The underwater propeller polishing (multi-stage micro polishing of all surfaces) and the maintenance of the smooth surfaces, is vital in order to save energy and optimize the performance of the ship (improvement of vessel’s performance). The rough propeller leads to power loss, which can be up to 6% as well as an increase of fuel consumption.
There are several factors which are responsible for increasing the roughness of the propeller and which act together achieving a reduction in the smoothness of the propeller. These factors are:
- Marine pollution (underwater fouling) , algae and marine elements that accumulate on the surface of the propeller.
- From its structure the propeller has a rougher surface, while an important role also plays the origin of the material.
- The deposition of calcium carbonate. After a short time in the water the propeller develops a hard, rough carbonate layer, which is produced as a product of the cathodic protection system of the ship.
- The bare metal of the propeller becomes the cathodic region and layers of calcium carbonate are created, which on one hand protect the metal and on the other hand create great roughness.
- The corrosion of the metal. The propeller is subject to both chemical and electrochemical corrosion, since almost all of them are without some coating and unpainted. Besides the marine environment is a very good corrosive agent.
- The hydrodynamic cavitation. This occurs by the turbulence of the fluid. Steam bubbles are created, there where the fluid pressure falls below the vapor pressure. The pressure rises round the bubbles, which break and impair the surface of the propeller.
- Mechanical damage from collision with objects that can be found at sea.
Surveys have shown that adopting regular underwater propeller polishing (uw propeller polishing) as an integral part of the scheduled maintenance of the ship, significantly contribute in savings of the total fuel costs (vessel total fuel costs). For example, in January 1991, the Cunard company reported that the ship “QE2″ (Queen Elizabeth 2) saved just $ 7,000 or 48.5 tons of fuel per day, through the underwater propeller polishing (uw propeller polishing). Extensive studies carried out by the British Research Association (BSRA) have shown that a rough propeller leads to power loss that can be up to 6%. Although the surface area of the propeller is microscopic in comparison with that of the entire hull, the effect of a rough propeller in a ship’s fuel consumption is proportionately higher. It has been proven that the propeller, which has a smaller surface area, can create loss of energy gain, half of which the ship’s hull creates. The cost of repairing the propeller relative to the cost of repairing the hull is much smaller. So the maintenance of the propeller is not only a simple and quick process, but it is a quick and high return investment.
Performing therefore underwater propeller polishing (uw propeller polishing), significant advantages are presented over the ever-growing subsea pollution (underwater fouling). The advantages of the underwater propeller polishing (uw propeller polishing) are:
- Increase and improvement of vessel’s performance
- Reduced fuel consumption up to 6%
- CO2 emission reduction of gases in the marine environment
- Increase of vessel’s (vessel’s speed)
- Reduction of unwanted vibrations due to cavitation (reduction of vibrations by cavitation)
- Stress Reduction of the propeller axis and the vessel’s machinery (stress of the vessel’s machinery)
- The propeller and rudder are cleaned simultaneously, to further enhance the performance of the vessel (propeller and rudder)
- Increased reliability
- Expansion of vessel’s maintenance cycles (expansion of vessel’s maintenance)
As a response measure is the planned underwater cleaning and underwater propeller polishing (smoothing, uw propeller polishing). Most often it is customary to make the underwater propeller polishing (uw propeller polishing) in dry–dock, i.e. over approximately 2.5 to 4 years, which is a long time period to be able to say as that the propeller has maximum hydrodynamic efficiency. The underwater propeller polishing (uw propeller polishing), presents more benefits compared to the execution of the corresponding works via dry docking. The process of underwater propeller polishing (uw propeller polishing) is usually conducted within 1½ – 2 working hours, while the ship is at the berth, thus saving both cost and docking time. Also underwater propeller polishing (uw propeller polishing) represents a faster process because of its natural lubrication of the liquid element, a process that has lasting and better results. Furthermore, underwater propeller polishing (uw propeller polishing) may be performed parallel with the underwater hull cleaning. After the procedure, high quality photographic material is presented with data before and after the polishing. The more often that the ship’s propeller is cleaned and polished, the more money is saved due to the reduction of fuel consumption (up to 6% of fuel consumption). Therefore the cost is outweighed for the underwater propeller cleaning (uw propeller polishing) and brings profit. Also, another profitable alternative is the combination of underwater propeller cleaning (uw propeller polishing) with the underwater hull cleaning and general inspection of the ship, which brings even greater economic benefit. With continuous cleaning of the hull, rudder and underwater propeller polishing (uw propeller polishing), the potential savings per case can exceed 6%! The time period, which the propeller takes to cover with marine growth, and then to proceed for underwater propeller polishing (uw propeller polishing), varies depending on the propellers’ source material, the nature of the roughness, as well, and the corrosion of the metal from which the propeller is made. The underwater propeller polishing (uw propeller polishing) is now part of the regular ship maintenance. The underwater services company PSOMAKARA Diving Services & Consulting Co performs underwater propeller polishing (uw propeller polishing) with diamond disc pads, achieving excellent results [Rubert “A” scale (1.00 Micron Ra)].
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