From contra-rotating to pulling ones, propellor design will change shipping in coming decades
By Ryan Skinner (email)
I'm no naval architect. Like any other lay person, I rely on the observations of the experts, then assess what it means. It takes no knowledge of hydrodynamics to conclude that novel propellor arrangements will change shipping.
Why? A few major reasons:
1) Time. Shipyards, suppliers and naval architects have more time now to play with designs in model basins, and more incentive to do so, than during the boom years. Now they can incorporate an accumulation of innovations and studies into tomorrow's stand-by designs. Propellor and hull shape innovations will come first.
2) Electrical power. Perhaps the last ship design to abandon traditional shaft-line arrangements will be a tanker floating out of a Filippino shipyard in 2050. The rest of the world's shippers will, however, have gone over to electric-based propulsion, enabling greater flexibility in design and thruster arrangements.
3) Fuel prices. As fuel prices are bound to go up, the simple efficiencies made possible by new propellor arrangements will look steadily more attractive.
Examples of the possibilities in new propellor arrangements are many. I sat recently next to an engineer from Rolls-Royce who explained how they were experimenting with a sail positioned behind the propellor. This apparently led to a much improved water flow, even if it sounded to this layman like a drag.
I worked on an article for another company, ABB Marine, that described how a Japanese ferry owner using contra-rotating propellors managed to save 10 to 25 per cent on his fuel bill. The propellors' ability to make better hydrodynamic use of the water flow, and the switch to a single skeg, made the difference.
Wartsila has drawn attention to a design with contra-rotating propellors, plus two podded pulling propellors (they call them wing thrusters) on each side. This, again, apparently improves hydrodynamic efficiency. Imagine four propellors for every ship - it's a propellor company's dream!
MOL's latest concept car carrier design features a contra-rotating propellor, in order to achieve the most of possible technological efficiencies. If anything, that may be the best evidence that this technology is one to count on for the future.