NORWEGIAN equipment maker Kongsberg Maritime has unveiled a design for a “super-efficient” bulk carrier that could cut CO2 emissions by 40%-50% while costing 20% less to run.

The 82,000 dwt kamsarmax would do this with a mix of sails, air lubrication, shaft power, a controllable-pitch propeller and other technology.

Kongsberg Maritime estimated fuel savings of 44% on an average global bulker route and more than 50% in the North Atlantic, where winds were better.

Kongsberg Maritime strategy and business development vice-president Oskar Levander said it would cost about $8m-$10m more than a conventional state-of-the-art bulk carrier, but save 30%-65% of fuel costs depending on the lifetime of the vessel. Levander estimated payback time would be five years.

“This is the kind of thing shipowners like to hear,” he told a press briefing in Oslo.

Bulk carriers make up the smallest share of alt-fuel newbuilding orders because of the bigger challenges of cost and fuel supply for ships with irregular routes. The goal was for the design to comply with the Carbon Intensity Indicator throughout its lifetime while using conventional fuel.

Levander said the higher estimated savings came about by using technology to predict the wind to adjust speed and ETA.

The ship would keep an average 12.5 knots and speed up, depending on the wind, to as fast as 19 knots.

By speeding up in good winds you get a larger energy saving than power saving, because you arrive sooner. “We get 10% more saving by operating the wind devices the right way,” Levander said.

The design has two Bound4blue suction wing sails and three Norsepower tiltable rotor sails. Suction wing sails are better in headwinds and rotor sails better in tailwinds (Kongsberg would have liked a sixth sail, but there was not enough space).

It also has changes to better use air lubrication, where the ship blows a layer of compressed air under the hull to lessen friction and cut fuel use (it has to be a layer of air; Levander said simply blowing bubbles under the hull “has little effect at the end of the day”).

The best way to do this would be a cavity under the ship, but that has not been done at scale on big ships and adds the problem of wave formation.

So Kongsberg designed a new hull with a bigger draft at the aft. The sloped hull slows the movement of bubbles aftward, trapping the air longer and cutting the need for new air, which takes power to compress.

The smaller draught in the bow, where the air is injected, also helps the ship use less power.

To stop the air escaping up the sides of the ship, Kongsberg took bilge keels — fins that stick out from the hull at a 45-degree angle to dampen roll — and pointed them straight down to form barriers.

The wider hull does add resistance, but you gain more from the air lubrication than you lose through friction, and can carry the same or  more cargo despite the lower draught. Kongsberg has filed a patent for the air lubrication design.

Levander said the inclusion of power take-off, known as PTO, or a hybrid shaft generator, was “very conventional, but this is ideal”.

The ship needs more electric power to run the sails and air compressor, but only when it does not need all its main power for propulsion.

“You only need it when you have lower power demand on the propeller, so it is ideal then to take out the power from the mains. So you save energy by putting in a PTO,” he said.

Levander’s estimated cost saving includes being able to run on cheaper fuel for longer; a less-efficient ship must start blending biofuels sooner. With 40% cheaper fuel and 30% lower consumption, a whopping 60% is theoretically possible.

“Is that a value proposition a shipowner would like to hear? I say yes,” he said.

Running a ship on methanol, on the other hand, would save nothing. The business case also works if the owner plans to use low-carbon fuels. “If you will consume 40%-55% less of that fuel, it will be very beneficial, because that fuel will be expensive,” he said.

“Whatever route you take, super-efficient is the way to go.”