Side paddlewheel vibration

Nice project you have there.

I'm still pondering your problem, but for now a few suggestions.

It looks like the engine bed is oak which should be alright. Is the 3/4" plywood on which it sits firmly secured and stiffened into the transverse frames and keel of the hull? It should be very stiff to prevent lifting and 'oil-canning' from the hull. As the vessel appears to be fairly light, this will occur just from the inertia of the engine, counter weight or not and may vary significantly in and out of the water.

I would also suggest that you tie the paddle wheel shaft bearing points into the engine bed foundation to prevent movement between the two.

Another suggestion; offset the paddle wheels so they are not in sync., i.e., one side on the 'clock' hour, the other on the half hour. Based on number of paddles and reduction this will make 4.8 impulses per engine revolutions versus 2.4.

One more: Try a double reduction rather than doing it in one 1:5.

'Another suggestion; offset the paddle wheels so they are not in sync'

I'm not sure what you mean here? If they were on a crank I'd understand, but it's a straight shaft..

PlbMak, if you look at the photo on the site, you will see that both paddle wheels have their paddles in the same plane; 12 paddles per side and they all line up from port to starboard, i.e., paddle #12 on one side is at 12 o'clock as is paddle #12 on the other side. My suggestion is to offset one side to the other, i.e., paddle #12 on one side is at 12 o'clock and paddle #12 on the other side is at 12:30 o'clock.

Is this a little clearer?

Ahhhh...I gotcha!

Great boat, better then my Mamod...Make sure the whole system is as solidly mounted as you can, the slightest movement will multiply with those big wheels! Also, is the gearing right? My gut feeling is a bit high for a steam engine? Make sure your gearing is an odd number multiple, although I don't know why I'm telling you that. I'm assuming the axle is solid? I've had experience of harmonics at low revs with fairly long drive shafts. Sort of a low frequency thrumming accompanied by a slight shake.. Good luck! I'd love to see a vid of the beast in action..

Lovely project looks like fun. As an old millwright I would suggest centering the drive, instead of offside as it is. On the side it pulls the one side with more pressure than the other which might contribute to a harmonic imbalance of the shaft that becomes more apparent at speed. The other potential problem is; are the paddles balanced in relation to each other, Much like a tires on a car, that too could cause an imbalance and the problem you describe.

It sounds like the system is out of balance, I know thats obvous, but I may have a solution. I work in the HVAC industry and we have our pumps and fans balanced. You might look for someone that does dynamic balancing in your area, for the HVAC and or industrial market. They can mount sensors on the shaft and you would be amazed at the amount of information they can give you. They can even predict bearing life. I will ask our balancer if he has ever worked on anything like this. I'm sure it would be a project that he would love to tackel but alas we are in Nebraska. We are a long way from Newyork. Your project is amazing and I wish you the very best of luck with it. I will see if there is someone that I can find in your area.

Looking at your pictures I wonder if your steam engine is some how matching the harmonics of the shaft, and throwing the whole thing out of whack. Maybe a harminic balancer would solve the problem.

Look up Harmonic Balancer in Wikipedia.

"Every time the cylinders fire, torque is imparted to the crankshaft. The crankshaft deflects under this torque, which sets up vibrations when the torque is released. At certain engine speeds the torques imparted by the cylinders are in synch with the vibrations in the crankshaft, which results in a phenomenon called resonance. This resonance causes stress beyond what the crankshaft can withstand, resulting in crankshaft failure."

LIke I said good luck.

From what I can see, I think that the load created by the paddle wheels (when in the water only) is making the connecting paddle wheel shaft flex and or wobble, creating a vibration. Also the distance between the pillow block bearings and the paddle wheels is excessive, giving a mechanical advantage to the wheel against the shaft. Try mounting a pair of additional pillow block bearings in the centre or equally spaced, supported by the engine and NOT the boat, then re-mount the driven sprocket(if possible) closer to one of the new bearings

Well I am about as far away from you as anyone, but I gotta say what a beaut project. Well done

I was going to rattle on about alignment of universal joints, until I saw your pics. My comment without sounding too basic, would be that the alignment from engine to the lay shaft would need to be very accurate. I cant see, but I assume the coupling on the output is indeed a flexible coupling. If not that would be the first thing, followed by really accurate shaft alignment. The chain looks a little loose...is it "flapping" about as you bring the revs up. Finally is the long shaft perfectly free and not developing any whipping in the centre. Does the top frame of the hull move thwartships (sideways) at all. A temporary diagonal brace may be worth a try also.

Great to see, and I hope someone will come up with a simple solution. I will be watching with interest.

The chain started out being tight but the vibration caused the engine to move slighty ahead and loosen the chain. I tried it again out of water and could measure about an 1/8" deflection at the center of the main shaft. The end of the jack shaft was also flexing a good 1/16" or more. The coditions weren't the same as in the water and the vibration was less at the same rpm. It looks like a few problems exsit with my method of driving the paddles. Ken

I'd go with the paddle shaft flexure theory first. Seems like there's an awful lot of potential for bending and your observation of worsening vibration with load might bear that out, i.e. it wasn't nearly so bad out of the water. I think engine imbalance is less likely. It would be ideal if you could measure whats's going on somehow. It would certainly be worth trying the paddles in a half-pitch offset position as previously pointed out.

As for measuring, perhaps rigging up a pointer on the hull close to the centre of the paddle shaft? We could also work out a natural frequency of the shaft and paddles on its bearings, calculating the inertias of the paddles. The hull unfortunately may also play quite a part though.

As an aside, I've always wondered why paddles were preferred one side of the Atlantic and screws the other?? I have one or two friends over here with steam launches.

Very nice boat! Dad had an1890 Lake Winnipesaukee Steam Launch he restored and ran for years. Propeller driven. I have designed and built 2 side wheelers, a few "Split" Stern Wheelers and a couple of normal stern wheelers. (All were hydraulic drive though.)

My first thought is to disconnect the engine and see if it is the source of the vibration. (Don't let your ego get in the way, just do it. I do not care how smooth it ran on the bench, a lot can happen between the bench and the boat.)

Secondly: Chain whip. Having restored an old Chain Drive MACK Truck I learned about this quickly.

Third: I really believe the shafts are too small a diameter and have too long of an unsupported length.
They are probably acting like torsion bars, winding up at the moment of maximum torque requirement, (maximum number of paddles in the water,) and then unwinding as a paddle comes out of the water.

This winding and unwinding does not have to be a large amount to cause this vibration.

And finally: Add more paddles! This will probably be the cure to your problem. (The more teeth on a gear set makes for smoother running and paddle wheels are like a gear meshing with the water.)

Balancing the wheels is not critical in a low RPM application.

Seems like the vibration could be caused by the paddles hitting the water. If you re into experimentation you could try spacing the paddles inconsitantly. For example 25 degrees than 35 degrees etc.

Yes, then the vibration would more likely be be load dependent, not speed dependent.

I'm not convinced the paddles striking the water would cause a vibration, the water surface is not that constant, and the strikes, as it were, would not be synchronous enough. Also the vibration appears to be amplified by putting the boat in the water, suggesting that loading is a factor. I like the axle hypothesis more and more.

Nice project, and lots of thoughtful suggestions. I recommend you run the boat and place your hand on the various components to try to determine which of them is responding to the vibrations which are likely resonanant in nature. It could be flexure of the boat itself, flexure or torsion of the main drive shaft, or something else. Using a text book, you might calculate the lowest natural frequency of some of the large components (like the main shaft). If the calculation indicates a mode anywhere near the actual vibration frquency, you will have likely found the source of the problem. If you find (for example) the problem is torsional resonance in the main shaft, you would likely try to raise the frequency by going to a larger diameter shaft, or maybe consider a hollow tube. There are other methods such as mounting sensors on various parts of the machine and hitting the structure with a hammer to determine which components give response in the frquency range of interest.

I agree that something in the drive train that causes varying torque application is a real possibility. I understand that IC and steam engines have power pulses but these are rarely a problem. Possibly because of the flywheel and the fact that the engine is ahead of the gear reduction. Of coarse the steam engine is very low RPM. Anyway, this experience may have some application: I owned a truck crane that the transmission had been swapped. The mechanic had set the U-joints up wrong and the third members tried to accelerate and decelerate with every revolution of the drive shaft. Even when the crane was up on its riggers (tires of the ground) and we ran the drive wheels, it sounded like a jackhammer. The drive-train slack was going from positive to negative multiple times per revolution! After I re-did the mountings so that the U-joint angles were correct (I won't go into that here) the whole problem went away.

I'm going to go do another test today in the water and will try to get some measurements as to whats going on. I'm not an engineer and really thank everyone for thier input. I since talked with a fellow owning the smae boat, but with a different engine. He also had the same problem that I encountered. He's cured most of the problems by putting two more pillow block bearing equal spaced across the shaft for a total of 4. He was also able to drive from both ends of his engine. He also went from chain drive to an adjustable type link belt were the links twist in place to adjust the length of the two belts. He still does have some vibration however. He claimed his was so severe that he thought the original pillow blocks would be ripped from the hull. I never opened the throttle wide but would think mine would also be that bad. I'll be sure to keep everyone informed to the progress. Thanks Ken

Instead of using a chain, why not try a toothed belt, like a cam belt?

My neighbor has a rear mounted paddlewheel with an 8 foot diameter paddle that is about 10 feet wide. The paddles are wood and he needs to rotate them to maintain equal soaking time so they weigh the same.

He is in a Paddlewheel association that has helped with many questions like this.

In his case the drive is powered by an old welding machine motor driving a hydraulic pump. The wheel is only driven on one side with a hydraulic motor. He may have a torque problem and thinks he needs to power both sides of the big wheel.

He had a vibration at a particular frequency also. We did a series of river trials and determined the vibration was the same frequency as the paddles hitting the water. (and leaving the water)

He ended up raising the center of the shaft so less of the wheel was in the water.

The result was that the paddle pushing down on the water at the entry and the paddle pushing up at the recovery was reduced by a lot. The arc of the wheel pushing back apparently was not reduced enough to cause any significant loss of propulsion.

The vibration stopped and boat moved faster with less hydraulic pressure (shaft torque) at a lower RPM. (Both measured with interesting devices)

The only down side was that he had cooling tubing on the back of the boat that used the splashing from the paddlewheel to wash over and cool the motor and hydraulics. He had to rethink this because most of the splashing stopped. He was talking about a "tickler" paddle to splash water on the tubes independent of the paddlewheel. I have to look and see what he did.

Good Luck

Perhaps you are experiencing a tortional instability. 10 RPM may be a critical speed. Does the vibration diminish above 10 rpm? You can move the critical speed by adjusting inertia of the system (flywheel modifications).

Regards,

Ken

It appeared to vibrate more as speed of the paddles increased. What I am doing first is stiffining up the plywood under the drive end of the jack shaft. I will install some braces between the ribs and make sure there is no movement there. I'm going to try and mount a third pillow block just to the other side of the sprocket on the paddle shaft. I will try to tie in into the oak engine/jackshaft mount as been suggested. If that doesn't cure the problem I will then try to put the paddles out of sync. by cutting another keyway in the shaft. I will keep everyone informed to the mods and if they've helped or not made a difference. I'm just glad to be retired and have the time to play with it. Ken

A laudable project indeed. Looks straight out of history and museam quality. Lots of good useful comments too. I'm thinking that the action of the paddles in water is causing the shaft to flex toward the stern, and with the rotation, whip. I also think you need a center pillow block (bearing), and advise suitable mounting/bracing against bow to stern flexure. Wish I could say that in plain english.

Hmm, isn't the captain supposed to be INSIDE the boat?

seriously, the shaft is way too thin for its length. yo will certainly have a harmonic problem and whip with that arrangement. There are also inadequate bearing points. I suggest you use self centreing ball or roller bearings, with one each side of each gunnell giving four shaft berings all up. yo can bolt them through with long SS bolts.

the drive sprocket also needs a bearing on the 'inside' to prevent paddle wheel and engine power vibrations excacerbating the whip. Placing the sprocket in the middle would help, however i think a bearing mounted in an A-frame attached to the hull floor would be best. this would help to remove the side thrust on the shaft caused by the drive chain tension. the best solution to that problem thouigh is to the sprocke on a hollow shaft with the paddle shaft runnnig throught it. double roller or twin bearings supporting the tube shaft to take the side thrust, drive to the paddle shaft by fixed dog clutch. thus their is no side force bending the paddle shaft.

the paddles need stiffening and/or curving. Stiffening is simplist, fix some right angle bar around the edge on the drive side. In addition curving the blades reduces the shock load as they hit the water. Later paddlewheelers sometimes used articulated paddles too, but they are really complicated. the idea is to introduce 'cut' the blade into the water slowly from tip to root rather than wacking a flat plate onto the water surface. Technically only the bottom third of the paddle should be in the water.

Hope this healps. I have some books on the subject if you want to read them.

I gave her a fast run yesterday and did some more examining of the problem. The first run I was so excited to even move under its own power I didn't observe these problems: The plywood floor is flexing under the engine and shaft. I will add bracing between the two frames to make sure it won't flex. It appears that the main shaft sets up a harmonic vibration at about 5 or 6 rpm and gets worst as the rpm is increased. The flex is about 1/2" total. I will install an extra bearing to the other side of the sprocket which will be tied to the oak engine mount at the same angle as the chain. A stifftener will be added down to the plywood as well. I would do an A-frame but have problems with clearances around the boiler. After those modifications I will give it another try. I can add a forth bearing to the other side but will involve moving a hand make-up water pump and a lot of other plumbing. I'll let everyone know how I'm making out. I need at least 3 or 4 days as fixing the plywood needs removmal of boiler, engine, paddle shaft and paddles. See you soon! Ken

Sounds good! Good luck...

I also feel that the shaft thickness you have used needs more bearings to stabilise it.

But have you removed the drive from the motor and turned its by hand in some way? Do you see anything that might leave you to believe that it also vibrates in a similar manner? (all done in air as #I suspect a human is not strong enough to achieve 10 RPM alone.....)

If yes, you will then know that the Steam engine vibration is, or is not the possible cause....

Hi Andy

At the present time I've suported under the engine as I could see movement there as well as adding a third bearing to the other side of the sprocket on the main shaft. I am almost done and will be doing a test this coming wekend. I tried what you sugested but it was out of water and probably need not reach 10 rpm. When out of the water it seems to vibarte at a higher rpm than when in the water, but this is hard to guess as I'm not using any means to check rpm. The 10 could even be 15. After the next test and I don't see much differnce I will try and get measurments of whats going on that could be causing it. Hopeful the two mods will help a lot.

Thanks Ken

Fantastic project, best of luck..