More Than Just A Propeller

Modern methods of propulsion offer ship operators a wide variety of efficient systems to move a vessel through the water. High levels of maneuverability and enhanced propeller geometry allow higher speeds to be achieved at the same fuel consumption, while side thrusters eliminate tug requirements when berthing — helping to reduce port costs and enhancing turnaround times.

The first of two new doubleended train and car ferries for DSB Rederi, the Danish state railways ferry operator, entered service between Rodby, Denmark and Puttgarden, Germany, in June. Built at Christian 0rskov Shipyard in Frederikshavn, Denmark, the two ships are operated on behalf of the owner by Scandlines. The second vessel is due to enter service this month. The ships are powered by four Kamewa/Aquamaster main propulsion units, powered by ABB Sami Megastar pulse width modulated (PWM) propulsion drives.

The Contaz propulsors use newgeneration azimuthing, contrarotating thruster propeller technology that has been developed to provide low noise and vibration levels.

Each of the double-bow vessels has two 3,000-kW propulsors at each end, giving the ferries a normal service speed of 16.5 knots with a maximum of 18.5 knots, and allowing the vessels to operate in all weather conditions.

Using this system, it has been possible to provide a bulbous bow and streamlined body which, reportedly, provides higher efficiency and speed compared to traditional propulsion systems. Two similar vessels using Contaz propulsors are currently building at van der Giessen de Noord in the Netherlands for German owner DFO.

Kamewa, Aquamaster's parent company, has supplied S112 waterjets to the SuperSeaCat class of high-speed monohulls, the first of which has been delivered by Fincantieri to its operator, Bermuda-based Sea Containers. Entering service on the route from Dover, England, to Calais, France, four Ruston 20RK270 engines, each rated at 6,875 kW are used to drive the four waterjets, giving the craft a fully laden service speed of 37.8 knots.

Ulstein Propeller of Norway is currently supplying thirteen model 250TV tunnel thrusters for a series of 2,500-TEU containerships building at Flender Werft and MTW in Germany for domestic owners. Each of the thrusters is fitted with a 1.9-m diameter CP propeller with an output of 1,100 kW.

The units are powered by an AC electric motor and Ulstein is also supplying the remote controls for the thrusters.

The contract for the thrusters includes an option for seven additional units.

In the Netherlands, Lips BV continues to supply a wide range of propulsion systems, including thrusters and waterjets — the latter for high-speed craft. Wateijets are used when a vessel's speed requirement exceeds that which can be generated by a propeller driven system.

In general, waterjets have a very high propulsive efficiency over a wide speed range, and without underwater protuberances, can operate in shallow waters. It allows reduced hull drag with good acceleration and crash-stop performance. The system also allows for considerable weight reduction onboard — a pre-requisite for high-speed craft — as gearing in direct drive installations and shaft lines are not required. A number of Lips waterjets have been supplied to Incat, an Australia-based fast ferry builder, for craft including Stena Line's Lynx fleet. Powered by Ruston 16RK270 series diesel engines, the LJ135D waterjets allow speeds in excess of 40 knots to be achieved.

Among thruster installations, three Lips steerable thrusters with 3.2-m diameter FP propellers each driven by a 3,500-kW electric motor — were fitted to an FPSO delivered earlier this year to Rasmussen Management AS of Norway by Mitsui Engineering of Japan.

The thrusters will be used for propulsion and for positioning the vessel when on station.

Schottel Werft of Germany has developed the twin propeller (STP) which seeks to significantly reduce efficiency loss due to vortices around the propeller. In trials, the system reportedly provided an efficiency increase of approximately 12 percent, with the use of tip-vortex- vane (TW) propellers and hub-vortex-vane (HW) propellers, over the more conventional rudder propellers.

The STP is a 360-degree steerable propulsion unit which has two similarly-sized propellers, both mounted on a single shaft and rotate in the same direction. Both propellers are driven via a bevel gear system through the underwater gearbox arrangement.

The forward unit operates as a pulling propeller and attains a very high efficiency level.

The water flow from this is deflected by two guide fins and the housing stem so that as it passes the second and pushing propeller, it is free from the swirling motion created by the first unit. This "clean" water also allows the second propeller to work at a high efficiency level at low loadings.

Since the introduction of the Azipod in 1990 by Kvaerner Masa- Yards (KMY) and ABB Marine of Finland, podded drives have captured the interest of two other consortia. In Germany, Siemens and Schottel Werft have developed their version of the concept, the Siemens-Schottel Propulsor (SSP). In France, Cegelec has teamed with Kamewa of Sweden and Delta Marine of Finland to develop the Kamewa-Cegelec Pod (KCP).

Podded drives are complete propulsion and steering units suspended below the ship, in place of conventional rudders or propellers. The pod contains an electric motor, the drive end of which is attached to an FP propeller.

Power and data transmission to the motor is delivered from the vessel's alternators via electric cables and a slip ring unit. The slip ring unit allows 360-degree rotation of the pod for steering purposes. KMY's Azipod systems are presently fitted to a waterways vessel, a river icebreaker and two icebreaking tankers.

Two 14-MW units have been fitted to Carnival Cruise Line's 70,400-gt Elation, with two similar units to be installed on Paradise. The podded drive system gives naval architects greater freedom in designing hull form, as well as eliminates weight and space as no steering gear, reduction gearing or shaftlines are required. It is suitable for most types of vessels and offshore installations, particularly in the dynamic positioning mode.