Electric-powered boat for under £8,000
Bob Shillito converts his classic 19ft (5.8m) clinker boat for near-silent river cruising
The 19ft river boat, Swift, now runs on a Waterworld 4. Credit: Bob Shillito
Just like many estuaries, here on the River Fowey in South Cornwall, it's a peaceful haven for nature, but motoring along in a petrol or diesel-powered boat shatters the tranquillity and harms the environment, writes Bob Shillito. Believing there is plenty of scope for converting existing boats to use quiet electric motors[1], even where there is little or no access to shore power[2], I set out to demonstrate that a professional-standard inboard motor conversion could be achieved at an affordable price for typical boat owners.
So I acquired the classic 19ft (5.8m) clinker-built river boat Swift for the conversion. Built in 1962, she was originally fitted with a 2-stroke Stuart Turner petrol engine[3], which may have been state-of-the-art 60 or more years ago but is certainly not in the 2020s!
The original noisy Stuart Turner petrol engine. Engineering masterpiece or an industrial relic?
The engine still worked but was very noisy, smelly and emitted a lot of oil.[4][5] I had no qualms about removing the engine as the boat is hardly a museum piece, and Swift would probably have been destined for the bonfire without this new lease of life. While marinas generally offer mains power and charging facilities, a river mooring is more challenging for an electric-powered boat.
While doing research, I kept being told that creating an electric-powered boat with no regular access to shore power was a non-starter, which was not what I wanted to hear! Thus, the challenge was set.
Speed and range of an electric-powered boat
Having launched Swift in late 2021 (and ensured that she'd float, which was not initially obvious), I set about establishing some real-world facts and fitted an ePropulsion Spirit 1.0 Plus[6] to an outboard bracket. This is a 1kW motor (roughly equivalent to a 3hp petrol outboard) with a 1.25kWh battery.
I wasn't expecting it to be enough, but it turned out to be remarkably effective. I could cruise the Fowey River for an afternoon at half power at about 3.5 knots.
Launch day after a major refit is always tense. First trials for the new electric-powered boat.
Credit: Bob Shillito Top speed was about 4.2 knots, which was similar to the old Stuart Turner. And, of course, the outboard was dragging the original prop through the water, too.
From this, I concluded that an inboard motor of about 4kW would be right, with at least 5kWh of batteries[7], giving a bit over an hour at full power but many hours at, say, 30%. The target range was set at 9 miles. Clearly, the boat needs to beat the powerful spring tide currents on the river but it's never going to exceed its hull speed of 5.9 knots.
With the existing 11/7 bronze propeller[8] (ie 11in diameter, 7in pitch) and estimated prop slip of 35%, I reckoned the top speed (at 1,500rpm) would be 5.6 knots.
Specifying the system for an electric-powered boat
Following the trials, the design criteria were set at:
- Quiet cruising for at least 9 miles (16.5km) at around 4 knots (7.5km/h)
- Top speed of about 6 knots (11km/h) - the hull speed of the boat
- Primary charging by solar
- Secondary mains charging at a pontoon
- Costing no more than a comparable new diesel engine and its ancillary systems
To meet the criteria, a balance needed to be struck when specifying the motor, batteries, solar array and mains charging. Motor manufacturers or their distributors generally offer a complete package, and while that eliminates much of the technical risk and saves the owner from having to grapple with some of the technical factors, it can be an expensive route to take. For example, one motor that seemed reasonably priced at first glance worked out at GBP18,000 when fully specified by the distributor.
Of course, there is always the hard-core route: get an old golf-cart or forklift motor and a retired Nissan Leaf or Tesla battery pack. These can be broken down and rebuilt using custom electronics for a very reasonable cost but we're talking about some seriously technical work, both mechanical and electrical. I did consider this approach, but the objective is to go boating, not spend years in the workshop grappling with tech issues to achieve the ideal electric-powered boat.
Furthermore, I wanted to achieve a repeatable, quality result that did not look or feel home-spun.
Motors
Dozens of inboard electric motors are listed on the excellent plugboats.com[9] website, but most are not available here in the UK. Three that are readily available were considered in detail. The Lynch Yellowtail/Marlin, the Bell Marine Drivemaster and the Waterworld range.
Lining up the Waterworld motor to figure out engine mountings.
Credit: Bob Shillito I selected the Waterworld 4 from Energy Solutions for several reasons: it is a compact design with good control systems and a significantly lower price than the alternatives. Waterworld also provides a very good manual, which helps ensure a trouble-free installation.
Indeed, the installation work was straightforward and completed in a couple of days, details are covered further down the article.
The engine connected to the original propshaft via a flexible coupler. Credit: Bob Shillito The motor runs at a top speed of 1,500rpm, which matches the nominal speed of the engine it replaced, meaning that the original propeller and shaft could be retained.
Batteries for an electric-powered boat
You can power a boat with traditional lead-acid batteries or with lithium.[10]
Lithium batteries are much lighter, can use their full charge, last longer (more charge-discharge cycles), but are much more expensive. Either way, the 48V motor system would need several batteries in some combination. A usable 5kWh of lead-acid batteries was going to work out at about 400Kg, which would overload the boat, so the decision was made.
But which lithium batteries? LiFePo4[11] is the preferred battery chemistry for this type of application, and there are a lot available. Furthermore, all lithium batteries require a battery management system (BMS) to ensure they charge and discharge evenly and safely, which may be within the battery or external.
The Victron mains charger, which has actually had little use due to the success of the solar installation.
Credit: Bob Shillito You can't get away from BMS: lithium batteries won't charge properly without one, and the early lithium batteries that lacked them suffered from reliability issues. Typically, the more expensive batteries have a data connection (called CanBus) which allows communication between them, the BMS and the motor's controller to keep everything in balance.
This is all very well, but do you want to rely on data connections more than necessary? What about the salty environment?[12] We all know how electronics on boats can pack up at the slightest opportunity.
Some of the batteries have fans in the side, which didn't seem like a great idea in a marine environment, either. With all this in mind, I selected a reasonably priced battery with an internal BMS, the Polinovel Novel 12100 from Quality Source. Four of these, connected in series, add up to 48V and a total store of 5.12kWh of energy.
A screen from the app used to monitor the status of each battery, and showing here the voltage, current draw and temperature when motoring.
Credit: Bob Shillito However, with no communication between the batteries, you need to keep an eye on their individual state-of-charge to ensure that they don't drift out of sync, with one battery at a higher or lower charge than the others. Fortunately, each battery has a Bluetooth link so you can use a phone app to monitor the state-of-charge, voltage and temperature.
The combined weight of the motor and batteries is a little less than that of the original 90kg petrol engine, with better weight distribution in the boat. The batteries fit neatly under the V-berths in the cabin, two on each side.
Charging for an electric-powered boat
Swift's large cabin provided an ideal area for solar panels,[13] although the curvature of the cabin top meant that flexible panels were needed. Several types of panel were considered, with the objective of fitting the largest area possible.
One supplier, the Italian company Solbian, custom builds panels to your dimensions, which is attractive but costs around three times the price of standard panels.
Three 110W SunPower panels were chosen for their fit, price and flexibility. My prior experience of solar charging was limited to bilge pump[14] configurations, so I carried out charging trials to ensure the system worked correctly before gluing the panels to the boat.
Testing the solar array with the charge controller and batteries to ensure they all behaved as expected before they were installed. Credit: Bob Shillito
The solar array supplies up to 1.5kWh each day to the batteries through a Victron MPPT charge controller. Victron is the market leader in this area, and this controller is a superb piece of kit: at under GBP200, it is fully configurable and has an excellent app that shows you where in the charge cycle it is operating, the maximum charge rate and the total for each day. The solar charge system always remains on, meaning that the batteries can be charged while the boat is in use, thereby extending the range.
A Victron Titan mains charger was also selected and installed, which can fully recharge the battery array in under four hours when shore power is available. Being an older design, the Titan's controls are far less sophisticated than the solar unit but it does the job - which is just as well because there is very little choice when it comes to 48V chargers.
The results
The boat has been in use for two months, and trials have shown not only that the design criteria were exceeded but that the revitalised Swift is a beauty to use. The target cruising speed of 4 knots is achieved at a surprisingly low 1.2kW power consumption.
Because the original propeller is smaller than the recommended size, at maximum revs of 1,500rpm, only 2.8kW is used - rather less than the rated power of the motor. This is good news, as it reduces current draw from the batteries and helps to extend the range while still achieving the maximum speed when needed, such as to beat the strong currents associated with spring tides in Cornwall.
Three screens from the app used to monitor the Victron solar charge controller showing (from left) the current charge status; settings; and a summary of the previous days' charging performance At around 18 nautical miles (33km), the range is at least double that of the original design criteria.
We have been able to make trips from the mooring, out to sea to a favourite beach and back - 8 miles - and been surprised to find that over 70% of the battery charge remains. After a day or two, the batteries are fully recharged, and, outside of testing, pontoon charging has not been needed. The lack of noise is an extraordinary experience: at the helm, it's perfectly possible to carry on a normal conversation with someone sitting on the bow.
Bob is now experiencing near-silent cruising on his electric-powered boat.
Credit: Bib Shillito When cruising the backwaters, wildlife no longer flees, and other water users are intrigued: people are amazed at how silent the boat is, particularly when manoeuvring at a jetty or pontoon. Gone forever is the lingering oily smell in the cabin that some find an acceptable part of boating and others - my wife included - definitely do not.
An electric conversion can be expensive. Sophisticated systems and lithium batteries increase the price. However, careful selection of components brought the total cost in at a similar price to a professionally-installed diesel engine, under GBP8,000 all in.
Swift is now set for a new lease of life, and hopefully, others can learn from the conversion.
Straightforward Installation
The installation of the electric system was remarkably straightforward in contrast to the renovation of the boat, which took months. Since this is an article about electric boating and not clinker boat restoration, I'll gloss over the eight weeks spent cutting in new pieces of plank and rib, and scraping greasy, flaking paint out of the bilges. The Waterworld motor has mounting brackets designed to adapt to most situations: they can be used either way up via various sets of bolt holes.
In most cases, where there are conventional longitudinal engine bearers in the boat, it would be simple to fit anti-vibration mountings (sold separately) and then bolt the engine to them. However, Swift has two hefty cross beams to which the old Stuart Turner was attached, which made mounting difficult since they were in the way
of the bolts.
The rear of the graphic display and the solar charge controller; data cables and wiring are above, power cables and isolator are below. Credit: Bob Shillito
Once these issues were overcome and the engine was in, the motor was aligned to a new flexible coupling attached to the original 3/4 in bronze prop shaft. The four 12V, 100Ah lithium batteries are not much bigger than regular car batteries and can be installed anywhere fairly close to the motor, to minimise cable runs and lost power. As the boat was a little stern-heavy with the old motor, I wanted to set the batteries forward.
As luck would have it, they fit perfectly under the V-berths in the cabin, two on each side, where they are secured with rack-straps. A benefit of lithium batteries is that they do not need to be fitted upright, so I could lay them against the hull on pieces of Correx floor protection sheet. As the cables had to pass through the bilge from one V-berth to the other, I ran them through lengths of plastic piping for additional protection.
The solar panels were stuck to the painted cabin roof with CT1 adhesive, while the cables pass through the roof and are sealed in place.
Parts of the installation showing the throttle, graphic display, ignition key, main relay and the motor. Plus a fire extinguisher. Credit: Bob Shillito
Through-deck cable glands would be a more robust solution, but at a higher price. The motor comes with a wiring loom for all controls and a master relay. This is very simple to wire up - just a matter of ensuring the cable runs are not too long before cutting holes for the throttle control, display and ignition key.
Power cables need to be made up to connect the motor to the batteries via a master fuse, isolator switch and bus bar. All these marine-grade items can be bought from a supplier such as 12 Volt Planet, along with terminals, insulator caps, and tools. The 35mm2 power cables are substantial and need perfect termination to avoid problems, so a proper crimping tool is essential.
It is worth practising some crimps on short lengths of cable first.
Swift's solar array, glued to the cabin roof. Credit: Bob Shillito The chargers were simply mounted in convenient locations where they are most protected from damp and any rainwater leaks.
The mains charger is fed by a standard marine/outdoor 16A cable inlet, to which a cable can be fitted when using shore power. Being a wooden boat, a reliable bilge pump is vital, so I decided to keep it separate from the motor installation. I retained the existing configuration, installed a year earlier, of an automatic pump, small 12V car battery, 10W solar panel and charge controller.
You can watch Bob's video about the conversion by clicking here.[15] Cost of conversion to an electric-powered boat
- Waterworld 4 motor, including controls: GBP3,360
- 4 x Polinovel 12100 batteries: GBP2,396
- 3 x SunPower solar panels: GBP728
- Victron chargers: GBP928
- Propshaft coupler & engine mounts: GBP230
- Cabling & electrical accessories: GBP337
- Total: GBP7,979
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References
- ^ electric motors (www.pbo.co.uk)
- ^ shore power (www.pbo.co.uk)
- ^ petrol engine (www.pbo.co.uk)
- ^ engine (www.pbo.co.uk)
- ^ emitted a lot of oil. (www.pbo.co.uk)
- ^ ePropulsion Spirit 1.0 Plus (www.pbo.co.uk)
- ^ batteries (www.pbo.co.uk)
- ^ propeller (www.pbo.co.uk)
- ^ plugboats.com (plugboats.com)
- ^ traditional lead-acid batteries or with lithium. (www.pbo.co.uk)
- ^ lithium batteries?
LiFePo4
(www.pbo.co.uk) - ^ his is all very well, but do you want to rely on data connections more than necessary?
What about the salty environment?
(www.pbo.co.uk) - ^ solar panels, (www.pbo.co.uk)
- ^ bilge pump (www.pbo.co.uk)
- ^ Bob's video about the conversion by clicking here. (www.youtube.com)
- ^ are available through Magazines Direct - where you can also find the latest deals (www.magazinesdirect.com)
- ^ Facebook (www.facebook.com)
- ^ Instagram, (www.instagram.com)
- ^ TikTok (www.tiktok.com)
- ^ Twitter (twitter.com)