While we see more and more electric cars on the streets these days, fully electric cruising boats are still a rare sight. In this blogpost we will discuss some reasons for that and try to determine for whom the switch to electric propulsion can already be worthwhile.
Understanding the Fundamental Differences Between Boats and Cars
There are two fundamental differences between boats and cars when it comes to electric propulsion. In cars, once you get up to cruising speed, the loads are relatively low, and you can recover braking energy. In boats, the loads when accelerating are less, but once you start to approach cruising speeds, the hull resistance goes up drastically, resulting in continuously high loads, and there is no braking energy recovery. The net result is cars can carry sufficient batteries to have hours of driving and a 300 mile range whereas for boats it is difficult to have more than an hour of operation at cruising speeds, resulting in an extremely limited range.
Current Challenges of Electric Boating
Other than purpose-built boats with a large surface area covered in solar panels and a massive bank of lithium-ion batteries, electric boats can only achieve short-range cruising.
Some high speed sailing catamarans can generate sufficient energy off a freewheeling propeller for modest subsequent electric propulsion but will still run up against the limitations of battery storage. For longer distance propulsion, a generator is required, resulting in what is known as a serial hybrid. Even with a generator, the overall efficiency and economics of electric boating are often not as favorable as a traditional propulsion system.
The Need for Higher Energy Density Batteries for Offshore Boating
To make electric boating viable for offshore cruising, or for any boat that requires more than a modest range under power, much higher energy density batteries are needed. Recent announcements from major automotive companies about anticipated advancements in battery technology by 2025, with double or even triple the energy density of current batteries, offer hope for the future of electric boating. In the meantime, every incremental increase in energy density expands the range of boats for which electric propulsion is appropriate.
Lack of Shore-side Infrastructure for Electric Boats
The more electric boats we get, the more likely we are to find a lack of shoreside infrastructure to support the charging needs. Unlike cars, where charging stations are becoming more widespread, many marinas and docks are not equipped with the necessary power supply to support a large number of electric boats. Currently, the Norwegian government is one of the few entities investing in the infrastructure needed for widespread electric boating.
Conclusion
At this time, electric propulsion is suitable for an ever-expanding range of boats with limited propulsion needs but is still not suitable for longer range propulsion or for extended runs at higher speeds. Parallel and serial hybrid systems show promise but are not yet well-developed.
Despite the potential, many have been disappointed with electric boating. It's important to be realistic and informed about current technology. Explore our Advanced Marine Electrics Course for more information!
If your interested in the past, present and future of boat propulsion, listen to Nigel's interview in the ShipShape podcast.