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Thru hull NPS thread vs Ball valve NPT thread-gctid373826

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    Thru hull NPS thread vs Ball valve NPT thread-gctid373826

    I've been doing a lot of reading about thru hulls and their NPS threads. An article authored by Steve D'Antonio in Passagemaker magazine points out the fallacy, namely that the NPT thread does not bottom out on the NPS thru hull resulting in only 2-3 engaging threads. I checked the thru hulls under the galley hatch and the factory head pickups were NPS to NPT. On my 3818 MY this thru hull is a mushroom covered by a strainer screwed into the hull sealed with caulk. Trying to remove the strainer makes me believe that the caulk is 5200. It also has been in place for 23+ years.

    Now my dilemma. Since it has been in place that long and might be very difficult to remove and create other problems trying to make it proper, what would you guys do? There have to be a lot of Bay MYs out there similar. I haven't seen or read of this being a problem to others. West Marine sells an adaptor that engages the NPS threads on the thru hull with NPT for the valve allowing full engagement.

    Am I biting off more than I can chew? What say you?

    Richard

    1988 3818

    #2
    Have you read through this guys info on thru-hulls vs seacocks? I replaced my thru hull this winter with a proper seacock after reading this.

    http://www.pbase.com/mainecruising/seacock_primer

    Comment


      #3
      Richard Tulip wrote:
      I've been doing a lot of reading about thru hulls and their NPS threads. An article authored by Steve D'Antonio in Passagemaker magazine points out the fallacy, namely that the NPT thread does not bottom out on the NPS thru hull resulting in only 2-3 engaging threads. I checked the thru hulls under the galley hatch and the factory head pickups were NPS to NPT. On my 3818 MY this thru hull is a mushroom covered by a strainer screwed into the hull sealed with caulk. Trying to remove the strainer makes me believe that the caulk is 5200. It also has been in place for 23+ years.

      Now my dilemma. Since it has been in place that long and might be very difficult to remove and create other problems trying to make it proper, what would you guys do? There have to be a lot of Bay MYs out there similar. I haven't seen or read of this being a problem to others. West Marine sells an adaptor that engages the NPS threads on the thru hull with NPT for the valve allowing full engagement.

      Am I biting off more than I can chew? What say you?

      Richard

      1988 3818
      You probably need a 1 1/4" or 1 1/2" thru hull, I have a 1" proper thru hull (Apollo) if that is what you need, there is or was a 1" strainer portion on ebay also. If you need it PM me. Pat S.
      Pat says: DO-IT-RIGHT THE FIRST TIME!

      Bayliner 3870 "ALASKA33)
      Twin 350 GM power
      Located in Seward, AK
      Retired marine surveyor

      Comment


        #4
        Richard, the west marine adapter is 1/2 or 3/4 NPT to 3/4 Garden hose.

        There is no such thing as an NPS to NPT adapter.

        Further the West Marine Garden hose adapter is not bronze, it is brass and not galvanically compatible.

        No brass below the waterline.
        "Adios Dinero"
        1997 3988 with new 330 Cummins
        Photo Credit: Whiskywizard

        Comment


          #5
          OK, leave the mushroom in place.

          Unscrew the ball valve, install a seacock.

          You might have to cut down the mushroom, and or clean up the threads a bit, but that isn't a show stopper.

          KEVIN SANDERS
          4788 LISAS WAY - SEWARD ALASKA
          www.transferswitch4less.com

          where are we right now?

          https://maps.findmespot.com/s/36S4

          Comment


            #6
            The Other Gary wrote:


            There is no such thing as an NPS to NPT adapter.

            No brass below the waterline.
            Here is the adapter RICHARD is referring to post #1.

            Groco IBVF Flanged In-Line Valve Adaptors IBVF-1500

            See page 9.

            http://www.groco.net/2011-GROCO/2011...-CAT-CD-V4.pdf

            I too have read about and pondered the need to resolve the thread conflict. Ultimately I will change it but it's not made it to the top of the list.

            The boats Steve D Antonio is dealing with are blue water ocean boats.
            Jim McNeely
            New Hope a 2004 Bayliner 305 Sunbridge Express Cruiser
            Twin 5.7s with Bravo2 drives
            Brighton, Michigan USA
            MMSI # 367393410

            Comment


              #7
              There actually is a NPS to NPT adapter for thru hulls. I have seen them in Fisheries supply in Seattle and J and G marine in Tacoma.

              Happy boating
              Richard
              1988 3870 Bayliner

              Comment


                #8
                An adapter is not a good idea, use a proper flanged seacock.
                Pat says: DO-IT-RIGHT THE FIRST TIME!

                Bayliner 3870 "ALASKA33)
                Twin 350 GM power
                Located in Seward, AK
                Retired marine surveyor

                Comment


                  #9
                  Boatworkfl,

                  The adaptor I was thinking of using is sold by West Marine. Their current catalogue has it on p. 524. The 1" model 8672743 is made by Groco and is bronze with a flange for fastening to the block. The ball valve screws to it. Do you have a reason this would not work?

                  Richard

                  Comment


                    #10
                    boatworkfl wrote:
                    An adapter is not a good idea, use a proper flanged seacock.
                    The Groco IBVF adapter is a viable option. See below. It gives you the proper flanged attachment, the threads are correctly matched between connections and saves a significant amount in cost.

                    It is better than leaving the mismatched thru hull to valve connection.

                    http://www.groco.net/08-scks-valves/ibvf-install.htm


                    Jim McNeely
                    New Hope a 2004 Bayliner 305 Sunbridge Express Cruiser
                    Twin 5.7s with Bravo2 drives
                    Brighton, Michigan USA
                    MMSI # 367393410

                    Comment


                      #11
                      That combination looks like it would be as good or better solution then a 1 piece seacock. If the valve goes bad you just replace that and dont have to redo the seacock.

                      Comment


                        #12
                        Richard Tulip wrote:
                        Boatworkfl,

                        The adaptor I was thinking of using is sold by West Marine. Their current catalogue has it on p. 524. The 1" model 8672743 is made by Groco and is bronze with a flange for fastening to the block. The ball valve screws to it. Do you have a reason this would not work?

                        Richard
                        I have a 1" Apollo bronze seacock with flange teflon seats new, I will sell for $40.00 new plus shipping.
                        Pat says: DO-IT-RIGHT THE FIRST TIME!

                        Bayliner 3870 "ALASKA33)
                        Twin 350 GM power
                        Located in Seward, AK
                        Retired marine surveyor

                        Comment


                          #13
                          Boatworkfl, thanks for the offer, I already have the Groco.

                          Richard

                          Comment


                            #14
                            Kevin,

                            I am concerned about getting the ball valve off of the mushroom, it has been in place 23+ years and there is no anchor of the mushroom to the hull. What is going to keep the mushroom from spinning with the valve? There is a nut on the mushroom holding it down on the block, not much of a nut. I have thought of backing the nut off to the ball valve, removing the strainer (back to the caulk 5200? and prying off the strainer). If I can get the strainer off I think I could push the assembly down out of the hull, grip the mushroom head with lock pliers then remove the ball valve. I would probably then throw away the mushroom and get another thru hull one piece with the strainer mounting to the hull.

                            Any thoughts?

                            Richard

                            Comment


                              #15
                              Richard Tulip wrote:
                              Kevin,

                              I am concerned about getting the ball valve off of the mushroom, it has been in place 23+ years and there is no anchor of the mushroom to the hull. What is going to keep the mushroom from spinning with the valve? There is a nut on the mushroom holding it down on the block, not much of a nut. I have thought of backing the nut off to the ball valve, removing the strainer (back to the caulk 5200? and prying off the strainer). If I can get the strainer off I think I could push the assembly down out of the hull, grip the mushroom head with lock pliers then remove the ball valve. I would probably then throw away the mushroom and get another thru hull one piece with the strainer mounting to the hull.

                              Any thoughts?

                              Richard
                              Carefully heat the valve with a heat gun-hair drier, or very carefully use a smallpropane torch, that will release any sealant and slightly expand the valve enough to remove it,also, look at the inside of the mushroom, there should be 2 nerrow bosses-like 2 reverse grooves, there is a tool that fits these, an expedient id a flat piese of steel that just fits the mushroom, that should help.

                              I wouls after removing the valve remove the mushroom, there should be a retaining nut on the inside of the boat since you have a regular valve on it, then re-seal it when installing the seacock.

                              let me know if you need more advise.

                              http://www.ebay.com/itm/THRU-HULL-IN...5f98ea&vxp=mtr
                              Pat says: DO-IT-RIGHT THE FIRST TIME!

                              Bayliner 3870 "ALASKA33)
                              Twin 350 GM power
                              Located in Seward, AK
                              Retired marine surveyor

                              Comment

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