Every time we have the term CPP coming up here, there is at least one self proclaimed “expert” popping up, with the idiotic statement: “nice but expensive” and / or “yes but that does´nt suit here” Nonsense!
Why a CPP?
There are several advantages provided by Controllable Pitch Propellers, here named CPP. This summary has the intention to outline several of the reasons why CPP should be favoured for motor vessels, as for sailing vessels, and motor sailers.
While of course it is true that a Fixed Pitch Propeller (FPP) can be more efficient than a CPP, it is never given that opportunity... The FPP can only be maximally efficient at one
rpm with one
amount of power input and at one
load condition: those, in example, for which it was designed. At that one rpm and load
, the FPP is capable to absorb all the power that the engine can produce. At any other rpm, or any other engine or vessel load, the FPP can not operate efficiently, that’s being either over - or under pitched.
A properly sized CPP on the other hand is able to be efficient over a wide rpm range, and over a wide range of engine loading. This is so because the propeller's pitch can be adjusted as needed in order to absorb all the power that the engine is capable of producing at any rpm.
With a CPP, you make pitch adjustments under-way to suit the complete variety of conditions. It is very easy to choose the appropriate pitch setting with a CPP. Though it needs some exercise.
At highly variable loads on a long range power yacht, if fitted with a CPP, the pitch can be increased when the vessel is light, and decreased when loaded without having to vary the engine rpm, and it will provide maximum load on the engine.
CPP installations do´nt have a reversing gearbox, only a reduction gear. Instead of changing the direction of rotation, the blades articulate clear around until they bite in the water in the other direction.
Than there will be no doubt as with a FPP whether the correct pitch has been choosen for the boat. Too many boaters have discovered, that calculating the ideal propeller pitch sometimes is not really a exact science...! But with the wrong FPP, efficiency is not as expected and your cost spiral begins to turn the wrong way. Is a CPP more expensive than a FPP installation? NO it is´nt!
When comparing the same quality of components (and a shaft tube as part of the stern gear), the purchase price is about the same as for a FPP arrangement. BUT……..
Lengthening the service life of your engine by the factor 4 at least, saving fuel on every single mile you operate outside the narrow window of max. efficiency, being able to operate a “beefy” Diesel as economical (or better), than a small toy at “handgrenade” setting, that all makes perfect sense!
And it comes for free once you got rid of the idiotic statement that a CPP is expensive.
The entire commercial fleet in Scandinavia is using exclusively CPP´s since about 100 years now!
There is ice in the Baltic and North sea ports almost every Winter, the CPP is still the choice, why?
The single blade is the weakest point in such arrangement! When it hits heavy ice or a log, it brakes. That is pretty easy to repair and does not affect the rest of the drivetrain. Have a spare one aboard, as every fisherboat there has.
Fisherman are not Yachties, they do´nt have money to waste, nor time for servicing coked engines. (and replacing them every other year)
But there is no fisherboat around up there with a FPP installation. So, whats cheaper?
I hope this short summary made some points clear enough, that we must NOT
discuss them again when the CPP is coming up next time!
some links: http://www.hundestedpropeller.dk/?id=4172 http://www.cp-propeller.com/ http://www.helseth.no/eng/products.htm http://www.frydenbosabb.no/index.php?mapping=16 http://www.servogear.no/pages/product.aspx?nr=33 http://www.nogva.no/?CatID=1191 ZF CPP´s http://www.grmo.dk/default.aspx?pageID=10002&lang=da http://www.bergpropulsion.com/ http://www.bukh.dk/uk/mainframe.htm http://www.westmekan.com/index.php?o...id=9&Itemid=11 http://www.masson-marine.com/de/prop..._03_01_01.html http://www.piening-propeller.de/de/v...lpropeller.htm http://www.wartsila.com/,en,products...4ED4,,8007.htm