Oldendorff Carriers, a major global dry bulk shipping company, has ordered the installation of energy-saving devices on the stern of 12 vessels to be delivered in the first half of next year.
“Mewis” ducts and rudder bulbs will be installed on seven babycapes (bulkers typically between 100,000 and 120,000 deadweight) and five post-panamaxes.
Mewis magic
A Mewis Duct is a wide, thin, ring that is installed on the external part of the propeller shaft, immediately before the propeller. The ring is affixed to the ship using broad blades / fins, which are installed at an angle relative to the forward direction of the ship.
The duct helps increase efficiency in several ways. Firstly, the presence of the duct causes the flow of water into the propeller to be straightened and accelerated, which creates a forward thrust.
Secondly, the angled fins cause seawater to swirl in a counter-direction to the spin of the propeller, which is said to recover rotational energy from the slipstream.
Ship propeller’s have a boss cap at the hub of the propeller, which causes a vortex to form when the propeller is in operation. So, thirdly, the improved slipstream reduces the hub vortex, which improves efficiency with improved thrust and inflow to the rudder.
Pre- and post-installation testing by the Mewis duct manufacturer on a 57,000 dwt bulker revealed a 5% saving in fuel consumption.
Bulb brilliance
If a bulb is installed on the front edge of the rudder and it extends to just behind the boss cap of a propeller it will straighten the flow of water (thereby reducing the amount of drag, which, in turn, reduces fuel consumption and greenhouse gas emissions). It also reduces cavitation (the creation of a void space caused when a propeller spins in sea water), which, again, increases efficiency. Rudder bulb test have shown that rudder bulbs can produce a 1.5% saving in fuel consumption.
Oldendorff Carriers has a variety of energy saving devices installed on many ships in its fleet.
“By next year, 45 of our ships will have a Wake Equalizing Duct, which will help achieve better C.I.I. ratings, lower fuel consumption and reduced emissions. In addition, at least 20 of our ships have asymmetric fins, rudder bulbs, boss cap fin propellers and other fuel savings devices. Furthermore, since 2019, we invested more than US$ 300 Million in Exhaust Gas Cleaning System (EGCS), which abate nearly all of the sulphur oxide emissions. Compared to ships that burn VLSFO without such systems, our ships emit up to 90% less particulate matter and up to 60% less black carbon than ships consuming VLSFO, which leads to much cleaner exhaust at sea and in port,” the company said in a statement.
