Pros and Cons of jackshaft power.

[Capt Sport]

I posted this in the boat design forum and only got a few responses. Maybe I'll get more response over here on the metal boat forum. I understand the jackshaft set-up, what I'm looking for is more information on how the boat performs.

I'm interested in jackshaft power for my next boat. And, was wondering if some of the more experienced designers on here could tell me the pros and cons of powering this way.

It seems to me that a boat with jackshafted power would be much better balanced, ride better and be more efficient. But I'm sure I'm missing something, or more boats would be built this way. It can't just be that outboard boats are cheaper to build.

Just to give a little background on the boat I have in my head:

Aluminum
Center pilot house (full walk around)
24-28' lenght overall
8'6"-10' beam (dependant on length)
diesel power

What I'm looking for is a rough water boat, with extended range. That is as cheap to run as possible. Think of it as some of the Pacific north west boat designs without the great big full width house and cabin. I'm not looking for the fastest boat on the water either, cruse at 20 knots top out at about 25 knots.

Thanks in advance for you help and input,

jr

[Frosty]

Capt -- weve all seen your thread, --and if like me,dont understand your question. A jack shaft is a method of driving a particular drive by an engine.


What do you think a jack shaft is?


All threads get posted on the "same" main notice board.

[Capt Sport]

Jack Frost,

Thanks for the reply, I understand what a jackshaft is and how it installed. But what I'm really interested in is how do boats of similar design handle given jackshaft power vs I/O power vs outboard power. I would assume that all things being equal (deadrise etc) each boat will handle the same conditions differently. And, the differences in ride characteristics, efficiency etc are what I'm after. For example is one design better in rough water than another, is one more effiecient then another design and why.

Thanks again for your reply,

jr

[alan white]

It's better to ask what fore/aft engine placement does to seakeeping characteristics.
Generally, an engine down low and centered fore and aft puts more mass at the center of motion, meaning the boat yields more easily to any forces applied to its ends, lifting or yawing more quickly, "feeling" its way through more efficiently.
Normal shaft drives work better and better the further forward the engine is located due to the ever-lessening angle of each parallel part of the system.
A jackshaft would place a third parallel shaft into play for reasons not associated with boats, perhaps to power hydraulics, winch, etc..
It wouldn't be needed to place an engine in a particular location, however, since there are gear drives for doing that, usually V drives or simple parallel setups (chain, belt, or gears).
Again, a jackshaft is parallel to, but not axial to either engine or prop shaft, and it might also be termed an intermediate or transmission shaft, and hence it would serve no typical location function. In other applications it might assist in further speed reduction or allow going around corners, something most all boats don't need.

Alan

[Bob S.]

I believe the OP is asking about the characteristics of a boat equipped with engine amidships driving a transom mounted I/O unit through the use of a lengthy horizontal shaft. I believe a few production glass recreational boats are so equipped.

In my opinion, if you really buy into the I/O type of drive then the jackshaft is the way to go if for no other reason than to rid the cockpit of the lousy big engine box that all conventional I/O boats come with.

http://www.yachtworld.com/edmondsyachtsales/images/e330413.jpg

[alan white]

And this is called a jack shaft? I see. Sorry jr.----- I stand corrected.

A.

[Willallison]

There are a host of pro's and cons for any drive system, a jackshaft being no exception. But there are two main reasons why you would emply a jackshaft. The 1st, as has already mentioned, is to free up cockpit space (possibly at the expense of space further fwd...) The second is to ensure that the boats centre of gravity winds up where you want it. Depending on the boats intended service and speed, this could be anywhere from between about 50 and 65% of the waterline length (aft of the bow) for a planing hull.

[Frosty]

A jackshaft can enable you to move the engine relative to your chosen drive by lengthening or shortening it ,--therefore a jack shaft does nothing for handling more than re-distribution of weight by being able to drive from the engine from vaious distances.

Calling a boat 'jack shaft' powered is extremely confusing.

[alan white]

The gear reduction appears to be in the I/O drive. The shaft must spin at engine speed... balancing that shaft must be important---- it would be going 2-3 times the speed of a regular prop shaft, right?

A.

[Frosty]

Yes,-- Engine speed-- hence lengthy shafts are not good,---well to be avoided if possible. But at least dont need to have splines unless very long.

[Capt Sport]

My apologies for the confusion, Bob S has it correct in that I'm interested in an I/O connected to a midship mounted motor as in the photo he's posted.

The shaft does spin at engine speed just like a drive shaft for an automobile. They can be made safer by passing the jack/drive shaft thru a tube designed to keep it from flailing about in the unlikely event a u-joint fails.

Thanks for the replys,

jr

[Rusty Bucket]

I know the term "jackshaft" and I thought it already had a home. If that's a jack shaft then what's a drive shaft? I think the terminology is confusing at best. regards rusty

[TerryKing]

I know the term "jackshaft" and I thought it already had a home. If that's a jack shaft then what's a drive shaft? I think the terminology is confusing at best. regards rusty

I learned from my Grandfather, who was the "belt wizard" at the old New Departure (GM) ball bearing plant in Connecticut, that the "Jack Shaft" was the main shaft that ran down the overhead of the factory and drove all the machinery by belts that came down to each machine.

This seems to be consistent with the definition from www.thefreedictionary.com:
(Mach.) the first intermediate shaft, in a factory or mill, which receives power, through belts or gearing, from a prime mover, and transmits it, by the same means, to other intermediate shafts or to a line shaft.

So, the shaft that receives power from the Prime Mover (Engine) and transmits it to (load or loads) sounds like a reasonable definition. "Drive Shaft" is, I think, more general...

Many years ago, when I was about 12, The Old Man (AKA A.C. Gilbert Sr. of Erector Set Fame) gave an old Wisconsin-powered garden tractor to me and my friend Mark. We eventually got it to run. A.C. and Mark's father conspired to give us absolutely no help, while keeping an eye on us. It had "The Jack Shaft" which was chain driven by the engine, had a 'twin-disc' clutch, and drove the chain to the drive axle.

So the term was pretty familiar. Of course, that was about 1950 :p

[rayk]

Drive shaft for propulsion, jack shaft is a PTO.
Jack is an assistant, for helping out around the place.
Plenty of jacks around a boat.

There is a meaning behind jack ****.:)

[alan white]

Yer an ancient tractor mariner, Terry. We used jack shafts on mini-bikes in the sixties to center the engine and to play with ratios (the rear sprocket was expensive and the front sprocket was part of the centrifugal clutch).
I can understand the definition of the jackshaft in a factory. It wasn't axial to either prime mover or machinary. I've got the feeling the name caught on with boats as slang, which is right and proper.
I worked out a V drive that used no gears (1:1 ratio) a few years ago. It used (on paper) a universal joint, so all power was transmitted through needle bearings. Would save, I assume, 5-10% power usually lost through gear contact. I just bought a digital camera (a first for me) and I'll have to upload a drawing of that design.

Alan

[TerryKing]

I worked out a V drive that used no gears (1:1 ratio) a few years ago.
I'd like to see that. My current boat (in USA) has a Casale V Drive with a (Shaft I always called "The Drive Shaft") made from a Chevy drive shaft, with universal joints at each end.. It's about 40 inches long, I think. But how did you "change direction"?? No gears.. Hmmm. Chain/Belt??

[Capt Sport]

Ok, to clear up the mystery of where I got the term jackshaft, which to my knowledge has been around in the boating industry for well ever. You can follow the links below.

http://www.albemarleboats.com/trailerable/242CCspecifications.html

http://www.volvo.com/vce/Templates/GoogleSearch.aspx?NRMODE=Published&NRNODEGUID=%7bC78DABCD-3296-4ED7-8A3B-914B7A30ACF3%7d&NRORIGINALURL=%2fvolvopenta%2fna%2fen-us%2fapplications%2fSearch%2fsearch%2ehtm&NRCACHEHINT=Guest

http://marine.cummins.com/public_cummins/content.jhtml?tlaId=1&anchorId=3&contentId=526&marketId=13&menuId=1

So, you can see some pretty big players in the marine industry use the term as well.

Thanks for your replys!

Cya,

jr

[Capt Sport]

I know the term "jackshaft" and I thought it already had a home. If that's a jack shaft then what's a drive shaft? I think the terminology is confusing at best. regards rusty

Rusty,

Driveshafts are what are in your truck, 4x4's have 2. Jackshafts are what there called when in a boat. Essentially they do the same thing in different platforms.

Cya,

jr

[alan white]

I'd like to see that. My current boat (in USA) has a Casale V Drive with a (Shaft I always called "The Drive Shaft") made from a Chevy drive shaft, with universal joints at each end.. It's about 40 inches long, I think. But how did you "change direction"?? No gears.. Hmmm. Chain/Belt??

It's based on a link at the juncture that has four bearings at ninety degrees to each other, like a u-joint. The inspiration came from a very old patent for an L-shaped link to turn a shaft around a corner without gears. I've got the drawings for the V-drive somewhere. I'll upload them when I learn how to use my new camera.
The concept of using bearings for gear reduction has always fascinated me. Most are called trochoidal drives. I designed a 5 speed sailboat winch a few years ago, got Harken interested enough to consider it, but no cigar.
That had a bottom (reciprocating) handle for four ratios and a top crank for fast 1:1.
It incorporated a rotating cam that shifted by twisting the handle. It had three moving parts. The efficiency I figured would be about 98-99%, contrast to regular winches at 85-90%. I've got hundreds of drawings of that one.
Trochoidal drives are probably used on submarines to reduce the turbines speed. They have zero pitchline velocity error, something that causes cut gear teeth to make noise (a micro-chatter that comes from an ever so slight speeding up and slowing down of the driven element due to imperfect polishing or wear. True of all gear drives, but averaged in helical cut gears, trading smoothness for frictional loss).
Subs gotta be real quiet. One drive I came up with showed up already patented in a search. In 1985 someone had sold it to the US Navy. It was identical to mine.
I do it for fun now. Too much bother trying to patent something people expect to come from an engineer. Very hard to get an audience as a non-professional.

Alan

[Frosty]

I always refer to it as a drive shaft too.( A shaft that drives)

A jack shaft is probably some American terminology that we have now and its just another word in the English language we just have to go along with.

Same --wrist pin --gudgeon pin
lifter --cam follower
Transmission ---tranny
gear shift----gear lever
Bonnet ---hood
boot ---trunk -----and it goes on

[rayk]

I think you are right jack frost.

Jack shafts normally have cogs/gears/pulleys on them, except on American boats.
http://www.jawa-oldtimer-clemens.de/images/artikel1/mm125ber4.jpg
http://www.claycritters.com/lathe/Bollinger_Elliptical_Lathe19.jpg
Snow mobiles, karts, diesel locomotives, motor bikes and mechanical engineers all illustrate a jack shaft as being geared and in parallel to its input and output.

Below, the jack shaft is part of the reduction gear, not a flange bolted shaft.
The illustration below is from NASA, so being wrong aint bad company.
http://www.nasatech.com/Briefs/June03/images/ABB-fig1.gif

[Frosty]

Input shaft -output shaft -1st motion shaft, layshaft , centre shaft, gear cluster shaft, transfer shaft, PTO shaft, propeller shaft

Normaly a shaft is described in the word preceding it--ie reverse gear idler shaft,---pretty descrptive? jack shaft? --not very clear.

Shaft fitted by Jack??? jack **** shaft-- does nothing?

[Capt Sport]

Wow, who’d of thought a simple question would cause so much controversy. What’s funny is that “jack shaft” is an accepted term in use by Cummins, Volvo and Mercury marine just to name a few. Which are undoubtedly major players in the marine industry worldwide. Yet so many people here on the boat design board seem to have never heard it.

Oh, since you seem so adamant about the fact that you’ve never heard the term, so it must be more made up American B.S. Just maybe you Mr. Frost, define the term “jack ****” as in your knowledge or lack there of. As apposed to being open to learning something one doesn’t know.

Cya,

jr

[Willallison]

now now gents, lets not let this get personal;)

It's not a case of being a US term - it's used throughout the marine industry as a description of the set-up as shown earlier by Bob S. It's a perfectly straight forward setup and is very common.

[alan white]

It's a troublesome term.

A.

[alan white]

I always refer to it as a drive shaft too.( A shaft that drives)

A jack shaft is probably some American terminology that we have now and its just another word in the English language we just have to go along with.

Same --wrist pin --gudgeon pin
lifter --cam follower
Transmission ---tranny
gear shift----gear lever
Bonnet ---hood
boot ---trunk -----and it goes on

And that British term for the thing that spins between the tranny and the differential on rear wheel drive cars...?

[Frosty]

Wow, who’d of thought a simple question would cause so much controversy. What’s funny is that “jack shaft” is an accepted term in use by Cummins, Volvo and Mercury marine just to name a few. Which are undoubtedly major players in the marine industry worldwide. Yet so many people here on the boat design board seem to have never heard it.

Oh, since you seem so adamant about the fact that you’ve never heard the term, so it must be more made up American B.S. Just maybe you Mr. Frost, define the term “jack shit” as in your knowledge or lack there of. As apposed to being open to learning something one doesn’t know.

Cya,

jr

Dear oh dear,- only 7 posts and into insulting outbursts. Im sorry that you dont like my interpretation of a jack shaft---you asked the question.


You may remember your first attempt at posting a thread met with similar confusion.

I was suggesting that shafts generally have a name preceding---Oh well you can read.

Myself and other members were now discusing why perhaps a jack shaft is so called. Not that it did not exist. This has obviously angered you because you are not getting what you expect from members who try to diplomatically help you,-- and I hasten to add for free.

As this is not enough ,--part B of you question is equally as confusing how does this affect manouvarability???????????????

The same way as moving the engine would!!!

You seem to have poor understanding of engineering terminology. Your question are confusing. If you dont know what it is, just say the thing that drives the!!! we will understand,-- rather than googling it and asking incorrectly.

Trying to talk engineer to an engineer will aways catch you out.

[Capt Sport]

Thanks to all that replyed, I sincerely appreciate the information.

Cya,

jr

[dsharp]

I knew exactly what you were talking about. I have a 23' Seacraft that was originally set up with a volvo i/o and a 4 cyl diesel mounted midship. I took it out and converted to straight inboard. I never liked working on i/o's after they have been in saltwater. On boats the size that you are talking about I don't know that the handling would be much different because fuel tank placement usually is going to be aft or mid depending on engine placement and the weights are similar.

[BillyDoc]

It's based on a link at the juncture that has four bearings at ninety degrees to each other, like a u-joint. The inspiration came from a very old patent for an L-shaped link to turn a shaft around a corner without gears. I've got the drawings for the V-drive somewhere. I'll upload them when I learn how to use my new camera.
The concept of using bearings for gear reduction has always fascinated me. Most are called trochoidal drives. I designed a 5 speed sailboat winch a few years ago, got Harken interested enough to consider it, but no cigar.
That had a bottom (reciprocating) handle for four ratios and a top crank for fast 1:1.
It incorporated a rotating cam that shifted by twisting the handle. It had three moving parts. The efficiency I figured would be about 98-99%, contrast to regular winches at 85-90%. I've got hundreds of drawings of that one.
Trochoidal drives are probably used on submarines to reduce the turbines speed. They have zero pitchline velocity error, something that causes cut gear teeth to make noise (a micro-chatter that comes from an ever so slight speeding up and slowing down of the driven element due to imperfect polishing or wear. True of all gear drives, but averaged in helical cut gears, trading smoothness for frictional loss).
Subs gotta be real quiet. One drive I came up with showed up already patented in a search. In 1985 someone had sold it to the US Navy. It was identical to mine.

Alan

Alan, you really have me curious about this, especially the "L" drive and your "V" drive . . . did you get your camera working? I would love it if you posted some details on these various concepts.

Thanks!

BillyDoc

[lazeyjack]

well down here we call a shaft driven off qnd running parellel to the main shaft, a layshaft, we call a jackshaft a filler shaft between inboard and outdrive
i guess we all call a prop shaft, just that. allthough some use it for cars, God knows why
I do know that on newbuilds, layshafts belted off the front end of the crankSHAFT, are seriously considered my the Engine makes, because of the torsional stress, , if you do this, then you must try have an equal and opposite force on the other side Cummin Cat give a CLOCK diagram that assists in setting up auxillary loads around the front of the crank

[alan white]

Okay, Billy, I've got the V drive scanned, but I don't know how to put it up here. Never did it before. any suggestions? I got lost real quick. Web ain't my thing...

Thanks, Alan

[alan white]

V-drive

[rayk]

Very clever alan white,

sincerely rayk.

[TerryKing]

VERY interesting.

Slightly like a mechanism I once saw with a horizontally-sliding plate with two vertical slots in it. There were two shafts with offset cranks that fit the slots. Kind of like a locomotive with side-rods.

A question: There is quite a bit of reciprocating mass, right? It would have some vibrational force, I think. Of course, the oscillating section could continue past the pivot point and have a counterweight balance, right?

This maybe brings up another possible configuration (I'm always looking for ways to re-use existing cheap junkyard parts that are hard to make yourself). OK, What If:

- We took a standard automotive/truck "rear end" with it's typical ring gear and pinion gear.
- Built a new housing with just the ring gear and it's bearing points, and
- TWO pinion gears together in the same housing, angled as closely as possible together.

So, there is this gearbox with two automotive type 'driveshafts' in a Vee.
All the expensive parts like bearings, gears, splines, universal joint adapters etc. are junkyard parts and easily available. Only the housing is new.

Truck rearends can handle large amounts of horsepower continuously. In a boat you'd want to build a water jacket into the gear housing if you were running 200 HP or so..

Anyone seen such an approach??

I'll have to look at a few existing rearends to see what the minimum angle could be....

I'm determined to come up with a Marine drive system that is mostly standard automotive parts...

[alan white]

A question: There is quite a bit of reciprocating mass, right? It would have some vibrational force, I think. Of course, the oscillating section could continue past the pivot point and have a counterweight balance, right?

Note the offset counterweight on one of the shafts---um---the left one, cause it was just a sketch and I drew more detail on one side.

a.

[Frosty]

what the hell is that? ---Thats not a v drive

This is a V drive, and the bit in the middle is a " jack shaft"

[alan white]

You mentioned the need to cool a gearbox, Terry. That is horsepower going down the drain, of course. That was why I worked out the V drive with dual cranks and needle bearings.
I don't know, but I'd guess V drive manufacturers recommend a 10% or so increase in engine horsepower unless the V drive is supplied at engine RPM (meaning the drive provides the speed reduction instead of a gearbox mounted on the engine).
I've worked with reduction drives too. My own approach used a trochoidal race, but unlike the ones out there already, which use ball bearings or parallel roller bearings, mine used tapered rollers and a wobbling stator. Picture 10 radially oriented tapered rollers in a cage. Now picture them lying on a round plate with a ring under the rollers. Then imagine the ring is shaped like the top surface of a pie-edge like mom used to make with her fingers--- a serpentine surface on the topface of the ring.
Now see the serpentine surface as a sine wave. Further, give it 9 or 11 humps to the roller cage's 10.
The roller cage now falls into 100% contact with the wobble plate, each roller in a slightly (1/10) different position relative to the humps and valleys of the wobble plate.
Take your imaginary hand and wobble the roller plate without rotating it. seen edge-on, any point on the roller cage is seen to revolve in a perfect circle, but the circles do not progress left or right. Many small cranks limit the movement.
Instead, the wobble plate rotates one revolution for every 10 revolutions of the cranks.
All of this contact (50% of the rollers push, 50% "ride the backside") is rolling and not sliding contact. The 10:1 reduction is achieved at perhaps 99% efficiency. Compare this to a worm drive at 60% efficiency, or a spur gear drive at 88% efficiency.
The drive also does not depend on two or three driving teeth that, in order to all settle into contact, require a certain backlash to develop. The power is transmitted instead at many points at once. The power driven through a common U-joint is tremedous relative to its size. Imagine a transmission that size putting out almost no heat!
These kinds of transmission devices become more viable where power is limited and silence and lack of vibration (related problems) are required, like on a nuclear sub or a space station. Even in a steam turbine at a power plant (although heat can be recycled somewhat there), a ten to fifteen percent savings in energy is achieved in switching to a trochoidal-race drive.
Another advantage of the wobble plate type is that it can be adjusted for wear if ever need be by moving the rollers inwardly. The other type (which I think is used (secretly?) on nuke subs for quiet operation) is not adjustable. Its rollers are parallel on the outside of a plate with a sinoid rim surface. As soon as I'd progressed to that design, I checked the existing patents, and saw that the US Navy had bought the identical patent in the early eighties. I saved the patent page, which I'll post (along with my identical design) when I figure out how (I emailed the last drawing to a friend in Holland, and she, god bless her, posted it for me).

a.
Alan

[alan white]

One note. The drawing shown actually requires an additional bearing between U joint and cranks which allows the crank socket (pie shape) to twist, something I noticed this early drawing doesn't show. Also can be done by allowing the fixed bearings of the U joint to revolve about an offset (as if the bearings were also cranking in addition to spinning).

[alan white]

what the hell is that? ---Thats not a v drive

This is a V drive, and the bit in the middle is a " jack shaft"

Ohhh. But wouldn't the boat go backwards? Does the whole boat have to be reversed in its position on the floor during installation? Isn't that somewhat cumbersome? And even then, the drive would stick out of the bow, which would be a lot of weight up there, not to mention dangerous when anchoring?

Alan

[BillyDoc]

One note. The drawing shown actually requires an additional bearing between U joint and cranks which allows the crank socket (pie shape) to twist, something I noticed this early drawing doesn't show. Also can be done by allowing the fixed bearings of the U joint to revolve about an offset (as if the bearings were also cranking in addition to spinning).


VERY interesting Alan! But, if I am understanding the drawing isn't that a "U" joint on the bottom with bearings oriented horizontally and parallel to the page as well as perpendicular to the page? If so, and the input shaft, the output shaft, and both of the "crank" shafts are all axial with the point where the two axis of the "U" joint bearings cross (which looks like how you have drawn it), then I would think no further equipment is required except the missing counterweight! I love it!

BillyDoc

[alan white]

Imagining this mechanism is a mind-f%&k, and I'm glad you see what is there so far and appreciate it.
The best way to see why another element of movement is required is to imagine the cranks further apart. What if they were 180 apart? See how at that orientation, the fixed U-joint pivot is axial to the two shafts if centered between them as it is in the drawing.
The vertical movement from BDC to TDC is impossible because now the fixed bearings of the U-joint don't do anything relative to the input and output shafts.
This is a lockup situation. While it is possible to run the shafts inline (at 180), they would also have to be indexed 180 apart. But inline of course needs no more than shafting.
This gets into an area that describes how my trochoidal wobble drive works in a torque multiplier (speed reducer).
You see, a crankpin rotates at a slower speed relative to the other as it gets further away from right angles to either shaft because the fixed U-joint bearings allow the pie-shaped arm to make the greatest arc when the fixed U-joint axis is closest to right angles to a given shaft.
It's counterintuitive, I know, and seems very puzzling. The idea, however, is to get the pie-arm to wobble like a pie-shaped portion of a spun penny would. Then any number of cranks could circle the U-joint, each a bit further around than the last, and the pie piece would become a whole wobbling pie.
Allowing the fixed U-joint bearings to ocillate on their own cranks makes for a control element (this would just be a bearing inside of a round cam shape with another bearing outside of that).

Fun, huh?

Alan

[alan white]

Imagine this: A spherical explosive mine (the kind with spikes sticking out all over) is fitted with pencils facing out instead of spikes. This assembly is fitted into an even larger sphere which just touches the tip of every pencil.
One grasps the outer sphere anywhere and rotates that chosen fixed point in a circle. What have the rest if the pencils drawn inside the outer sphere?
A bunch more circles? How many other circles could be drawn by the "slave" pencils?
Heh heh.

A.

[BillyDoc]

Fun, huh?

Alan

Not sure that "fun" is the right word . . . but certainly intriguing!

I'm still missing something here. If I'm reading your drawing correctly the "U" joint shafts cross at a common point, and the bearings shown near the center-bottom are oriented on a shaft perpendicular to the page and the other bearings on the "U" joint are aligned horizontally. So, the motion of the "pie" is spherical around that crossing common point and a simple ball centered on that point would also work . . . except that it would have another degree of freedom and allow the "pie" to rotate around it's long axis. Not a particularly good thing in this case. Perhaps a CV joint would be better!

I can certainly see where the 180 degree case would not work, but this seems to me to be a special case and not applicable where the angle between input and output shafts plus the additional angle from the offset crank is less than say, 30 degrees (whatever the normal angle a "U" joint can usually accommodate is) and a line bisecting the axes of input and output shafts is perpendicular to both bearing sets on the "U" joint. In this other special case it seems to me that an input shaft with an axis aligned with the crossing point of the two "U" joint bearings, and with a crank pin also so aligned and not so far from the input shaft axis to exceed the normal range of the "U" joint, would rotate very nicely and simply impose a "wobble" on the "pie." The output shaft would be similarly constructed and would follow this "wobble" in the same fashion. (I'm assuming normal bearings on input and output shafts.)

So, what did I get wrong?

BillyDoc

BillyDoc

[alan white]

You got it but for one important detail. The same detail causes two u-joints to be required any time shafts are not exactly inline on a rear wheel drive car. Otherwise, the driven shaft would speed up and slow down relative to the driving shaft.
Remember too that a V drive eats power, so we want a better V drive to offer the oppertunity to downsize the engine with no real power loss at the prop. The smaller engine saves the weight of extra fuel, and its own weight is less, and so even if a 100 hp engine at 88% transfer efficiency were putting out a true 88 hp at the prop, an 88 hp engine at a 98% efficiency is putting out about 86 hp driving a lighter boat, meaning the power to weight ratio is higher and the boat will actually do the same thing with maybe 84 hp!
That amounts to a 16% real difference.

Getting back to the improved V drive, you have noticed that a 180 degree offset wouldn't be parallel any longer. The clue is in the fact that it WILL work at 180 if the arm (now a wobbling plate) is down on one end and up on the other.
This cannot be said, however, for any other positioning without another element of movement and control.
I mentioned the sphere within a sphere because it helps visualizing this. Those pencils could describe two side-by-side circles, but if one of them is a perfect circle, the other will be ever so slightly elliptical. Remember that to make a single circle, it is guaranteed that a spot exactly across the sphere will make a perfect circle too, but starting at the bottom instead of the top.
A second prayed for perfect circle next to it (say 10 degrees away) would make (if it could) an upside down circle opposite its location also. Now you have something interesting. The first (really perfect) circle drawn isn't exactly across from the upside down circle of the (wishfully perfect) circle 10 degrees away. There are four circles now, but two of them aren't perfect circles. In fact, if a ring of (dreamed for) circles were drawn around the whole thing, they would progressively become ellipses, then at 90 degrees straight lines, and then ellipses drawn upside down, and finally, a perfect upside down-drawn circle at 180.
A way to defeat this paradox is to place the only true circle invisibly between the two shafts. Each shaft speeds up on the longer part of the ellipse and slows down on the shorter part.
The eccentric around the fixed bearings does this. You can imagine this with effort. The two cranks both describe slight ellipses simultaneously, neither of them taking the perfect circle position. The ellipse isn't on the drawing, or relative to the gearbox. It is what would happen on a piece of paper if you drew a circle at a constant speed and someone moved the paper up and down under your pencil while you drew twice for each revolution. You would "speed up" across the paper sometimes and "slow down" at other times. So the ellipse lives in an imaginary world where that picture is the being drawn in accelleration and decelleration curves by an index line on a point somewhere on the outer face of a shaft crankpin. It could be shown by a pencil attached to the pie-part facing a wheel on either shaft that had paper on it. Remember, the pie part is tilting, speeding and slowing that pencil even while the shaft spins at a constant rate.



Alan

[alan white]

Hope that last comment was helpful. My mechanical explanations are not very technical, not knowing the engineering terminology I should be using.

A.

[BillyDoc]

Good morning Alan,

Well, you may be right about the "fun" thing, I found myself looking forward to getting to the office to continue this discussion! Weird, I know.

I think I'm beginning to get it here, but I'm not at all sure! I understand about the prop shaft (or jack shaft, or drive shaft) issue with two "U" joints in it. The driving shaft has a constant rotational speed, the shaft between the two "U" joints speeds and slows every revolution if there is a displacement of the input and output axes, and the output shaft is again constant as the final "U" cancels the effect of the first. Your "V" drive mechanism seems to me to be a horse of a different color, though. Namely, because the output of the mechanism does not travel through the "U" joint at all. The "U" joint's only function that I can see is to constrain the "pie" in rotation about it's long axis.

But if I understand you correctly, this long axis constraint is not quite perfect, just like in the prop shaft example above, but instead of a rotational velocity variation like with the prop shaft there is a "path" variation at the second crank, i.e., the path described is not quite circular! Which would lock the whole mechanism up, of course.

Now it seems to me that the problem can be cured by substituting a CV type of joint for the "U" joint you show. Is this correct?

BillyDoc

[alan white]

The funny thing is, I never took a CV joint apart. I could intuit (given some time) how to make one, but the term "constant velocity" means, to me, friction because i am guessing there are sliding surfaces within to accomplish the same pitchline velocity.
It is simple to add the mini-cranks (eccentrics) on the two fixed bearings of the U joint and manitain the original design as shown which has high efficiency compared to other V drives. I haven't contemplated the pie arm being supplied with a bearing allowing the arm to tilt, but that's even simpler.
Here is how I look at drive design: There is no use in simply getting the job done because I can come up with ten ways to replace gears if the ratio is limited to 1:1, but all ten have friction contact, and if one can stay with rolling contact, then it's worth putting an effort into a design.
You should see my wobble plate reduction drive, which works on the same principles. It transfers a lot of power at maybe 98-99% efficiency.
Also, differentials can be built with trochoidal races.
The importance of high efficiency is underrated. A sailboat winch, for example, can waste 15 % of the operator's power, which means the winch handler in a race situation must be 15% stronger to do the same work.
Another example is the shaft-driven Harken pedestal winch crank that two men operate. Three gearboxes are used minimum, meaning a loss of the power of nearly one whole man! I improved that system on paper, using my own right angle bearing drive, calculating about a 4%-6% loss.
I also designed a 5 speed winch with only three moving parts that was at least 98% efficient.
The use of gears is a matter more related to interchangability of jobbers and gear sets, and close ratios like 1.1:1 (11 teeth, and 10 teeth). those ratios are hard to get with roller drives (but not impossible).
I also like roller drives because almost nobody understands them, leaving the door wide open for experimentation. If you played around with them, you'd get hooked, Billy. Even knowing you probably will never do anything with a design, it's cool to know you are actually creating something new in your head. Something that's never existed before that is better.
I gave up on the idea of patenting years ago. I realized that I just love to think like a dancer likes to dance. I can, for instance, spend a long roadtrip alone and arrive hours later with a whole new mechanism done.

Alan

[SamSam]

what the hell is that? ---Thats not a v drive

This is a V drive, and the bit in the middle is a '' jack shaft'';

I got this from Google, apparently there's more than 1 kind...''1. v-drive The V shaped part of a women's body below the waist.At bikini or wet tee shirt contest: Look at that v-drive on contestant seven. I think the number nine has the best v-drive.''

[alan white]

Talk about Jack shafts invariably shifts to V-drives, usually at about age 12.
The V-drive simply offers more positions to run the shaft. It's not as efficient, of course, as using a jack shaft. It costs more to install it, and maintenence is higher.
After it's been installed, the rear end usually is quite a bit heavier. It's unavoidable, and a lot of sailors go back to the simple reliable jack shaft eventually.

A.

[alan white]

This is the L drive.

[alan white]

The L drive would serve as a variable angle drive, so that the angle could be adjusted easily. It's shown with two outputs, but a single output (the top shaft) would link with another L drive next to it which would swing on the (as drawn) vertical axis. Two internal bearings are used. The little picture on the side is a winch crank station showing three of these boxes, the last one under a winch.
Again, cranks are used. The upper shaft is pressed around the lower one and a ring on needle bearings between them has a pin onto which the horizontal shaft is attached via a needle bearing (upper right corner).
This setup has almost no friction, as would a U joint.
It should handle a huge torque load in a very compact case. It is not much more complicated than a universal joint.
I've never seen such a drive anywhere, and I don't know why not. It's simple and reliable, has no backlash, and uses almost no energy. It replaces a set of bevel gears, which make noise and will not last as long, nor run as efficiently.
Many people don't realize that worn gears can set up vibrations that wear bearings (which wear gears more, etc., ad infinitum).

Alan

[BillyDoc]

Alan, you will love the CV joint. Go here to look at a drawing: http://en.wikipedia.org/wiki/Constant-velocity_joint. There are no sliding surfaces, only rolling. In fact, it functionally resembles a bunch of ball-bearing sections with deep grooves to take axial loads. I think using one in your design would make one hell of a good "V" drive!

And I see how the "L" drive inspired you, that is also a damn good idea.

Your comments about driving and designing also touched a chord, I do exactly the same thing. I actually like to take long road trips alone for exactly this reason. Of course, I sometimes arrive somewhere I didn't intend to go . . . but at least (so far) I have arrived intact, albeit in a bit of shock as I realize no one was driving for the last 50 miles or so.

I fear we hijacked this thread, and I did the same thing on the "Pirate" thread not too long ago (mea culpa everyone, sorry!) but on that thread a little piracy is to be expected. I would, however, hate to see your "V" drive concept get lost, so I wonder if there is any way to clip out this part of the discussion and move it over to the "propulsion" thread where it belongs. Does anyone know how to do this?

BillyDoc

[TerryKing]

(snip)...I fear we hijacked this thread, and I did the same thing on the "Pirate" thread not too long ago (mea culpa everyone, sorry!) but on that thread a little piracy is to be expected. I would, however, hate to see your "V" drive concept get lost, so I wonder if there is any way to clip out this part of the discussion and move it over to the "propulsion" thread where it belongs. Does anyone know how to do this? BillyDoc

This is too good a discussion to lose it. Jeff can move a section or a whole thread to another name/forum. If you make a new thread in PROPULSION, um... Hmmm. There are only sub-forums, not a general discussion. INBOARDS (Inboard and Vee-drive hardware) is OK if you think this is primarily propulsion-related. Or ask Jeff to make a new sub-forum on "Mechanisms and Drive Systems" or something like that??

Then this part of the discussion can be moved there...

I want to start a thread on using modern integrated transverse auto/truck engine/drive systems, but that fits pretty well in "DIY Marinising".

Maybe there should be a "General Discussion" section in PROPULSION where tradeoffs and decision-making and stuff like this could go???

What do you guys think??

[alan white]

The discussion began with a drive component. I leave it up to others to decide if the thread should be moved. I vote for a thread entitled "investigating devices and mechanisms".
Thanks for the word on the CV joint. I would have assumed balls in semi-circular curved grooves (I haven't yet gone to that link). The contact is rolling, yes, but not without sliding surfaces. If you don't agree, make a gutter out of sandpaper and roll a billiard ball down it. See how the sides of the ball scuff, but not the middle. They are efficient, but in theory no part of them actually rolls! You could say ONE line on the balls rolls, but it is really a nonexistent line on a perfect sphere. Finding it is like finding the last distance to the wall that can't any longer be divided by two.
I'm glad to have some comrades here who enjoy the challenges of geometric thought. I find it very rewarding. If anyone remembers the German airplane designer from "Flight of the Phoenix", they might guess that character was the one I relaed to.

Alan

[TerryKing]

..(snip)..If anyone remembers the German airplane designer from "Flight of the Phoenix", they might guess that character was the one I related to.Alan

Great Movie!!

Alan, you mean you only make MODEL boats?????? We're depending on you to float US!!

[alan white]

Having gone to the CV link, I see it is as imagined. I invented a similar mechanism when I was nineteen. My next door neighbor had a friend who was a retired GE turbine designer. My neighbor sent him the drawing and wrote back a short note telling me the mechanism would lock up.
I was a bit miffed! I got his number and called him. It took about ten minutes to explain to him why it wouldn't lock up, and he was pretty embarrassed.
So much for engineers with phds.
My device was a 90 degree drive, any ratio. A wheel with ball bearings contacted (dipped into) a wheel (as if one took a cartridge off a turntable tone arm and replaced it with a wheel that rolled. Like a turntable, the ball wheel axis was offset (also like a differential hypoid gearset). The semi-circular grooves on the "platter" wheel were shaped like the letter S, starting towards the center and ending near the rim.
Soon after, I showed the design to a Ratheon engineer (who was also the owner of a 42 ft Alden cutter), an old friend of my fathers with whom I had more in common with than my father ever did).
He was quite astute in mechanical stuff. He was the one who pointed out the scuffing problem with balls in grooves. Aha, I said.

Alan

[alan white]

Great Movie!!

Alan, you mean you only make MODEL boats?????? We're depending on you to float US!!

Es macht nichts. Aber ich brauche doppel freuleinen so mein kopf kann klaar sein. Verstehen?

Alan

[BillyDoc]

Es macht nichts. Aber ich brauche doppel freuleinen so mein kopf kann klaar sein. Verstehen?

Alan

"It does not make anything. But I need double being pleased linen so my head can klaar be. Understand?"

But on a completely different topic, I think the grooves on the (C)V joint can be designed so that there is no more scuffing than in any other ball type mechanism. I agree that needle-type bearings are far better though! And they fit in tighter enclosures as well. I reference your post #50, above.

BillyDoc

[TerryKing]

Es macht nichts. Aber ich brauche doppel freuleinen so mein kopf kann klaar sein. Verstehen?Alan

Nicht nur kenne Ich nicht die antwort, aber verstehe Ich nicht die frage!

(And I thought I forgot all that high school Deutsch)...

It seems your head can see mechanisms very clearly... but I really have trouble visualizing some of your ideas. Maybe you can get to drawing in some CAD or Visio thing.. (I could mail you Visio if you want...)

[alan white]

Better all around, I think!

Thanks for the offer, Terry. Let me first decide if such an offer is going to convince me to finally learn CAD.
Regarding the last drawing... if a common auto crankshaft has its bottom bearing at 45 degrees, and there is a chopped-off connecting rod wrapped around it, you could replace the chopped off part with a pin like the male part of a U joint has (so the pin is on an axis at 45 degrees to the crank axis). If another crank is located with an axis at 90 degrees to the crankshaft (seen in the drawing coming on the right), which has a bearing the pin fits into (upper right corner inside the case), rotary motion can be transmitted from either direction.
The ring that is similar to the bottom end bearing of a con rod is shown trapped between the two pressed-together ends (top and bottom) of the crankshaft. You see it sectionally in the drawing, tilting to the right at the top in the center of the case. The pin inside the bearing of the shaft on the right (the biggest shaft) is a solid part of that ring. Each time the vertical crankshaft makes a revolution, the ring is tilted, so that a half revolution ahead of the drawing would show the ring angled down 45 degrees to the right instead of up 45 degrees.
Every shaft and bearing in the drawing has an axis that passes through the very center. The lines where the two crank halves are joined by a press fit should be disregarded in terms of function. I show them as simple lines only, whereas all actual bearing connections are shown as either needle or tapered roller bearings.

Alan

[BillyDoc]

Alan, please do me a favor and take a look at this old post: http://boatdesign.net/forums/showthread.php?p=137612#post137612 showing a design for a wind-vane self steering device. I am very curious to see if you can improve it and get rid of some of those gears. The friction from some of them doesn't matter as they are just for setting a course, but the friction from the ones in the error signal path matter very much!

I didn't know how to upload images when I made that post so I had links to a web site that had them . . . which no longer exists. So the images got lost and the post is too old to edit. To correct this I just added them again in post #10.

By the way, for your information you can upload images by clicking on the "Manage Attachments" button when you are composing a post, entering the image location (using the Browse button is easiest) and then clicking on the "Upload" button to the right of the "Browse" buttons.

BillyDoc

[alan white]

I read what you wrote back then. I saw the pictures. I haven't used windvanes, but I know what they do. I know that the position of the vane is relative to wind direction, and tab position is relative to the rudder/boat. I know that the degree difference between the two changes depending on point of sail changing, so reindexing is required as the wind shifts and also when on a different point of sail.
Then the tab is mounted on the rudder (usually), and it serves to swing the rudder in the direction opposite the tab is angled, causing the boat to maintain an ongoing relative angle to the wind. The other type is an entirely seperate rudder. Which type are you designing?
I've seen several methods of pivoting a windvane. The one you show appears to be the type that pivots on a horizontal axis. Your coil-spring "shaft" accomplishes the turn to a vertical axis, fine.
I imagine the coil is pretty efficient but weak for its bulk, and is well suited to the task you've asked it to do, since high rpm would eventually fatigue it, but small movements won't for a long time. It has zero backlash and it also absorbs a bit of shock, which so far looks good.
Down to the gears...
Here is where I'm mystified. There appears to be a lot of gearing (each connection between will add to backlash). The effort is to get mechanical advantage and something else I think.
Alan

[alan white]

A sketch of the L drive... still learning about attachments. Disregard the picture on the keft. It's the one to the right I wanted to upload. I think longliner was asking for a more descriptive sketch.

[BillyDoc]

Alan,

I can see that I really screwed up my description of the self-steering gear so I'm going to give it another try, but I don't want to hijack this thread doing it so please meet me over at: http://boatdesign.net/forums/showthread.php?t=9751&highlight=self-steering in an hour or so.

BillyDoc

[alan white]

Alan,

I can see that I really screwed up my description of the self-steering gear so I'm going to give it another try, but I don't want to hijack this thread doing it so please meet me over at: http://boatdesign.net/forums/showthread.php?t=9751&highlight=self-steering in an hour or so.

BillyDoc

Okay.

A.