Bulkhead / U-joint Placement?

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  • Rhino
    Lieutenant, Junior Grade
    • Aug 2022
    • 21

    Bulkhead / U-joint Placement?

    Hi there,

    Im adding a bulk head, not sure on ideal placement. My WTC drive shaft is below the prop so I will be using a U-joint. Should the u-joint go between the WTC and bulkhead or between the bulkhead and prop?

    thanks for any advice

    Ryan
  • trout
    Admiral
    • Jul 2011
    • 3545

    #2
    If I understand you correctly, it would go between wtc and bulkhead, I am assuming bulkhead like what I have attached.
    If you can cut, drill, saw, hit things and swear a lot, you're well on the way to building a working model sub.

    Comment

    • Rhino
      Lieutenant, Junior Grade
      • Aug 2022
      • 21

      #3
      Thank you. Yes, similar to what you attached. I’m adding a bulkhead to support the drive shaft better and Wasn’t sure where the u joint should go, before the bulkhead or after it.

      Comment

      • He Who Shall Not Be Named
        Moderator
        • Aug 2008
        • 12253

        #4
        Originally posted by Rhino
        Hi there,

        Im adding a bulk head, not sure on ideal placement. My WTC drive shaft is below the prop so I will be using a U-joint. Should the u-joint go between the WTC and bulkhead or between the bulkhead and prop?

        thanks for any advice

        Ryan
        Ideally the propeller shaft -- if it has to extend any significant length into the boat -- should, at its after end, terminate just aft of a bulkhead mounted Oilite bearing that will damp out lateral motion of the shaft and in some situations take thrust loads as well. The projecting after end of the propeller shaft secures to a universal coupler/Dumas coupler. This after bearing centered to the shafts longitudinal axis.

        The ahead propeller shaft load should, ideally, be presented to the after bearing upon which the base of the propeller hub pushes; the astern load absorbed by the forward bearing -- which can double as a thrust bearing if it is impractical to take the load directly from the hub of the propeller -- at the forward face of the universal coupler/Dumas coupler.









        If there is enough 'meat' of structure aft to house a long enough propeller shaft with forward and after bearings, then there is no need for a discrete bulkhead mounted after bearing. An example is the Hogner-stem of this ALFA model:



        Note that the pump-jet of this SEAVIEW running gear absorbs both ahead and astern thrust loads, which simplifies the structure of the intermediate drive-shaft situated between WTC and pump-jet rotor.



        David

        Who is John Galt?

        Comment

        • Rhino
          Lieutenant, Junior Grade
          • Aug 2022
          • 21

          #5
          Thank you David. I have lots of room between the WTC and the end of the stern. What I’m ultimately not sure about is my drive shaft isn’t perfect level, has a very slight angle. Is that ok? I had thought no so was planning to add a dog bone dumas coupler. And while I was at it, add a bulk head with another olite bearing for better support. So my question is do I need the dog bone or can I just go with what I mocked up in the pic above?

          Comment

          • He Who Shall Not Be Named
            Moderator
            • Aug 2008
            • 12253

            #6
            The propeller drive shaft proper (the length of shaft that is attached to the propeller) on this boat has to have its axis of rotation in the same plane as the boats longitudinal axis. Imparting that 'slight' angle to the thrust line -- the arrangement you want me to sign off on -- is wrong! Doing so will result in a constant pitch-up force each time you propel forward. Absolutely wrong!

            You'll need a propeller shaft AND an intermediate driveshaft.

            Your propeller shaft should be captured between a forward and after Oilite bearing, like this:







            Who is John Galt?

            Comment

            • Rhino
              Lieutenant, Junior Grade
              • Aug 2022
              • 21

              #7
              Thanks David, that’s what I want to understand. So split the shaft, roger that. Pls excuse my rough diagram, is this setup as I have terribly depicted correct? If I split the drive shaft, I’m not sure where best to put the Dumas coupler.

              Comment

              • He Who Shall Not Be Named
                Moderator
                • Aug 2008
                • 12253

                #8
                Originally posted by Rhino
                Thanks David, that’s what I want to understand. So split the shaft, roger that. Pls excuse my rough diagram, is this setup as I have terribly depicted correct? If I split the drive shaft, I’m not sure where best to put the Dumas coupler.
                Your drawing is perfect. Now you have a handle on things!

                What drives the choice between placing the two bearings on the propeller shaft, without a supporting bulkhead or with a supporting bulkhead, is the amount of solid structure at the aft end of the hull well aft of the yokes. In other words: is there enough solid structure back there to provide for a propeller shaft that will not have its forward coupler interfere with the stern plane and rudder yokes? If the answer is yes, then you don't need the bulkhead.

                But, as in the pictures below, you don't have that kind of room at the extreme stern, you place the propeller shaft forward bearing well forward, within a supporting bulkhead, clear of the stern control surface linkage rats-nest.













                Who is John Galt?

                Comment

                • Rhino
                  Lieutenant, Junior Grade
                  • Aug 2022
                  • 21

                  #9
                  Awesome! Glad to have a handle on this, resuming construction! Thanks again for taking the time and for the detail toward helping me figure this out.

                  Comment

                  • He Who Shall Not Be Named
                    Moderator
                    • Aug 2008
                    • 12253

                    #10
                    Originally posted by Rhino
                    Awesome! Glad to have a handle on this, resuming construction! Thanks again for taking the time and for the detail toward helping me figure this out.
                    Anytime, my friend.

                    David
                    Who is John Galt?

                    Comment

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