Looking for efficient low HP, need opinions!

Discussion in 'Boat Design' started by Wavewacker, Jun 21, 2016.

  1. Wavewacker
    Joined: Aug 2010
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    Location: Springfield, Mo.

    Wavewacker Senior Member

    LOL, after two marriages I'm familiar with demoralizing expectations and failed attempts, both cost much more than small used boat!

    It's just to be a lumberyard boat, taped seems, ply on frame, work boat finish, if you want to succeed, simply lower your expectations LOL.

    In 8 or 10 years this boat may become part of a landscaping project in the backyard. I'll try to maintain it, but it could become a picnic table, toss a liner in it, plant flowers around it and I might have some carp to watch.

    Where's the fun in building if I buy one? I'll almost be satisfied if it floats.

    Besides, I can't buy this type of boat in these neck of the woods, my market is full of bass boats, jon boats and aluminum 14 or 16 footers, tossing in a few party barges here and there.

    But you're right, buying is faster than building and buying a good boat that has been well designed is often the better course to take. :)
     
  2. Wavewacker
    Joined: Aug 2010
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    Location: Springfield, Mo.

    Wavewacker Senior Member

    Par, I would entertain an electric motor to an OB lower unit.

    I'm not an engineer, I can't take the time to learn the hp created from a gallon of fuel or to produce electric power, but I was considering running a gen set to a charger, charging a 3 or 4 battery bank. Golf cart batteries, inverter. Seems that by the time I'd drain one battery another could be on line to switch over, this can be done electronically too. A 2KW generator burns about 4 to 5 gallons in 8 hours.

    With a narrow beam I mentioned a flat roof, I meant with posts and no walls to catch the wind. I know some gusts can get caught under roof as the boat pitches but I doubt it would be as bad as if I had solid walls. I could then use canvas curtains to enclose the boat. I mentioned too having a decked bow as a cuddy, not too high for a v berth. Just trying to keep the weight down with less windage.

    I'll look up your boat and contact you.

    Sure wish I knew how to post pics on here! We all love pics!

    As always everyone, thanks for your comments. :)

    Bill
     
  3. Caroute Motor
    Joined: Jun 2016
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    Caroute Motor Junior Member

    The electric trolling motor use the new brushless techical. The motor is under the water, no reducer so power out directly. 9HP is compared with gas motor. Brushless electric motor can achieves 65% efficiency, gas motor only can achieves 25%-30% efficiency. 160LB trolling motor had been used for Albin 79 which is about 25.9 feet and 2,100 kg, the speed can reach 7 miles.
     
  4. messabout
    Joined: Jan 2006
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    messabout Senior Member

    Caroute Motor asserts that Gasoline engines are 25 to 30 percent efficient. That depends entirely on what one means by, and what measurements are used to assess efficiency.

    A modern gasoline engine will convert gasoline to energy in proportion to fuel consumption which is a measure of fuel weight. An engine will have an average brake specific fuel consumption in the region of 0.50 pounds of gasoline per horsepower per hour. Note pounds, not gallons. Gasoline weighs about six pounds per gallon. By that standard a modern outboard could produce about 12 HP for an hour while consuming one gallon of gasoline.

    That is all very well but output HP is measured at the end of the crankshaft. An outboard or inboard with a transmission or geared lower unit will lose some of its efficiency by turning all those gears and auxiliary items like alternators, water pumps, and gear losses.

    An electric motor is a different breed of cat. The out put of an electric motor is some function of the input energy. One electrical horse power is equivalent to 746 watts of input...(745.7 watts for detail sticklers) Sad to say that you will not get a whole horsepower out of the 746 watts you fed the thing. There are internal electrical losses as well as some friction losses.

    Watts can be calculated as voltage time amperage. SO if you have a 24 volt battery bank you will need 747/24 = 31.125 amps input to have a potential of one horse power. Now multiply that by 12 to compare to the 12 HP output of the gasoline outboard. You would need 12 times 31.25 amps = 373 amperes of input. That would sap the batteries right away. Now you have to charge the batteries...probably with some sort of gen set. Likely a fuel powered generator. Might as well just use the outboard in the first place and bypass all the intermediates. The gas outboard is much lighter than the electric motor with all the batteries that are needed to get you more than an hour or two of running time. The lighter overall weight of the boat will translate to somewhat better energy consumption figures with the gas engine.

    I hasten to concede that electric motors are more energy efficient than gasoline engines. But the price you pay in cost, weight, and aggravation is not worth the hassle for the presumably more efficient power system. Disclaimer: if stealth and silence is the more important consideration then electric is clearly the better choice. Failing that then go for a good gasoline power unit.
     
    1 person likes this.
  5. Caroute Motor
    Joined: Jun 2016
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    Location: CN

    Caroute Motor Junior Member

    160LB electric boat motor's input power is 2100W, Propulsive Power is around 1370W. 24V type is 87.5 amps, 48V type is 43.5 amps. Current trolling motors are designed for some smaller boat. If your boat happend to have 24V, 36V or 48V batteries, why not consider the electric boat motor. The electric motor also can cruise more than 2 hours with lower cost than gas. You are also right, the gas motor is still a good choice for big and large boat or longer cruising time.
     
  6. kerosene
    Joined: Jul 2006
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    kerosene Senior Member

    Double post
     
  7. kerosene
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    kerosene Senior Member

    You are using total nonsense. Its so wrong that combined with your handle its false marketing.
    Yes gas motor has efficiency of about 30% but that has zero relevance to comparing shaft output. It just means that it used more fuel to create that 9hp. 9hp is still 9hp and electrical hp is not any mire magical than human/horse/combustion engine created hp. The trolling motot props are not specially efficient either so there is zero performance gain there.

    Again 3 electric hp equals 3 gasoline powered hp - not 9.

    and electric can cruise for less than gas - well that depends. Usually that claim means comparing apples to orranges. Do you include the cost of batteries? Are we talking about a boat that needs over 5hp? Do we need to account for reserve if wind picks up? Do we mean speeds over 3-4 knots?
     
  8. Caroute Motor
    Joined: Jun 2016
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    Caroute Motor Junior Member

    For input power, you are right. 3HP electric brushless and 3HP gas motors' input power are almost the same. But electric brushless motor can achieve 65% efficient, the output thrust can be 160lbs. Does a 3HP gas motor have output thrust 160lbs? I think you know the result is not.
    And 160lb electric brushless motor is 3HP input, and equivalents to 7HP gas motor's output thrust. 180lb electric brushless motor is 4HP input, and equivalents to 9HP gas motor's output thrust. We had never said that a 3HP electric motor can equal 9HP gas motor.
    Due to that electric brushless motor has high efficient. A 3HP electric brushless motor can do a 7HP gas motor job. For the same job, the electric motor can save the energy and cost. If there happend to have the batteries in boats, you can consider to use electric motor. Or pepole always like cruise. The saving costs can afford to buy batteries costs. High efficient is also more eco and green for our earth. Like TESLA, many peoples are crazy for it. Currently electric brusless motors are just for smaller boats which are using below 15HP gas motor. They are just give peoples another choice for these area. For bigger boat, it's not our focus. But some companies do it.
    From your reply, we know that you are a very professinal man in this area. Thank you for your reply and interesting.
     
  9. Wavewacker
    Joined: Aug 2010
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    Wavewacker Senior Member

    Kerosene, thanks for pointing that out!

    Messabout, thanks for the details for comparison of electric and gas power.

    I think I'll just use my 55# trolling motor for what it was designed to do.

    For this boat (and thread) let's assume we will use a gas OB.

    I'll be paying closer attention to the burn rate and displacement cruise speed than the HP. Having some reserve is a good thing, but there is also the issue of manhandling the OB at times.

    BTW, my comments as to the quality of materials and workmanship, I'll be doing my very best with what I have.

    Another question as to design, I suppose a longer boat, say 28' could be achieved as with the "TIMS" project and a bolt together hull. Say two 14' sections or any combination with a narrow beam. A "lift top" and fold down windshield to address transporting the boat in sections. I don't mind another 30 minutes of cranking bolts to launch. The tow vehicle is an F-150 4X4. Any ideas?
     
  10. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    I didn't want to be the one and glad to see others have caught on, but this continued absolute BS about your electric motors is pure garbage. First you're seemingly and arbitrary mixing thrust with HP, which is clearly not the same thing and 3 HP is 3 HP, regardless of the type of power. Second, I don't know what kind of math you're doing, but you seem to be getting a lot more HP for thrust in your conversion, then everyone else. Now don't say it's because of the "brushless motor" because everyone is using them and understandably, consider it's working enviroment. Besides externally commutated motors have been around for many decades, so nothing new here to brag about.

    Wavewacker, your 55 pound motor is about 2/3's a HP, though if you listen to this fella, it's a about 1 1/4 HP. I'll leave it up to you who to believe. Bolger has a folding sharpie schooner that comes apart, into a couple of pieces. You can skip the rig and centerboard and go with a low power putt putt. In fact, the two pieces are designed to stack on each other, while on the trailer. Something to think about. A F-150 is capable of towing a lot more boat than you're willing to build. I used to drag around my 28' Chris Craft with a F-150 4x4. That was a lot more boat (about 9' beam, twin small block Chevy's, etc.) than you're looking for.

    [​IMG]

    Small trailer, so you know it's light.

    [​IMG]

    As you can see, it's a sharpie (not the skiff everyone tries to tell you is a sharpie), so it's low and lean. The folding schooner is about 30' long, with a tad under 4' in beam, so plan your accommodations wisely.
     
  11. Caroute Motor
    Joined: Jun 2016
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    Location: CN

    Caroute Motor Junior Member

    :) It's a new techical for market, not old type Minn Kota or MotorGuide carbon brush electric motor. Torqeedo is the leader of this area. We just a new competiter for this market. Actual using is better to type words with keyboard. If you are intersting, you can buy one in Amazon or ebay. If actual using can not make you feel the 3HP electric brushless boat motor can acheive a 7HP gas motor's power, please just tell us. The motor will free for you. We respect you as Yacht Designer/Builder and Business man. It's our promise.
     
  12. kerosene
    Joined: Jul 2006
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    kerosene Senior Member

    Power=thrust*speed
    If you think that for a second you realize that at lower speed same power can create higher thrust. Trolling motors have props chosen for very low speed operation so they get relatively high bollard pull (static pull, think bolted to a dock) thrust. I am positive that this originates from the fact that trying to sell 0,28hp motor is harder than selling "55" lbs motors.

    The nonsense about inputs and outputs is rdiculous.
     
  13. kerosene
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    kerosene Senior Member

    So at 1kn the trolling motor with 3hp might push as hard as 9.9hp outboard but at 5kn the power required might be such that trolling motor simply could not deliver it while the 9.9 will keep accelerating further. Thrust is NOT a meaningful measure of motors output unless speed is defined but then we are already back at talking about power.
     
    Last edited: Jun 25, 2016
  14. Wavewacker
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    Wavewacker Senior Member

    WOW, let me say that again.......WOW!

    If that doesn't scream river camp cruiser I don't what does. :))

    I did look it up and was directed right back here;

    http://www.boatdesign.net/forums/boat-building/folding-schooner-first-boat-53557.html

    Now for the concern PAR, in that thread you were giving caution about a first time builder biting off this much boat.

    Seems to me you'd build the first 15 feet as one project, heck it might even be a boat by itself. Then phase two, build the second boat......well, sorta.

    Like sticking two Little Cruisers together, it's a big folding Little Cruiser! I really like Matt's boat, I know others here do as well, but it's just too small by itself for us.

    Just a bit bigger than Troy's flat canoe, that's a nice river runner as well.

    So everyone, which boat takes the chop better, the dory I mentioned or this big sharpie?

    As a power boat seems stability might be an issue, I suppose some amas could solve that but reducing efficiency. A Tri configuration could increase usable space.

    Looks like any cabin would be slightly above the rails as a covered deck, not much of a cabin but a pop top or separate top and canvas might cure that when not underway.

    It's a third more boat, almost so I guess the budget goes up. LOL

    A big advantage for me is two fold, my trailer doesn't need much modification and folding the boat up means less storage space, being covered outside that clam shell will probably keep kids from trying to play inside it too.

    Now, I'm back in the spiral, just when I thought I had it figured out!

    What's you take on this? How many boxes of the SOR does this stretched limo check off? :)
     

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

    PAR Yacht Designer/Builder

    In that previous thread, the builder wanted to build from the plans printed in a book. They weren't complete and quite small, making scaling anything impossible, unless cutting to the closest half a foot is good enough.

    Both a dory and a sharpie will pound in a chop, but if the boat is long and lean, it'll be less uncomfortable, partly because it'll bridge over most wave trains. You might want to look at some of the Bolger skinny box cruisers. These tend to be quite long, but because they are, most chop gets chewed up under the entry and forefoot. A lean boat also has less frontal area to mash into, so pounding is diminished. Additionally, the longer hull shape will have a less dramatic rocker, so again, less tendency to bash the chop down.

    Yeah, making a SOR can be daunting, but the more you look and realize, the more refined it becomes, usually.
     
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