Electric outboard drive for small cruisers

  • 12 Mar 2020 20:08
    Reply # 8823963 on 8809939

    You raise some interesting points, Darren.

    I chose one large panel because that way I get 72 cells and a quoted max power voltage of  38.9V . I can afford to lose some output, and still stay over the 28V I will need to charge the battery. If I'd gone for two smaller panels in parallel, to get the same wattage, I would have less max voltage to eat into. If I'd gone for two smaller panels in series, the voltage would stay up, as I could get up to 72 cells again, so maybe that would be an alternative. Within the space I have available, I could get the maximum wattage with the single panel.

    Then there's the question of how the controller processes up to 38V and up to the panel's max 10A, to put the maximum power at 28V into a 24V battery. What proportion of the nominal 360 watts will the MPPT controller pass on to the battery? 360 watts at 28V means the current would be 12.8A.

    My intention is to see whether the output of the panel limits me in any way, other than having to have enough patience to chill out at anchor waiting for some power to be generated. That would be good for me, to develop a bit more zen. If I genuinely need more power for safety, my preference would be for a wind generator. Having got rid of the drag of a prop in the water, I'm loath to put one back in for hydro-generation. It seems to me that to get good efficiency they need a variable pitch prop, like the Oceanvolt. That way, when there is full boat speed and an excess of wind power in the sails, the hydro power can be turned up to max, but when trying to make headway against a light breeze, the blades can be set to feather.

    With the batteries under the aft end of the cockpit, the weight distribution is very similar to how it was with the Tohatsu, and with that, there was a tendency to go bows down, with water collecting at the forward end of the cockpit. As I carry more ground tackle than normal, for cruising, and as the hull was designed to race with three up, I'm probably a bit light at the stern. I wouldn't want to put the batteries further forward.

    The Haswing comes with 4AWG/25mm2 cables, with a length of about 1.9metres built into the motor, then an Anderson connector, then a further 0.8 metre with ring terminals for the battery connection, in the normal open fishing boat usage. I will put in a 150A circuit breaker at that point, and  then I need a further 1 metre to reach the batteries under the cockpit. That 3.7 metres sounds like a reasonable length to me, for 25mm2 cable, and I'll hold off going up to 35mm2 for the moment. The voltage drop at full power is 2.64% according to this calculator.

  • 12 Mar 2020 20:05
    Reply # 8823958 on 8809939

    I don't know how this boat will sail and, for that matter, I don't know if my mental attitudes will have changed much in the five years that I will have been building her.  I might want to motor for more than 2 hours; I might want to motor sail.  I am watching with interest and, as ever, am astonished by your ever-agile brain, David, but for me I still see it as too much input and not enough out.  The time will undoubtedly come when I shall happliy convert to electric, but I don't believe that the technology has come of age.  For that matter, it's hard to justify buying all these new goodies, which have used a lot of resources to make.  I would have to use a lot of petrol to produce the equivalent carbon footpirnt.

    However, I can understand the intellectual challenge and the simple curiosity to see how it will work.  I am following this story with great interest!

  • 12 Mar 2020 19:19
    Reply # 8823850 on 8823175
    Jim wrote:

    Oh dear, what have I done!? well, David, we will be watched. :-)

    It doesn't make economic sense to me either. I just feel compelled to do it. I think it's hard-wired in my DNA.

    For both of us it's an interesting project, rather than an essential change. You had a working diesel, I had a working outboard.

    Hey, someone has to be first! Not so long ago, electric cars were rare, and not very good. Now, the Powers That Be want everyone to be driving one within a decade or two. Boats will go the same way, as the technology improves.

  • 12 Mar 2020 17:03
    Reply # 8823559 on 8809939

    This looks like another interesting project David, I've been playing it though my head as I work on Leeway.  I have two thoughts, largely related to the projects I've been working on, rather than of real importance to what you're doing.

    On a boat Weaverbird's size it is difficult to fit a lot of solar and one large panel might be as good as any compromise.  We just finished purchasing solar and I came to the conclusion that the number one problem was shading, even just a few shaded cells essentially knocks out the entire panel.  The flexible panels and controllers we looked at were also largely priced by watt, such that several smaller panels and controllers were the same price as one equivalent large one.  Smaller panels and controllers allow you to dedicate a single MPPT controller per panel.  Thus, if one panel gets slightly shaded, the other still has full output.  Controllers used to be much more expensive, the drop in price makes this kind of system more attractive.

    It would be nice to be able to generate power under sail in addition to solar.  You don't mention a wind or water generator, given your extensive experience you probably have a reason for this.  I don't really care for the noise of wind generators, and their of limited use if you like protected anchorages, but I wonder if there might be some merit in a water generator to ensure that you arrive with more charge in the batteries?  It doesn't look like the Haswing would be easy to turn into a generator, and that might be just as well given the backwards prop is going to be fairly inefficient as a generator.  Before the advent of cheap solar, water generators seemed to be more popular.  Do you have any thoughts on their utility?  I have a half-baked plan to make one out of a hoverboard motor and use some photogrammetry to mirror a prop with the 3D printer to see if I can make an efficient matching prop.  Admittedly, a good part of the motivation for this project is to have an interesting build with my sons.

    We had a Hurley 20 that came with a 80lb, 9.9hp power motor, when it died we temporarily used a featherweight 2hp evinrude and then a British Seagull.  The boat was far happier with either of the two lighter motors on the stern.  If it weren't for the cloud of smoke, I'd of been entirely happy with the Seagull. In many ways, the Haswing is an electric British Seagull.  It might be beneficial to mount the batteries far enough forward to keep the weight out of the stern.  I wonder if it might make more sense to put the batteries under your setee berth.  Although batteries close to the motor is nice, some heavy gauge cable can overcome distance and it would be nice to take the weight out of stern, maybe less so with the broader stern of a Hunter Duette than I experienced with the Hurley 20.  Although tinned cable is best, I pulled a lot of old untinned welding cable out of Leeway during the refit.  Despite some shoddy installation practices, it was all in excellent condition.  Sealed with some glue-lined heatshrink, welding cable might make an inexpensive way to move the weight of the batteries  out of the stern.

    Looking at the photo of the Haswing, it looks like they might have done what so many manufacturers do, which is to put wires that are too small for the rated current (sized by max ampacity of the wire, rather than for a low voltage drop) in order to save a few bucks in production.  I'd check the wire size and maybe it would be worth replacing the wires on the Haswing while you're still in the comfort of home.  Sizing for 3% voltage drop will give you higher output power, less wasted power and make you less likely to damage the motor (amperage increases as voltage drops which risks overheating).

    Looking forward to hearing your results.

  • 12 Mar 2020 14:24
    Reply # 8823175 on 8809939

    Oh dear, what have I done!? well, David, we will be watched. :-)

    It doesn't make economic sense to me either. I just feel compelled to do it. I think it's hard-wired in my DNA.

  • 10 Mar 2020 22:30
    Reply # 8820051 on 8809939

    I should have said that I also bought a remote meter for the solar charge controller, which is capable of real-time monitoring of all aspects of the charge and discharge cycles. I should be aware of how many Ah I'm generating and using.

    The difficulty with trying to estimate how much running time I will have is that petrol outboards are not directly comparable to electric outboards. All the electric outboard manufacturers quote an "equivalency", but it's hard to pin down exactly what they mean. The input power of the Protruar 5.0 is given as 105A x 24V = 2520W, which is only 3.37HP, not 5HP.

    I have in the past used a Bison 68lbs (42.5% of the thrust of the Protruar 5.0) motor, which has a max input power of 768W (31.7% of the input power of the Protruar 5.0) and a max output power of 696W quoted. This is where I derive my belief that 1HP is probably enough for "trickling speed" in a calm, but nowhere near enough for manoeuvring in fresher conditions, and also that it's difficult to compare apples with oranges with bananas.

    It may be the case that the Protruar 5.0 has the same thrust as a 6HP petrol outboard, despite having less input power, as the prop is larger and slower turning, but in the end, the proof of the pudding will be in the eating.

    Last modified: 11 Mar 2020 11:07 | Anonymous member
  • 10 Mar 2020 21:32
    Reply # 8819975 on 8809939

    According to the back of my envelope:

    Your batteries probably won't be brim full so you're discharging from 90% to 20% which is a useable 70Ah, the voltage under load will average about 24v giving 1680watt hours.

    I agree with the mechanical rule of thumb that 750w=1HP but the data given by Haswing is that for their 1hp outboard they get 1 shaft horse power from 50A at 12v = 600w. 

    And for your 5hp model they claim 5 shaft horse power from 105A at 24v or 504w per shaft horse power. Make of that what you will.

    I would guess you'll be drawing 30A as you glide along toward harbour over a glassy sea, so with other losses taken into account you're looking at 2 hours capacity and leaving a margin of error perhaps banking on an hour and a half of motoring might be sensible. 

    Very interested in finding out how it turns out. I wonder if you could incorporate an amp-hour meter into the system, something like a dr.wattson meter or an old second hand e-meter or equivalent. 

  • 10 Mar 2020 18:31
    Reply # 8819531 on 8809939

    With lithium batteries, it's OK to discharge 80% of their nominal capacity. At 25.6 volts (the nominal voltage of these batteries is 12.8) that's ~2000 watt-hours. I know that 1 HP (750 watts) is enough to move Weaverbird at better than 2 knots in flat calm and flat water, so I have better than 2.5 hours or 5 miles range. That should be enough to get me into harbour when the wind dies at sunset.

  • 10 Mar 2020 18:04
    Reply # 8819438 on 8809939


    have you estimated for how long you can drive the motor with 2-3 kts speed with your battery choice?

  • 10 Mar 2020 11:48
    Reply # 8817617 on 8809943
    Annie wrote:

    I should love to trade the BBB for electric, but dare I ask what it all cost?  And please could you give me the dimensions of the ginormous solar panel?

    As Fanshi should be able to carry more weight, I would go for something more like these: good deep cycle AGM 130Ah batteries at £390 and 62kg for a pair. Sadly, I don't think Weaverbird and I could cope with batteries as heavy as that.
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