UNDERWATER PROPELLER POLISHING

The Underwater Propeller Polishing in Hong Kong (multi-stage micro polishing of all surfaces) and the maintenance of the smooth surfaces, is vital in order to save energy and optimise 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.

DIVING TASK Underwater Services, provides high quality underwater cleaning  and underwater propeller polishing (u/w propeller polishing), achieving immediate and effective reduction of fuel consumption and reduces the total cost of the ship. Propellers convert mechanical energy to the propeller shaft to thrust energy of the water. The propeller blades function as a spoiler.

 

The development of thrust that they generate is a result of flow which is generated around the blade. As the propeller turns the blades generate a pressure difference in the water, pushing the ship forward or backwards, depending on the way that the propeller turns, as well as the pitch of the blades. There are fixed pitch propellers and variable pitch propellers. An important problem in shipping is the increase of roughness the ships propeller, as the fuel consumption and the emission of gaseous pollutants in the environment is increased and significant losses are caused to the propulsion system.

Propeller Polishing Result

BEFORE

AFTER

Cause Of Propeller Roughness

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:

  1. Marine pollution (underwater fouling), algae and marine elements that accumulate on the surface of the propeller.

  2. From its structure, the propeller has a rougher surface, while an important role also plays the origin of the material.

  3. 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.

  4. 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.

  5. 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.

  6. The hydrodynamic cavitation. This occurs by the turbulence of the fluid. Steam bubbles are created, there where the fluid pressure falls below the vapour pressure. The pressure rises around the bubbles, which break and impair the surface of the propeller.

  7. Mechanical damage from a collision with objects that can be found at sea.

Underwater Propeller Polishing

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 the 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 the vessel’s maintenance cycles (expansion of the vessel’s maintenance)

Measure and Process of Underwater Propeller Polishing

As a response measure is the planned underwater cleaning and underwater propeller polishing (smoothing, u/w propeller polishing). Most often it is customary to make the underwater propeller polishing (u/w 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 (u/w propeller polishing), presents more benefits compared to the execution of the corresponding works via dry docking.

 

The process of underwater propeller polishing (u/w 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 (u/w 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 (u/w 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 (u/w propeller polishing) and brings profit. Also, another profitable alternative is the combination of underwater propeller cleaning (u/w propeller polishing) with the underwater hull cleaning and general inspection of the ship, which brings even greater economic benefit.

Advantage of Underwater Propeller Polishing

With continuous cleaning of the hull, rudder and underwater propeller polishing (u/w 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 (U/W 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 DIVING TASK underwater services  perform underwater propeller polishing (u/w propeller polishing) with diamond disc pads, achieving excellent results Rubert «A» scale (1.00 Micron Ra)