|Ship Fore Nozzle|
US ships and boats, not including military vessels, used 626,000 barrels (26.3 million gallons) of petroleum per day in 2010 according to USDOE statistics (its EERE office, referred to in previous posts in this short series). With an average container ship consuming about 3600 gallons per hour, fuel costs represent a major fraction of the operation of a cargo ship.
“Device for reducing the power demand for the propulsion of a ship”This patent, US 8,123,578, was issued to Friedrich Mewis of Dresden, Germany, (assigned to Becker Marine Systems GmbH & Co., Germany), on February 28, 2012. The invention consists of a nozzle housing fins or hydrofoils; the assembly is mounted to the ship’s hull just forward of the propeller(s).
It is a passive device (other than being able to be tilted to provide proper alignment with respect to the prop). The nozzle/hydrofoil assembly operates by increasing the speed of water flow against the propeller in areas where the main flow stream is very high, and of decreasing the flow against the propeller in areas where the main stream is low. In addition, the nozzle itself provides some thrust. The fins or hydrofoils arranged within the fore-nozzle generate a rotational swirl, that serves to counteract the swirl (and resulting energy losses) imparted by the propeller. Both of these effects increase the overall efficiency of the propulsion system.
A device for reducing a power demand for the propulsion of a single-propeller or multi-propeller ship, wherein the device is attached to a hull of the ship proximate to the propeller, the device comprising a fore-nozzle with fins or hydrofoils arranged within the fore-nozzle, wherein the fore-nozzle, at a top thereof, is tilted forwards relative to a horizontal transverse axis that extends through the center of the fore-nozzle, wherein the fore-nozzle is rotation-symmetrically arranged with an upwards-shifted axis that is situated above the propeller axis, and wherein the fins or hydrofoils have different lengths.As part of his invention summary, Mewis states:
"With a device constructed in this manner it is possible to reduce the power demand for the propulsion of a ship. The possible gain increases as the extent of thrust loading on the propeller increases. The device is particularly suitable for slow, broad-built ships, such as tankers, bulk transports and tugs, and also for not-very-fast ships of any type. The device itself is affixed to the hull so that it is upstream of the propeller of the ship, with said device comprising the two functional elements of fore-nozzle and fins or hydrofoils."He estimates that,
"[t]he power savings which can be achieved by the device depend substantially on the propeller load, they are from 3% for small multi-purpose ships to 9% for big tankers and bulkers. The power savings are almost independent of the draught of the ship and from the speed."A potential 9% power saving for large tankers and cargo vessels translates to a significant fuel and cost savings.