Does a stream lined prop dog work

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  • martin
    Fast Electric Addict!
    • Aug 2010
    • 2887

    #1

    Does a stream lined prop dog work

    Any one know if this makes any difference to speeds as ive seen it mentioned a few times. Where the front face of the dog has a taper so you dont have the square shoulders of the strut & dog together with the gap between them causing drag. Thanks Martin.
  • m4a1usr
    Fast Electric Addict
    • Nov 2009
    • 2038

    #2
    I dont think it would make any difference if the drive dog is smaller then your strut/ stinger diameter and the same diameter as the hub on your prop. When I size a drive system I go out of my way to ensure that the drive dog is approximate in diameter to the strut. Its sort of a tough job on small and mid size hulls. Thats why I no longer buy any flex shaft assy with the dog pinned or welded to the stubb shaft. I want to make the diameter choice based on my prop choice and what strut/stinger I plan on installing. Just my opinion.

    John
    Change is the one Constant

    Comment

    • detox
      Fast Electric Addict!
      • Jun 2008
      • 2318

      #3
      Grimracer once stated taper is needed on larger drive dogs to prevent lift.

      Comment

      • egneg
        Fast Electric Addict!
        • Feb 2008
        • 4670

        #4
        Originally posted by detox
        Grimracer once stated taper is needed on larger drive dogs to prevent lift.
        What is considered a large drive dog?
        IMPBA 20481S D-12

        Comment

        • detox
          Fast Electric Addict!
          • Jun 2008
          • 2318

          #5
          Originally posted by egneg
          What is considered a large drive dog?
          Larger than strut diameter...or same size I guess.

          Comment

          • 785boats
            Wet Track Racing
            • Nov 2008
            • 3169

            #6
            Martin.
            I think the idea of the angled front face of the dog was to reduce the shockwave of water from a vertical face that forces it's way past the strut bearings & up the shaft.

            Cheers.
            Paul.
            See the danger. THEN DO IT ANYWAY!!!
            http://forums.offshoreelectrics.com/...hp?albumid=319
            http://forums.offshoreelectrics.com/...hp?albumid=320

            Comment

            • egneg
              Fast Electric Addict!
              • Feb 2008
              • 4670

              #7
              Ok that makes sense but then what do you do when the prop hub is larger than the drive dog?
              IMPBA 20481S D-12

              Comment

              • 785boats
                Wet Track Racing
                • Nov 2008
                • 3169

                #8
                The outside diameter of the dog is not changed. Just the front face of the dog angled back say, 15 degrees or so. This leaves the rear half of the dog at the original diameter.
                If the dog is a smaller diameter than the hub of the prop to start with, then I'd be getting a bigger dog to match the prop.
                Cheers.
                Paul.
                See the danger. THEN DO IT ANYWAY!!!
                http://forums.offshoreelectrics.com/...hp?albumid=319
                http://forums.offshoreelectrics.com/...hp?albumid=320

                Comment

                • lomdel
                  Senior Member
                  • Nov 2008
                  • 708

                  #9
                  That refers to the dog, what about a streamlined prop nut? The one with the sharp pointy end at the back. Does that make a difference in the flow of water around the shaft/prop at speed?

                  Comment

                  • martin
                    Fast Electric Addict!
                    • Aug 2010
                    • 2887

                    #10
                    [QUOTE=785boats;321498]Martin.
                    I think the idea of the angled front face of the dog was to reduce the shockwave of water from a vertical face that forces it's way past the strut bearings & up the shaft.

                    Cheers.
                    Paul.
                    Thanks Paul, Yes i seem to remember hearing that as well.

                    Re pointed prop nuts i dont know whether it makes a difference but i do use them. Thanks Martin.

                    Comment

                    • tharmer
                      Senior Member
                      • Mar 2009
                      • 342

                      #11
                      I think a squared end is better. If it's goo for the sponson transoms, it's goo for the prop nut.

                      Comment

                      • Chris Harris
                        Senior Member
                        • Oct 2007
                        • 182

                        #12
                        Tapering the front of the drive dog even if it is the same diameter as the strut can make a difference. Because of the gap between the strut and the dog to allow for shaft wind up the water can not completely jump that gap and will reach the flat face of the dog. Any water hitting a blunt surface is going to cause drag.

                        I have seen tapering the the front of the dog make a 2mph difference in SAW boats.

                        As for coned prop nuts the only real benefit in my opinon would be on a subsurface drive. On a surface drive most of it is out of the water when the boat is at speed.

                        Chris
                        I.M.P.B.A. Record Holder P-Hydro 111.001mph Q-Hydro 120.192mph S-Hydro 139.233mph

                        Comment

                        • Boaterguy
                          Fast Electric Addict!
                          • Apr 2011
                          • 1760

                          #13
                          Even with subsurface drives, there is so much turbulence behind the prop, a bullet nut is not required (thats the pointed one). Plus they come off so easily (Already lost some props that way) and the difference is so minimal (i haven't noticed a change) that it's not worth it. I don't know about the tapered drive dogs though.

                          Comment

                          • egneg
                            Fast Electric Addict!
                            • Feb 2008
                            • 4670

                            #14
                            The whole point I am trying to make is that there is quite a bit more turbulence from other areas. Unless you have access somewhere to test for turbulence caused by prop dog/shaft/prop interaction it's all speculation without the data.
                            IMPBA 20481S D-12

                            Comment

                            • fatboyelectric
                              Member
                              • Feb 2011
                              • 84

                              #15
                              Originally posted by Chris Harris
                              Tapering the front of the drive dog even if it is the same diameter as the strut can make a difference. Because of the gap between the strut and the dog to allow for shaft wind up the water can not completely jump that gap and will reach the flat face of the dog. Any water hitting a blunt surface is going to cause drag.

                              I have seen tapering the the front of the dog make a 2mph difference in SAW boats.

                              As for coned prop nuts the only real benefit in my opinon would be on a subsurface drive. On a surface drive most of it is out of the water when the boat is at speed.

                              Chris

                              ........but a conical prop nut does help me sleep at night...LOL

                              Comment

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