The crankshafts may set the limits.
Three engine manufacturers have come to dominate the market for the giant low-speed two-stroke diesel engines used in the largest container ships, bulk carriers, and tankers: MAN SE of Germany, Mitsubishi Heavy Industries of Japan, and Wärtsilä of Finland.
Stricter environmental legislation around the world is only part of the increasingly more challenging environment these three firms – and the shipyards and contractors they work with – have to deal with.
The shipping industry does not merely demand cleaner and more fuel-efficient engines, but also engines that will last the design life of the ship (usually 25 years) with only scheduled maintenance and minimal repairs. Several shipowners (led by CMA CGM) are coming to like the single engine/single propeller configuration for its efficiency and reduced running costs – as long as it doesn’t impact cruising speed too much.
Technical solutions range from the use of plates of corrosion-resistant materials such as Inconel (a family of nickel-based super-alloys originally developed for jet engines) welded to the piston crown to using crankcase oil to cool not just the pistons themselves but the rod as well to reduce the likelihood of heat-induced failures.
To give an example of what the shipping industry demands nowadays, Maersk’s Triple-E container ships – the largest container ships in the world with a capacity of over 18,000 twenty-foot-container equivalent units (TEU) – are powered by two MAN two-stroke diesels, each driving its own propeller. Each engine has eight cylinders with an 800 mm bore. The engines are designed to deliver their maximum efficiency at 73 rpm. Their combined power of 59,000 kW allows the monster-ship to cruise at 16 knots.
These MAN engines are not the most efficient offering from the German firm, and there are several single engines that put out a lot more power. For example, the much celebrated 14 cylinder version of the Wärtsilä RTA96C is rated for over 80,000kW.
But MAN’s twin-engine configuration allows to reduce engine room size relative to the size of the ship, thus giving more room for cargo. It allows to install one 3000 kW electric generator per shaft, thus almost doubling power from thermal-fired generators and the waste heat recovery (WHR) system.
This increased electricity generation allows each Triple-E ship to carry up to 1,800 climate-controlled containers, a huge boon when carrying heat-sensitive cargo (such as some electronic components) through the hot Indian Ocean.
The Triple-E 25-year design lifespan may be cut short if there are technical breakthroughs that make the ships uneconomical to run, repair, or retrofit. So, just in case, according to both Maersk and Daewoo, the Triple-E were designed to be “easy to break up” when their time comes, but until that day comes we won’t know how much truth there is in this statement....MUCH MORE