Having read lots of articles and watched dozens of YouTube videos on electric engine conversion on yachts, I couldn’t get the idea out of my head, writes Norman Rubenis.

Over a year or two, I kept going back to previously watched videos to check the finer details of each system and found the most well-known YouTube channel on this subject was Sailing Uma.

I started to look into a small electric pod drive unit to convert my 21ft Corribee fin keeler, but the cost was way more than the boat was worth.

I only paid £1,600 for it including an outboard and road trailer, so spending several thousand on an electric engine conversion didn’t make sense.

A move to cleaner motoring

Then in 2022, I purchased Charlotte, a 1980 Contessa 32. The plan was to convert to a full electric motor when I got her back to Grimsby Marina.

The sail down from Sunderland where I bought her did not go smoothly.

The first day was downwind motor sailing in very light wind following several days of rough weather; not a good combination!

Diesel fumes blowing into the cockpit the whole day coupled with a big swell meant I was very sick. I don’t normally get seasick, but I was throwing up constantly.

I pulled into Scarborough Marina looking very green and it took several days for me to recover and feel ready to set sail again.

After a few days, I set off for Grimsby with a flat sea and a good beam reach to the mouth of the Humber.

Every sailor’s worst nightmare became a reality when the engine refused to start. Approaching a very busy shipping lane just added to the stress and after having spent almost an hour wrestling with the engine I finally had to resort to calling for help.

The amazing RNLI came to the rescue and towed me into Grimsby docks.

A few days later I hauled out to start the process of engine removal and clean up of a very oily engine bay and bilge.

Before even purchasing Charlotte I’d been researching electric engine conversions and asking for recommendations on a few Facebook groups for electric sailboats.

The one name that kept coming up was Thunderstruck in the USA. It also seemed one of the best value options with a complete kit excluding the batteries.

The basics of the system is a 10kW 48V brushless DC air-cooled motor powered by two lithium battery banks; with a total of 560Ah at 48V this gave me a capacity of 28kWh.

At the time, off-the-shelf lithium batteries suitable for a set-up like this were very expensive and the choice was still fairly limited.

The logical route was to build my own battery system using 3.65V 280Ah Eve cells.

I could have managed with one battery bank (16 cells) but decided to double up to double the range – definitely the right decision.

The motor kit with gear reduction assembly was ordered from California and arrived in a few weeks.

Batteries were purchased from Fogstar in Worcester UK and the 32 Eve cells arrived the next day.

To balance each battery bank, I used Daly 200A 16s BMS (Battery Management System) units.

The whole system was easy to install with very clear instructions and diagrams. A hydraulic crimper is a must for this as you’ll be working with very thick cables (35mm2) to take the DC voltage, so it’s best to get the right tool for the job.

Other pieces in the puzzle: Victron 48V 3,000W inverter charger, DC to DC chargers to reduce the 48V down to 12V for the other systems on board, 800W of high voltage Sunpower Maxeon solar panels, Victron solar controllers, various fuses, monitoring/shunts etc. and lots of very thick DC cables.

A slower pace

So the big question is, how does she perform? The simple answer is, if you want to motor at 6 knots and have a decent range then electric is not for you.

But if you like the idea of free fuel forever with quiet running and are prepared to be a little more patient and motor conservatively, then perhaps you should look into this further.

It’s also worth noting that I did get the whole conversion signed off by a qualified marine electrician and, after doing this, my DIY electric engine conversion is now fully covered by my insurer, GJW Direct.

After numerous sea trials and a few teething issues to iron out, I set off from Grimsby in 2023 heading north up the East Coast towards Scotland.

Initially, I enjoyed good sailing but as I ventured further north the winds started to die.

Ironically, I was becalmed near a huge offshore wind farm east of Dundee. I’d already been motoring slowly just to keep moving but by the next morning, the sea was glassy smooth!

This is where range anxiety really kicks in.

Although I purposefully added that second battery bank I was still aware that I didn’t have the range a diesel would offer.

As the sun rose, I was able to motor from solar alone. I was drawing the same power as the solar was pumping in, so this gave me the confidence to keep motoring slowly at just a few hundred watts.

Battery percentage was quite low at this point so I reduced speed a little to add more into the batteries. I arrived at Peterhead Marina in the early hours with just 23% power remaining, something you definitely can not do with lead-acid batteries.

This one trip alone would probably have killed a conventional lead-acid battery set.

After a few days of waiting for a weather window and getting the batteries fully topped up, I set off for the Caledonian Canal.

I motored all of the canal sections and most of the lochs; I was able to charge up along the route as there are regular mooring pontoons with power hook-up, so it’s all very easy and clean.

During the next few weeks cruising down the west coast of Scotland, I was constantly amazed by how this system had coped, especially considering the amount of motoring and motor-sailing I’d done.

The ability to just feed in a small amount of motor when the wind dropped was an absolute joy. No need to start a noisy diesel engine, and then switch it off later. It really is that easy, it feels like cheating.

I left the motor switched to standby when sailing so it was always there when needed.

The throttle control is like a small engine control; forward, stop, reverse.

In the centre stop position, the motor is off, but the system is fully energised and ready, allowing you to add a little extra push when needed, for example when tacking in very light wind where there is not enough momentum to carry through the tack.

There is a key switch to turn the system off completely, much like any other engine ignition key switch.

The thought of going back to diesel honestly fills me with dread.

Obviously, there are pros and cons to every system – an electric engine is not for everyone.

Being a brushless unit there is, of course, some noise, unlike many electric motors which spin almost silently.

However, this type does have advantages.

For example, there are no brushes to wear out so essentially zero maintenance.

Also, a brushless motor offers some power regeneration, typically 1-3A, (50-150W) which is only a small amount due to the speeds a Contessa can sail at – but it’s enough to keep the systems running overnight when there is no solar input.

A question of balance

Originally I hard-mounted the motor and reduction gear to a stainless plate which was bolted to the engine beds.

This was my first mistake, as the high-frequency vibration was transmitted through the entire boat.

It was far noisier than I’d hoped and vibration was, at best, unpleasant. I later bought some lightweight engine mounts and had some new stainless brackets fabricated.

This made a big difference as it was much quieter and a lot smoother – lesson learnt.

If you plan to do this, use proper engine mounts specified for the weight of your set-up.

Mine were from R&D Mounts purchased through ASAP Supplies.

As I was removing over 150kg from the engine bay I was keen to put one of the batteries in there so boat trim could be maintained as close as possible to the original set-up.

Each battery bank is contained in an 18mm plywood battery box and weighs around 100kg.

So the motor assembly (approx 35kg) and one battery in the engine bay are similar to the diesel engine that was removed.

The second battery was added a bit later next to the mast.

However, this was a much bigger job as I had to rip out the entire port side bench seating and table.

A complete redesign allowed me to add a second battery under one seat and also a drawer fridge under the other.

There is also lots more storage. A new drop-down table sits between the seats to form a bed the same size as the original.

As this seating sits much higher, it allows clear views out of the windows while sitting at the table, a much nicer dining experience for sure.

Teething problems with my electric engine conversion

Overall, the conversion went as expected and initially performed well.

However, after running in the marina at different power levels I noticed the motor was cutting out at higher speeds.

I contacted Thunderstruck and was told the company had a bad batch of encoders and would send a replacement out straight away.

This arrived five days later. I fitted the new encoder which is a 1in square circuit board which plugs into the back of the motor.

This seemed to do the trick and the motor was back to running at full power. But, the issue was not totally fixed.

I contacted Thunderstruck again and was told the motor and controller may need to be completely reprogrammed.

The firm did offer to do this for me, but that means removing the motor and controller and sending the whole thing back to California – not ideal, so I’m looking for an alternative company in the UK to do this.

The 400W Sunpower Maxeon solar panels are amazing, regularly putting out way over their rated wattage.

Every report I’ve read about these panels puts them as the best. I’ve seen over 1kW of solar from 2 x 400W panels!

The reason I chose them is the panels run at a 60V output so are ideal for charging a 48V battery bank.

Lessons learned from a DIY electric engine conversion

What would I do differently if I had to do this again?

1. The first mistake was to assume it would be totally smooth and quiet; I was wrong. The motor still needs to be isolated with flexible motor mounts of the correct rating for the relatively small loads they are subjected to. Although it is not as quiet as hoped, I did remove all of the smelly diesel-stained soundproofing so if I were to add replacements in the future this would make it even quieter. It’s still comfortable inside even with the motor running, unlike the deafening noise and vibration of the old 3-cylinder diesel.
2. As the second battery is next to the mast, the cable length is considerably longer than the battery in the engine bay. This results in an imbalance between the two battery banks, so the solution is to rewire the engine bay battery with cables of the same length as the second bank. To achieve this means running the cables around the engine bay to use up the additional length.
3. I needed a new propeller as the original was badly corroded; the zinc had all but dissolved away. Next time I’d choose a feathering prop, allowing me to stop it completely so the motor is not spinning when sailing; I’d still have regeneration if needed by briefly running the motor in reverse to open the blades. I’m told feathering props run better for regeneration in reverse mode as the blades are in a more efficient orientation. In conclusion, I feel I made the right choice. Electric drive suits me and the type of cruising I am doing. If I have wind on the nose I’ll either tack or wait for a better weather window. I may add a small suitcase generator as a backup, but so far I’ve not needed one.

• Editor’s note: always consult your insurance company before making significant changes like this to your boat as it could invalidate your insurance. If fitting any battery system yourself, it’s advisable to get it checked and signed off by a qualified marine electrician.

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