Twin screw designs have been suggested for novel containership design, as they have counteracting propellers, pod solutions, and multiengine designs. Yet none have been adopted. “One engine, one propeller” solutions prevail, essentially because of the lower investment prospects of some 10%. To date, the required power has been available using one engine. The DNV-classed Hyundai Kingdom was the first containership to be fitted with a 12 cylinder max bore engine in 2001.

The first 14 cylinder ships are at sea. The length of a 14 cylinder engine will be close to 30 metres and weigh some 2,300 tonnes. Will a flexible hull support the engine? DNV are currently conducting several research studies with focus extensively on the interaction between engine and ship. On top of the 14 cylinder solutions, engine manufacturers are prepared to deliver even 16 cylinder designs.

When looking at the order book for the large containerships, the great majority are to be fitted with 12 cylinder solutions. It appears that even the big ships can obtain an acceptable speed of 24-25 knots. A general speed reduction is also becoming an attractive alternative as the fuel price continues to soar.

The big engines require propellers of close to 10-metre diameter. With some clearance to the bottom and some margin for the upper tip, a 13-14 metres water depth is needed to accommodate the propeller, even though ships move at slow speed in restricted waters with low draft. In fact, the propeller may be the effective restricting factor for ships size at the moment.