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Old 22-02-2015, 20:30   #16
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Re: Too many flexible bits.

Hmmm, rather a lot to digest here. I will read, re-read, and see if I can make sense of it all.

To clarify one point though, I have kept the engine alignment very close to the original hard mount position by the simple expedient of a couple of reference marks at strategic positions, and by replacing the mounts one at a time. My desire for the engineer to have a look at the setup was so that an expert could second guess my assumptions (possibly very relevant in this case) and someone with experience can get the alignment just right. As it is, it SHOULD be very close, and I designed the replacement engine mounting brackets with as much flexibility as possible, so adjustments should be simple to make. There is no evidence of problems, the system is silky smooth (by comparison to the old setup), though I am aware of a small tremor that feels like an out of balance prop to me, originating from the rear of the boat, nowhere near the engine or transmision.

Someone made a remark about the whole thing being a bit of a dark art. Too right I say!

Thank you all for your thoughts so far, I am processing what has been written.

Matt
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Old 22-02-2015, 20:34   #17
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Re: Too many flexible bits.

Quote:
Originally Posted by Oceanride007 View Post
However your first sentence "asked him if he was available to check the alignment on my engine" suggests you have no idea if the shafts are parallel and in line, and if you asked me to do it, (I'm an Engineer also) I'd probably avoid you, as it would be extremely difficult to raise lower, move front of engine left right, and how much do your squat in the engine mounts has occurred, no idea I bet.
Yes, well, thanks for that remark. It kind of assumes a lot really. But thankfully I won't be asking you to do it so neither of us have a problem.

Matt
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Old 22-02-2015, 20:51   #18
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Re: Too many flexible bits.

Quote:
Originally Posted by jimbunyard View Post
Do you have an actual problem, or just the concern of the engineer?

...

Since this is a new installation, if it were me, I'd make sure the alignment is good, run it a little, tie it off at the dock and throttle it up maybe if you're worried about it, just generally keep an eye on it. Meanwhile, find the manual you're seeking (ask the engineer, after all, he brought it up) and verify if there are or are not any restrictions or guidelines on allowed limits of movement and numbers and types of mountings.

You've kinda got my curiosity up now, if I get time I may call'em tomorrow. If I do I'll let you know what I find....
Thanks Jimbunyard,

In answer to your specific questions, no problems are apparent at the moment, this is just the concern of an engineer, but he is an engineer I respect.

Yep, I have tied off at the dock and run to full power for nearly an hour without apparent problems. (Except I had to throttle back a couple of times to let people pass me, my stern points across the main entrance to our club and I risked blowing boats onto the rocks.) Oh yes, then I had to apologise to the boat next to me after realising the poor buggers were enteraining on their afterdeck the whole time. They said there was no problem with the noise, but I think they were being nice. (Not to self: I had better drop a bottle into the cockpit this week just in case.)

I too see the polyflex coupling as a quasi rigid device, hence I am having trouble visualising excessive movement, but I defer to those with long and relevant experience and conceed that the strangest harmonics can occur in moving systems.

Dark art really sums it up, I know enough to know I don't know enough.

Matt
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Old 22-02-2015, 21:21   #19
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Re: Too many flexible bits.

Quote:
Originally Posted by banjoship View Post
1. My PSS manual (circa 2000) has nothing to say on the issue. Online manual is identical to the paper manual, no surprise there.

2. For accurate engine alignement with a flexible coupling, you should replace the coupling with a solid spacer while aligning. There is too much "squish" in the flexible coupling to enable fine measurement. Do you have a solid spacer? If not, you can get one made up at a machine shop, complete with bolt holes, etc.

3. There is a view that flexible mounts + flexible coupling can lead to harmonic vibration at certain revs. Seems to depend on the boat and length of prop shaft. There have been threads on CF. I have never seen anything set down in books or elsewhere. With your solid spacer, you can try both solid and flexible coupling to see if there is any difference.

4. My boat is the same as yours, with identical drive train setup. There is some vibration at high revs, evident with both solid and flexible coupling. Its in a rev range that I never use. I have stuck with the flexible coupling.

5. As a previous poster noted, the PSS is designed so that the faces remain in contact and the bellows takes up any slight movement. If under drive there is visible movement of the PSS and/or leakage, it would suggest there are problems to me.

6. A cutless bearing inside the boat I am not sure of, how would it be lubricated? If you decided to positively locate the shaft I would have thought a proper bearing block as suggested by others would be the way to go. If I was to go to that sort of trouble , I would do a proper job and put in an aquadrive.

Don't know if this helps, Lee
Lee, it helps. Very much, thank you.

In answer to your good points, no detectable movement of the drive shaft between forward and reverse, though a noteable change in drive noise suggests that the thrust bearings on my gearbox are due some attention. But that is no surprise, eliminating the engine vibration noise allows me to hear all sorts of new stuff.

You've got a much more modern engine/gearbox on Banjo than I have, do you know your shaft revs and if so, how do they compare with my maximum 1300 rpm? If I remember correctly you also had a 1.5 inch drive shaft? Curious about this following your remarks about harmonics at some revs.

I love the idea of comparing the solid spacer with the polyflex. I have to get the spacer anyway, as my polyflex proved to be too old and wobbly to make any meaningful analysis of the alignment after changing the engine mounts, another reason to ask the engineer for his professional input.

Lubrication of the upper cutless... well I understood that bit of the shaft log would normally be full of water anyway? Certainly water travels a short distance up the breather hose on the PSS shaft seal. I did wonder if the water in that area might become hot in the presence of a cutless and without the surrounding water at the back of the keel... but I have no sense of the sorts of friction loads generated by such a setup.

Finally, I know you say your setup is identical, but just to be really clear on this, are you saying that you have flexible engine mounts, a polyflex coupling and a PSS shaft seal? If so, and if you are happy with it, then I am greatly reassured.

Matt
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Old 22-02-2015, 21:25   #20
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Re: Too many flexible bits.

Quote:
Originally Posted by SVJennie View Post
... I would consider supporting the forward end of the shaft just to be safe, but then again, I overbuild everything. : o)
Nothing wrong with that logic in my books, I try to be belts and braces when I can.


Sadly, supporting the foward end of the shaft from anywhere but the log or the drive coupling would be very difficult in my setup. Not a lot of space to play with.

Matt
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Old 22-02-2015, 21:50   #21
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Re: Too many flexible bits.

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Originally Posted by Snowpetrel View Post
Ha, I have just gone through all this myself. I was told that it was simplest to use a floating shaft, with only the one bearing near the prop, and let the rest become flexible, but to do this properly a rigid shaft connection was needed to help reduce the chance of the shaft whipping. For this to work the shaft lengths and diameters needed to be within tolerance. Looking at the Nanni N100 guidelines it seems yours looks ok, subject to your exact rpm and reduction ratio.

If you go a solid shaft with two (or more) bearings then the polyflex drive saver coupling is needed/advisable to reduce the loads on the gearbox output bearings.

This all seemed logical to me and so far I have had no issues with my floating shaft and rigid coupling, but then I haven't done much running yet.

Interested to hear how you go with it all, as it seems like a bit of a dark art. for me it was a no brainer to avoid the polyflex drivesaver as they cost money, and in my case the advice was that they wouldn't work well with my floating setup.

At any rate the system should be setup so that it can be direct coupled if the drivesaver does it's job and shatters, so you should be able to easily try it with and without, and for alignment the drivesaver should be out, and the flanges directly coupled and aligned anyway. Just make sure the couplings are both actually true, it's quite common for them to be a couple of thou out, and some orientations of the shaft vs gearbox couplings can make things worse, and others can cancel out or reduce any small misalignments.
Ben, thank you for those notes. The Nanni diagram was very interesting and your point about preventing the shaft whipping seems to be the key point here. This is what I suspect the engineer was concerned about.

Hopefully Banjo's experience is indicative of what to expect, I feel like the drive shaft on the Swanson is relatively short in relation to its diameter, and hence less likely to start whipping, but I have no other boat that I know well to compare it with.

So, to clarify, did you go with a solid coupling between the shaft and the engine?

Matt
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Old 22-02-2015, 22:09   #22
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Re: Too many flexible bits.

I did not read all the elloquete words previously written, sorry if I repeat this advise but after straightening out many driveline problems over the years the most correct (smoothest) drive line arrangement consists of an Aquadrive or similar device ( the heart of a proper driveline), soft engine mounts, water feed PYI-PSS. This system works!
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Old 22-02-2015, 22:22   #23
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Re: Too many flexible bits.

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Originally Posted by Captain Bill 3 View Post
I did not read all the elloquete words previously written, sorry if I repeat this advise but after straightening out many driveline problems over the years the most correct (smoothest) drive line arrangement consists of an Aquadrive or similar device ( the heart of a proper driveline), soft engine mounts, water feed PYI-PSS. This system works!
Those Aquadrive units look nice. I will not depress myself at this stage by enquiring as to their cost.

Matt

Actually, looking at the product description, I suspect the engineer at the club has one of these in his boat. He was very happy with what he described as some kind of CV joint that could handle thrust... seems similar.
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Old 22-02-2015, 23:19   #24
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Re: Too many flexible bits.

Quote:
Originally Posted by GILow View Post
So, to clarify, did you go with a solid coupling between the shaft and the engine?
Yes I solidly connected the shaft coupling to the gearbox output flange. It seems to work even though my prop shaft is a lot more spindly than yours (25mmx1400mm long) I have a volvo seal (actually a radice variant) that does give a small amount of support being slightly firmer than your PSS, with a bearing inside it. I think the key is to get a halfway decent alignment, a straight shaft and true couplings. The floating shaft system certainly is a very simple system.
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Old 22-02-2015, 23:56   #25
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Re: Too many flexible bits.

Matt,

My setup: BW velvetdrive 2.5, 1 1/2" shaft, polyflex engine mounts, polyflex coupling, PSS.

Optimum engine revs are1600 - 1650, maximum 2200 (I think). Doing seatrials after fitting the new engine there was a slight vibration around 1800-1900rpm. Fitting my solid spacer in place of flexible coupling made no change. I put it down to either a harmonic vibration in the drive train, or a problem with the prop, which does have a few nicks in it.

Either way, I left it. The vibration is slight, and I rarely run the engine at those rpm.

Lee

PS A rough and ready way to check your drivetrain is to feel your flexible coupling after extended motoring...if it is warm/hot to touch, its working too hard to cover up misalignement.
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Old 23-02-2015, 00:11   #26
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Re: Too many flexible bits.

Thanks Lee.

That's a MUCH lower reving prop you have there. I got the impression our setup was a bit high reving, and have received various opinions on that, but I'd rather the lower revs of your setup, all else being equal.

On my numbers, our prop will be doing double your prop revs, so vibration could become a problem, though it has not manifested itself yet.

I like your heat test idea, a good one to try before there is a chance of the gearbox heating the connection.

Matt
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Old 23-02-2015, 00:17   #27
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Re: Too many flexible bits.

Quote:
Originally Posted by Rustic Charm View Post
Well, I can't help but I'm interested in the replies you get.

I recently had a new cutlets bearing installed in the end of the tube to support the pss seal too. And I have a solid coupling.
Hey RC, I just realised what you had written here. This is very interesting to me, that makes TWO hard mounting points at least (taking a cutless at the PSS end as a hard mount in this context.) Is your engine hard mounted or soft mounted?

Can you elaborate on your setup? HP, gearbox, shaft diameter etc.

Matt

P.S. If I remember correctly, you have soft mounts on the engine, right? (You were pricing some newies recently?) If so, I wonder how that all works, does the upper cutless allow enough movement to accomodate the movement of the engine?
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Old 23-02-2015, 01:40   #28
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Re: Too many flexible bits.

I have installed PSS shaft seals in various boats. I do not remember the installation manual mentioning this issue. Ever. But it is na old engineering approach, to have 2 out of three flexible points, it is not specific for the PSS. So your engineer was probably referring to it, as general approach, and not the pss installation manual itself.

One of the crucial moments here, though, is how stiff the flexible engine supports are. If they are chosen correct, no problem. They are not meant to allow the engine jump up and down as a wild goat, but just to dampen the vibration. If they are to soft, they will cause a problem, especially on low engine revs and during acceleration / decceleration. For 4 cylinder engine, let say up to 1/3rd of nominal revs. But even if this is the case, the PSS should be able to compensate for it.

With or without the flexible coupling, on an shaft as short as this is, there should really be no difference, as long as the engine is properly aligned to the shaft.

As somebody has already mentioned before, check for leaks. If the pss is leaking extensively, when the shaft is not rotating, something is wrong. if not, few drops are ok.

If there is no room for an external support, there will be no room for aquadrive, (as it needs a support for thrust bearing) too. However, if you really want to make this extra mile, you might have a look at this:

04555 - Powertrain brosjyre A4_trykk

This is similar system, but without thrust bearing support. Have very good experience with them.

As for the vibration from prop, even slight deformations (not visible) in pitch, can be causing a problem. any damage or dent, are not good. If the prop is OK, and you are using a 3 blade prop, 4 blade prop of the same pitch, with 1" smaller diameter will solve the problem.
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Old 23-02-2015, 01:59   #29
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Re: Too many flexible bits.

Thank you Bob, that's putting things in perspective for me, and seems to be consistent with Banjoship's experience.

As a guide to the amount of engine movement, I can place my finger between the underside of the mounting top cap (mount pictured below) and the base plate while the engine is running, in drive or neutral at all revs, and barely feel the relative movement of the two surfaces. I am not sure what is acceptable in these circumstances, but that seemed safe from my layman's perspective.



No leaks from the PSS, which has been wonderfully dry since I installed it last year. What a great device.

The prop is very old, installed in 1986, and has done 2000 hours, so could easily have struck something too. I am not too worried by the slight tremor, at the moment I am trying to decide whether to pull it off and have it checked for balance or to simply put it in the spares box and fit a Kiwiprop in its place. That's a whole other head scratching exercise.

Matt
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Old 23-02-2015, 02:04   #30
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Re: Too many flexible bits.

Matt, i do not see the picture. But as you have described it, it should be ok. I suggest a new prop. It is good idea to check the old one, and have it as a spare onboard. You never know when you can damage the new one.
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