Splined Props... Okay... Splined Couplings?

Discussion in 'Surface Drives' started by fpjeepy05, Jan 11, 2013.

  1. fpjeepy05
    Joined: Jan 2010
    Posts: 194
    Likes: 4, Points: 18, Legacy Rep: 31
    Location: Connecticut

    fpjeepy05 Senior Member

    I'm wondering, everyone runs splined shafts at the prop end, so that there are no stress concentrations. But does everyone still run a keyed shaft coupling at the other end? So do people break shafts at the coupling end? Or is the torsional flexing of the shaft enough to minimize the impact loading. I'm asking because I'm going to have to order some shafts here shortly and I'm not sure what type of coupling to get.
    Also the prop guy recommends against a flex coupling, Anybody got any input on that? Boat is going to be run a lot (600-700 hours a year) and I'd like to protect the tranny if possible.

    Thanks.
     
  2. michael pierzga
    Joined: Dec 2008
    Posts: 4,862
    Likes: 114, Points: 0, Legacy Rep: 1180
    Location: spain

    michael pierzga Senior Member

    The only broken shafts Ive seen fractured at the propeller shaft taper. Possible from over torquing or damaged prop and vibration. Ive never seen a shaft damaged inside the boat, at the coupling.

    Coupling. ?? Every boat Ive ever sailed had one. They compensate for misalignment.

    If its a new build The Aquadrive coupling is worth considering.. Expensive.
     
  3. midnitmike
    Joined: Apr 2012
    Posts: 257
    Likes: 20, Points: 0, Legacy Rep: 167
    Location: Haines and Juneau

    midnitmike Senior Member

    It maybe that I'm so far out in the sticks that I don't see all of the newest innovations...so I'm a little confused by your assertions. You see spline couplings in props for outdrives, but the inner hub shears to protect the powertrain.

    Conventional inboards have keys on both ends of the shaft (coupling and prop) and so far I haven't seen one that uses a spine at either end.

    Almost every failed shaft I've seen or heard of has failed near the prop just forward of the keyway. I'm sure they fail in more places then that it's just the most common one I see.

    Flex couplings do work and can provide a safe, reliable and repairable failure point in a system. To take full advantage of them you should always carry a spare because you're not going to put one back together out of the nuts and bolts in your tool box.

    MM
     
  4. fpjeepy05
    Joined: Jan 2010
    Posts: 194
    Likes: 4, Points: 18, Legacy Rep: 31
    Location: Connecticut

    fpjeepy05 Senior Member

    Surface Piercing

    My apologies. I should have prefaced this by saying that this is specifically a Surface Piercing drive line. Because a surface piercing propeller is half in and half out of the water the it experiences very high impact loading and without a splined shaft at the prop end it will break shafts relatively easily. Most systems are Arneson, and I don't know if the coupling end on those is splined.
     
  5. michael pierzga
    Joined: Dec 2008
    Posts: 4,862
    Likes: 114, Points: 0, Legacy Rep: 1180
    Location: spain

    michael pierzga Senior Member

    Ive never seen any shaft failures on Arneson drives...plenty of hydrualic and seal problems.

    What kind of boat ? 600 or 700 hours is mega mileage on a fast boat
     
  6. midnitmike
    Joined: Apr 2012
    Posts: 257
    Likes: 20, Points: 0, Legacy Rep: 167
    Location: Haines and Juneau

    midnitmike Senior Member

    To be honest I have no experience with surface piercing drive systems, so I'll let someone else answer your question.

    MM

    Your turn Mike
     
  7. fpjeepy05
    Joined: Jan 2010
    Posts: 194
    Likes: 4, Points: 18, Legacy Rep: 31
    Location: Connecticut

    fpjeepy05 Senior Member

    The reason they don't fail is because they are splined at the prop end. If I had to guess I would say they might be splined at the coupling end as well.
     
  8. midnitmike
    Joined: Apr 2012
    Posts: 257
    Likes: 20, Points: 0, Legacy Rep: 167
    Location: Haines and Juneau

    midnitmike Senior Member

    I'm not sure you can equate the two...there may be other factors involved. Do a search on here for "surface drives" and see if the question hasn't already been answered.

    MM
     
  9. fpjeepy05
    Joined: Jan 2010
    Posts: 194
    Likes: 4, Points: 18, Legacy Rep: 31
    Location: Connecticut

    fpjeepy05 Senior Member

    Frosty, any thoughts?
     
  10. CDK
    Joined: Aug 2007
    Posts: 3,324
    Likes: 145, Points: 63, Legacy Rep: 1819
    Location: Adriatic sea

    CDK retired engineer

    You could use Spicer universal joints with splined input and flanged output. They cost approx. $ 200, can easily be replaced and also avoid alignment difficulties.
     
  11. powerabout
    Joined: Nov 2007
    Posts: 2,901
    Likes: 61, Points: 48, Legacy Rep: 719
    Location: Melbourne/Singapore/Italy

    powerabout Senior Member

    most large ones I have seen are just on a plain taper with no key
    usually need a hydraulic nut to get them on and a a serious amount of hydraulic pressure to get them apart

    ( BMW sterndrives are all driven by tapers and designed to never come apart)
     
  12. powerabout
    Joined: Nov 2007
    Posts: 2,901
    Likes: 61, Points: 48, Legacy Rep: 719
    Location: Melbourne/Singapore/Italy

    powerabout Senior Member

    If you want a custom drive train to last you need to have someone do a torsional vibration analysis before you build it
    what rpm and torque are we talking?
     
  13. baeckmo
    Joined: Jun 2009
    Posts: 1,108
    Likes: 114, Points: 63, Legacy Rep: 1165
    Location: Sweden

    baeckmo Hydrodynamics

    I take it that your question is about the preferred attachment of the inner drive flange to the shaft??

    Industry standard nowadays is using a "clamp" fitting, preferably without a shaft key (since it produces stress concentrations in the shaft). With a well designed stress relief profile in the coupling hub, you have a very reliable coupling-hub-to-shaft-connection.
     
  14. Frosty

    Frosty Previous Member

    Surface props have a larger dia hub to take the larger blade root requir ed for surface drives.

    I know that Areneson offer both spline and taper.

    I use taper, I can remove and replace underwater (3 inches under) I have a puller.

    My shaft is 4 feet and is designed reversable. The hub coupling is identical to the prop.
     

  15. powerabout
    Joined: Nov 2007
    Posts: 2,901
    Likes: 61, Points: 48, Legacy Rep: 719
    Location: Melbourne/Singapore/Italy

    powerabout Senior Member

    ask a class suryeyor on the specs on how a prop/key and keyway should be machined
    Get it right and you never have a problem, wrong and you see shafts snapped off
    If its small enough it wont matter, the bigger it gets the more important to get it right
    Frosty is right, having a shaft same at both ends is a good idea
    There are 3 1200m bronze props sitting with small piece of shaft in them just off singapore till someone decided there was a machining problem
     
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.