In Controllable or Variable Pitch Propellers (CPP), the propeller blades are attached to the boss and their pitch can be altered via a hydraulic system. The blades are removable so if they incur damage, can be repaired without removal of the whole propellor.
For the advantages that a CPP system gives, the CPP propellor is also more complex. Instead of the Monoblock design of a Fixed propellor, the CPP has multiple moving parts in the propellor and shaft, and a hydraulic system with which to control the pitching.

ATZ can support you with inspections and repairs afloat, in dock or even with a dive team. Either way, ATZ can support all your class approved CPP propellor requirements.

CPP

With a CPP you can control the pitch of the entire propeller, by changing the orientation of the root section of the propellor relative to the hub. This is done by the means of a hydraulic cylinder.

When the required orientation or pitch of the propeller is reached, the blades are locked in that position. So, the blades are not an integral part of (or not casted along with) the propeller hub. They are mounted on spindles that have axes perpendicular to the shaft axis.

Advantages of a CPP

A non-reversible engine can be used for both forward and astern operation of the ship, therefore overall propulsion machinery weight can be reduced

CPP is useful in changing the speed of the ship without changing the rpm of the main engine

Therefore, the speed of the ship can be handled from the navigation bridge directly. For FPP, the marine engineer is required in order to change the ship’s speed. CPP technology is useful for obtaining a faster response of speed change

Astern operation is more efficient than when using FPP propellors

Disadvantages of a CPP

The pitch control mechanism is sufficiently complex to require regular inspection

CPP propellors have a higher initial cost than FPP propellors

Hub length and diameters are larger than for FPP, in order house the pitch control mechanisms

CPP are typically used in ships that are required to operate at variable speeds even when operating at constant power requirements. 

Typical applications are:
  • Tugs,
  • Trawlers
  • ferries
  • ice breakers
  • small warships with gas turbines.
Potential propellor damage and resulting intervention is like an FPP type propellor.
  • Propellor blade straightening due to grounding 
  • Cavitation repair 
  • Cracking due to impact damage or secondary effects of corrosion or cavitation
  • New blade tip installation by welding if tip damage is excessive
And like FPP also requires a minimum amount of servicing at dry dock including:
  • Polishing due to build-up of marine growth
  • Blade modification for increased efficiency
  • Balancing to reduce vibration
  • Inspection and non-destructive testing to meet class survey requirements
But unlike FPP requires additional works:
  • Shaft survey and shaft removal
  • Blade foot O-rings replacement
  • Hub inspection
  • Oil distribution box check
  • SKF coupling check

Propellor Servicing or Repair needs. 

ATZ with our partner Aegir Marine are in a position to meet your propellor servicing or repair needs. 

CPP repairs will mostly take place afloat or at the shipyard but we can offer all options:

  • Vessel afloat, we work with qualified and experienced diving companies.
  • At the shipyard (basically anywhere), our propeller expert will carry out or supervise any required works to your propellor.
  • In-house, in our fully equipped workshop an excellent propeller repair team will carry out the repair. Our repairs are comprehensively supported by our in-house hydrodynamic engineer to ensure we return you and efficient and well-balanced propellor.

All our repair procedures are set up in close partnership with the classification society and are followed by detailed reports.


FAQ’s

What’s the difference between a fixed pitch propellor (FPP) and controllable pitch propellor (CPP)?

A fixed pitch propeller is typically cast in a single piece and has its pitch set at the factory. The propellor is tailor made for the vessel and is optimised for efficiency and minimised noise and vibration.
A controllable pitch propellor has separate blades that can rotate relative to the hub of the propellor. This means that the direction and speed of travel of the vessel can be changed without changing shaft rpm, or even changing the direction of shaft rotation. CPP propellors are typically required where a far greater range of manoeuvrability is required, or the vessels operational profile is more varied.

How often do I need to maintain my CPP system?

Classification societies require five and ten-year inspections. 
During the five year inspection expect: Cleaning, Inspection, Preventative replacement of some parts, External inspection for wear and damage. During the ten year inspection expect a more comprehensive inspection of CPP components is required. Then a decision can be made on what needs refurbishment or replacement.

Do I have to remove my complete propellor to repair damage to blades?

No. Repairs such as polishing cracks and cavitation damage, tip repair and straightening can be performed on individually removable blades. Dependent on the level of damage, the best option may be to just replace the damaged blade with a spare.

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