Duoprop system for Poweryachts 100FT +

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?

 

on larger motor yacht shafts no, on big ship shaft yes
have had bravo III's and agree they make sense
think R&D is the reason we dont see them

 

The bigger the yachts, the bigger the props, the lower the prop revvs. In that case a CPP is the preferred choice, providing far more gain in efficiency than a duoprop.

There have been systems tested on merchant ships with counter rotating props, mainly passive. Not the big winner.

Regards
Richard

 

your rite again apex but i have my doubts whitch best in efficiency
for boats, ships and planes all propulsion systems are compromises
and i dont see the counter rotating prop as a loser yet eighter
it does not walk and transfers gyrational forges directional very well
this old noisy CR GE jet with a kwarter fuel saving is back in 2010
granted its now ducted high bypass but thats another story

 

Well,
I did not say counter rotating prop is a looser. On high revving installations it is a winner in fact.
But on larger craft which always install the biggest prop possible (the most efficient), it can never compete with a CPP installation. Most probably hardly with a conventional fixed pitch prop. We must not forget, that most merchant ships go continuous speed (rpm) almost all their life long.

Regards
Richard

 

ZF makes a pod drive for larger yachts (Pod 4000):
http://www.zf.com/corporate/en/products/product_range/boats/poddrives/drives.html

Not saying it makes sense for the passagemaker types usually discussed here but if you want moderate speed and like gadgets they have lots of features to play with such as joystick controls, automatic station keeping and integrated autopilot. Takes three or four of these to drive a 100+ vessel

 

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

 

here some more to think about http://www.boatdesign.net/forums/di...oach-boat-other-propulsion-systems-14569.html
and more http://www.youtube.com/watch?v=7E6KglXPmTs
should be doing something worth while tho

 

...........:?:...............

 

CRPCPP was my thinking but i think to much

 

The reason that you don't see CR sets on large vessels is the addded cost and weight for only slight gains in efficiency and the loss of maneuvering ability. Large yachts have proportionaly higher loaded but smaller wheels compared to "small" boats, but require similiar impluse for maneuvering. CR sets, by dividing blade area between the two disks increase maximum efficiency, but reduce the ability to generate propulsion impluse on demand. As I pointed out in the cat yacht thread, yacht owners are more interested in the bottom line than in the last decimal of efficency.

Just for laughs and giggles, go look to see what proportion of large 60+m yachts are for sale in any given month. They are "turned" just like houses, thier owners are not looking to retire to them, they are capital storage devices and/or tax devices. Also notice how many of them are held by holding companies and available for purchase or charter.

I just think it needs to be pointed out here that in terms of absolute effeciency, CR and Grim wheel sets are slightly better than standard fixed pitch props which are slightly more efficient that CPP sets.

What forces the prop selection (only considering fixed displacement applications like small boats, yachts, and cruise ships) is maneuvering ability and gear set cost. For small boats with proportionaly larger wheels and low absolute HP, a reversing or CR gearset to support maneuvering is just as easy as anything else. When you start getting into large HSD's, small GT's, and MSD's, reversing and CR gear sets lose out to CPP's because of the cost of moderate HP gear sets. By the time you get to ships with high HP steam/GT/LSD's the wheels are so proportionaly small that the need and usefulness to quickly reverse is greatly reduced and easily handled by electrical/pods/black gang.

In large ships, CR and Grim wheels sets have not been successful becase the blades and blade roots need to be thin compared standard wheels in order to see efficiency gains. This had lead to more prop damage and loss. As I have said in other threads, the selection of propblade material and blade/root section has more to do with acceptable damage tolerance than with absolute efficiency.

 

Not in efficency over a fixed pitch CR set, but I do have a design for something like this that I did for a HPV submarine, as well as a composite CR VPP wheel set. Lots of work and cost for little real gain.

 

had to check grim wheels that at first sight looked like crpcpp but are fluid dynamics add-ons that i've seen in various forms.

did find QM2 topless http://www.roblightbody.com/liners/qe-2/1987_Refit/ and down the page sought info.

wikipedia reads however:
"Commodore Doug Ridley was demonstrating the "flexibilty" of the new power plant and new props to journalists who were on board. While QE2 was travelling at about 30 knots, he ordered "full astern". As the ship was slowing down there was a horrible shudder and it was obvious something had gone wrong. It is possiblethat some vanes were already cracked and this was just the Last straw, but that is conjecture"

as for crp the zf site writes:
"The increased propulsion efficiency, compared to traditional shaftline
systems, can give up to 15% faster cruise speed and up to 15%
faster top speed. Better performance translates into improved fuel
economy up to 30%, environmental footprint reduction and both
initial and through-life cost reduction"

sure when your props get nicked or damaged but otherwise not bad i think

 

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