Using Trolling Motor as an outboard

Discussion in 'Outboards' started by Stumble, Jul 6, 2009.

  1. Stumble
    Joined: Oct 2008
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    Stumble Senior Member

    I just got back from testing out a 40lbs thrust electric trolling motor as an outboard for my sailboat (Olson 30, weighs abt 3600lbs). The motor worked pretty well pushing the boat at about 2.1kn into a 10kn headwind, and at about 2.5kn running beam to the wind. Before I buy a motor though (this one was borrowed) I am trying to decide if it would be worth the extra cash to step up to a 55lbs motor, and or switch from a weed cutter prop to a standard one (and is so what pitch). All in the desire to get a little more speed out of the rig. If I could get 4kn out of it I would be thrilled, even what I have now will work, but sometimes having the extra speed would be nice.
     
  2. pistnbroke
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    Location: Noosa.Australia where god kissed the earth.

    pistnbroke I try

    have a look at the Briggs and stratton electric outboard...its 3 hp ..we have some 86 lb thrust ones here on ebay.com.au at only $US 160 . 24v is better and remember you can always turn it down if you are going too fast ( ha ha ) but you carnt go up in power once you buy it
    As always the prop must match the motor or you overload and burn it out ...so measure the current with the std prop ..try others but dont exceed that current ....testing in the swimming pool is the simple way to go
     
  3. Stumble
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    Stumble Senior Member

    Pistnbroke,

    The goal is to find a lighter weight option than the Nissan 3.5hp 4 stroke I have now (about 40 lbs). The B&S weights in at 68lbs which is a major step backward for this application. Not to mention the 4 12V batteries it takes (48V).

    I am really trying to keep from installing a 24V system since that would probably require removing the battery I have now and installing two smaller batteries. I could do it, but this is a stripped down race boat, so any complexity or weight added has to be seriously justified.
     
  4. PAR
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    PAR Yacht Designer/Builder

    A 55 pounds of thrust trolling motor is about 2/3's a single HP, which isn't much to push a 1.55 ton boat. You can kiss off getting anywhere close to hull speed, let alone over 3 knots. Your boat would need a few if not 5 HP to reliably maintain hull speed, in moderate chop, contrary currents and wind.

    If the boat is able to take a shaft, I'd consider a 12 VDC washing machine motor (or similar), V belted to the shaft. With suitable pulley diameters, you can swing a fairly big prop. Jump over the side and yank the prop come race time or use a folding unit. One battery to get you out there, another to get you back, charge at the dock.
     
  5. ondarvr
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    ondarvr Senior Member

    I may be a little confused, you want something lighter than a 40 lb O/B so you’re going to a 50 lb (minimum) battery plus the trolling motor?

    If you just want something lighter, find one of the 3.5 hp two strokes from a few years back, they weigh in at about 30 lbs.

    A 55 lb thrust electric won't last all that long running full throttle to move a hull that size, the battery will run down fairly quick.
     
  6. PAR
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    PAR Yacht Designer/Builder

    . . . and speeds will be quite low.
     
  7. Stumble
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    Stumble Senior Member

    Ondarvr,

    The battery I have to have anyway, so this just means I am useing a larger percentage of its storage capacity. Not really a problem since I have electricity at the dock.

    As for the older light weight two strokes... I have been looking for one, but they are nearly impossible to find, and are selling for as much as or more than a new engine of the same horsepower. At least until you get to the five horsepower versions.

    Par,

    I understand I won't be hitting hull speed, but that isn't really the goal. Just making enough speed to get in and out of the harbor is. Right now with the 3.5hp gas engine I can hit 7kn. If I could get the trolling motor to half that I would be thrilled. And I am really not concerned about trying to use the motor in heavy seas, since the boat never leaves the dock without being fully crewed rigged to go sailing.

    I guess there are a few deliveries a year to regattas, but I still plan on keeping the gas engine for these.
     
  8. pistnbroke
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    Location: Noosa.Australia where god kissed the earth.

    pistnbroke I try

    I have a Archimedes Penta 4 HP air cooled 1976 in my collection weights under 8 kg ..pity I am not in the states I could ship it to you cost me $25 us
     
  9. Fanie
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    Fanie Fanie

    Stumble,

    The trolling motor does not match the power and long term capability of a small outboard. The one time you will need a bit more power is when the battery will let you down - from experience. You can rather use the battery for instrumentation or radio. The battery will also last longer if you don't have a trolling motor on it.

    Keep shopping around, you will find your baby outboard. I have a 2hp on a 5.5m tri, but a 5hp is much more common and would have been a better choice. You don't have to run the motor flat out either, the extra torque comes in handy when the wind goes up and you cannot sail.

    Trolling motors are great if you want to move slowly and softly around fishing in relative windstill conditions. Bigger trolling motors are power hungry, a 56lb thrust is going to draw 30 to 50 amps off the battery, bigger ones get worse and you need beeeg batteries.

    Go for the outboard.
     
  10. Stumble
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    Stumble Senior Member

    So I know a lot of people were critical of this idea, and if it wasn't for the limited use that I need it for I wouldn't even have considered it. However haveing now used a 40lbs trolling motor for a few weeks I thought I would report back on the results.

    Boat - Olson 30, 3,600lbs, +1,000lbs of crew
    Engine Min-kota 40lbs thrust with the largest prop I can find.

    Results-

    With one person on board the engine will do about 3kn fully loaded the boat hits 2.7 eventually, though it does take a while to get there. Which while slow does satisfy the requirements I need it too. As a system is works but I would be hesitant about recommending it to anyone UNLESS you have the same criteria that I do.

    Criteria - An engine that can move a lightly loaded sailboat from its slip to the mouth of the harbor (about 1000 yards) at a speed sufficient to not drive me nuts. The engine must be lightweight (including any additional equipment that would need to be carried) and easy to remove from the transom for racing.

    Note that there is no intention to use this engine to:
    1) ever go further than from the dock to the mouth of the harbor and back
    2) return to the harbor from the race area
    3) achieve an otherwise reasonable speed
    4) Be able to act to push the boat off of a lee shore


    In other words a paddle would almost fit my design requirements, except that the harbor master and out lease requires an engine, otherwise I would just sail out of the slip. So yes it works for these limited requirements, but is not generally a good idea.

    BTW I also have a 3.5hp Nissan for non-racing uses
     
  11. BHOFM
    Joined: Jun 2008
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    BHOFM Senior Member

    Stumble;

    I don't know why when you mention using a trolling motor
    as a secondary power source people get so excited. One
    site I post on, it turned into almost a rant, flame thing.
    Around here, lakes, no tide or currents, it is common for
    small boats to use them as a primary power source. You
    see a lot of 12/14' fishing boats with a trolling motor
    and a couple of batteries. They often fish up to ten miles
    of the lake in an evening.

    For my 12' sail boat, 222lbs, I have a Motorguide 30 with
    a very small battery, 450ah, for a VW bug. The motor weighs
    17lbs and the battery 28lbs.
    I have run the motor three hours on setting #3 of five and
    covered about ten miles in under three hours.

    I shorten the shaft a little over a foot to make it fit my
    boat and not be in the way all the time.


    [​IMG]

    [​IMG]
     
  12. matrix
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    matrix New Member

    Trolling motor

    Stumble/BHOFM,

    Good posts... and thank you for some real world application experiences. Most threads I've come across about this subject are full of people chiming in telling the poster to go with a gas outboard.:p

    Stumble, I have an American 14.6 sailboat that I want to power with a trolling motor for the exact same reason you mention. Just to get me away from the dock and back in a straight line if a thunder storm should pop up unexpectedly, not to motor around with (isn't that the point of the sails?). I see that 40lbs of thrust would be more than enough if it can push a 4,600 lb boat around...I'll probably go with the 30lb.

    BHOFM, thanks for the battery idea. I've also been searching for the lightest battery....at 45lb auw you've come close to the weight of the little 2-2.5 hp gassers from Honda and Suzuki....:) If you know of a lighter battery for this application please post.

    Thanks again!
     
  13. BHOFM
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    BHOFM Senior Member

    I think this is about the smallest practical battery I could
    use.

    But I don't have to deal with gas. And with out gas on
    board, I can get by with a small kitchen fire ext. Not the
    big red one.

    AND.. The motor was $99 at Wal Mart. On line order only.
    The battery is a "blem"! New, $24.

    I think the little Hondas are around $700?

    I got in some bad weather Monday, winds over 45mph.
    The motor on high was able to hold the boat into the
    wind and let me get the sail down. I surfed back to the
    marina with a bare pole and the the motor was more
    than enough to turn into the wind and get to the lee
    side of the docks to wait out the storm.

    Another thing, the battery is in the center of the boat,
    not hanging on the transom.
     
  14. matrix
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    matrix New Member

    Battery

    Exactly, no gas and many lakes (e.g. reservoirs) do not allow gas engines...

    Sorry, I didn't understand your comment about the battery. Can you tell me where you got the battery and what brand? Was the battery only $24? if so, Wow...
     

  15. pistnbroke
    Joined: Jan 2009
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    Location: Noosa.Australia where god kissed the earth.

    pistnbroke I try

    Your quote of 450 ah is wrong you have quoted the cranking amps ...Look for the marking RC which is reserve capacity ...how long in minutes it will supply 25 A .....typical for a small battery is RC 60 min dont run it down below 10.8v and charge as soon as you can .
    remember the difference in weight between a 30ib and 55ib thrust is minimal but you might need it one day ..
    It looks like Min Kota have revised there range but have sold the tooling for the old ones to china ..just bought a 86 lb thrust 24v for $us 160 ..you can always run it on 12 .....i force was the brand.
     
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