The Sumpners Afloat

After nearly five years of living, working and cruising on “Old Nick”, managing the Electric Narrowboats FB group and organising Electrika for two years, we have had lots of opportunities to observe, discuss and ponder on what makes the perfect serial electric hybrid narrowboat.

This article will try and distill what we have learnt, in the hope that it will help other potential owners to specify a suitable serial hybrid for their needs and help boat builders to design a balanced and desirable electric narrowboat.

A serial electric hybrid (aka series hybrid) is currently the most efficient, “Greenest” Narrowboat design available. Propulsion is performed by the electric engine and an efficient, low RPM, inboard diesel generator is used to charge the battery bank (if needed) providing a “safety net” that makes continuous cruising possible on the UK canal system.

In addition to the diesel generator, power can also be provided by solar panels and, when in a marina, by shore power supply. We estimate that, over the course of our cruising season, our diesel usage is 30% of a comparable diesel powered narrowboat.

All About Balance

When it comes to the key components in the serial hybrid system, our advice would be to go as large as possible (budget permitting), you will not regret it. We originally specified a Victron Quattro 48v/5000VA, Leoch 48v 600A/Hrs Lead Carbon batteries and 8 x 160W (1280W) Solar Panels for “Old Nick”. Then at the eleventh hour, we decided to upgrade to a 48v/8000VA Quattro, 800A/Hrs of batteries and 12 solar panels (1920W) and although it stretched our budget to breaking point, it was definitely the right decision.

With some of the components, you will have physical limitations that restrict how large you can go i.e. space in the engine room or roof space for solar panels. Once you have identified your physical and budgetary limits, it is important that you then make sure the balance is right.

There is no point having a massive battery bank if it is going to take forever to charge them up, and there is no point having a massive generator, if your battery charger cannot handle all of the power it receives.

The Engine

Starting with the engine, in reality, on a typical 55-60ft narrowboat, your electric engine is going to spend most of its time consuming between 0.5kW (1.5 MPH) and 5kW (3.5 MPH) of power, depending upon the speed you like to cruise at. On “Old Nick” we like 2MPH at 1kW, so that when the sun is out, we experience what we call “State of Nirvana” – free propulsion.

Out 10kW Vetus E-Line engine has done us proud over the last 5 years, but if we were doing it all again, we would probably go for their new larger 22kW engine, which was not available at the time, but which Vetus recently launched (image below). We would also look at some of the latest low RPM, high torque, permanent magnet AC motors (PMAC), from such companies as; Lightning Craft, Torkmar, etc. which can turn larger propellers and profess to offer higher efficiencies and lower operating temperatures than other types of electric motors..

The Prop

It is very important that you correctly match the engine to a suitably sized prop. We are now running a 16″x12″ 4 blade, after replacing the original 13″x9″ 3 blade that Vetus supplied, and are very happy with this. Our larger prop is quieter (biggest reason for change) and accelerates and stops much quicker. We can no longer get the full 10KW power out of the engine, as larger props cause electric engines to hit their “torque limit” at lower power output, but as we have never needed the full 10KW of power in 3-4 years of use, we consider this a small price to pay for the other improvements.

In general a larger KW engine, is able to turn an even larger prop – see the results of Ortomarine’s recent Prop Trial for more information – but the design of your hull, in particular the skeg to prop shaft and prop shaft to uxter plate distances will decide the largest size of prop you can realistically fit.

The Battery Bank

The size of your battery bank will depend on the battery technology you choose. In our view, there are only two options; Lead Carbon (which “Old Nick” has) or Lithium LiFePo4 as these are the only two technologies that allow regular partial state of charge (PSOC) i.e. you do not have to fully recharge them every day like traditional Lead Acid batteries.

Back in 2020, when “Old Nick” was built, 48v LiFePo4 battery banks were few and far between and just too expensive for our budget, so we went with Lead Carbons and have been very happy with them. If we were doing it again in 2025, we would probably go for LiFePo4 as they allow you to discharge to <10% SOC without damaging them, where as Lead Carbons don’t like to discharge <40% SOC, except in extreme/rare situations.

That said, if you are in the “anti-Lithium camp”, for whatever reason, Lead Carbons are a very good alternative.

We average around 9kWh of power consumption every day when moored, which includes cooking an evening meal, but not water heating which typically consumes around 3kWh for enough hot water for two people to shower. In addition our propulsion typically consumes around 1.5kW per hour of cruising.

The size of your battery bank will dictate how often you have to run the generator, so it is an important decision to make. Our 48v 800Ah battery bank on “Old Nick” provides 38.4kWh of power of which 23kWh (60% is useable). With no solar at all (never happens) we could cruise for 1.5 days (6hrs per day), without running the generator.

For most of this month we have been averaging 7-10kWh of solar, so that significantly reduces the amount of time the generator is on and with the odd visit to a marina every couple of weeks, this reduces even further.

We feel 800Ah of Lead Carbon or 600Ah of LiFePo4 is about the minimum battery bank required on a boat fully dependant on electricity i.e. no gas or solid fuel. However, it goes without saying, that space and budget permitting, the larger the battery bank the better.

The Generator

The “dirty” component of the serial hybrid, is the diesel generator but this is also one of the most important parts if you wish to continuously cruise or spend weeks out of a marina.

They are expensive bits of kit, but surprisingly the cost to buy and install a Vetus 14kW model is only 20% more than the 6kW model that we have on “Old Nick” and yet you are getting over twice the power output and only marginally higher fuel consumption.

Much as we try not to, we sometimes have to run the generator to charge our batteries, so it would be far better to run a larger generator for less time (particularly when moored near other boats), have the extra generator power to help preserve battery life on long river passages or charge the batteries in less time, while cruising on a canal.

A larger generator, is definitely something we would seriously consider, if we were starting again.

The other decision to make with the generator is whether to have a dry exhaust or wet exhaust system. A dry exhaust is technically a better solution, where you have a skin tank of coolant that cools the engine/exhaust. If you decide to have one of these, make sure that the skin tank design is suitably large and capable of efficiently transferring the large amount of generated heat. We have heard reports of, some dry exhaust installations, overheating when the boat is stationary in summer months.

A wet exhaust, as we have on “Old Nick”, uses canal water to cool the engine and its exhaust gasses. Then it uses a separator to discharge the cooled gas and water through different outlets. This is quite a common and well proven system on sea-going vessels, but the muddy canal water can cause filter blackages and shorten the life if the water pump impeller. We have a regular routine of cleaning our raw water inlet, basket filter (every 2 weeks) and replace the impeller every year, just to be on the safe side.

Battery Charger/Inverter

At the heart of the serial hybrid system is the battery charger/inverter, which in the case of “Old Nick” is a Victron Quattro 48v/8000VA – a 110A battery charger and a 8000VA (6500W) inverter. A Quattro has two AC inputs – one for the generator and one for the shore connection.

With our 6kW generator, we typically set the Quattro to limit AC output to 23A, just over 5KW so that the generator is not always operating at its maximum output. When on shore power the Quattro is set to limit AC output to 13A, to minimise the chances of tripping the marina’s electricity bollard.

We have never needed more onboard AC power than the Quattro can provide, regularly running the kettle, hob and oven at the same time. but if we had a larger generator, it would make sense to fit the larger 10000VA version so that the battery charger is better matched to the generator.

Solar Panels

One area where it makes sense to go as large as possible, is solar, after all once the panels are bought, it is all free energy.

The biggest decision is whether to go for rigid panels or semi-rigid panels. There is no doubt that the rigid panels are more efficient, but only if you remember to tilt them towards the sun, which when regularly moving is an extra chore. By comparison, the semi-rigid panels will always provide a good level of solar yield and have the added benefit of not snagging ropes and being walkable on.

Our 12 x 160W panels have generated over 6 Mega Watts in the last four and half years and despite being relatively old now, are still regularly keeping “Old Nick” in the daily top 5 of Ortomarine boat’s solar yield, despite some of the latest boats having 14 x 200W panels.

240v AC Shore Connection

One final design decision to make, is what size of AC Shore connector and cable to fit. When we were specifying “Old Nick” we decided to go for the larger 32A connector, in the hope that more marinas would start to fit them. Adoption has been pretty slow and for most marinas that we visit, we have to use our short 32A to 16A adaptor and accept that we will need a full overnight charge (approx. 10-12 hours).

Last year when we did the Grand Union, we did get to plug in to a few 32A charging points and managed a full charge in 4-6 hours, which was great and I would probably recommend fitting a 32A connector and cable if you have the budget. Aqua Vista fitted a new Rolec fast charge bollard at Electrika last year and I hope that more marinas will follow their lead.

Data Monitoring

We have been spoilt with our “Ortomate” control and monitoring system, that Ortomarine boats have as standard. Every aspect of the serial hybrid’s performance can be monitored and displayed and it is amazing how it has become part of our daily routine.

Three key data measurements should be mandatory on all electric narrowboats – Motor RPM, GPS speed and Motor Current or Power. With these three key pieces of information you can optimise your cruising behaviour for minimum energy consumption, quickly detect issues like weed on the prop and avoid excessive current draw because you cannot hear you are going too fast!

For those not lucky enough to have an “Ortomate”, Victron are now making it a lot easier to monitor most of this critical data on their Cerbo GX with the latest V3.60 firmware. Connect a GPS sensor (via USB or NMEA2000), feed in the engine data via NMEA2000 and the Cerbo GX will create a rather good new “Boat” Page.

In Summary

We along with many other happy owners, have proved that the technology needed to design a reliable and efficient serial hybrid, is definitely available now. That said, it is still possible to make mistakes. Our hope is that if people like us share our positive experiences, shows like Electrika help educate potential owners and the industry follows the lead taken by boat builders already creating successful designs, more and more boat owners will be able to safely enjoy “going electric” and the benefits this technology brings.