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Thread: Prop' shaft flexible drive couplings....

  1. #1
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    Default Prop' shaft flexible drive couplings....

    ..I’m wondering what others are using for drive shaft flexible couplings and what their impressions/reviews might be?
    Larks

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    Default Re: Prop' shaft flexible drive couplings....

    I have both flexible drive and flexible mounts. With wooden sailboats you have things change tack to tack, over a sea, and with time of year. During regular maintenance I true things nigh on perfect with all at rest on a quiet mooring. That way even under stress of heel and the boat working things stay true enough that there's no vibration shaking my fillings out. Or, if there is, it means a barnacle on a prop blade, a warp on the shaft, or worse.

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    Default Re: Prop' shaft flexible drive couplings....

    Larks, flexible is often misleading, they still need to be in alignment.

    Buck Algonquin is just about everywhere.

    PYI is another (also known for the PSS shaft seal and "drive saver" )

    shafting and dissimilar metals is always a concern when time to take things apart comes.
    Last edited by DeniseO30; 01-11-2017 at 08:08 PM.
    Denise, Bristol PA, Oday30, Anchor Yacht Club, On tidal Delaware River. my current project; http://forum.woodenboat.com/showthre...0-Ducker-Resto

  4. #4
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    Default Re: Prop' shaft flexible drive couplings....

    Thanks for the responses guys.

    Ian, what sort of flexible drive coupling do you have fitted?


    My work, for the last so many years, has dealt with the fitment of engines and all of their component parts and options, including flexible couplings, though mostly on somewhat larger commercial and naval vessels.

    I’ll be fitting a new 20hp (ish) diesel to my H28, replacing a Volvo Penta 18 that I ripped out, and of the engines that I’m considering I’m happy with the engine mounts that they are supplied with as standard and, because I’ll be making a new engine bed and fitting the engine myself, I will be able to align everything suitably with or without flexible couplings.

    So at the moment, what I am most interested in is what types of flexible drive shaft couplings members here may be using, how far they’ve gone with them and what they’re experiences have been with various types and options.

    Most common are the simple flexible and sometimes sacrificial type couplings that are fitted to dampen vibration (in partnership with the engine mounts) and thrust shock and, depending on the type, to assist with alignment. I’m thinking at this stage of fitting a Polyflex or Isoflex type coupling:






    But then there are all of the various Hydradrive, Vector drive type couplings which are "supposed" to also support/compensate for misalignments:



    Larks

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  5. #5
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    Default Re: Prop' shaft flexible drive couplings....

    On all my boats - 35' Garden ketch 'Suzanne', 43' Alden Schooner 'Goblin', 55' LFH Marco Polo 'Granuaile', 25' catboat 'Marmalade', and now 'Meg' I've had the basic traditional flex couple, mated discs that can flex a few thousandths between them due to the cushioning material. Not like the lower pix in #4. Pretty much whatever Buck Algonquin specs for the size engine and service.

    And to reiterate - At least once a year we make sure that the alignment's right.

    Marmalade has a Yanmar three banger and those are notorious for jumping about at idle. Compared to boats without flex mounts and couple, we're really calm in idle which makes for very smooth ultra low speed stuff. She'll lay at a dock pushing against a spring line very nicely with no fuss the way a more rigid installation will even when well aligned.

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    Default Re: Prop' shaft flexible drive couplings....

    When i was a poor bloke i used a Hillman Imp driveshaft "rubber doughnut", as i didnt quite fathom why the Volvo unit was around 10 times the price. Have used the flex coupling on several installs. I usually plumb an installation to work out bed heights and shaft angles, so would not have to use something like a hydra-drive, i would be a little uneasy if my own boat needed one due to an tolerance issue. Flex feet can be had in different grades of hardness and flex, i thought the standard mounts with a Yanmar 1gm10 were too soft, made for a tricky alignment. You might need a thrust bearing depending on your gearbox, but i wouldnt look beyond a standard flex coupling unless the boat itself was really prone to movement.

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    Default Re: Prop' shaft flexible drive couplings....

    I've always wondered a bit about the flex couplings which effectively must act as a single pivot point for the engine to move around. Seems to me that to really allow for the full range of vibration you need 2 points of flexibility, as in the lower picture. My point is not about alignment, so much as about freedom for the engine to move on its flex mounts without transmitting vibration to the boat via the shaft.

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    Default Re: Prop' shaft flexible drive couplings....

    Quote Originally Posted by Phil Y View Post
    I've always wondered a bit about the flex couplings which effectively must act as a single pivot point for the engine to move around. Seems to me that to really allow for the full range of vibration you need 2 points of flexibility, as in the lower picture. My point is not about alignment, so much as about freedom for the engine to move on its flex mounts without transmitting vibration to the boat via the shaft.
    That’s pretty much how I see it too Phil and why I intend to fit something this time around. The previous set up had no flexible drive shaft coupling and you could really feel the clunk through the shaft and stern tube as the engine torqued against the resilient mounts, which were quite soft (they actually pretty much fell apart when I removed the engine so there may have only been two or three holding it in place by the end).

    I know the Vetus engine, for example, is supplied with quite soft mounts, but the guys there are pretty good with their advice on what’s available to suit and they don’t seem out to rob you blind in the process, i.e. they suggest a range of coupling options from the cheaper Isoflex coupling - about $230ish, through to one that they seem to have had a lot of call for being a Bullflex coupling, which also helps to align the shaft - not to compensate for misalignment but to make proper alignment easier. However these are up around the $540 mark.

    http://www.vetus.com/stern-gear-systems/flexible-couplings/vetus-flexible-coupling-bullflex-1-shaft-1.html


    I’ve dealt with Isoflex, Polyflex and Vetus through work so I trust them and their advice, but other than Ian’s commitment across each of his boats - and so his obvious satisfaction - I haven’t really heard any reports on long term use of any of these things and whether owners would change from one type to another.
    Last edited by Larks; 01-12-2017 at 03:18 AM.
    Larks

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    Default Re: Prop' shaft flexible drive couplings....

    Quote Originally Posted by Larks View Post
    ..I’m wondering what others are using for drive shaft flexible couplings and what their impressions/reviews might be?
    Funnily enough, just fitted one today. An R & D nylon coupling which seems pretty good so far at about $160 nz to join a Yanmar 16hp to a 13" prop. You do need to align the coupling flanges to within a few thou.
    whatever rocks your boat

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    Default Re: Prop' shaft flexible drive couplings....

    Common practice on wooden launches here is a double universal with thrust bearing. Takes all the alignment issues away but you need about 350mm of space.
    whatever rocks your boat

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    Default Re: Prop' shaft flexible drive couplings....

    Quote Originally Posted by Paul G. View Post
    Common practice on wooden launches here is a double universal with thrust bearing. Takes all the alignment issues away but you need about 350mm of space.
    An interesting input Paul! http://www.naismith.com.au/list_products.php?m=133
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    Default Re: Prop' shaft flexible drive couplings....

    Quote Originally Posted by Paul G. View Post
    Funnily enough, just fitted one today. An R & D nylon coupling which seems pretty good so far at about $160 nz to join a Yanmar 16hp to a 13" prop. You do need to align the coupling flanges to within a few thou.
    Seems a reasonable price by comparison to alternatives Paul. What made you choose the R&D coupling?
    Larks

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    Default Re: Prop' shaft flexible drive couplings....

    The Aquadrive units are fantastic, though expensive, solutions to reducing vibration and noise. Partly because they have a thrust bearing assembly that must be very solidly attached to the hull to take the prop thrust, then the CV joint assembly allows the engine to move about without transmitting vibration and also reducing strain on the transmission output seal. The thrust bearing allows very soft motor mounts since they do not need to take thrust, and this further reduces noise and vibration. The system also allows some flexibility in engine location.
    That all being said, many people have never experienced a truly aligned prop and shaft system, thinking all this vibration is normal. There are a lot of components in a smooth drive train: Prop Balance to Class 4, shaft really straight, cutless bearings aligned perfectly, coupling fit and faced, engine alignment of couplings center to center and face to face to the proper allowable amount, even checking the taper on the prop to shaft fit. Then there is looking at all the many different kinds of prop style, blades, etc, etc.
    Then all the above can be ruined because the boat is blocked improperly during alignment, or has longitudinal strength issues causing all kinds of problems if a little bit of sea is running.

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    Default Re: Prop' shaft flexible drive couplings....

    Quote Originally Posted by Larks View Post
    Seems a reasonable price by comparison to alternatives Paul. What made you choose the R&D coupling?
    The alternatives were OEM or perhaps one of the couplings you mention but for such a low horsepower motor you dont need them. R&D have a good reputation and I have used them before, and it's pretty easy and straightforward to line a motor up.
    whatever rocks your boat

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    Default Re: Prop' shaft flexible drive couplings....

    Quote Originally Posted by Paul Schweiss View Post
    The Aquadrive units are fantastic, though expensive, solutions to reducing vibration and noise. Partly because they have a thrust bearing assembly that must be very solidly attached to the hull to take the prop thrust, then the CV joint assembly allows the engine to move about without transmitting vibration and also reducing strain on the transmission output seal. The thrust bearing allows very soft motor mounts since they do not need to take thrust, and this further reduces noise and vibration. The system also allows some flexibility in engine location.
    That all being said, many people have never experienced a truly aligned prop and shaft system, thinking all this vibration is normal. There are a lot of components in a smooth drive train: Prop Balance to Class 4, shaft really straight, cutless bearings aligned perfectly, coupling fit and faced, engine alignment of couplings center to center and face to face to the proper allowable amount, even checking the taper on the prop to shaft fit. Then there is looking at all the many different kinds of prop style, blades, etc, etc.
    Then all the above can be ruined because the boat is blocked improperly during alignment, or has longitudinal strength issues causing all kinds of problems if a little bit of sea is running.

    Thanks Paul, that’s great info’. Re engine alignment, my practice has been to do final alignment in the water and usually at least a day or two after launch - or even longer if its not an urgent job - allowing the vessel to sit back into its floating shape, rather than the hardstand “blocked" shape.
    Larks

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    Default Re: Prop' shaft flexible drive couplings....

    One way is to fit the engine, gearbox, coupling, shaft, stern tube and strut all in one go, let the epoxy set and you are lined up. If the boat changes shape in the water and I suspect a small solid boat like yours would move minimally if at all in the engine area, then you can twiddle with it later if need be. Aquadrives, double universals and other flexible couplings are all wonderful if you have the space and $$$ but most H-28's don't have them. I am beginning to suspect that perfection might be getting the way of your rebuild!
    whatever rocks your boat

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    Default Re: Prop' shaft flexible drive couplings....

    Quote Originally Posted by Paul G. View Post
    One way is to fit the engine, gearbox, coupling, shaft, stern tube and strut all in one go, let the epoxy set and you are lined up. If the boat changes shape in the water and I suspect a small solid boat like yours would move minimally if at all in the engine area, then you can twiddle with it later if need be. Aquadrives, double universals and other flexible couplings are all wonderful if you have the space and $$$ but most H-28's don't have them. I am beginning to suspect that perfection might be getting the way of your rebuild!

    Not after perfection Paul, just looking at all options to educate myself and interested to know what others have used. As I said, I’d been considering a Polyflex or Isoflex type unit but they seem to be a bit pricier again than your R&D coupling so I’m moving towards one of them.

    Re engine alignment, even with aluminium, steel and fibreglass boats that you’d think would be quite stiff we’d not try and align them until they are in the water. With chock-fast mounts we’d get everything bolted down and lined up but we’d certainly leave it a few days for the boat to settle before realigning and then pouring the chock fast.


    BTW, the only thing getting in the way of my rebuild has been a couple of thousand kilometres..
    Last edited by Larks; 01-13-2017 at 01:14 AM.
    Larks

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  18. #18
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    Default Re: Prop' shaft flexible drive couplings....

    I have a WM 22 ( Aust marinised Kubota). On the prop shaft I used a 1 inch Polyflex steel 434 tapered clamp coupling ( no need for a shaft taper or keyway) , together with a R&D flexible coupling onto the Hurth gearbox output flange. With limited fore and aft space between the gearbox and the stern gland this arrangement took up the least space .

    R&D and Polyflex also do a steel clamp type shaft coupling, but they are slightly longer that the Polyflex 434 .

    I imagine the space between the gearbox and stern gland on the H28 will be limited

  19. #19
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    Default Re: Prop' shaft flexible drive couplings....

    Quote Originally Posted by Neil C View Post
    I have a WM 22 ( Aust marinised Kubota). On the prop shaft I used a 1 inch Polyflex steel 434 tapered clamp coupling ( no need for a shaft taper or keyway) , together with a R&D flexible coupling onto the Hurth gearbox output flange. With limited fore and aft space between the gearbox and the stern gland this arrangement took up the least space .

    R&D and Polyflex also do a steel clamp type shaft coupling, but they are slightly longer that the Polyflex 434 .

    I imagine the space between the gearbox and stern gland on the H28 will be limited
    Thanks Neil, much appreciated mate. What do you think of the WM22? I looked at that and their 18 but they’re physically big engines going by the spec’s they sent me back in 2012. They are both a similar weight but the 18 is roughly 100mm taller and 70 mm longer than the Volvo that I took out and the 22 is the same taller but 120mm longer.

    Having said that though, I’m rebuilding the engine bed and box from scratch so pretty much have a blank page to work with and as I’ve also moved the bridge deck forward about a foot from the original build (to make the cockpit bigger while replacing a bit of rot in the deck framing) I’m not really limited by space in terms of what engine I use or what coupling I fit.
    Larks

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  20. #20
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    Default Re: Prop' shaft flexible drive couplings....

    I completely agree with Paul Schweiss about the Aquadrive.
    But don't use it with a V drive, it comes UNDER the engine...
    I have both of them on Anthéa with no latéral access, and checking the transmission and the bearing is a pain in the ass, since I have each time to take the transmission off...
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    Default Re: Prop' shaft flexible drive couplings....

    Not too proud to admit that I did not align my engine very carefully after replacing the cutlass bearing and drive saver,now , after only a few hours of motoring, some of it into strong wind and banging into roughness,my dripless stuffing box is damaged. My own stinking fault. One assumes the plastic thingy allows for some mis alignment. That is not what it is for. Now I have to go back into the hot dark upside down place and check for broken motor mounts as well .rn

  22. #22
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    Default Re: Prop' shaft flexible drive couplings....

    I bought an Aquadrive in the early 80´s and used it in a wooden swedish snipa, with an Albin AD2 diesel engine. It worked very well. And as Paul Schweiss wrote you can use very flexible engine mounts.

  23. #23
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    Default Re: Prop' shaft flexible drive couplings....

    A bit of a bump on this one to see if there any updates on experiences, or perhaps new options that anyone has come across which might be worth investigating before I commit to a flexible drive coupling .....

    Paul G - are you about? What are your thoughts on the R&D coupling a few years down the track???
    Larks

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  24. #24
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    Default Re: Prop' shaft flexible drive couplings....

    We've installed an aquadrive unit, and while they allow misalignment of the engine they need to be installed without misalignment ! The thrust bearing support structure needs to be positioned correctly to the stern tube.

    Cheers,
    Mark

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    Default Re: Prop' shaft flexible drive couplings....

    Quote Originally Posted by Mark0 View Post
    We've installed an aquadrive unit, and while they allow misalignment of the engine they need to be installed without misalignment ! The thrust bearing support structure needs to be positioned correctly to the stern tube.

    Cheers,
    Mark
    Thanks Mark, I’m not concerned about alignment but I am interested in vibration dampening performance and durability - what do you think of the Aquadrive in that regard?
    Larks

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  26. #26
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    Default Re: Prop' shaft flexible drive couplings....

    In spite of my thorough calculations i got it wrong when i installed my new motor. It sat 15mm higher on the feet than i anticipated, above half way up the flexible mounts. Really good alignment with the shaft, faces met nicely.

    The shipwright told me it'd rattle and vibrate badly, and he was right.
    I made up pads to lift the feet so the motor sat almost at the bottom of the mounts - amazing how much quieter the motor is, and far less vibration.

    I don't think the coupler is the place to look for vibration dampening or noise dampening - thats in the mounts, the coupler is just to deal with it so it doesn't damage the stuffing gland.
    It's all fun and games until Darth Vader comes.

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