Duoprop system for Poweryachts 100FT +

[yipster]

gosh glad its not my spelling, back to subject, think there is no future in "medium" sized simple CRP shafts on single engined pleasure boats?

Originally Posted by jehardiman

Yipster is right i spelled it wrong... should be Grim Vane propeller systems.

This was not entirely correct either:

..... standard fixed pitch props which are slightly more efficient that CPP sets.

Because the FPP can be more efficient only at ONE given situation (load/rpm), the CPP is the far more efficient choice over the entire range of possible operations. Though in the merchant fleet of the past, that was not very important running almost always at the same speed.
But whom am I telling that, of course you know.

Regards
Richard

[jehardiman]

Originally Posted by yipster

gosh glad its not my spelling, back to subject, think there is no future in "medium" sized simple CRP shafts on single engined pleasure boats?

It is an immutable fact: more gears and prop castings means greater cost and weight. For the real gains acheived by a CR set, you could just specify a larger in diameter wheel with less blade area. See this thread/post could widely spaced in-line props reduce cavitation while

Edit; what I meant to say, but forgot to state explicitly, was that the cost of a CR set doesn't really make a compelling economics argument because the real efficiency is not there. It's like trading in a paid-off 25 MPG car for a new $35,000 35 MPG car when gas is $4 per gallon. You never recoup the initial investment or sunk energy costs.

[jehardiman]

Originally Posted by apex1

the CPP is the far more efficient choice over the entire range of possible operations. Though in the merchant fleet of the past, that was not very important running almost always at the same speed.
Regards
Richard

I think we as naval architects always need to be careful in how we portray the suitability of one propeller type or another, because it can be confusing given all the vendor hype that come with the trivial or major differences between products.

From a fuel saving prespective, CPPs excell if the thrust to speed is greatly varying over the required operational range, such as a tug, towboat, or other ships that is forced to operate at greatly varying tonnage or rapid maneuvering loads. The situation of a small boat, yacht, or ship running for long periods at any set speed, a well matched propeller operates at almost fixed J, rarely varying 5% over the entire speed range and does not justy the increased cost and complexity of a CPP unless it is used in place of a reversing gear or because of prime mover considerations (i.e. MSD's fitted with limited reduction and unloaded by the CPP). USN DDGs have GT's and use CP props with only two positions, ahead and astern.

Originally Posted by jehardiman

I think we as naval architects always need to be careful in how we portray the suitability of one propeller type or another, because it can be confusing given all the vendor hype that come with the trivial or major differences between products.
Correct
From a fuel saving prespective, CPPs excell if the thrust to speed is greatly varying over the required operational range, such as a tug, towboat, or other ships that is forced to operate at greatly varying tonnage or rapid maneuvering loads. The situation of a small boat, yacht, or ship running for long periods at any set speed, a well matched propeller operates at almost fixed J, rarely varying 5% over the entire speed range and does not justy the increased cost and complexity of a CPP unless it is used in place of a reversing gear or because of prime mover considerations (i.e. MSD's fitted with limited reduction and unloaded by the CPP). USN DDGs have GT's and use CP props with only two positions, ahead and astern.

That was a longer version of my former comment. We are not really of a different opinion.

In general the CPP will replace the gearbox on a displacement yacht, so the cost will be about equal. The fact that most of these yachts are preferrably operated far below max speed, but owners have the desire of being able to go faster, makes the CPP by far the best option for these craft. And that is not just a opinion, and sure not born by sales drivel, that is my personal experience.
On planing boats, that picture changes, of course. But here we were asked for a size above 100ft or 30m, read, displacement vessel.

Regards
Richard

btw, the US acro illness is a pita

[mydauphin]

Originally Posted by yipster

CRPCPP was my thinking but i think to much

NOt another mnemonic to learn .... Please stay with a simple prop...

[yipster]

that was my guessed abbreviation reply to

Originally Posted by powerabout

I wonder if counter rotating CPP is a gain or not?

just to avoid confusion i see a real CRPCPP does exist and is described here http://www.tpub.com/gtss/35.htm and here http://www.google.nl/imgres?imgurl=h...26tbs%3Disch:1 havent figgered that CRPCPP out, does not look like a simple prop, sorry mydauphin

Originally Posted by PsychicWarrior

Has anyone seen a Volvo Penta Like Duoprop system consists of two counter-rotating propellers work for large motor yachts?

The idea makes a lot of sense yet I cant understand why it wouldn't scale and work for larger vessels?

and for the original question by threadstarter we may look at pod drives but they too aint exactly kiss (keep it simple stupid) neighter

but hey, what do i know

[jehardiman]

A Controlable Reversable Pitch (CRP) Controlable Pitch Propeller (CPP) is just a specalized CPP with , usually, a electronicly controled hydraulic operated pitch system. This system is linked to the MPU's to prevent overspeeding the MPU's or overloading of either the reduction gears or shafts during pitch changes, especally reversing. They are sometimes refered to as Controlable Pitch Reversing propellers, but the term "CPR" can lead to confusion. While there are some mechanical and structural differences between CRP and normal CPP's, these are generally limited to the method used to set and control the pitch, especally in consideration of casuality conditions.

The CPP systems we refer to here, are in general fully reversible CPP`s.
The term CRP is not very common (thanks god). The combination CRP CPP is not used.

Regards
Richard