Pacific Maritime Magazine - Marine Business for the Operations Sector

Propulsion Options for Better Steering and Fuel Efficiency


Extensive model tests suggest the VectRA 3000, built by Turkish shipbuilder Sanmar Shipyards to a design by Robert Allan Ltd with Voith Schneider Propulsion, can generate escort steering forces in excess of 100 tons and a direct bollard pull of 70 tons. Photo courtesy of Sanmar.

The last year has seen continued development of propulsion systems to meet the needs of operators of specialized vessels like Harbor and escort tugs, ferries and fireboats. These range from controllable-pitch (CP) propellers all the way to Voith cycloidal drives, but the azimuthing stern drive (ASD), combining propulsion and steering in a single unit, remains the most popular.

Azimuthing Stern Drive

The Schottel company, builders of the first ASD in 1950, continue to be a major supplier of the product they call the "Rudderpropeller." The prototype was designed and built in 1950 by Josef Becker, founder of the present-day Schottel Group in Germany, and was utilized in the earliest European ASD applications. The original design has been subject to continuous development to reach power ratings up to 6,000 kW in a variety of configurations.

The Rudderpropeller has become standard equipment on many classes of tugs in the Northwest. Western Towboat has fitted Schottel drives on the most recent of the company's fleet of 120-foot Titan-class tugs, and this design by Jensen Maritime has now been used by Hyak Maritime to build three more Titans and Harley Marine for two more – all fitted with the same ASD's. Jensen also specifies Schottel units for many of their other tug designs built on the East and Gulf Coasts – as do Canadian specialists Robert Allan Ltd of Vancouver BC.

In order to strengthen its leading market position, Schottel GmbH opened a new Rudderpropeller factory in the summer of 2015, built near company headquarters at a total investment volume of 45 million Euros. It includes 23,000 square meters of production and office space and accommodates 290 employees in production and administration. This has allowed the company to increase its production capacity by roughly 30 percent.

This expansion was followed by the appointment of Dr. Christian Strahberger as the new managing director of Schottel. Aged 42, he studied in both Germany and the United States to earn his doctorate in physics and began working for Siemens AG in 2001 and later for Voith Turbo Schneider Propulsion in 2009, moving up to the post of chairman of the marine division. One of his first public duties was to accept an award at the Marine Engineering Conference in Amsterdam on April 14 for one of the company's newest products – the EcoPeller (SRE).

Based on the proven "Combi Drive" design principle, an electric motor is vertically integrated into the support tube of the EcoPeller. This design saves space and eliminates the upper of the two angle gears as well as any necessary shaft lines. It offers overall propulsion efficiency and excellent course-keeping stability with unbeatable comfort, thanks to extremely low vibration and low noise levels. Additionally, the integrated High-Torque-Gear (HTG) technology provides enhanced durability and uptime of the thruster. The EcoPeller will be available in mid-2016 in a variety of sizes for power ratings between 1,000 kW and approx. 5,000 kW, each as fixed- and controllable-pitch variants.

As a world leader in azimuth thruster design and development, the Rolls-Royce US range comprises standard Z-drive units with input powers from 330 – 5,000 kW to deliver a bollard pull ranging from 11 to 170 tons. On the west coast, Foss Maritime fitted all ten of its Dolphin-class tugs with twin Rolls Royce ASD's. The company's international reputation also brings many orders from around the world: a new 28.8m x 10m tug launched in Argentina this year features Rolls Royce ASD's. The Brutus was designed by a local naval architect and built by the Astilleros Unidelta S.A. of Buenos Aires. Power comes from a pair of 16-cylinder Cummins QSK60M diesel engines generating 2,700 HP (2,013 kW). It is certified Lloyd's Register Class Notation ✠100A1 tug.

In January, Rolls-Royce and Turkish shipbuilder Sanmar Shipyards signed a letter of intent for the supply of twelve Rolls-Royce MTU engines for six Robert Allan Ltd designed ASD tugs for Danish operator Svitzer. These RAstar 2800-E ASD tugs will be powered by MTU Series 16V 4000 M63 and M63L diesel engines connected to Schottel propeller systems with a 70 Ton bollard pull. Rolls-Royce states that the engines of this series are "extremely efficient" and that in addition to offering low fuel consumption, the engines offer low maintenance costs due to high TBO (Time Between Overhaul) figures.

Voith Schneider Propeller (VSP)

In March 2016, Robert Allan announced another contract with the Turkish yard for the VectRA 3000 class, designed exclusively for Sanmar for its highly successful stable of progressive tug designs for the world market. This innovative vessel is a high performance VSP Tractor tug designed for maximum efficiency in the towing, ship handling and escort of large ships. Performance has been verified with extensive model tests and this hull form matched with VSP's can generate escort steering forces in excess of 100 tons and a direct bollard pull of 70 tons.

The unique propulsion arrangement features of CAT 3516C high-speed diesel engines, each rated 2525 kW at 1800 rpm, driving Voith 32R5EC/265-2 cycloidal propellers. The engines are connected to the Voith drives through a pair of Reintjes WAF 863 gearboxes and Vulkan composite shafts, rather than using the more traditional turbo coupling. This combination is smaller, lighter and less costly than the traditional medium-speed drive system.

As in a traditional tractor configuration, the stern is the working end of the tug, and as such features heavy duty cylindrical fendering with a course of 'W' fenders below. Hollow 'D' fenders protect the sheer lines and tie neatly into the 'W' fenders at the bow. All towing, ship handling, and escort work is performed using a double drum escort winch and escort-rated staple fitted on the aft deck. In the wheelhouse, the split console is biased aft to ensure unobstructed visibility of the working deck.

One drum can store 710 meters of steel wire line, while the other stores 150 meters of synthetic towline. For increased operational flexibility radial type tow hooks are installed on the main deck forward and aft. Crew accommodations are all located on the main deck level for optimal crew comfort. There are 4 single crew cabins plus 1 double crew cabin, each with an en-suite bathroom. A comfortable lounge/mess area and galley facilities are also in the deckhouse, with galley stores and laundry room located below the main deck forward.

The electrical plant consists of two identical diesel gensets, each with a rated output of 86 ekW. Additionally, the design has fire-fighting and oil recovery capabilities and is fully Maritime Labor Convention compliant. The first vessel in the series, the Ares, built for Italian owner Tripmare S.p.A., was successfully launched at Sanmar's new Altinova advanced shipbuilding facility in February 2016.

Controllable-Pitch Propellers (CPP)

The Seattle-based company Coastal Transportation runs a half dozen refrigerated cargo vessels up to 250 feet long between Puget Sound and the small ports of Western Alaska and the Aleutian Islands, year-round. The company's newest vessel, The Coastal Standard was built at Dakota Creek Industries Shipyard in Anacortes, Washington with a design from Naviform Consulting and Research of Vancouver BC to maximize cargo carrying capacity while providing the excellent maneuvering properties needed in these remote harbors.

The 2,200-dwt freighter vessel is the first purpose-built Jones-act reefer vessel for several generations. It is 242 feet long and propelled by a single Tier 2 Caterpillar C280-8 main engine that produces 3,084 HP a (2,300 kW) at 900 rpm. This drives a Schottel controllable pitch propeller (CPP) to provide a high free running speed and excellent maneuverability and operability, with no need for a reversing gear. The pitch of the propeller blades can be adjusted to adapt to changing operating conditions.

The CPP is supported by two Schottel Pump Jets of 360 kW each. These are fully capable azimuthing thrusters, enclosed completely in the vessel's hull. They act as maneuvering aids and, at the same time, redundant take-home devices. The rudder was also designed by Schottel to match the CPP propeller's performance.

Washington state's car ferries also need superior steering qualities, and the four new Olympic-class car ferries will all be fitted with Rolls Royce controllable-pitch four-blade propellers and high-lift rudders. The superstructure of the third of the class, the Chimacum arrived by barge in Seattle on April 7, where it will be joined with its hull at the Vigor Shipyard. The double-ended vessels are 362.5 feet long with an 83-foot beam and carry 144 cars. The efficiency of the bow shape was improved by tank tests to feature a more streamlined "wake-adapted" stern shape. This required a thin tapered shape for the stern tube and skeg, which required special castings and heavily-rolled plating.

Rolls Royce is unique in having their own hydrodynamics research center, equipped with two cavitation tunnels. In more than 40 years of operation the center has tested around 1,400 propellers and waterjet pumps, including the Rolls-Royce Azipull, a new low drag, high efficiency pulling thruster 900-5,000 kW that provides both steering and propulsion. It combines the advantage of the pulling propeller with the flexibility of using almost any type of drive to suit specific vessel requirements.

Boosting Rudder Power

The three Arctic-class 132-foot tugs being built at the Foss Rainier, Oregon Shipyard are built to tow and maneuver ships, barges and oil-field cargoes in the arctic in broken ice and severe weather conditions. Stern gear is of particular importance in handling these challenges, so Foss selected Nautican Research and Development's Integrated Propulsion Unit (IPU) – built in Vancouver, BC. The IPU combines the company's high-efficiency nozzle with pre-swirl stators, a 126-inch diameter propeller and linked triple rudders.

Nautican explained that this IPU was custom-built to "Ice-class" standards; the five-blade, Kaplan-style stainless steel propeller has thicker leading and trailing edges. The nozzle is assembled with a large head box that slots into a recess in the stern, anchoring it firmly into the hull. "This Nautican unit offers increased bollard pull, greater maneuvering and efficiency through ice and rough sea conditions," said Elizabeth Boyd, Nautican owner.

The popular Jensen Maritime-designed Titan-class boats built by Western Towboat, as well as other tug and barge companies, uses Schottel Azimuthing Stern Drives. Photo courtesy of Western Towboat.

The first of the tugs, the Michele Foss successfully completed a sealift to Point Thomson, Alaska on her maiden voyage in the summer of 2015. Four Foss tugs towed four barges carrying oil field modules from Ulsan, South Korea 2,300 miles to the Alaskan petroleum field. The second arctic class, the Denise Foss, will be launched this year.

Deflector high-lift rudders, built in SW Washington, have now been fitted to a couple of Shaver Transportation tugs, the 110-foot Clearwater (draft 10.5 feet) and the 65-foot Umatilla (draft 8 feet), demonstrating that the high-lift concept can provide superior maneuverability with a shallow draft at reasonable cost. This upgrade is especially valuable for Shaver's Columbia River push-tugs that navigate through the Columbia Gorge with its notoriously high winds and the eight sets of locks on the Columbia-Snake River System. Deflector rudders have also been successfully supplied to a number of large Alaskan trawlers, including the 219-foot F/V Ocean Peace, which required the rudder to be certified by DNV.


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