Image courtesy Arc Boats

Port Electrification Series, Part 3

The Port of Los Angeles has shifted its decarbonization goals into overdrive. A handful of small but stout tugboats perform critical duties but produce an outsized portion of harbor emissions. Clean diesel fuels have already been optimized. A zero-emissions tugboat solution is more complex than simply swapping a diesel engine for an electric motor.

Tugboats are great candidates for electrification because they start and finish at the same base. However, they are not light equipment. Electrifying them is not as simple as electrifying a truck or a forklift, not when they push and pull 100,000+ metric-ton cargo ships that can be 10 times larger.

It is an order-of-magnitude engineering shift defined by power density, energy storage, and reliability under extreme load.

The Physics of Harbor Assist

Harbor assist tugboats are peak-output machines. Their duty cycles consist of short, repetitive missions that require tons of force, known as bollard pull. In other words, the physics of harbor assist vessels don’t cleanly translate to those of everyday road vehicles. Electrifying tugs isn’t simply a matter of scaling up existing tech. To accommodate short bursts of multiple thousands of horsepower output at very high load, quite a bit of engineering is required.

In passenger EVs, power fade is inconvenient. In harbor assist, power fade could lead to navigational hazards. Loss of thrust during a pivot could mean contact with a berth or another vessel. Considering the immense monetary value of giant container vessels, both in their cargo and the ships themselves, tug performance is critical.

Many cargo vessels carry hundreds of millions of dollars in cargo, sometimes more than a billion dollars. A propulsion lapse in these conditions is not a minor inconvenience; it could spell financial disaster. The stakes are incredibly high in designing a reliable, duty-ready harbor assist tug.

Capture courtesy Arc Boats

The Battery Scale Problem

Arc Boat builds electric vessels that don’t produce fumes, require little maintenance, and use zero fuel. It has been developing prototype electric workboats at the Port of Los Angeles since early 2025. Through a $160 million contract with tugboat operator Curtin Maritime, Arc is building a fleet of eight electric ship-assist tugboats that will deliver more than 4,000 horsepower per tug for the Port of Los Angeles.

Each tugboat will be powered by Arc’s vertically integrated electric powertrains and backed by a 6–8 megawatt-hour battery buffer. For reference, the battery size of a typical passenger EV is only ~60 kilowatt hours (kWh). That 6–8 megawatt-hour tug battery is in a whole different class, some ~130 times larger than the most common EV batteries.

The real challenge is not propulsion. Electric motors produce torque instantly. The constraint is energy density and recharge time under commercial duty cycles. With battery density improving, electrifying tugboats is no longer speculative. It is entering the early stages of what marine electrification can support.

The question then becomes not whether electric tugs can be built, but how ports will power them reliably without disrupting operations.

Next up, how to deliver megawatt power to vessels with no room for downtime.