Guinness World Record holder Simon Milward explains how he built and motored his solar-powered boat across the English Channel...
Developing the first boat to cross the English Channel powered directly by solar panels (with no batteries) was a rather circuitous journey.
It had started a couple of years earlier when I’d seen a massive, bright orange Tucker Sno-Cat in London’s Science Museum. This had been part of the first convoy of motorised vehicles to cross the Antarctic.
Looking at the Sno-Cat, I’d wondered if I could make a solar powered vehicle to cross Antarctica. After all, the Antarctic actually contains the biggest desert on earth and has 24-hour daylight in the Austral summer.
So it should be the perfect location for a solar powered vehicle (but for all the ice, snow, freezing temperatures and blizzards).
I mentioned this to my dad as a joke and he said he thought the Sahara would be better. So I made a solar powered electric bike and, in 2013, traversed the Western Sahara on it.
I contacted Guinness World Records after the crossing, but they said there would potentially be limitless similar challenges and they could only provide records for travelling between specific, clearly defined areas such as crossing a body of water from one country to another.
I asked if crossing the English Channel would do and they said yes (with certain stipulations, including having a support boat, at least two independent, qualified timers, not using batteries and taking less than 12 hours).
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I’ve always been environmentally conscious and with an increasing concern about climate change, converting my new-to-me sailboat to fully electric…
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Building the boat
I therefore set about building a boat. I had a solar panel company and so had plenty of panels including the two that were optimised for directly powering the 24V electric bike to cross the Sahara.
I looked for a catamaran hull on eBay, thinking something between 14ft and 17ft would be good as it could both fit on our van and have enough space for about 10m2 of panels.
In 2014 10m2 equated to about 1,200W of solar power at maximum insolation. I found a man on eBay selling a Dart 15 catamaran base that was in good condition, apart from the transom of one of the hulls, and I bought it.
We repaired the transom and set about looking for second-hand motors on eBay. I found a 400W 12V Torqeedo and a 500W 12V unbranded trolling motor.
As with the solar bike crossing the Sahara, I was not using batteries. And the simplest way to avoid using batteries was to ensure the ‘Voltage at Maximum Power’ (Vmax) of my panels was as close a match as possible for the motors’ voltage.
Then I could wire the panels directly to the motors. This is different from normal solar battery systems where you typically size solar panels to have a Vmax up to 50% higher than the nominal voltage of your system (eg around 18Vmax for a 12V battery system).
You then use a charge controller to bring the voltage down to the appropriate voltage for the batteries.
This means that, even with less than perfect sunlight, the panels will still produce enough voltage to charge your batteries well.
Such panels, optimised for charging a 12V system, are often sold as ‘12V’ panels even though they’ll typically have a Vmax of 17-18V and a voltage at open circuit (Voc) of a bit over 20V when minimal current is being drawn.
So I needed panels that produced a Vmax within the voltage range of the motors, and the way to do this was to use panels with the right number of solar cells wired in series.
The two 220W panels that I made for the Sahara crossing each used 55 cells. Each cell gives a little under 0.5Vmax in good sunlight and so 55 cells gave 26.9Vmax.
In less than perfect sun the Vmax would drop slightly below this but should still remain around 24V. The key thing is not to draw too much current as this causes the output voltage of the solar cells to drop below their Vmax.
And for typical brushless motors using complex electronic controllers (on both the bike and the 400W Torqeedo boat motor), low voltages will cause them to cut out.
For the rest of the power I took four standard 180W panels designed to charge 24V batteries. These had 72 cells wired in series to give around 36Vmax.
I tapped these series strings of cells (by cutting holes in the backsheets of the panels) to create three strings of 24 cells within each panel. Wiring these three strings in parallel gave a Vmax of just under 12V for each panel.
The right combination
This formed an acceptable combination. I wired these six panels to a ‘junction box’ that consisted of three 10mm bolts, bolted in through the wooden superstructure that fixed the panels to the Dart hulls.
These three bolts were arranged in a neat line with each bolt around 10cm from its neighbour. I attached the two 26.9Vmax 220W panels to the outer two bolts and then wired two of the [approx] 12Vmax 180W panels to the first and second bolts and the other two 180W panels to the second and third bolts, all with simple ring-connectors.
I attached the 400W Torqeedo between the first and second bolts and the 500W trolling motor between the second and third bolts.
When run together, each motor would therefore obtain 12V from the junction box (12V directly from the two 180W panels wired to it and half of the 26.9V coming from the two 220W panels).
And, because solar panels have a very significant internal resistance, running just one motor would effectively just obtain the 12V from its two 12Vmax panels.
The first test was on the Thames with just three of the 180W panels and the Torqeedo. This worked pretty well despite relatively cloudy weather and the boat, now called AKT Solar after my solar panel company, easily made headway against the current.
So I prepared for a sea trial. For this we went down to Poole Harbour where in my childhood we’d moored a 24ft Trident sailing boat and spent every summer on it, sometimes even crossing the Channel to Alderney and the other Channel Islands.
We started putting AKT Solar together on the beach at Hamworthy near the water’s edge. It took nearly an hour to bolt everything together and by the time we were ready the tide had gone out and the water was about 20m away.
I tried to drag AKT Solar down to the water but she wouldn’t budge. Even with my dad we could barely get her to move at all and I realised she must weigh around 250kg. Fortunately two strong kayakers were nearby and readily offered a hand.
We then set off with both of us perched on the transoms. AKT Solar moved like a dream and we were quickly confident to go all the way to Pottery Pier on Brownsea Island.
I’d calculated that we would need to average at least 3 knots in order to be able to cross the Channel before the sun would start to get too low in the sky and I felt we easily achieved this, estimating our average speed to be around 4 knots. But I did not test this.
Given this success, I was ready. Over the next few weeks I looked for potential support boats. They were not cheap but I found a friendly one – Full Throttle Boat Charters – that worked out of Rye harbour and said they could shadow us to go from Dungeness to Boulogne Harbour.
They said they couldn’t guarantee the French coastguard would let us through, but they’d helped several pedalos to cross successfully. While I did not much like the comparison, I hoped that we’d be at least as fast as a pedalo.
They had given me a new concern though, that the French coastguard might not let us enter French waters. To try to reduce this possibility I registered AKT Solar as a Small Ship and also bought a French courtesy flag, a red ensign and boat insurance.
Time to go
In 2014 the sun was at its highest and the day longest on 24 June. A cloudless day around then would therefore be the best to cross, so I took the week off work from Monday 23 to Friday 27 June and on Sunday 22 June headed down to Rye in our Transit van with my dad and the disassembled AKT Solar.
The weather looked pretty good for that week but I needed clear blue skies for a whole day so I was expecting to have to wait. Full Throttle Boat Charters were very good about this and said I’d just need to tell them the day before leaving and they’d do their best to make themselves available.
Fortunately, by around 1500 on Sunday 22 June the forecast for the next day had improved to predict glorious sunshine.
That evening I wrote to a few media companies, including the BBC, to let them know of my plans, although I had no idea whether they’d be interested. I hardly slept that night. My worry was not one of personal safety but of failure, particularly given the time and money spent on getting this far.
The next morning, at 0630, Full Throttle Charters arrived to launch their support boat and tow me out to Dungeness, just beyond the power station.
At about 0830, with smooth seas and clear blue sky, I untied from the tow rope and headed AKT Solar for Dungeness’s steep shingle beach. I set up my GPS tracker, made sure my Go-Pro was on and that my dad was filming from the support boat.
I shouted “Go!” to the support boat to start timing as I jumped onto AKT Solar and set the Torqeedo. I had no idea if the motors or electrics would hold up and I was worried clouds may form or the winds pick up or the French coastguard not let me enter French waters. But at least I’d started and was on my way.
I quickly optimised the motors with the trolling motor on full power and the Torqeedo turned up as high as it would go without the voltage dropping below 10V and causing it to cut out. I could see a lone sailboat ahead but apart from that nothing except the support boat which travelled a few hundred metres in front.
For the first hour I felt we were doing quite well and the coastline behind me became encouragingly smaller and smaller.
After about two hours though, the white cliffs of the English coast were still clearly visible. But the sun was getting higher and there were still no clouds so I’d now been able to put both motors up to full power. I felt, again, I must be doing about 4 knots.
The support boat pulled closer to speak and said we were averaging about 3.5 knots which apparently compared quite favourably with a pedalo.
I was very happy with the speed, but not with the now-repeated comparison to a pedalo. But if the clouds stayed away, the wind stayed low and the motors and electrics kept working I felt I might actually make it.
After another hour we approached the first shipping lane and the support boat navigated me through it with no trouble.
Another hour later we approached the second shipping lane and had to spend about five minutes going round in circles waiting for a ship to pass.
Once it had passed, I headed straight into its wake and the Dart 15 hulls rode through the waves wonderfully, despite the weight of panels pressing us down.
The wind was picking up though, and with it the waves. Although AKT Solar continued to ride them well, I actually started to feel a bit seasick – which I’d previously thought could only happen to me on larger boats.
I was also getting rather sunburnt and uncomfortable from half lying, half sitting on the wooden board at the back of the boat.
But I could now see the French coast. And the clouds that had been slowly building in the distance looked to be over the land. I felt increasingly optimistic.
Unfortunately the sky had become a bit hazier and so the panels were producing slightly less power. This meant I again had to run the Torqeedo at less than full throttle as several times the voltage had dropped below 10V and tripped the controller, meaning I’d had to turn the engine off to reset it and then turn it on again.
Although the process of resetting the motor didn’t take long, it was a bit annoying, particularly as it slowed us down each time.
Fortunately, the unbranded, brushed motor, although not as propulsive, had no such requirements and would keep going at almost any voltage.
So I just kept this motor at full throttle and used its rudimentary power indicator as a way to measure the voltage coming out of the panels.
With nicely charged, reasonably-sized batteries I wouldn’t have had to do any of this because, as long as the batteries were big enough, they could have kept their voltage throughout the trip.
But that would have effectively made the trip a battery challenge rather than a solar challenge. As an extreme example, I could have charged up a couple of Tesla batteries using solar power over the preceding few days and then stormed across the channel.
I would still rightfully have been able to claim I was using solar power – although in that case it would have been stored solar power rather than using the power directly from the sun.
After another two hours, now a total of about six, the support boat drew alongside and asked if I’d turned down the throttle.
I sensed they were getting a bit bored and I certainly didn’t want to receive any unfavourable comparisons with a pedalo.
So I explained I thought it must be a bit hazier meaning the sun was a bit less powerful but that everything was still looking good.
Boulogne Harbour in sight
The support boat pointed out Boulogne Harbour to me and this raised my spirits considerably. The tide was now taking us quite quickly to the west but over the next hour the support boat guided me in perfectly and I breathed a sigh of relief as I finally passed the harbour walls into safety and calm waters.
A few minutes later I eased my aching body off the boat onto a lovely sandy French beach after exactly 6 hours, 59 minutes and 7 seconds. The support boat reckoned I’d averaged about 3.5 knots which I felt was excellent.
We then found a visitor berth for AKT Solar in Boulogne marina and I stumbled off to have a shower and get changed.
I was still feeling rather dazed when I turned my phone on and was surprised to have received some voice messages, including one from the BBC. I called them back and they asked me how it had gone.
I mumbled about sunburn and waves before thinking a bit more clearly and saying that in general the trip had gone very well showing the versatility and power of solar energy.
We left AKT Solar in the marina and headed back to England in the support boat. The trip back only took around 30 minutes and as we approached the South Coast the water was calm enough for us to get to over 50 knots – by a long way the fastest I’ve ever travelled on water.
That evening we took our van through the Channel tunnel and drove to Boulogne where we parked up overnight.
The next morning we drove down to the marina, took AKT Solar back to the sandy beach, dismantled her for the last time, and fitted her back onto the roof of the van for the journey back.
After getting home I had a few more phone interviews and made the full application to Guinness World Records. I was awarded the record on 16 December 2014. And now, eight years on, I’m still thinking about Antarctica.
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This feature appeared in the October 2022 edition of Practical Boat Owner. For more articles like this, including DIY, money-saving advice, great boat projects, expert tips and ways to improve your boat’s performance, take out a magazine subscription to Britain’s best-selling boating magazine.
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