Propellers To Undergo A ‘Paradigm Shift’!

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What drives the shipping industry?

The answer to this question may vary depending upon the cargo, type of the ship, supply & demand and global trade.
1However, the answer to the question “What drives a ship?” has always been a ship’s propeller for centuries.  Though the shipping as an industry has seen a sea change, a ship’s propulsion system has always been a propeller.  Right from the day of propeller’s inception, there has been no change except the size and shape of it.  Phosphor bronze or NAB (Nickel Aluminum Bronze) are still being widely used as a material for construction of propellers.

The use of Phosphor bronze or NAB has many advantages in terms of strength.  However, there are limitations to it.

  1. Availability of Copper – Copper is an exhaustible material and most of it are not recyclable.
  2. The price of oil may not be of concern with the current market, but the same is not with copper.  The cost of copper soars high and it is expected to increase with more demand and less supply.

The two reasons stated above are the most critical components where it is increasing the drive to search for an alternate raw material for future propulsion concepts.  Not to forget, the industry is marching ahead with energy efficiency concepts coming out to make shipping sustainable.  Thus, in a nutshell, we can say that there is a strong need to adapt to a new raw material for propellers, thereby the cost and carbon footprint are kept in check.

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The industry is currently exploring the use of composite materials like Glass fiber reinforced plastic (GFRP) or Carbon fiber reinforced plastics (CFRP) which are already being extensively used in aerospace, wind turbines, and automobile industries.  The advantage of using Fiber reinforced plastic (FRP) are more pronounced and they are:

  1. Light weight – means a bigger propeller – thereby increasing propulsion efficiency
  2. Lower weight than the metal propellers – reduced vibrations and easy to assemble, transport and replace
  3. Lower mass – could it lead to a reduction in operational costs by improving the propulsion efficiency?
  4. Research conducted by Class NK – by fitting a CFRP propeller resulted in a reduction of shaft power by 9% when compared with conventional propellers for the same speed.
  5. Class NK and the R&D Team from Imabari shipyard replaced a conventional propeller with a CFRP one where such a replacement offered an enlarged diameter (2.12m in place of 1.95m diameter of the original NAB propeller) thanks to its ultra-lightweight composition (60 percent less than conventional NAB propellers).
  6. It was also reported that the use of the propeller resulted in a noticeable decrease of onboard noise caused by hull vibration, most likely attributable to the greater flexibility of the propeller blades which distribute flow pressure evenly across their surface to greatly lower the occurrence of cavitation.

Based on the knowledge obtained through this joint R&D project, ClassNK also summarized the requirements for the approval of the manufacturing process for composite propellers and the testing/ inspections in the world’s first Guidelines on Composite Propellers (Part on Manufacturing/ Product Inspection).

It is not far that the merchant ships are away from being fitted with a CFRP propeller and probably this could be a “Paradigm shift” from the time the propellers were incepted.

Source: CLASS NK Magazine

Images: Marine Log & Maritime Executive

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