dual prop shaft ?

[yipster]

hello techno's,
does anyone know something about "single"shaft(s) for dual counter rotating prop's ? maybe info or an adres ? :) thanks !
yipster

Are you asking about inboards or surface drives which have two in-line counter rotating props? I've never seen that (nor am I sure it's even practical), but I'm interested if you have see something like what is available with the duoprop outdrives.

Or are you asking about twin shafts and one engine? Or twin engines and one shaft?

[yipster]

hey, no answer yet but thanks for the interest!

merc. bravo3 drives have like the volvo penta heckdrives dual counterrotating props.
i liked them a lot becouse they gave great grip all over the speed range, wheel effect was absent, good system, big improvement!

now, like you, i am interested if dual counterrotating props also
come on a -say single- inboard engine prop shaft.

just had a call back from vetus here where i informed on this but the guy didnt know about wheel effect of props, counterrotating props, only the basics and partnumbers. i did ask merc and penta, the forum here also, but you are so far the only reply.
not an answer, just another lost soul wondering. using the i-net search engines dont give much hope eighter. maybe such shafts still are to be "invented" for boats? hey guys, come on, wake up!

http://www.boatdesign.net/gallery/data/511/690bravoo3.jpg
http://www.boatdesign.net/gallery/data/511/690counterrotating_prop-thumb.jpg [B]

[Willallison]

Must confess that I've often wondered why counter-rotating props have never really taken off for conventional drive systems. The technology is hardly new - ever seen a torpedo with just one prop?
I guess the main reason is cost. The duo-prop and Bravo 111 are both standardised systems - you simply buy off-the-shelf props to suit your own application. But, for the most part, every inboard installation is a custom one. Shaft length, diameter etc etc, varies with each boat. So any counter-rotating system would have to be designed specifically for the task.
Surface drives are more closely related to sterndrives (in that companies such as Arneson produce standardised models) - perhaps the gains simply aren't there for a counter-rotating surface drive....

[yipster]

Originally posted by Willallison
I've often wondered why counter-rotating props have never really taken off for conventional drive systems. The technology is hardly new - ever seen a torpedo with just one prop?

thanks Will, exellent example! :D
still it seems that this technology is unknown to many.
like i knew from experience and got confirmed: counterrotating props have less slip, more grip and no wheeleffect. (what would make that single propped torpedo ( AND ALL SINGLE PROP PROPULSION SYSTEMS ) go in spiraling in circles when not corrected. a frend of me even came to the idea of putting the drive system of centre or in an angle and unfortunatly enough that's about the spirit i found. eighter hp or size seems important, not the design. sure, one can have dual (and even counterrotating) drive systems. or get a fast volvo or mercruiser heckdrive with duoprop. but now i want, based on my good experience, a single (economic) engine shaft for a displacent hull(s). i am still amazed i cant find it. maybe got to custom make it...? i made a simple drawing here without pressure bearings or seals etc. to illustrate the simplicity. price can hardly be the issue it seems to me. it could also be implemented in a V drive. i havent given up my search. than again nobody gave me a convincing answer yet, maybe your rite, maybe the price and the gains aint big enough... i doubt that and do realise this counts than for allmost all boats! [B] [U]http://www.boatdesign.net/gallery/data/500/690sunnylady-thumb.jpg there is a price for doing things, this was overdone i admit. but fast! fast also is the ventilated cavitating arneson surface drive that fits on bravo1 2 but not on3? drives. (not their reply) wish someone could explain or convince me better. like you said: [QUOTE]ever seen a torpedo with just one prop?

ÿipster[SIZE=4]

[FRANKIEFRANKIE]

Yes, I ran across some data on this subject. Schoell Marine produces an efficiency number chart for hulls, drive train, with % added to conpensate for two and four propellers. This was given out at IBEX in Ft. Lauderdale in 2000 with the keynote speaker Mr. Schoell. He is know for his towing models and propellers and his mechanical patents in the marine industry.

The duo prop is a very efficent unit. There are many methods to make a surface drive into twin props, with the best coming out of marine transmissions, as you can run these in either direction off the shelf, with two shafts. Have done this and it runs great. Also, sold some surface propellers to a gentlemen who had also done one on his own but could not get propellers for them.

Pulse-Drive sells a single trimmable unit surface drive that is the same in efficiency numbers as the duoprop. The reason is that you can trim the whole unit and the other is it has two rudders, each flanking the propeller which counteracts the torque of a single propeller. I do not believe any other trimmable surface drive company sells a single.

I'll see if I can scan the efficiency numbers and post later.

Frankie

[yipster]

frankiefrankie

yes and no, yes efficiency is it, no i like that duo prop (shaft)..

for volvo duoprop and patent see:
http://www.land-and-sea.com/public/articles/popular_mechanics/popular_mechanics_prop_article.htm
(and realise torpedos are much older than this article) but i cant find that shelf.

for tech. stuff like Cycloidal Rudders also at:
http://www.******************/BugattiMarine/Technology.htm

greetings yipster

[FRANKIEFRANKIE]

Did not understand the yes and no. The duo prop is great and is as efficient as a surface drive, just not the shallow draft capability of the surface drive or the five year warranty that some offer.

I too, like the duo prop and a long time coming. The cost of dual propellers in a single application on a surface drive is cost prohibitive.

Have one in the shop for racing application again the cost is more than the engine.

[yipster]

FRANKIEFRANKIE

liked to hear your duoprop feelings!
but maybe you are toooo fast?

i expand; YES is: efficiency is it, when a single prop is just as efficent as a duo and rudder(s) are dealing with torque, look no further you might say. still in my imagination however the rudder(s) must even be twisted than to really counteract torque. better shallow draft capability and 5 year warranty also is valid to some.
live can be easy, why make it difficult. thats the NO. i also liked that duoprop, seems to me the better system, and aldo it probably also had very little torque left and other flaws like construction and price i asume. than again in the PM article link it said (i forgot price) they are only a few hundred $ more. also that patents, as far as such can be patented are running out at the turn of the century. elaborating more: beeing interested in technics i agree that forexample a small turbine's cost is only feasable by forexample gouvernements. but still i look at specs, and 1200 or 1800 HP from a 550? pound engine is impressive. apart from that, apart even from surface drives, i started simply looking for such a -whats simple!- duo prop shaft for a displacement hull. wanted to know a price or where to find them. assuming such was of the shelf. maybe its just an old bad dream i have from my first shakespeare 140 pk volvo inboard pulling hard to one side.... than again, its more or less real for many.
http://www.******************/images/BMTurbine.jpg

From: POPULAR MECHANICS * SEPTEMBER 1989
Because the Duoprop is running two counterrotating props, it outperforms single-screw installations by taking a firmer prop bite and losing less energy through the water. The former is the result of increased blade area, nearly double that of a single screw, and the latter the result of cavitation, ventilation and slip losses reduced by low prop rpm and the neutralization of the paddle-wheel effect (sideways torque) and the spinning motion of the water column's exit flow. Why is Duoprop so quiet? This isn't as easy to understand, but it has to do with a vibration frequency less prone to amplification by hulls. Duoprops cost only a few hundred dollars more than single-prop units. Two-in-one props easily out perform single-screw units and many marine companies, no doubt, will try to copy them. But don't look for this to happen any time soon. Current patents don't run out until the turn of the century.

so all together i think you make sense, torpedos are there for 2 century's, the duoprop is from the last century and i better wait another century for a shaft. i might be writing allready to prohibitive. meanwhile surface drives probably are more efficient than anyway.
cheers, yipster
http://www.******************/images/cycloidal.jpg

[yipster]

answer to my qeustion lies in that turbo also, counterrotating props might have more setbacks.....?

[Willallison]

If it's for a displacement boat application, I can't see the efficiency gains outweighing the cost. Say you gain 5% by using counter-rotation: at 8 knots you've picked up less than 1/2 a knot - unless you're a commercial or trans-ocean traveller, it simply wouldn't be worth the cost of a custom engineered driveline.
There are numerous driveline systems available which improve upon the old conventional shaft / prop / rudder - but few find their way onto recreational vessels for exactly that reason - cost.

[yipster]

Will,

i think the cost is not neccesairly what you guy's make of it. than again say it was an big oceanliner, the more i read about it, less noise, low vibration etc. the duoprop system as i feel it also, is great and better than only 5% i think. and as is, only a few hunderd bucks more than a conventional. efficiency sure counts and surface drive props say they equal duo props in that. i like to think of a displacent multihull that makes 60% more than 8 knots. regret your cat "napkin" was voted quikly out. (i sometimes even make "thumbnail" drawings.) sure cats must be big but it had much potential. i like Mikes spreadsheet now but would much rather have seen one on displacement multihulls. that would have been a new way and a challange out of the meanstream. a low speedgain as you describe may be real, and better bite, less slip may be advertising, but is not! remains the torque, when reading magazines it appears silly to me to read that almost all pleasure boats (but bigger ones more or less also) have different turning circles over starboard and portside. reasons known. the newer drivetrains you mention must be much better than that old runabout i once had, but since than i had some others, but not a surface drive. ìf you however know of more driveline systems available which improve upon the old conventional shaft / prop / rudder / wheeleffect etc. give me the links. not direct to buy, i'm just interested, in general also. and just becouse something is expensive it does not always need to be good and vica versa. i really thought such conventional dual shafts were allready fairly priced on the market. maybe i'll settle for the torp tail (plus props!) haha! as said; just havent found that shelf. than again yes, maybe i'll better shut up and think simple; a cat with 2 engines, not a tri with one, with 2 counter rotating singles saves a small homecoming outboard also. thanks for the thoughts anyway. have a good sunny day, yipster

[Willallison]

When I refered to the added cost of a counter-rotating system, I was talking about a custom built job. It's true that the duo-prop and Bravo 3 legs are only a bit more expensive than their single-prop counter-parts - but try building one from scratch and see how much it costs you!!

[yipster]

yes Will and Frankiefrankie, technically we agree. remains the question: "does anyone know something about "single"shaft(s) for dual counter rotating prop's ?" and "I've often wondered why counter-rotating props have never really taken off for conventional drive systems." it even makes me think now why mills and turbines dont counter rotate, there must be flipsides to counter rotation also. but have a (heavyer!) maritime dual prop and shift on the same engine and it makes you fly out of the box without accelerating! talking about slip and grip! and it has more good specs. no, dont think i'll try to build one soon myself.... wish i / somebody was do! yipster

[FRANKIEFRANKIE]

The reason we do not produce such a system is the cost versus the gain. You get counter rotating via the transmission on dual installation which make the need for this mute. There is no need to make turbines (cost) counter rotating when 90% of the installations are dual, triple, and quads which there is no need for the counterrotation.

I am sure just to answer your question there is not enough need for the single to warrant the cost.

[Mike D]

Do I sense a note of frustration, Frankie? You beat me to the punch.

Yipster, it always comes down to cost versus performance. That is why you don’t hear much about contrarotating propellers because they are higher performance, higher cost, higher maintenance with reduced reliability. Below you’ll see a chart of propeller efficiency for various systems and although it is graduated at the top for ships it applies equally well for boats and small craft.

The vertical axis is efficiency and the horizontal axis is the propeller loading coefficient Bp which is Prop RPM x Power^0.5/Speed^2.5. Power is the power in horsepower delivered to the propeller and speed is a little less than boat speed, reduce it by 1 knot to keep things simple.

So if we took a boat running at 15 knots, 1800 rpm and 100 hp Bp is 24.5, or 25 knots, 1500 rpm and 200 hp is 7.5, making a twin screw instead of single screw multiply Bp by 0.7 assuming no change in speed, revs and total hp.

In this range you can see the typical recreation boat propeller – Gawn. It is less efficient than the B series but cheaper. However, if you check the luxury yachts and commercial vessels the B series is very popular or propellers having the same general characteristics.

The best are the contraprops, about 5.5% better than a Gawn but a B type is about 3.5% better. I have read many times about gains of 15 or 16% for contraprops on ships but I take a pinch of salt.

You must be careful when talking about percentage improvements. Use the cube law when comparing power and speed, in other words power is a function of speed ^3 and expressing things is percentages is the best way. It is accurate enough to use one third of the power increase for the speed provided the power increase is less than about 12% or 15%, beyond that use a calculator :) So Gawn to contra would give only 1.8% more speed.

If you really want improved propeller performance you should investigate the “manually operated” controlled pitch propellers. When the boat is moving slowly for prolonged periods you need something with a fine pitch whereas you need coarse pitch for speed. I have no idea about their cost but it makes as much sense as contraprops.

There is a cross-river ferry service where I live and the single screw wheel effect was awful when it was being manoeuvred. Until another skipper came on the scene, he did everything wrong and the docking was smooth! If you fight the wheel effect you’ll lose, every time, work with Mother Nature’s laws and she’ll smile at you.

Michael

Counter Rotation inboard drives would probably handle better than a single rotation propeller that is countering the torque of another single rotation propeller.

The boats that use the Volvo Duo Prop or the Bravo III Drives tend to be more docile in the slow speed manners than a non duo propeller installation, but exactly how much of your boating time are you going to be spending idling or very slow speed cruise?

There has to be more parasitic loss of power to turn an I/O with counter rotating propellers than one with non-counter rotating propellers, so I do not believe they will automatically gain a substantial amount of speed due to the power loss combined with the increased drag of the second propeller.

As for a rudder fixed shaft application, they have had very little success on any form of boat. The I/O’s are a better solution over the rudder concept, especially in slow speed maneuverability. When using the marine gear to counter rotated the propellers, you loose a tremendous amount of hp through the marine gear. It is far more efficient to have the drive units counter rotate, as they will not waste as much hp to counter rotate the propeller as the marine gear will.

A counter rotating Surface Drive was developed in the 80’s but there wasn’t sufficient market need to warrant production. With today’s market, possibly there is a need?

[lockhughes]

eCycles 2003 9.9HP (equivalent) electric outboard motor...
http://www.boatdesign.net/gallery/showphoto.php?photo=705

Hey! They went CR prop instead of a kort nozzle... intereresting

Lock
http://groups.yahoo.com/group/QCYCTender/

[yipster]

electric guy lockhughes

and what a beautifull baby it is!
got specs or a URL? i noticed http://www.schottel.com also tends to go for CR instead of the nozzle, electric too!
still occasionally think of the above guest that said
far more efficient to have the drive units counter rotate how wise! is that ever done - can that work :?: :?:

[lockhughes]

Hi Yipster

Originally posted by yipster
electric guy lockhughes
and what a beautifull baby it is! got specs or a URL? both:
http://www.ecyclemarine.com/outboard.htm

i noticed http://www.schottel.com also tends to go for CR instead of the nozzle, electric too! BTW, I have Schottel at:
http://www.schottel.de/index_e.htm

Dot-com didn't work for me

still occasionally think of the above guest that said
how wise! is that ever done - can that work :?: :?: :)

`spect the CR's make more sense at higher (boat) speeds. So I was a little surprised to see eCycle go this route on their little electric outboard. There are a few e-outboards that use a kort.

Cheers

Lock
http://groups.yahoo.com/group/QCYCTender/

[Birdman55]

Hay guys

I just wanted to say that I know just what your talking about. I am just 18 years old and I have seen one in person at a private marina that i used to work at. It is too late now for me to get som pictures of the props but by this weekend i will have some if yall are still interested. It is not my boat nor do I know the owner so don't ask any specifics. Just wanted to see if this is what you were talking about.

Get back with ya later.
Birdman55

[Willallison]

send 'em on in Birdman!....

[yipster]

dito, show us what you mean and a pic can tell a thousend words they say! :cool: yipster

[yipster]

going true the new honda outboards folder here i read: counter rotating engines are deliverable for the bf115 up to bf225 when using dual OB's. really!? or is that a gearbox?

[Peter_T]

Two shafts in the same axial!! This is going to be expensive to machine.

I admired your 3d running propeller picture in web!!!

For single screw with CP system, the shaft is hollow to allow hydraulic fluid to activate setting of the blade pitch. The makers made so many units in history, so there is no hardship, except they will bill you 20% to 25% more. The CP propellers also cost more.

Aquamaster produced a tandem counter rotating propeller style for Z-drive to compete with Z-drives with nozzles. That style did not get much market share.

The new propulsion series with POD only use pitch propellers. Since, CP system is a good combination and can be added to the system if the customer wanted. But Z-drives can rotate within a minute, so they drop the application. What matters is the cost advantage in marketing.

What tandem propellers offer can be gained by selecting better propellers with accelerated pitch like the patented work-wheel by Bird-Johnson. At least we are contended with the average propeller suppliers to offer skew propellers that can be as efficient as the tandem propeller system in a line shaft.

To save cost, perhaps look to the method used by attaching a counter-rotating hub "PBCF" www.motech.co.jp This is for application to ocean vessels, but can also applied to small craft, yachts. When fitted, the power loss in the wake stream behind the propeller can be recovered, so you gain a few percent back. This feature does not need power to drive. It will turn itself in a passive mode.

Some early invention is to reshape the rudder to gain a few percent, but this change is not as effective as the "PBCF". The powered counter rotating propellers work in the same principle.

One must be satisfied, that if you apply two or three upgrades in same area, the final gain is directly added up. You will certainly gain in combination to some extent.

It is interesting to see the torpedoes are fitted with two propellers. This may be to offer reduntancy. Note: their propellers are very simple shaped.

All the thruster companies are looking in adding new form of POD propulsion, this is the best so far. Of course this meant for the bigger vessels. I think there is a lot to improve on outboard in re-focusing the tiny propeller they supply to some reasonable sizes. Look at Volvo Penta system.

Taking two propellers, one at each end of the Z-drive shaft axle is a good idea, as adopted by "Schottel".

Peter

[brian eiland]

Someone on this forum subject might find this latest posting of interest:

Duo-Prop shaft drive design 7/8 complete
http://www.boatdesign.net/forums/showthread.php?t=1038&page=1&pp=15

[yipster]

and that is me for one :D thanks Brian, and compliments on your site! fisherman did not list one but who knows, i'll reply!

[Joel]

yipster those images are going straight on my science project, which is due tomorrow....

You saved me!

[IHTFP]

Mercruiser used to make a counter rotating surface drive. It was called the Blackhawk. Works very well, the only drawbacks are durability and availability of parts. http://home.earthlink.net/imagelib/sitebuilder/misc/show_image.html?linkedwidth=560&linkpath=http://home.earthlink.net/~slypaul/sitebuildercontent/sitebuilderpictures/blackhawk.jpg&target=tlx_new&title=Efficient%20surface%20drive%20-%20Blackhawk

[yipster]

Mercruiser used to make a counter rotating surface drive. It was called the Blackhawk. Works very well, the only drawbacks are durability and availability of parts. http://home.earthlink.net/imagelib/sitebuilder/misc/show_image.html?linkedwidth=560&linkpath=http://home.earthlink.net/~slypaul/sitebuildercontent/sitebuilderpictures/blackhawk.jpg&target=tlx_new&title=Efficient%20surface%20drive%20-%20Blackhawk
yes thats rite, its a sterndrive however, not a propshaft driven duoprop

[IHTFP]

I realize it is a sterndrive, but thanks for pointing out the obvious. Actually, I have one on the back of my boat, so I know quite a lot about these units. I wasn't necessarily responding to you, I was responding to the ealier posts that asked if there were any counter rotating surface drives.

[RANCHI OTTO]

I've installed on the same boat the single and the duoprop of Volvo Penta.
At the same displacement and power the gains in speed have been:

single duoprop
---------------------
25.0 > 27.5 knots
30.0 > 32.4 "
35.0 > 37.6 "

In effect 2.5 knots more. Better acceleration too.

RANCHI OTTO