VII International forum
“Marine Industry of Russia”
Hotel complex
Department of affairs of the President of the Russian Federation

Moscow, 24, B.Yakimanka Str
24-25 May 2017
Forum bulletin

More on propulsive systems

Propulsive system consists of the ship hull and propulsive unit. The propulsive unit is an executive part of the main ship power plant designed for conversion of the mechanical energy produced by the engine into the vessel moving work. The propulsive system consists of:

  • a ship hull,
  • a main engine;
  • a main gear;
  • a shaft line;
  • a propulsion device.

The components of the propulsive unit are selected with a glance to the efficiency of the main ship power plant being the key indicator of the perfection of the whole propulsive system.

More information on engines and propulsors can be found in the relevant section of the Forum website . In the same section, information is provided on other components of the propulsive system.

The main gear (power transmission) is a complex of elements which transmit torque from the crankshaft of the internal combustion engine or the turbine rotor to the propulsor, total torque of several engines with their subsequent transmission to one shaft, and reverse the shaft train and propeller of irreversible engines. The most popular transmissions are mechanical ones, although other transmissions are also used (electrical, mixed and complex).

The standard transmission of the medium running engine consists of a coupling, reducing gear, and shaft train. With high running internal combustion engines and turbines, double- or triple-reduction gear units are installed. The reducing gear is not used in the propulsive unit with low-running engines. It should be noted that the transmission is necessary in case of the vessel equipped with a single-machine ship power plant, and a fixed pitch propeller used as its propulsor, as well as when the engine torque is insufficient for rotation of a propeller screw with giver frequency.

Electrical main gears have a number of benefits, among which are a short shaft train, possibility of use with high-running irreversible internal combustion engines, main SPP employment for general need energy supply, survivability and self-regulation ability. With that electrical transmissions are expensive, low efficient, and, at low rate speed, have big dimensions and weight.

The hydraulic transmission is low efficient, so most frequently it is used in combination with the mechanical one.

The shaft train is an assembly of mechanisms, devices and connections used for coupling of the propeller screw with the screw shaft as well as for thrust transmission from the propeller screw to the vessel. It consists of a screw shaft, line shafts, plummer blocks, thrust shaft with bearings and stern gear. Besides, bearings and thrust shafts can lack some designs of shaft trains. And there are designs of the engine-propulsor system without a traditional shaft train.

Propulsive System Application: New Trends

Propulsive system efficiency upgrading can be achieved by various means – upgrading of efficiency of the propulsor or engine, optimization of the hull shape.

Bulb fore end can reduce wave-pattern resistance by 15 or more per cent, however often ship vibration nullifies its effect. Wave-pattern resistance can also be reduced by design of the maximum narrow hull with simultaneous increasing of the ship length.

Recently, some wave-piercing catamarans were built abroad. In addition to a narrow hull, they differ in a breakwater at the forebody.

Another way of raising efficiency consists in optimization of the propeller-rudder system shape, aft end design and propulsive unit operation.

Engine-propulsor coordinated interaction is necessary for optimal performance of the propulsive unit. Most frequently, propulsive indicators can be raised via propeller diameter increase with shaft speed down. Application of steerable propellers with single-shaft screws also improved performance. This way, the diameter of steerable propellers could be decreased while raising efficiency by 20%.

Replacement of the large diameter propeller screw with two reverse coaxial propellers is another trend. In such event, since a special reducing gear and hollow screw shaft is necessary, the design of the whole propulsive unit becomes more complicated. Vessel propulsive properties can also be improved via employment of multi-shaft main gears.

Introduction of electric propulsive installations is very promising. Thus, vessels equipped with electric propulsive installations and water-jet propulsors are able to accelerate up to 60 knots. The combination of this system with steerable propellers ensures light mass decreasing by 10-15% and raising engine efficiency up to 98%.

At the speed up to 25 knots, water-jet propulsors are inferior to popular propeller screws in respect of propulsive properties, however at the speed of about 40 knots, their properties are comparable. At the speed over 50 knots, water-jet propulsors leave propeller screws behind.

Potential of raising performance of water-jet propulsors is being sought both in our country and abroad. For the most part, such search is focused on decreasing hydraulic loss in the duct and improving water-intake devices.

One of the prospective methods to decrease hydraulic loss in the propulsor duct can be modification pipe streamlined surface microgeometry by means of flow direction micro-grooves (riblets).

Domestic professionals offered the standard concentrated water intake through a hull aperture or special-purpose nozzle which is usually used in modern water-jet propulsors to be replaced with so-called distributed shear layer water intake through the transverse edgewise conduit.

Propulsive performance can be improved by decrease of hull roughness. Cover plate cockle, weld flatness and dimensions, lacquer coat properties, hull and propeller antifoulant application and so on are of importance in this case.

Neither use of heavy-duty engines, nor modernization of a screw design or optimization of a hull shape ensure significant increasing of the ship speed. In such case, one of the solutions can be installation of propeller screws in the bows and not in the aft. Under certain conditions, this creates so-called following wake which significantly improves propulsive properties of the ship.

Control system for propulsive complex performance is also important. Such device contains fuel flow rate, power, revolution, and navigable depth transducers. It also includes engine and propulsor diagnostic, logic processing, data display and individual alarm units.


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