Seeking speed with a 3hp electric outboard ...

Discussion in 'Boat Design' started by istock1, May 15, 2009.

  1. istock1
    Joined: May 2009
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    istock1 New Member

    All,

    Brand new to the forums, but it seems like just the place I need to be. I am in the beginning stages of building or purchasing/modifying an electric-only boat for use in medium size lakes (the reservoirs in Maryland are electric only). I just purchased a 3hp (150 lb/ft) Briggs and Stratton electric outboard, and am shopping for batteries for it. I have a 14' flat bottom aluminum jon boat, but am looking to upgrade to something larger.

    So, my question is this: What is the best choice for me to maximize my top speed with my propulsion restriction? I am expecting hull speed on the 14' (say 5.5 knots I think?), but I am willing to put a little time/money to get that up to 8 or so with a larger/different boat. I was looking at these stern lifters things, but am kind of skeptical:
    http://www.allinflatables.com/shopping/lifters/

    Any help would be appreciated as I am pretty much a newbie. Thanks!
     
  2. marshmat
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    marshmat Senior Member

    Hi istock, welcome aboard :)

    There aren't many (if any) boats that will plane with 3 hp and still be able to carry a fully-grown person and their gear. With this little power, you're stuck at displacement speeds. Neither trim tabs, nor any other planing aids, will compensate for there not being enough power to get up on plane.

    Now, if you're looking for a larger boat than your 14' aluminum, and you want it to be reasonably quick with this motor, you're looking at something long, light and thin. Anything that even vaguely resembles a normal, wide-transom utility skiff is out. But dory or semi-dory forms, canoe shapes, kayak-like shapes, sharpies, and other long, light, skinny boats all have the potential to be fairly quick with relatively little power. They also have the advantages of being nicer looking, more comfortable, and often more seaworthy than small utility skiffs and jon boats.

    There are a few guys on here who have done a lot of experiments on human-powered vessels, where you can't get much more than 0.3 hp for any length of time. Hull shapes definitely exist to provide good speed and stability on very little power. I bet a few of these guys will chime in with some more advice shortly....
     
  3. masalai
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    masalai masalai

    Look up the efforts of Rick Willoughby and you will find the best knowledge base that I know of for fast low powered boating.... also have a look at torqeedo as an electric drive for canoes & kyak type hulls....

    Now kerosene, that is neat (your post below = #4)...
     
  4. kerosene
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    kerosene Senior Member

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  5. lewisboats
    Joined: Oct 2002
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    lewisboats Obsessed Member

    long and narrow to maximize waterline length and minimize wave making. Double ended would be best or at least have the transom start above the waterline. You want an clean entry but an even cleaner exit for maximum speed. Light weight is a must so capacity won't be much. The above would be ideal for speed...compromising everything else. All you gotta do now is figure out how much speed you want to lose to start making it something you can live with and that meets your needs.

    Steve
     
  6. Guest625101138

    Guest625101138 Previous Member

    If you select the right battery you should be able to get the Jon boat to plane with the 3HP electric if it is a nice light boat. It might need a different prop.

    A 3HP electric will get a purpose built boat on the plane if you are only interested in speed with one person.

    If you wanted to do a test of what might be possible then buy a couple of these:
    http://www.hobbycity.com/hobbycity/...roduct_Name=ZIPPY_Flightmax_5000mAh_6S1P_20C_
    They will give 100A for a few minutes and allow you to check out what speed is attainable in the Jon boat. You will also need a 6 cell charger. They will take the motor to 4kW if it is the outboard with the Mars Etek motor.

    If you want to go at reasonable speed for long periods then you need a long slender hull. I have been working on a solar boat design shown here:
    http://www.boatdesign.net/forums/at...8-m-electric-powercat-sw_tri_8m_linesplan.png
    It is designed to do 8kts with one person in calm conditions with 900W. Should get to 14kts at the 4.5kW possible from a Mars motor.

    I can hold 6kts in my V11J pedal boat with 130W:
    http://www.boatdesign.net/forums/at...5d1230111804-pedal-powered-boats-pc240005.jpg
    So with long slender hulls you do not need much power to do a decent turn of speed.

    The fastest though with 3HP electric would be a small planing hull with lithium batteries. However it will have quite limited range. More a toy like a jet-ski than a boat.
     
  7. alan white
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    alan white Senior Member

    The trick is to decide how to build the boat around the target speed and the target charge duration, as each speed/charge duration combination translate to a different boat waterline length AND displacement figure.
    If 5 1/4 knots continuous is the goal, 16 ft is the ideal length, but what would the boat weigh if the target charge duration were 4 hours? An efficient hull at the required weight including passenger, motor, and batteries might weigh too much using lead-acid batteries, so would you opt for lithium ion batteries and could you afford enough batteries to give you the required wattage for 4 hours?
    What's changed to achieve all the targets of weight, charge, and speed? If the technology/budget won't allow the boat to achieve it's design goal, then what comprimises would come closest?
    It's a challenging equation, involving a lot of interplay between variables like weight (friction) and battery cost per pound saved, with each shift in emphasis calling for a slightly altered hull form.
    It takes practically a genious to cleverly balance all those variables and come close to the most efficient ideal for the needs of the user.
     
  8. mydauphin
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    mydauphin Senior Member

    If you want to plane with two people fuel and a cooler, you need 5hp. Sounds like I pick number from thin air. No I did it, 3 or 4 won't do it. May be 4hp with one. Canoe type vessel will have to be wide enough and long enough but would have to site half out to plane.
     
  9. istock1
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    istock1 New Member

    Thanks for all the input guys. The boat will primarily be used for fishing, so I don't think the long-light-thin thing will work. Maybe I'm stuck with the jon boat ...
     
  10. mydauphin
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    mydauphin Senior Member

  11. marshmat
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    marshmat Senior Member

    If you're OK with the jon boat at 5 knots or so, it's still a durable, economical fishing platform for your inland reservoirs. It won't be fast, but it'll get you to the fish and back.

    If you really do want more speed while still having good stability for fishing, you'll end up in the spiral Alan is talking about. It could be a fun exercise, if you're the type who likes math, simulation and optimization. If you're the type who would rather just cast a few lines and land a trout or three, you might find the process of coming up with a new design rather tedious and dull.

    Or you could take the shortcut way- find a (roughly) matched pair of used canoe, kayak or rowing scull hulls that are long, thin and light, make them into a catamaran with some wooden beams and a deck, and mount your electric motor on that. It might be a bit faster than the electric jon boat, certainly so with two people and their fishing gear, and it'd most likely have a longer range from the same battery capacity. Not nearly as fast or as long-range as a carefully optimized custom design, but also a lot simpler.
     
  12. BertKu
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    BertKu Senior Member

    Batteries.

    I would strongly advise to visit website of EEstor . They are in the process of manufacturing super capacitors, which holds the power of 10 x a normal lead acid battery, but at half of the weight. Siemens AG, made 9 years ago a similar type of product, but the automotive industry requested Siemens to close the plant down. They sold it. I am worried that the automotive industry will also close down the factory for this very sensible product . It is logical, the electric car, boats etc will be pushing their old fashioned product of the market. But I hope that I am wrong and that EEstor is able to stand up against the powers of the automotive industry, as I also am in the process of building an electric mototboat with 20 - 30 KW motors, but need EEstor type of batteries.
    Succes with your project , Bert
     
  13. marshmat
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    marshmat Senior Member

    EEStor has a working device and a patent, Bert, but are still a while away from a production model. On the bright side, they do have a contract with ZENN Motors to supply ultracapacitor modules for the ZENN car- an urban commuter runabout about the size of a modern Mini Cooper- as soon as the production line is ready. It might be a bit tricky to integrate one into a home-build design though- as the EEStor ultracapacitor discharges, its operating voltage swings from a peak of over 3,000 V fully charged to just a few tens of volts when it can't swing your motors any more. I'm really looking forward to seeing what kind of control circuitry they come up with to tame the thing's output for useful purposes.
     
  14. BertKu
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    BertKu Senior Member

    I assume that they will use switch mode principles and burst technology to flatten the curve a little, similar to a certain extend as with Solar panels. I am a great believer that as long EEstor can stand up against the very powerfull automotive industry and that they will not be bought out and put asleep, it will help Istock1 to keep the weight light and maybe he is able then to increase his motor from 3 to 5 to 6 horsepower and he will increase speed. Bert
     

  15. BertKu
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    Location: South Africa Little Brak River

    BertKu Senior Member

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