Controllable Pitch Propellers CPP (adjustable pitch propellers)
The blades of this type of propeller can be turned, thereby changing the propeller pitch. These propellers are more complicated than fixed-pitch propellers. The mechanism that adjust the propeller pitch is located in the boss of the propeller. It is activated from the engine room, remotely controlled from the bridge by a hydraulic cylinder. The most striking features of the controllable pitch propellers is that it only rotates in one direction, making the reversing clutch or the reversible engine obsolete. Unlike the fixedpropeller, the controllable pitch propeller is an integrated part of the propulsive system. This makes it possible that power and necessary propulsive forces can all be controlled by simply changing the position of the blades. Long Range Cruisers (LRC's) will necessarily carry quite a sizable fuel load, often amounting to around 15% or more of the vessel's displacement. With such a highly variable load on a long range trawler yacht or other long distance power vessel, if fitted with a CPP, the pitch can be made greater when the vessel is light, and made more fine when loaded without having to vary the engine rpm, and still provide maximum use of the engine's power. When running free with wind and waves the pitch may be made greater. Conversely when headed into the weather, the pitch may be made more fine. Much like shifting into overdrive or second gear, depending on the requirement. While it is true that a Fixed Pitch Propeller (FPP) can be more efficient than a Controllable Pitch Propeller, it is rarely given that opportunity. The FPP can only be maximally efficient at one rpm with one horsepower amount and one load condition: i.e. those for which it was specifically designed. At that one rpm and load, the FPP is able to absorb all the power that the engine can produce. At any other rpm, or any other vessel loading, the FPP cannot, either being over pitched or under pitched. A correctly sized Controllable Pitch Propeller on the other hand is able to be efficient at a wide rpm range, and at a wide variation in vessel loading. This is so because the propeller pitch can be adjusted as needed in order to absorb all the power that the engine is capable of producing at nearly any rpm. Even aboard a planning power vessel, one can use a CPP to provide fine pitch and higher rpm to get going, and a heavier pitch with reduced engine rpm once up to speed. If the vessel has two engines, and speed is to be low, one engine can be dropped out, and its propeller feathered fully to remove the drag of the stopped propeller. The Controllable Pitch arrangement will permit a skipper to vary the engine rpm in service as needed to obtain the most favourable reduction in engine vibration and noise, as well as to vary the pitch (and therefore alter blade loading) to eliminate cavitation at any rpm. Finally, there will be no anxiety as with a Fixed Pitch Propeller over whether or not the correct Fixed Pitch has been calculated for the combination of vessel and engine. With the wrong fixed pitch propeller, efficiency can be very poor indeed.

Hydrolic System of CPP
The pump and motor unit forms an essential part of the hydraulic system. This assembly delivers the oil quantity needed for adjustment of the propeller blades and produces the pressure required for pitch control. Two electrically driven pumps (1 active pump, 1 standby pump, each with 100% capacity) are mounted on the cover of the hydraulic tank, with the pumps running in the oil. The compact control block, incorporating all the indicators and the individual instruments necessary for pitch control, is located on the top of the tank.

The piping between the pump and motor unit and the oil supply unit is part of the shipyard’s scope of supply. Lubrication oil is fed through the stern tube into the hub. This system is not connected to the hydraulic system of the controllable-pitch propeller unit. Optionally a two-pipe system can be supplied, in which case the hydraulic oil is used to lubricate the hub. Fig.1 In Fig. 2 it is to recognizable the inlet of the hub.

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Typically hydraulic scheme for a CPP Fig.3

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Principal Work of CPP Blades for Moving
The blades of this type of propeller can be turned, thereby changing the propeller pitch. These propellers are more complicated than fixed-pitch propellers. The mechanism that adjust the propeller pitch is located in the boss of the propeller. It is activated from the engine room, remotely controlled from the bridge by a hydraulic cylinder. The most striking features of the controllable pitch propellers is that it only rotates in one direction, making the reversing clutch or the reversible engine obsolete. Unlike the fixedpropeller, the controllable pitch propeller is an integrated part of the propulsive system. This makes it possible that power and necessary propulsive forces can all be controlled by simply changing the position of the blades.

Adjustable blades by means of hydraulic oil pressure Fig.4 In Fig.5 drawings of a single propeller blade and its cross-sections. The pictures show the controllable pitch propeller; the upper blades is the blades in the drawings.

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The Advantages and Disadvantages of CPP vs FPP
CPP Advantages:
Better cavitation and noise reduction or prevention by controlling the pitch. It can propel the ship at all speeds, even at very low speeds without loss of power. It can change quickly from ahead to astern and vice versa Improved efficiency on ship with a alternating loads like fishing crafts and tugs. It can be easily combined with a shaft generator. It can stop a ship with maximum power. In case of a damaged blade easy and fast change possibilities, without demounting of the shaft

CPP Disadvantages:
It is a vulnerable system due to the hydraulic components and many sealing rings. A damaged sealing ring results in oil pollution.

FPP Advantages:
They are less fragile over CPP The propeller does not revolve when berthing, so it poses less danger to mooring boats and there is less risk of ropes getting entangled in the propeller

FPP Disadvantages:
In adverse weather the propeller may turn too heavily, this can hamper propulsion. Limited RPM. Reverse engine needed to move astern.

Usage of CPP in Ships
Usually CPP is used in type of ships where the draft and in this case the resistance will be changed in a journey. To optimize the RPM for the specific draft journey we can use the pitch of the propellers to set the performance to a optimum. It usable witch reduction gears or directly mounted shafts if a high speed engine like ferries or navy ships. Typical ships which uses CPP are: Container vessels, Cruise ships, Fast ferries, Naval vessels, Yachts, Trawlers, Tugs Here some example ships which uses the CPP technology from Schottel
COT WOLGASTERN SCP 1414 XG (7860 kW) Shipyard: Gdynia Shipyard, Poland Owner: Rigel Schiffahrt, Germany Open Top Container Vessel, Type 168 A 1 x SCP 1294 XG (8400 kW) Shipyard: Sietas-Werft, Germany RoPax ferry NORRÖNA 2 x SCP 1294 XG (10,800 kW each) Shipyard: Flender Werft AG, Germany Owner: Smyril Line, Faroe Islands Offshore Supply Vessel C. LIBERTY 2 x SCP 0774 ZG (2110 kW each) 2 x STT 1010 T-LK CP (1000 kW) Shipyard: North American Fabricators, USA Owner: Edison Chouest Offshore, USA EGV BERLIN 2 x SCP 1414 XG (5280 kW each) Shipyard: Flensburger Schiffbaugesellschaft, Germany Owner: German Navy Chemical tanker

Container ship

Ferry

Supply vessel

Navy

In the researches about costs of CPP and FPP was noT clearly defined which system is more affordable. But in some calculation it was to recognize that the cost in all will be like the same amount. It makes sense to use a FPP for engines up to 1250 KW, for other applications of CPP, it makes sense to use it from 0,5 MW up to 75 MW. There is no limitation for CPP. Although CPP can BE used for commercial applications and Naval ships. For Naval ships it is useful because of the noise reduction. The appliance of CPP in diameters 1,5m to 9m is possible.

First controllable pitch propeller from Wismar built in 1963 for a fishing trawler 1,210 kW, diameter 3.3 m