Ships return to renewable energy power

Since the earliest days of sailing, boats and ships have been powered by renewable energy. At first, the motive energy came from muscles manipulating oars. I would have said human muscles, but boats predate modern humans. Almost a million years ago, Homo erectus settled several Indonesian islands that couldn’t have been reached without boats.

Boats with sails aren’t known to be that ancient; the first evidence of their existence starts around 7,000 years ago. Recreational sailboats, and various types of boats with oars, are still commercially viable.

On commercial and military ships, bigger and bigger arrays of sails gave way to propellors powered, at first, by coal-fired steam engines, and then by liquid-fuel powered internal combustion engines. Starting just after World War II, nuclear-powered military ships were developed. They represented the last major change in power system for aquatic vessels for decades…

…Until now. Innovative renewable energy systems are starting to show up in boats and ships of all sizes.

Cargo shipping companies, having realized that wind energy can be used to reduce the amount of fuel needed for engines, are working on cargo ships that have sails in addition to engines. Modern cargo ship sails are computer controlled. Their designs look like vertical airplane wings. They’re based on composite materials like fiberglass instead of canvas.

These technological advances have been combined to enable wind energy to be added back to ships without also adding back the huge crews that used to be needed to manage sails. Several tests are at advanced stages. Large-scale commercial use seems imminent. Fuel cost savings can be very significant. The Pyxis Ocean, a full-scale prototype cargo ship that completed a six-month test in early 2024, reported savings of up to 11 metric tons of fuel per day.

Recreational boats are starting to add batteries and solar recharging systems, either in addition to sails, or by themselves as the primary motive power systems, or as part of hybrid systems in which the batteries supplement internal combustion engines. The boating industry hasn’t adopted batteries as quickly as the automotive industry, but virtually all boat types are now available with partial or full battery power.

Hybrid boats, like hybrid cars, reduce the amount of fuel used while still retaining the ability to use fuel for extended-range trips. Although the use of regenerative braking isn’t as valuable for a boat as it is for a car, a propellor operating in reverse can recapture energy to help recharge batteries. Solar panels can productively be put on the top surfaces of designs with large surface areas, like catamarans or trawlers. Solar enables the batteries to continuously recharge and extends the range of the boat.

Batteries in a boat can be used as ballast, making their weight an advantage, rather than the disadvantage it is in cars. In a pure electric boat, the batteries can be placed just above the hull, with the space that would otherwise be used for engines and engine cooling systems available instead for additional passenger accommodation or storage.

As one might expect, prices for electric boats are still higher than they are for conventional boats – much more so than for cars – because mass production effects haven’t occurred yet. Recharging infrastructure availability at marinas is also a concern, even more than recharging system availability is for cars.