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!

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.

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.

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.

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.