guys fishing from a 1236 Jon boat, but with something large enough to fit mom, dad, and two kids you're going to run out of juice fast with a large motor or get pushed around by the wind with a small motor. I am going to be building this boat from Bateau:

    http://www.bateau.com/studyplans/GF18_study.htm?prod=GF18

    I will be scaling the boat down 10%, so LOA will be 15' 7" with a max beam of 6' 5", essentially it's going to be a very wide and stable jon boat. As you can see it has a very wide bow transom which would be perfect for a bow mounted trolling motor or motors. I was thinking of doing the following:

    [​IMG]

    At the bow, I would mount two 35lb trolling motors. I already have one and they can be found on Craigslist any day of the week for about $75. At the stern I'd mount a larger trolling motor, perhaps as large 75lbs if I can find one. The stern mounted trolling motor would be controlled in the conventional sense-I would sit at the stern seat and operate the tiller/speed control. The front two motors would be rewired so that both operated from a switch mounted near the stern seat. Both motors would be fixed on the max power setting and would be turned on or off by me from the stern seat.

    I'd envision getting underway to be something like this: With the bow motors switched off, I gradually turn up the power on the stern motor until we're at maximum speed. Then I switch on the bow motors (both controlled by the same switch so they would turn on and off at the same time) which would bring us up (perhaps too abruptly, so that might have to be tweaked) to maximum power. I'm not so much looking for speed with this setup, but rather enough power to move the weight required and to ensure that we're not going to get blown around by the slightest breeze. These are small lakes (less than 500 acres) and we would only be going out on the nicest of days. For larger lakes and potentially rougher weather I'll be relying on a 15HP gas outboard.

    Obviously this setup will require a lot of power, but with the generous displacement of the GF18, (even scaled down 10%), it shouldn't be a problem to carry four fairly large trolling motor batteries-one for each 35lb motor at the bow and one for the 75lb motor at the stern. What I'm looking for is a critique on my theory as far as how much power this will provide. Does it sound like a viable idea or just a waste of weight and electricity?
     
  2. michael pierzga
    Joined: Dec 2008
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    Location: spain

    michael pierzga Senior Member

  3. YotaTruck
    Joined: Jun 2013
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    Location: NJ

    YotaTruck Junior Member

    I've seen the Torqeedo and it looks great, but with the cheapest unit retailing for about $1500 it's out of my price range. Sourcing two trolling motors from Craigslist (I already have one bow mounted motor), wiring and switches from Surplus Center, and new batteries I should be able to spend about $500 on the setup total.
     
  4. gonzo
    Joined: Aug 2002
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    Location: Milwaukee, WI

    gonzo Senior Member

    The problem with wide short boats is that they have a high resistance. We were building 30' canoes in the UK to carry 12 passengers. With a trolling motor and two 24 series batteries I could run it for about 1.5 hours at 4kts. That was with 7 persons onboard.
     

  5. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    The problem with electric trolling motors is the prop is geared to 3 to 4 MPH and that's what you get, regardless of how big it is. The biggest commonly available trolling motor is about 1.25 HP and requires 24 VDC. As Gonzo points out a short, fat boat will suck down the battery in no time at all, because of the lack of hydrodynamic efficiency.

    If you use twins, ideally they should a matched set, preferably both purchased at the same time. An electric "putt putt" is possible, but you'll need to rethink what shape boat you'd like to use. A jon boat isn't beneficent until it gets over 15 MPH, which you can forget about on an electric trolling motor, so a better choice might be a worn out sailboat, with it's rig and appendages removed. It's designed to be efficient underway, so the little motors will not cough up their armatures, trying to offer some speed.
     
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