The Controllable Pitch Propeller, a summary.

You are welcome mate.

In the end it was roughly what I estimated.

Yes, you say it, people like to find a confirmation of their preconception, not experts advice.
And even here, where I clearly pointed out, that we are talking about highest quality for commercial applications, it was compared with cheapest stuff, like a Velvet drive, only.
There is a hughe difference in quality awareness between boaters and pro´s.
The same is valid between the Central European and the US market.
It is not a coincidence that the Chinese and some other brands failed to conquer the (central) European automobile market with their cheap tin cans.

We know that quality pays.

Regards
Richard

 

Hello

it looks great if i understood well but concretly how it work for change the pitch when the boat is running is it possible or not

kind regards
pascal

 

Yes, that's the tricky part but it will change pitch on the fly.

 

Hello Pascal! Does this explain the trick?

 

Splendid diagram Teddy, a picture is worth a thousand words!

 

yes

yes
thanks Teddy
kind regards

pascal

 

well said

my philosophy is roughly the same in that if someone hires me to build something then I better make dam sure its done properly lest someone end up hurt or dead cause I cut a corner.

B

 

"It is not a coincidence that the Chinese and some other brands failed to conquer the (central) European automobile market with their cheap tin cans.

We know that quality pays."


Will be interesting when the Chinese start selling a $59.00 computer ,
and India sells its 50 MPG auto for under $2000 , just how the Euros value "quality".

Cheap Indian car , $2000 cheap,, German car $30,000 HMMMM we will see.

FF

 

Actually the Indian company producing that $2000 car is developing another "cheapo" model to be marketed in Europe.. the cost estimate was (if I recall about right) was up from $8000.. And a cheap east european car ~$14000.. No sense to compare to MB

 

Hey guys....I'm a naval architecture student and I'm strongly considering using a CPP system on my senior design project. I was hoping you could answer some questions for me....this is all a learning process for me regarding this type of system so any and all info you have would be great. First, the boat is a 35m catamaran patrol boat (hard-chine hullform, similar in style to a fast ferry hull) that will have a patrol/cruise speed of around 25 knots and a max speed of 35 knots. I think we are slightly too slow for waterjets and I'm shying away from a FPP system because we will be operating at varying speeds....so a CPP system seems attractive.

As I'm getting into the propulsion design, I'm not really sure where to start for a CPP system. I like the servogear system...but I'm wondering if it is more of a "package" deal (since exact design is less crucial for CPP compared to FPP...I think) or is it optimized for your individual project? Basically, what are the steps I should take for this preliminary design? Do I match the required craft thrust with the propulsor thrust and choose an operating RPM, gear ratio, etc just as you would for a FPP system?

I'm kinda shooting in the dark here and I haven't found many resources on design of a CPP system so any info would be great! Thanks!

 

all the early 35m-ish tin cats only did 35kts and were all jet powered in OZ?

 

powerboat is correct, most of the newer patrol craft are using waterjets.

The reason isn't efficiency, it is the ability to get into shallow water, have less chance of damage that will take the boat out of commission and manuverability. All of these favor the waterjet over the other modes of propulsion. Exposed props see damage a lot easier from floating or semi-submerged objects, as well as running aground.

Also remember that the users may not be well trained, and are more prone to damage exposed props so there is a benefit to waterjets in that case.

Finally, your maximum speed of 35 knots is low. Most new patrol craft in that size class are talking speeds closer to 50kts if not higher. Unless the maximum speed is specified as part of your design task you need to be thinking faster. This will present a different set of trades in terms of powerplant weight, payload, equipment and range than a 35 knot boat. IMO a 35 knot boat is going to be a lot easier to design than a 50kt boat and that is where the rub comes in.

 

The yards like jets as well as its a simpler installation
drive shaft /crankshaft level
no rudder
rev and steering systems combined to one unit
I would guess engine, clutch and jet might be cheaper then shaft prop and rudder?
more choice as the where engine sits
for same power max speed usually higher than a prop
and as Yellow jacket says pretty close to unbreakable...

I witnessed one megayacht (that had them why?) anyway,it picked up a mooring rope that that was connected to a chain and when the chain went inside the housing it exploded it and now you have a very large hole in your boat...quick thinking crew ran over to a local worksite and got the cement mixer to come over to the dock and fill up the lazarette with concrete to prevent it from sinking..clever!

 

Welcome here.

You are right assuming that the systems mainly are sold as a thoroughly engineered package, rather than a assembly of pieces as common with a FPP.
The optimization though is just choosing the right reduction ratio for the gear, the optimal (usually biggest) prop diameter and the according shaft dia.

In your case (relatively high speed), the blade shape is another issue which will be engineered / choosen.

You have not to do more than choosing the right RPM for the given thrust requirements and given max. prop diameter, as you would do with a FPP.

The Jet btw. is NOT easier to install and by no ways cheaper.

You ARE in the Jet range at 35kn if the operating speed is constantly around that figure, and it would be a sensible choice in that case, therefore the fast Ferries usually use Jets. But you mentioned different operating conditions, so, the CPP will be the right choice again.

Regards
Richard

 

Just to make that clear!

This is MY THREAD! Do NOT spread opinions here!

The one megayacht you witnessed maybe a fine example of the possibilities.

The 6 megayachts I owned, had only one time a jet driven propulsion! And never again.

Regards
Richard