Electric outboard drive for small cruisers

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  • 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.
  • 09 Mar 2020 09:26
    Reply # 8809969 on 8809939

    Sounds almost excactly like the plan I’ve had in mind in case some kind of surpirise funding would suddenly appear. The Haswing has changed the situation a lot more appealing.

  • 09 Mar 2020 09:23
    Reply # 8809952 on 8809939

    The Haswing motor - £587

    The Relion batteries - £1600

    The 360W panel - £300 and it measures 195cm x 99cm

    The solar panel controller - £85

    The step down converter - £9.35

    The shoreside charger - £85

    Last modified: 09 Mar 2020 10:13 | Anonymous member
  • 09 Mar 2020 09:07
    Reply # 8809943 on 8809939

    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?

  • 09 Mar 2020 08:56
    Message # 8809939

    Jim's electric drive project for Hobbit got me thinking. I'd investigated electric drive before, when I was looking for sensible auxiliary drive for Weaverbird, but couldn't see how to work it out, so bought a Tohatsu 6HP Saildrive.

    Things have moved on a bit now. It still makes absolutely no financial sense, but it does now make practical sense. As I have said before, I will never be a petrolhead, and I will always dislike having to have an infernal combustion engine aboard. Add to that the fact that the outboard well does not accept a large 4 stroke outboard very well, needing it to be left in place in the water all summer, and something had to be done. Weaverbird and I could not accept the weight of the Tohatsu on a transom-mounted bracket, and I thought that I would have difficulty starting it in that position, but an electric outboard is half the weight, and starting it is non-existent issue.

    So I've started on an electrification project. 

    I have bought a parallelogram outboard bracket and mounted it on the transom. I am currently making up a removable plug for the outboard well, so that water doesn't splash up it and into the cockpit at speed (another annoyance I'll be glad to get rid of).

    I have bought a Haswing Protruar 5HP 24v electric outboard. This weighs 14kg, half the weight of the Tohatsu. The Haswing is the thing that has become available recently to make the project reasonably sensible. It is claimed to be equivalent to a 6HP petrol outboard in thrust, but I rarely need that much. I need half an hour of full throttle motoring on rare occasions (strong tides on the UK west coast, mainly), but mostly, trickling along at 2 - 3 knots will be enough, using much less power. It's good to have the extra power in reserve, just for the occasional burst when necessary, and I will feel comfortable with using it so long as I can then wait a day to recharge.

    I have bought a pair of Relion 100Ah lithium batteries to be wired in series. This is the expensive part of the project, but all the available electric outboards with integral batteries use lithium - it's the only way to get enough energy stored within an acceptable total weight. The Haswing and the Relion batteries weigh 40kg together. Using any form of 120Ah lead acid battery would make the total weight 76kg, with less usable stored energy, and I really don't feel able to lift 31kg batteries aboard and into place. The Tohatsu with a full tank of fuel also weighs 40kg. I have a sliding tray under the cockpit that has held six 10litre water containers, but I will sacrifice two of these to put the Relion batteries in the best place - low down, and as near to the motor as possible without having to make a watertight battery box to mount outside over the old outboard well.

    I have bought a 360W rigid solar panel - the largest that I can squeeze onto the deck between the mast and the companionway. When I added up what I would have to do to mount a lighter semi-flexible 350W solar panel, there wasn't much saving in weight, there was a lot of fabrication to do, and  the rigid panel cost a lot less. The panel will extend over the forehatch, but the hatch can still be cracked open for ventilation. I've not used it to get in and out of, so I don't think this will be a problem.

    I have bought a high efficiency 20A MPPT solar charge controller, to wring every last available watt out of the panel.

    I have bought a 24v to 12v step down converter, to run the existing 12v systems off the 24v battery.

    I have bought a high-spec battery charger for those occasions when I go into town for stores, and shoreside power is available.

    There will be some other sundries to add, but those are the major components.

    Last modified: 17 Apr 2020 07:29 | Anonymous member
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