Electric inboards
Can electric inboard engines fully replace marine diesels for cruising boats? It’s complicated, as Jake Kavanagh reports
Is it time to convert to green power? We quiz four owners who have done just that
Just a few years ago there were perhaps half a dozen manufacturers making electric outboards. Now there are nearly 40. We covered that market in detail last month; here we look at the latest tech for inboard electric solutions – and the remaining unsolved issues – for a hybrid or ‘electric-only’ conversion. There is also the possibility of installing a DIY electric inboard, relatively inexpensively, from equipment used in other sectors. The fork-lift industry, for example, often has a surplus of new and used DC motors that can be easily converted to marine applications.
Apart from the obvious advantages of silent motoring, renewable fuel, minimal servicing and precision control, electric propulsion allows for other possibilities. Very often the boat can be configured around a high-capacity battery bank that not only provides the energy for the motor, but for everything else as well. Plus the extra usable space reclaimed in the engine room, as demonstrated by Mark Johnson on page 48, means a Pogo 30 can hold the same crew and gear as a Pogo 36 – a saving of £50,000 up front!
Several builders now offer new models designed around a renewable energy system. Examples would be the Hanse Emotion with its ingenious rudderembedded pod drive, the Sunreef Eco catamarans, the Swedish-built Arcona 435Z (Z for zero emissions) and the eye-catching wood/epoxy Spirit 44E.
For the motorboat sector, the use of foils has allowed relatively small electric inboards to greatly increase both speed and range. German-based Torqeedo, for example, has co-operated with Swedish designer Candela to produce a stylish motorboat that has a top speed of 30 knots and a cruising range of 50 nautical miles on a single charge. Meanwhile, smaller electric ‘toys’ such as personal watercraft, surfboards and even pedalassisted water bikes can also eke out an impressive range by foiling to minimise the power required.
The two obstacles
However, two big obstacles to marine electric propulsion remain, especially for fast motorboats. The first is cost. The kit is expensive, sometimes double the price of an equivalent new diesel installation. However, once the initial outlay is covered, there is very little else to fund and so payback begins. Electric motors and batteries – if well looked after – should need almost no servicing or ongoing maintenance for years. Modern lithium-ion chemistries can deep-cycle without damage up to (and even beyond) 2,000 cycles, and brushless DC motors are pretty much sealed for life.
The second obstacle is range. We don’t yet have the battery chemistry to match the energy density of a gallon of diesel, which is why many yachtsmen still choose the hybrid route. Most battery banks of a manageable/stowable size can only provide about four hours of electric cruising speed in smooth conditions.
However, with so many recent advances in energy storage, that is also changing. Lithium-sulphur, for example, is now a cheaper and longer-lived
alternative to the staple lithium-ion, with higher energy densities per kilogram evolving every year. Meanwhile, the inventor of the lithium-ion cell, John Goodenough, has recently announced the lithium-glass battery, which he says will ‘finally make electric cars more affordable’. The range is said to be three times greater than existing chemistries, with the ability to fast-charge in minutes.
Meanwhile, the hydrogen fuel cell is seeing rapid development and is already being trialled for leisure marine.
For those not yet ready to invest thousands in the latest batteries, dependable lead-acid (98% recyclable) technology still provides a simple and relatively inexpensive solution that is mainly being used on the inland waterways. On flat-bottomed narrowboats, for example, the weight is also useful as ballast.
Hybrid or electric-only
For coastal sailors, who don’t expect to spend more than two or three hours under power, an electric solution is already proven. The boat can often put some of the charge back while sailing, with renewable power harvested from wind turbines, solar panels and by a freewheeling ‘hydro-regen’ propeller.
However, for passage-making to a timetable, such as during the annual summer holiday or a long weekend, a hybrid is often a better solution. This allows for electric manoeuvring in port, while on a long, windless passage the diesel takes over, with the electric motor becoming generator to recharge the batteries.
However, the hybrid does still present the owner with the need to buy and store fuel and have the engine regularly serviced, with ongoing outlay for labour and consumables. On the plus side, there is no real issue with range (just carry more fuel) and there is no need for a separate generator.