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!


[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!
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] 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/a...op_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.yachtboutique.com/Bugatti...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.


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

[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.