DNV Data Shows Bulbous Bow Redesign Gives 5% Fuel Savings

Bulbous bows must be designed for specific speeds to optimise fuel use

Redesigning a container ship's bulbous bow for slow steaming can produce fuel savings of 5 percent or more per year, which means the retrofit can pay for itself in less than a year, according to classification society Det Norske Veritas (DNV).

DNV conducted a study of a series of 8,600 twenty-foot equivalent unit (TEU) containerships operated by Hyundai Merchant Marine (HMM), which were designed to operate at up to 27 knots.

Today those vessels, like most in the global fleet, are slow steaming at 15 to 18 knots, making the ships' original bulbous bow shapes inefficient.

DNV developed a new bulbous bow shape for the vessels based on expected conditions, and the first conversion, done by Daewood Ship Engineering Company (DSEC), was completed in March at a cost of $680,000.

Onboard measurements showed that the modification reduced fuel use by almost 1,000 tonnes per year.

"The performance of the new bulbous bow has carefully been evaluated as part of verification over about two months period after delivery and fuel saving in operation so far has been found to be around 5 percent or above," said Taeg-Gyu Lee, executive vice president of HMM.

"The payback period is expected to be much shorter than the one year originally estimated."

DNV said it expects other ship owners to modify their vessels' bows to improve the competitiveness of older vessels.

"Existing ships have to compete with a new breed of efficient and flexible designs," said Jost Bergmann, DNV's business director for container ships.

"One result of the high design speed of many existing container ships is that the bulb is highly tuned to reach the maximum speed.

"The new reality for much of the existing fleet is that this affects efficiency at lower speeds."

Maersk Line has already made similar retrofits to several vessels.