Controllable Pitch Propellers

Advantages associated with maneuvering:

  • Where extensive low speed maneuvering is required for a diesel powered vessel.
  • When the operating conditions vary widely and maximum thrust is desired throughout operating conditions.
  • Where shaft reversing capabilities are not provided by engine design.
  • When improved maneuverability and a minimum ship stopping distance are desired.
  • Where a constant shaft rpm is an advantage over a wide range of operating powers.
  • The main engine may be started earlier prior to sailing thus giving time for the temperatures to settle down, to reduce thermal shock.
  • When there is a need for a quicker fuel type changeover.

Disadvantages:

  • Cost and maintenance.

Brief operation description:

The input signal from an operator acts on the diaphragm in the valve housing and directs hydraulic oil via one piston valve through the tube to one of two sides of the servo piston (ahead movement or reverse). The movement of the servo piston through a crankpin ring and sliding block rotates the blades and varies the pitch. The piston valve however must be restored to its neutral position, at the correct pitch position. When propeller blades reached a desired angle hydraulic oil stops to push the servo piston and a valve on an oil return line closes, thus fixing the pitch. Among other things a hydraulic oil system has safety valves to relief an oil pressure if the propeller blades somehow be immobilized from the outside.

In my practice I almost never had any problems with CPP. There was a curious situation when the vessel had two independent medium speed engines and accordingly two separate controllable pitch propellers. We were sailing on one engine. The bridge called to start the second one. Engineer at watch gone to prepare the engine and cranked it on air. Since we were sailing at sea the engine did not stop to rotate. In order to stop it we had to gently change the propeller pitch angle from the engine room control station. Then it stopped.

2 Комментариев
  1. Indeed problems with CPP are not very common, but the ship that I am working on now has constantly problems with it. I think I have to mention here that it concerns a Chinese replica of a MAN CPP. The problems that we have, started with oil leaking from the OD-box on the shaft, where the Non Return Valves are fitted. To solve this leakage, it was necessary to take out the coupling and for that the propeller shaft had to be shifted, so it became an unplanned dry docking.

    In dry dock we discovered several things that were not okay and I guess that we solved them all, with help from real MAN engineers.
    Now we have some new problems:
    There is oil leaking from the OD ring. It is normal that there is some leakage, but it is collected in the drain tank and pumped back into the system. However, in our case there is so much oil leaking away that the drain pipe cannot keep up and it is leaking away from between the bearing and the shaft coupling.
    Another problem (not sure if they are related) is that we are not able to change the pitch at full rpm. It is possible to change the pitch, but the first 40% have to be done at 100 rpm. This problem started to get worse over time. A few weeks ago it was not possible up to 10% pitch, then it became 20% and now it is 40% already. When trying to change the pitch at 129 rpm, then the pressures get really high (80 bar after the pump and 65 bar at the line towards the CPP.
    I will try to keep you updated about this.

  2. Hi Koos! Cheers for sharing 🙂 If I understand right, such job – to solve leakage from NR valves is forcing you to shift/remove an oil transfer tube and thus braking the connection between a OD-box ring and stub shaft. Can it be, that after a dry dock job they are a bit misaligned or contact services sized unequally? Do you have an external OD-box or integrated?
    The second one has something in common with the problem I have encountered in my practice recently. On 80% + load we had hunting of pitch. During full ahead the pitch was slightly altering by it self and automation was bringing it back. You could hear it too. It was not so bad as your example, it was a deviation of a few percent from the set point, but anyway we proceeded to troubleshoot. In our case it was clear that the problem is somewhere in the hydraulic system it could be one of NR valves was passing… So than RR technical advise department suggested to leave it as it is 🙂 I image it would be quite difficult to find a problematic peace of equipment while vessel is in operation.
    Please keep updated! 🙂

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