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Old 06-08-2011, 05:16 AM   #1
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CPP, Controllable Pitch Prop

This is lifted from another board,

http://www.boatdesign.net/forums/pro...ary-30695.html

*

IT covers the CPP* both the + and - are discussed .

*
The Controllable Pitch Propeller, a summary.
<hr size="1" />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!


CPP RATIONALE


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, thats 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!

Regards
Richard

edit:
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
<hr size="1" /> Last edited by apex1 : 12-30-2009 at 03:34 PM.
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Old 06-08-2011, 10:13 AM   #2
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CPP, Controllable Pitch Prop

As with many other "ideas' I've tried on my boat, I have been interested in CPP's for years but have not successfully identified a manufacture that makes a CPP for the size of my boat. I know I'm opening myself up to some "slings and arrows" from those who are on a tight budget but my enjoyment of boating is not derived from long distance cruising. Rather, it entails using my boat for fishing and light cruising but also as a "test bed" for the latest technology available, (Within reason, of course.) Having flown CPP planes for the biggest part of my flying career, it just makes sense to me that a CPP on my single engine boat would (could) make a huge difference in the overall performance of the vessel, at any RPM.

Can anyone recommend a source for a CPP that will fit my boat? The links provided by FF seem to be all directed at large commercial vessels.







-- Edited by SeaHorse II on Wednesday 8th of June 2011 10:18:59 AM
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Old 06-08-2011, 03:12 PM   #3
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RE: CPP, Controllable Pitch Prop

Even if they bring in most of their money from REALLY BIG installations, most Norwegian CPP/bow thruster*manufacturers also supply stuff for smaller vessels. My dad used to have a Nogva CPP*on his small fishing boat powered by a 33 HP Yanmar.

The major reason for fishing vessels over here uses CPP's is not only to load their engines correctly, but also to be able to have just a small amount of water flowing past the rudder to keep her into the wind as they haul nets or longlines. Much like what a trolling valve on your gearbox would do, only the CPP could to this for hours and days on end and at any any engine power setting.

The article indicates fishermen keep a spare blade to change at wil at any time. Sorry to say someone has misled the author. No diver will be able to dismantle and reassamble a CPP on a vessel in North Atlantic winter 30 - 50 foot seas! If anything happens to their drivetrain, they are towed back to a lee fjord on the mainland to clear the propeller of nets*or to a yard if they experience any*mechanical problems.
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Old 08-11-2011, 05:48 AM   #4
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CPP, Controllable Pitch Prop

There is one danish CPP manufacturer which is not mentioned:

Korsor propeller:

http://www.cp-propeller.com/*

http://www.propeller.dk/

*

They are located very close to Hundested Propeller and they produce propellers to the smaller yachts, the fishing industry and larger coasters, tugs etc.

Quality is the same as Hundested (might even be better)....

Price is half of Hundested (this IS better).

Btw, I bought one myself...not installed yet.

*


-- Edited by Singleprop on Thursday 11th of August 2011 05:50:55 AM
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Old 11-22-2014, 02:21 PM   #5
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Bump

Just curious...how long does it take for the blades to rotate between forward and reverse? I'm trying to imagine docking a boat with CPP...
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Old 11-23-2014, 07:09 AM   #6
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The old style (usually fish boat) install used the CPP as gear box , and clutch by feathering the blades.

This was performed with a hand wheel , and was no bother , tho today backing 200ft into a slip might be exciting.

It saved the cost and complexity / maint of a reversing gear box.

Today the CPP is usually installed with a modern gear box and clutch , so it handles docking like most boats.

With the no gearbox setup , one trick was to operate the engine at 700-800 rpm , and adjust for no thrust before engine shutdown..

Then when cold starting the goal of the last shut down rpm was easy to set , and the boat would not move fwd or aft , while warming the engine.

Weather a cruising boat could recover the installation cost from fuel saving and longer engine life is doubtful.

For a blue water boat that does thousands of operating hours , a 15 to 50% fuel saving might add up?

For a motor sailor a CPP is the gold standard.
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Old 11-23-2014, 07:37 AM   #7
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"For a motor sailor a CPP is the gold standard"
When we had a 40 Jeanneau Sailboat I had switched to an Autoprop. Not exactly the same thing but works on similar principal. IE have the pitch of the prop set for the direction you are going and adjust the pitch based on conditions.
It worked very well on this vessel. No adjustment as you went, the prop did all the adjustments as you went along. It resulted in about a 10% improvement in fuel economy, significant more push in rough seas, about 1 knot faster at cruise for a given RPM, and the big one for me was a reverse that tracked well.
Given this is on a sailboat coming from a fixed two blade prop so a lot of improvement could be gained and was. On trawler type vessels I have no idea if it would make improvements but I thought it was worth adding the info to the conversation.
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Old 11-23-2014, 10:30 AM   #8
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Autoprop interests me but there is little if any hard information about their use on powerboats, most is about sailboats, motorsailing, and feathering. That is even anecdotal. I can't understand why Bruntons doesn't publish some real data to help justify the price of their product.
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Old 11-23-2014, 11:19 AM   #9
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I found this on autoprops and thought it may be interesting to you. Go to the following link and then look at the useful downloads and open the one about maximizing trawler range. Interesting but it is really expensive.
Mayrik Yacht Design, Autoprop
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Old 11-23-2014, 11:59 AM   #10
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Quote:
Originally Posted by Rogerh View Post
I found this on autoprops and thought it may be interesting to you. Go to the following link and then look at the useful downloads and open the one about maximizing trawler range. Interesting but it is really expensive.
Mayrik Yacht Design, Autoprop
If one was putting lots of miles under the keel, realizing a 20% fuel savings and/or an increase in range would be significant enticements to consider this propeller.
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Old 11-23-2014, 12:17 PM   #11
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This fellow says he achieved a 15% fuel savings which he put to use in his Atlantic crossing with a 21' "trawler";

http://www.autoprop.info/no/Testimon..._Atlantic..pdf
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Old 11-23-2014, 03:25 PM   #12
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I know the US Navy uses them on the gas turbine powered ships. Heard tales of sea trials when a "crash back" astern put a wall of water over the stern of the ship. They use a computer program to make adjustments in the pitch and for going astern since the gas turbine drives in only one direct.
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Old 11-23-2014, 03:28 PM   #13
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It really worked for me.
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Old 11-23-2014, 04:14 PM   #14
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Although not educated in the physics involved, I'd love to see some testing data/information on how they came up with and refined the Autoprop design. It must have taken some real tangential outside the box thinking to originally visualize the way it works!
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Old 11-23-2014, 07:04 PM   #15
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There's an interesting article about the Autoprop-benefits in the February 2000 issue of PMM*. Test subject is hull #1 of the Great Harbour 37.


Regarding the VPP: I don't understand the need for a clutch in a classic VPP-installation**, as the prop in "neutral"-position will turn, but without effect. So why a clutch? Maybe some experts are able to shed some light on this issue.

*) PassageMaker Magazine
**) reduction gear with built-in pitch-control like Frydenb°/Sabb HVP
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Old 11-23-2014, 08:48 PM   #16
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A clutch is not completely necessary, but does make some things easier. Engine maintenance runs, easier to start, easier to unfoul a line in the prop, etc.

Also, unless using a slow speed engine, you will need a gear reduction. Many commercially available reduction gears out there with clutches. Could be taken apart and hardware necessary for reverse removed. That will reduce drag a bit.
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Old 11-24-2014, 10:55 AM   #17
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Quote:
Originally Posted by HiDHo View Post
I know the US Navy uses them on the gas turbine powered ships. Heard tales of sea trials when a "crash back" astern put a wall of water over the stern of the ship. They use a computer program to make adjustments in the pitch and for going astern since the gas turbine drives in only one direct.
Yep the drive on a gas turbine is a balance of shaft RPM and pitch. The more pitch the faster the boat goes. But also more power required to turn the shaft. So to run high speeds all four GTMs need to be online and turning then you just keep increasing the pitch. And away you go
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Old 11-24-2014, 05:22 PM   #18
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I have always assumed that the Autoprop load curve is more of a straight line rather than the "drooping" curve of a standard propeller as such it could more closely match the "rising" curve of an engine power band. This would give better specific consumption at cruise speeds.
Bruntons doesn't publish anything like this, the 2 magazine articles and a couple of testimonials is all I have found. How do they expect to sell these expensive things? They don't even speak the language of pitch, diameter, blade area, and the 20" model is only good for 100 HP so would be unsuitable for many (although fine for me) Their representative nearest me, quoted me a price but no data to back anything he or Bruntons claimed.
It might have been great but just too expensive to buy w/o data to know what you are getting IMHO.
I have seen a few used ones for sale but the sellers don't, of course, know what pitch range they have either.
So, for me, Autoprop is a great idea, way ahead of it's time, but they really need a sales department.
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Old 11-24-2014, 08:01 PM   #19
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So, for me, Autoprop is a great idea, way ahead of it's time, but they really need a sales department.
No kidding. If they had half a clue they wouldn't have gotten the owner of a Great Harbor trawler to test it and write an article for them, they would have gotten a Nordhavn owner to do it. Such is the herd mentality of those being advertised to.

Some solid test data confirming claims of higher efficiency, using several styles of boats, would go a long way to building trust.
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Old 11-24-2014, 11:11 PM   #20
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if anyone cares.. the boat in the other thread has a VPP.
HOLLYWOOD

http://www.yachtworld.com/boats/2006/Diesel-Duck-Custom-Diesel-Duck-2724632/Port-Townsend/WA/United-States#.VHP-b8mPPRh
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